L-Proline

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary full text

experimental_model

Mouse embryonic fibroblast and immune-cell experiments with halofuginone; model and assay-specific concentrations.

limitations

Not every proline-processing defect is competitively reversible, and this is not a clinical drug-interaction dose recommendation.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Restoring access to a blocked loading step can turn off a shortage-like signal.

primary_references

Halofuginone and other febrifugine derivatives inhibit prolyl-tRNA synthetase. · 2012 · https://pubmed.ncbi.nlm.nih.gov/22327401/ · DOI 10.1038/nchembio.790

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 238–244

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Mouse embryonic fibroblast and immune-cell experiments with halofuginone; model and assay-specific concentrations. · source_derived_draft · unverified_draft

## l-proline-eprs-stress-rescue Restoring access to a blocked loading step can turn off a shortage-like signal. Exogenous proline reversed halofuginone-induced amino-acid response signaling and selected cellular effects in the study, consistent with competition at the prolyl-tRNA synthetase step. Model: Mouse embryonic fibroblast and immune-cell experiments with halofuginone; model and assay-specific concentrations. Limitations: Not every proline-processing defect is competitively reversible, and this is not a clinical drug-interaction dose recommendation. Evidence access: Primary full text Halofuginone and other febrifugine derivatives inhibit prolyl-tRNA synthetase. · 2012 · https://pubmed.ncbi.nlm.nih.gov/22327401/ · DOI 10.1038/nchembio.790

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary full text

experimental_model

Human NADK2-knockout cell cultures; DMEM compared with DMEM/F12 and individual amino-acid add-back.

limitations

Cell-culture rescue does not establish a treatment for inherited NADK2 disease.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

An external supply can bypass a synthesis bottleneck in these cells.

primary_references

Mitochondrial NADP(H) generation is essential for proline biosynthesis. · 2021 · https://pubmed.ncbi.nlm.nih.gov/33888598/ · DOI 10.1126/science.abd5491

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 70–76

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human NADK2-knockout cell cultures; DMEM compared with DMEM/F12 and individual amino-acid add-back. · source_derived_draft · unverified_draft

## l-proline-nadk2-rescue An external supply can bypass a synthesis bottleneck in these cells. Adding proline restored growth of NADK2-deleted human cells in minimal medium, whereas the defect was largely absent in nutrient-rich medium. Model: Human NADK2-knockout cell cultures; DMEM compared with DMEM/F12 and individual amino-acid add-back. Limitations: Cell-culture rescue does not establish a treatment for inherited NADK2 disease. Evidence access: Primary full text Mitochondrial NADP(H) generation is essential for proline biosynthesis. · 2021 · https://pubmed.ncbi.nlm.nih.gov/33888598/ · DOI 10.1126/science.abd5491

evidence_access

Primary full text

experimental_model

Purified human enzymes; product-inhibition assays, with PYCR2 losing about 90% activity at 0.3 mM proline.

limitations

These assay concentrations are not blood targets or supplement recommendations.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Accumulating product can slow further production, with unequal sensitivity among enzymes.

primary_references

Functional specialization in proline biosynthesis of melanoma. · 2012 · https://pubmed.ncbi.nlm.nih.gov/23024808/ · DOI 10.1371/journal.pone.0045190

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 46–52

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Purified human enzymes; product-inhibition assays, with PYCR2 losing about 90% activity at 0.3 mM proline. · source_derived_draft · unverified_draft

## l-proline-product-feedback Accumulating product can slow further production, with unequal sensitivity among enzymes. Proline inhibited recombinant PYCR2 more strongly than PYCR1 or PYCRL; approximate apparent inhibition constants were 0.1, 0.6 and 8 mM, respectively. Model: Purified human enzymes; product-inhibition assays, with PYCR2 losing about 90% activity at 0.3 mM proline. Limitations: These assay concentrations are not blood targets or supplement recommendations. Evidence access: Primary full text Functional specialization in proline biosynthesis of melanoma. · 2012 · https://pubmed.ncbi.nlm.nih.gov/23024808/ · DOI 10.1371/journal.pone.0045190

evidence_access

Primary full text

experimental_model

Isolated human cancer-cell mitochondria.

limitations

Fuel use in this model does not quantify whole-body energy contribution or show a supplement benefit.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

In this model, proline can help fuel mitochondrial respiration.

primary_references

Sources of superoxide/H2O2 during mitochondrial proline oxidation. · 2014 · https://pubmed.ncbi.nlm.nih.gov/25184115/ · DOI 10.1016/j.redox.2014.07.003

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 134–140

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Isolated human cancer-cell mitochondria. · source_derived_draft · unverified_draft

## l-proline-proline-respiration In this model, proline can help fuel mitochondrial respiration. Isolated mitochondria from human ZR75-30 breast cancer cells consumed oxygen with proline as the sole added substrate. Model: Isolated human cancer-cell mitochondria. Limitations: Fuel use in this model does not quantify whole-body energy contribution or show a supplement benefit. Evidence access: Primary full text Sources of superoxide/H2O2 during mitochondrial proline oxidation. · 2014 · https://pubmed.ncbi.nlm.nih.gov/25184115/ · DOI 10.1016/j.redox.2014.07.003

evidence_access

Primary full text

experimental_model

Isolated human mitochondria; inhibitor combinations used to distinguish ROS-generating sites.

limitations

Results in Drosophila instead emphasized complexes I and II; these species-specific observations do not identify a universal source.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

A pathway can increase ROS without its first enzyme being the direct ROS-producing site.

primary_references

Sources of superoxide/H2O2 during mitochondrial proline oxidation. · 2014 · https://pubmed.ncbi.nlm.nih.gov/25184115/ · DOI 10.1016/j.redox.2014.07.003

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 142–148

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Isolated human mitochondria; inhibitor combinations used to distinguish ROS-generating sites. · source_derived_draft · unverified_draft

## l-proline-ros-source-boundary A pathway can increase ROS without its first enzyme being the direct ROS-producing site. During proline oxidation in ZR75-30 mitochondria, the main measured ROS sources were complex I and 2-oxoglutarate dehydrogenase, with no significant direct PRODH contribution under the tested substrate/inhibitor conditions. Model: Isolated human mitochondria; inhibitor combinations used to distinguish ROS-generating sites. Limitations: Results in Drosophila instead emphasized complexes I and II; these species-specific observations do not identify a universal source. Evidence access: Primary full text Sources of superoxide/H2O2 during mitochondrial proline oxidation. · 2014 · https://pubmed.ncbi.nlm.nih.gov/25184115/ · DOI 10.1016/j.redox.2014.07.003

evidence_access

Primary abstract

experimental_model

Polarized human fetal RPE culture, carbon-13 tracing and metabolite measurements.

limitations

Culture preferences do not establish a universal human dietary proline requirement or AMD treatment.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

The eye support layer can turn proline into fuel intermediates for its neighbors.

primary_references

Human retinal pigment epithelial cells prefer proline as a nutrient and transport metabolic intermediates to the retinal side. · 2017 · https://pubmed.ncbi.nlm.nih.gov/28615447/ · DOI 10.1074/jbc.M117.788422

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 302–308

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Polarized human fetal RPE culture, carbon-13 tracing and metabolite measurements. · source_derived_draft · unverified_draft

## l-proline-rpe-carbon The eye support layer can turn proline into fuel intermediates for its neighbors. Cultured human fetal RPE consumed proline preferentially among the measured nutrients and used its carbon in the TCA cycle and reductive citrate synthesis, with preferential apical citrate export. Model: Polarized human fetal RPE culture, carbon-13 tracing and metabolite measurements. Limitations: Culture preferences do not establish a universal human dietary proline requirement or AMD treatment. Evidence access: Primary abstract Human retinal pigment epithelial cells prefer proline as a nutrient and transport metabolic intermediates to the retinal side. · 2017 · https://pubmed.ncbi.nlm.nih.gov/28615447/ · DOI 10.1074/jbc.M117.788422

evidence_access

Primary abstract

experimental_model

Mouse acute RPE-injury study; primary abstract.

limitations

Diet concentration and injury-protocol details are not asserted from the abstract; this does not establish treatment for chronic human AMD.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

A dietary intervention helped in a specific experimental eye-injury model.

primary_references

Proline mediates metabolic communication between retinal pigment epithelial cells and the retina. · 2019 · https://pubmed.ncbi.nlm.nih.gov/31110046/ · DOI 10.1074/jbc.RA119.007983

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 342–348

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Mouse acute RPE-injury study; primary abstract. · source_derived_draft · unverified_draft

## l-proline-rpe-diet-model A dietary intervention helped in a specific experimental eye-injury model. Dietary proline improved visual function in an acute model of RPE-induced retinal degeneration. Model: Mouse acute RPE-injury study; primary abstract. Limitations: Diet concentration and injury-protocol details are not asserted from the abstract; this does not establish treatment for chronic human AMD. Evidence access: Primary abstract Proline mediates metabolic communication between retinal pigment epithelial cells and the retina. · 2019 · https://pubmed.ncbi.nlm.nih.gov/31110046/ · DOI 10.1074/jbc.RA119.007983

evidence_access

Primary final published full text, replacing the earlier preprint

experimental_model

Human RPE matured for 20 weeks; 1 mM nitrogen-15 proline, sampling at 24 and 48 hours.

limitations

Atom transfer involves multiple enzymes; this is not thirteen direct proline-conversion reactions.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Proline supplies nitrogen as well as carbon to the retinal support system.

primary_references

Proline provides a nitrogen source in the retinal pigment epithelium to synthesize and export amino acids for the neural retina. · 2023 · https://pubmed.ncbi.nlm.nih.gov/37741457/ · DOI 10.1016/j.jbc.2023.105275

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 326–332

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human RPE matured for 20 weeks; 1 mM nitrogen-15 proline, sampling at 24 and 48 hours. · source_derived_draft · unverified_draft

## l-proline-rpe-nitrogen Proline supplies nitrogen as well as carbon to the retinal support system. Human RPE used nitrogen from labeled proline to synthesize and export thirteen amino acids, including glutamate, aspartate, glutamine, alanine and serine. Model: Human RPE matured for 20 weeks; 1 mM nitrogen-15 proline, sampling at 24 and 48 hours. Limitations: Atom transfer involves multiple enzymes; this is not thirteen direct proline-conversion reactions. Evidence access: Primary final published full text, replacing the earlier preprint Proline provides a nitrogen source in the retinal pigment epithelium to synthesize and export amino acids for the neural retina. · 2023 · https://pubmed.ncbi.nlm.nih.gov/37741457/ · DOI 10.1016/j.jbc.2023.105275

evidence_access

Primary abstract

experimental_model

Primary human RPE culture and isotope tracing.

limitations

This is not a direct one-step conversion or a clinical serine-repletion trial.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Using one amino acid can support production of another.

primary_references

Proline mediates metabolic communication between retinal pigment epithelial cells and the retina. · 2019 · https://pubmed.ncbi.nlm.nih.gov/31110046/ · DOI 10.1074/jbc.RA119.007983

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 310–316

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Primary human RPE culture and isotope tracing. · source_derived_draft · unverified_draft

## l-proline-rpe-serine Using one amino acid can support production of another. Proline supported de novo serine synthesis and reductive carboxylation in cultured human RPE. Model: Primary human RPE culture and isotope tracing. Limitations: This is not a direct one-step conversion or a clinical serine-repletion trial. Evidence access: Primary abstract Proline mediates metabolic communication between retinal pigment epithelial cells and the retina. · 2019 · https://pubmed.ncbi.nlm.nih.gov/31110046/ · DOI 10.1074/jbc.RA119.007983

evidence_access

Primary abstract

experimental_model

Mouse embryonic stem-cell culture with proline exposure; primary abstract.

limitations

This is a cell-culture state transition, not evidence that proline changes adult human identity or universally activates oncogenes.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

An amino-acid exposure can alter a cell-state program in a developmental model.

primary_references

L-Proline induces a mesenchymal-like invasive program in embryonic stem cells by remodeling H3K9 and H3K36 methylation. · 2013 · https://pubmed.ncbi.nlm.nih.gov/24319666/ · DOI 10.1016/j.stemcr.2013.09.001

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 390–396

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Mouse embryonic stem-cell culture with proline exposure; primary abstract. · source_derived_draft · unverified_draft

## l-proline-stem-cell-state An amino-acid exposure can alter a cell-state program in a developmental model. Proline addition drove a reversible mesenchymal-like, motile state in embryonic stem-cell culture, accompanied by changes in H3K9 and H3K36 methylation. Model: Mouse embryonic stem-cell culture with proline exposure; primary abstract. Limitations: This is a cell-culture state transition, not evidence that proline changes adult human identity or universally activates oncogenes. Evidence access: Primary abstract L-Proline induces a mesenchymal-like invasive program in embryonic stem cells by remodeling H3K9 and H3K36 methylation. · 2013 · https://pubmed.ncbi.nlm.nih.gov/24319666/ · DOI 10.1016/j.stemcr.2013.09.001

evidence_access

Primary full text

experimental_model

Human fibroblast stable-isotope tracing under specified media conditions.

limitations

Atom contribution is not a one-step alanine-to-proline reaction; other enzymes, carbon sources and cofactors remain necessary.

nutrient_topic

L-Alanine collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Alanine

plain_language

One amino acid can supply material used to make another.

primary_references

TGF-β coordinates alanine synthesis and import for myofibroblast differentiation in pulmonary fibrosis. · 2026 · https://pubmed.ncbi.nlm.nih.gov/42024472/ · DOI 10.1172/jci.insight.199449

L-Alanine: carbon, nitrogen, protein synthesis and cross-nutrient mechanisms (2026-09-19) · lines 520–526

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human fibroblast stable-isotope tracing under specified media conditions. · source_derived_draft · unverified_draft

## alanine-fibroblast-proline One amino acid can supply material used to make another. Isotope experiments showed alanine supplying carbon and nitrogen to glutamate and proline synthesis in human lung fibroblasts, particularly during glutamine deprivation. Model: Human fibroblast stable-isotope tracing under specified media conditions. Limitations: Atom contribution is not a one-step alanine-to-proline reaction; other enzymes, carbon sources and cofactors remain necessary. Evidence access: Primary full text TGF-β coordinates alanine synthesis and import for myofibroblast differentiation in pulmonary fibrosis. · 2026 · https://pubmed.ncbi.nlm.nih.gov/42024472/ · DOI 10.1172/jci.insight.199449

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary full text

experimental_model

Engineered mouse PTEN model; transcriptional, microdialysis and electrophysiological observations.

limitations

Multiple consequences of PTEN mutation remain possible; the model is not ordinary dietary deficiency. Correction record: Author correction PMID 39242973 / DOI 10.1038/s44321-024-00125-y corrects the human embryonic stem-cell neuron protocol IRB approval number to KH2017-109 from KA2018-61 and KH2020-55. It does not report a change to experimental results. https://link.springer.com/article/10.1038/s44321-024-00125-y

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Transporter regulation can alter the extracellular supply of two amino acids together.

primary_references

SLC6A20 transporter: a novel regulator of brain glycine homeostasis and NMDAR function. · 2021 · https://pubmed.ncbi.nlm.nih.gov/33428810/ · DOI 10.15252/emmm.202012632

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 214–220

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Engineered mouse PTEN model; transcriptional, microdialysis and electrophysiological observations. · source_derived_draft · unverified_draft

## l-proline-brain-transporter-increase Transporter regulation can alter the extracellular supply of two amino acids together. Mice carrying C-terminally truncated PTEN showed increased Slc6a20a expression, lower extracellular brain proline and glycine, and reduced NMDAR currents. Model: Engineered mouse PTEN model; transcriptional, microdialysis and electrophysiological observations. Limitations: Multiple consequences of PTEN mutation remain possible; the model is not ordinary dietary deficiency. Correction record: Author correction PMID 39242973 / DOI 10.1038/s44321-024-00125-y corrects the human embryonic stem-cell neuron protocol IRB approval number to KH2017-109 from KA2018-61 and KH2020-55. It does not report a change to experimental results. https://link.springer.com/article/10.1038/s44321-024-00125-y Evidence access: Primary full text SLC6A20 transporter: a novel regulator of brain glycine homeostasis and NMDAR function. · 2021 · https://pubmed.ncbi.nlm.nih.gov/33428810/ · DOI 10.15252/emmm.202012632

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary full text

experimental_model

Human cell deletion, isotope tracing and rescue experiments.

limitations

The limiting step was cofactor-dependent synthesis, not a demonstrated lack of glutamine in the diet.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Proline production needs reducing power in the right compartment.

primary_references

Mitochondrial NADP(H) generation is essential for proline biosynthesis. · 2021 · https://pubmed.ncbi.nlm.nih.gov/33888598/ · DOI 10.1126/science.abd5491

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 62–68

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human cell deletion, isotope tracing and rescue experiments. · source_derived_draft · unverified_draft

## l-proline-nadk2-proline Proline production needs reducing power in the right compartment. NADK2 deletion reduced glutamine-derived proline synthesis; mitochondrial NADP(H) was needed for the P5CS step reducing glutamate toward P5C. Model: Human cell deletion, isotope tracing and rescue experiments. Limitations: The limiting step was cofactor-dependent synthesis, not a demonstrated lack of glutamine in the diet. Evidence access: Primary full text Mitochondrial NADP(H) generation is essential for proline biosynthesis. · 2021 · https://pubmed.ncbi.nlm.nih.gov/33888598/ · DOI 10.1126/science.abd5491

evidence_access

Primary abstract

experimental_model

Recombinant human wild-type prolidase, high-resolution substrate/product complexes.

limitations

This does not mean prolidase by itself cleaves an intact collagen triple helix.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Recycling a proline-containing peptide requires a suitable peptidase.

primary_references

Substrate specificity and reaction mechanism of human prolidase. · 2017 · https://pubmed.ncbi.nlm.nih.gov/28677335/ · DOI 10.1111/febs.14158

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 262–268

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Recombinant human wild-type prolidase, high-resolution substrate/product complexes. · source_derived_draft · unverified_draft

## l-proline-pepd-recycling Recycling a proline-containing peptide requires a suitable peptidase. Human prolidase hydrolyzes dipeptides with C-terminal proline or hydroxyproline; substrate- and product-bound structures explain its terminal peptide-cleavage reaction. Model: Recombinant human wild-type prolidase, high-resolution substrate/product complexes. Limitations: This does not mean prolidase by itself cleaves an intact collagen triple helix. Evidence access: Primary abstract Substrate specificity and reaction mechanism of human prolidase. · 2017 · https://pubmed.ncbi.nlm.nih.gov/28677335/ · DOI 10.1111/febs.14158

evidence_access

Primary full text

experimental_model

Lu1205 cells; 1 mM labeled precursors for eight hours; ornithine labeling required omission of extracellular proline.

limitations

The ornithine experiment used conditions the authors regarded as likely nonphysiological; no universal exclusive routing rule is inferred.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Two precursor routes can feed the same product through differently placed enzymes.

primary_references

Functional specialization in proline biosynthesis of melanoma. · 2012 · https://pubmed.ncbi.nlm.nih.gov/23024808/ · DOI 10.1371/journal.pone.0045190

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 38–44

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Lu1205 cells; 1 mM labeled precursors for eight hours; ornithine labeling required omission of extracellular proline. · source_derived_draft · unverified_draft

## l-proline-precursor-routing Two precursor routes can feed the same product through differently placed enzymes. Isotope tracing with gene silencing linked glutamine/glutamate-derived proline mainly to PYCR1/PYCR2 and ornithine-derived proline mainly to PYCRL in human melanoma cells. Model: Lu1205 cells; 1 mM labeled precursors for eight hours; ornithine labeling required omission of extracellular proline. Limitations: The ornithine experiment used conditions the authors regarded as likely nonphysiological; no universal exclusive routing rule is inferred. Evidence access: Primary full text Functional specialization in proline biosynthesis of melanoma. · 2012 · https://pubmed.ncbi.nlm.nih.gov/23024808/ · DOI 10.1371/journal.pone.0045190

evidence_access

Primary full text

experimental_model

Purified human enzyme; comparison with 0.1 mM P5C and 0.1 mM reduced cofactor, 37 degrees C.

limitations

Cofactor preference depends on assay conditions and does not make the alternative cofactor unusable.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

One mitochondrial enzyme finishes the synthesis of proline.

primary_references

Functional specialization in proline biosynthesis of melanoma. · 2012 · https://pubmed.ncbi.nlm.nih.gov/23024808/ · DOI 10.1371/journal.pone.0045190

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 14–20

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Purified human enzyme; comparison with 0.1 mM P5C and 0.1 mM reduced cofactor, 37 degrees C. · source_derived_draft · unverified_draft

## l-proline-pycr1-reduction One mitochondrial enzyme finishes the synthesis of proline. Recombinant human PYCR1 reduced P5C to proline with NADH or NADPH; in the tested conditions its specific activity was higher with NADH. Model: Purified human enzyme; comparison with 0.1 mM P5C and 0.1 mM reduced cofactor, 37 degrees C. Limitations: Cofactor preference depends on assay conditions and does not make the alternative cofactor unusable. Evidence access: Primary full text Functional specialization in proline biosynthesis of melanoma. · 2012 · https://pubmed.ncbi.nlm.nih.gov/23024808/ · DOI 10.1371/journal.pone.0045190

evidence_access

Primary full text

experimental_model

Purified human PYCR2 and human melanoma-cell localization experiments.

limitations

PYCR2 has its own identity and disease associations; it is not interchangeable with PYCR1.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

A second mitochondrial enzyme performs the final reduction.

primary_references

Functional specialization in proline biosynthesis of melanoma. · 2012 · https://pubmed.ncbi.nlm.nih.gov/23024808/ · DOI 10.1371/journal.pone.0045190

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 22–28

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Purified human PYCR2 and human melanoma-cell localization experiments. · source_derived_draft · unverified_draft

## l-proline-pycr2-reduction A second mitochondrial enzyme performs the final reduction. Recombinant human PYCR2 reduced P5C to proline and favored NADH over NADPH under the reported comparison conditions. Model: Purified human PYCR2 and human melanoma-cell localization experiments. Limitations: PYCR2 has its own identity and disease associations; it is not interchangeable with PYCR1. Evidence access: Primary full text Functional specialization in proline biosynthesis of melanoma. · 2012 · https://pubmed.ncbi.nlm.nih.gov/23024808/ · DOI 10.1371/journal.pone.0045190

evidence_access

Primary full text

experimental_model

Lu1205 cell fractionation and recombinant human PYCRL kinetics.

limitations

The melanoma routing pattern is not asserted to apply identically in every human tissue.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

The cytosolic version has different preferences from the mitochondrial enzymes.

primary_references

Functional specialization in proline biosynthesis of melanoma. · 2012 · https://pubmed.ncbi.nlm.nih.gov/23024808/ · DOI 10.1371/journal.pone.0045190

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 30–36

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Lu1205 cell fractionation and recombinant human PYCRL kinetics. · source_derived_draft · unverified_draft

## l-proline-pycr3-reduction The cytosolic version has different preferences from the mitochondrial enzymes. Human PYCRL/PYCR3 localized predominantly to the cytosol in the tested melanoma cells and was more efficient with NADPH in the biochemical comparison. Model: Lu1205 cell fractionation and recombinant human PYCRL kinetics. Limitations: The melanoma routing pattern is not asserted to apply identically in every human tissue. Evidence access: Primary full text Functional specialization in proline biosynthesis of melanoma. · 2012 · https://pubmed.ncbi.nlm.nih.gov/23024808/ · DOI 10.1371/journal.pone.0045190

evidence_access

Primary abstract

experimental_model

Rat protein in Xenopus oocytes; alanine and lysine did not inhibit the reported proline transport.

limitations

This is not a human dietary sodium or chloride threshold.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

The driving ions and membrane voltage affect how this transporter works.

primary_references

Identification of mammalian proline transporter SIT1 (SLC6A20) with characteristics of classical system imino. · 2005 · https://pubmed.ncbi.nlm.nih.gov/15632147/ · DOI 10.1074/jbc.M413027200

transport_effect

raises Sodium-dependent, chloride-stimulated, voltage-dependent proline transport, which is inward.

transport_pool

the expressing cell Sodium-dependent, chloride-stimulated, voltage-dependent proline transport, which is inward.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 174–180

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Rat protein in Xenopus oocytes; alanine and lysine did not inhibit the reported proline transport. · source_derived_draft · unverified_draft

## l-proline-rat-sit1-ion-coupling The driving ions and membrane voltage affect how this transporter works. Rat SIT1 expressed in Xenopus oocytes transported proline with apparent K0.5 about 0.2 mM; transport depended on sodium, was stimulated by chloride and depended on voltage. Model: Rat protein in Xenopus oocytes; alanine and lysine did not inhibit the reported proline transport. Limitations: This is not a human dietary sodium or chloride threshold. Evidence access: Primary abstract Identification of mammalian proline transporter SIT1 (SLC6A20) with characteristics of classical system imino. · 2005 · https://pubmed.ncbi.nlm.nih.gov/15632147/ · DOI 10.1074/jbc.M413027200

evidence_access

Primary abstract

experimental_model

Human SIT1 heterologous expression in the mammalian transporter identification study.

limitations

Rat concentration-response and ion-substitution details are recorded separately rather than assumed identical in humans.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Cell entry depends on transport machinery and ion gradients.

primary_references

Identification of mammalian proline transporter SIT1 (SLC6A20) with characteristics of classical system imino. · 2005 · https://pubmed.ncbi.nlm.nih.gov/15632147/ · DOI 10.1074/jbc.M413027200

transport_effect

raises Functioned as a sodium-dependent proline transporter, which is inward.

transport_pool

the expressing cell Functioned as a sodium-dependent proline transporter, which is inward.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 166–172

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human SIT1 heterologous expression in the mammalian transporter identification study. · source_derived_draft · unverified_draft

## l-proline-sit1-uptake Cell entry depends on transport machinery and ion gradients. Human SIT1/SLC6A20 functioned as a sodium-dependent proline transporter when expressed for functional testing. Model: Human SIT1 heterologous expression in the mammalian transporter identification study. Limitations: Rat concentration-response and ion-substitution details are recorded separately rather than assumed identical in humans. Evidence access: Primary abstract Identification of mammalian proline transporter SIT1 (SLC6A20) with characteristics of classical system imino. · 2005 · https://pubmed.ncbi.nlm.nih.gov/15632147/ · DOI 10.1074/jbc.M413027200

evidence_access

Primary abstract

experimental_model

TGF-beta-stimulated fibroblast experiments; primary abstract, with mouse NIH3T3 model identified in the primary study.

limitations

No dietary dose or general antifibrotic benefit is inferred.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Activated matrix-producing cells can use proline synthesis to handle metabolic demand.

primary_references

Proline biosynthesis is a vent for TGFβ-induced mitochondrial redox stress. · 2020 · https://pubmed.ncbi.nlm.nih.gov/32134147/ · DOI 10.15252/embj.2019103334

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 366–372

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · TGF-beta-stimulated fibroblast experiments; primary abstract, with mouse NIH3T3 model identified in the primary study. · source_derived_draft · unverified_draft

## l-proline-tgfb-proline Activated matrix-producing cells can use proline synthesis to handle metabolic demand. TGF-beta induced glutamine-derived proline synthesis in a Smad4-dependent fibroblast program; manipulations of mitochondrial redox potential or ATP production changed that synthesis. Model: TGF-beta-stimulated fibroblast experiments; primary abstract, with mouse NIH3T3 model identified in the primary study. Limitations: No dietary dose or general antifibrotic benefit is inferred. Evidence access: Primary abstract Proline biosynthesis is a vent for TGFβ-induced mitochondrial redox stress. · 2020 · https://pubmed.ncbi.nlm.nih.gov/32134147/ · DOI 10.15252/embj.2019103334

availability_state

nutrient_deficiency Imported condition classification; unverified.

evidence_access

Primary abstract

experimental_model

Rat dietary comparison; liver enzyme assay.

limitations

Activity change does not prove silicon is an OAT cofactor or a direct link to vitamin B6 depletion.

nutrient_topic

Silica collection; molecular form, preparation, species, exposure and manipulation remain explicit. · Silica and soluble silicon

plain_language

A proline-related metabolic enzyme changed alongside collagen endpoints.

primary_references

Silicon deprivation decreases collagen formation in wounds and bone, and ornithine transaminase enzyme activity in liver. · 2002 · https://pubmed.ncbi.nlm.nih.gov/12462748/ · DOI 10.1385/bter:89:3:251

trigger_kind

nutrient_deficiency Imported condition classification; unverified.

Silica: soluble silicon, cellular transport and particle-specific mechanisms (2026-09-19) · lines 360–366

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Rat dietary comparison; liver enzyme assay. · source_derived_draft · unverified_draft

## silica-rat-oat A proline-related metabolic enzyme changed alongside collagen endpoints. Rat liver ornithine aminotransferase activity decreased with silicon deprivation. Model: Rat dietary comparison; liver enzyme assay. Limitations: Activity change does not prove silicon is an OAT cofactor or a direct link to vitamin B6 depletion. Evidence access: Primary abstract Silicon deprivation decreases collagen formation in wounds and bone, and ornithine transaminase enzyme activity in liver. · 2002 · https://pubmed.ncbi.nlm.nih.gov/12462748/ · DOI 10.1385/bter:89:3:251

evidence_span

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experimental_model

Review of prolyl 4-hydroxylase enzymology and subunit structure

exposure

Hydroxylation of proline in X-Pro-Gly sequences

limitations

An authoritative enzymology review rather than a single experiment. It is the source for the cosubstrate list, which is the point at which oxygen, iron and vitamin C meet in collagen synthesis.

nutrient_topic

Hyperbaric oxygen research collection; topical membership is not evidence of a direct clinical effect, and a therapeutic exposure is not a dietary intake. · Hyperbaric oxygen therapy

organism

Mammalian enzyme

plain_language

Making collagen needs oxygen, iron, vitamin C and a Krebs-cycle acid, all four at once.

primary_references

[hbot-p2537773] Protein hydroxylation: prolyl 4-hydroxylase, an enzyme with four cosubstrates and a multifunctional subunit. (1989). https://pubmed.ncbi.nlm.nih.gov/2537773/ DOI: 10.1096/fasebj.3.5.2537773

tissue_or_cell_type

Endoplasmic reticulum

Hyperbaric oxygen: the exposure, its reactive species, the signals they carry, and the nutrient-dependent enzymes that handle them (2026-09-19) · lines 855–866

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Review of prolyl 4-hydroxylase enzymology and subunit structure · source_derived_draft · unverified_draft

### hbot-p4h-cosubstrates Prolyl 4-hydroxylase catalyses formation of 4-hydroxyproline in collagens by hydroxylating proline residues in X-Pro-Gly sequences, and the reaction requires Fe2+, 2-oxoglutarate, O2 and ascorbate, involving oxidative decarboxylation of 2-oxoglutarate. Condition category: normal nutrient_topic: Hyperbaric oxygen research collection; topical membership is not evidence of a direct clinical effect, and a therapeutic exposure is not a dietary intake. plain_language: Making collagen needs oxygen, iron, vitamin C and a Krebs-cycle acid, all four at once. organism: Mammalian enzyme tissue_or_cell_type: Endoplasmic reticulum experimental_model: Review of prolyl 4-hydroxylase enzymology and subunit structure limitations: An authoritative enzymology review rather than a single experiment. It is the source for the cosubstrate list, which is the point at which oxygen, iron and vitamin C meet in collagen synthesis. exposure: Hydroxylation of proline in X-Pro-Gly sequences evidence_span: {"source_cache": "artifacts/hbot-research/2537773.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "3fdda2e4cf4392ec7a88b137274cee8f321255473992a2d8df781df12cad6cfe", "start_char": 0, "end_char": 2024, "text_sha256": "3fdda2e4cf4392ec7a88b137274cee8f321255473992a2d8df781df12cad6cfe"} [hbot-p2537773] Protein hydroxylation: prolyl 4-hydroxylase, an enzyme with four cosubstrates and a multifunctional subunit. (1989). https://pubmed.ncbi.nlm.nih.gov/2537773/ DOI: 10.1096/fasebj.3.5.2537773

evidence_access

Primary full text

experimental_model

Bovine articular chondrocyte monolayers; 15-day concentration series and collagen ELISA.

limitations

The paper proposes dietary implications, but the experiment does not establish human glycine essentiality, osteoarthritis causation or cartilage regeneration.

nutrient_topic

Glycine collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · Glycine

plain_language

Collagen-producing cells responded to extra glycine in a culture assay.

primary_references

High glycine concentration increases collagen synthesis by articular chondrocytes in vitro: acute glycine deficiency could be an important cause of osteoarthritis. · 2018 · https://pubmed.ncbi.nlm.nih.gov/30006659/ · DOI 10.1007/s00726-018-2611-x

Glycine: supply, one-carbon allocation, receptors and cross-nutrient mechanisms (2026-09-19) · lines 402–408

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Bovine articular chondrocyte monolayers; 15-day concentration series and collagen ELISA. · source_derived_draft · unverified_draft

## glycine-collagen-culture Collagen-producing cells responded to extra glycine in a culture assay. Increasing medium glycine from the millimolar range increased type-II collagen production in cultured bovine chondrocytes, with larger sustained effects than the tested proline/lysine increments. Model: Bovine articular chondrocyte monolayers; 15-day concentration series and collagen ELISA. Limitations: The paper proposes dietary implications, but the experiment does not establish human glycine essentiality, osteoarthritis causation or cartilage regeneration. Evidence access: Primary full text High glycine concentration increases collagen synthesis by articular chondrocytes in vitro: acute glycine deficiency could be an important cause of osteoarthritis. · 2018 · https://pubmed.ncbi.nlm.nih.gov/30006659/ · DOI 10.1007/s00726-018-2611-x

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary abstract

experimental_model

Recombinant human mutant/wild-type structures and kinetic analysis.

limitations

This tests one inherited variant and does not establish a nutrient-addition rescue.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

A structural defect can block proline breakdown even when substrate is plentiful.

primary_references

The three-dimensional structural basis of type II hyperprolinemia. · 2012 · https://pubmed.ncbi.nlm.nih.gov/22516612/ · DOI 10.1016/j.jmb.2012.04.010

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 110–116

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Recombinant human mutant/wild-type structures and kinetic analysis. · source_derived_draft · unverified_draft

## l-proline-aldh4-failure A structural defect can block proline breakdown even when substrate is plentiful. The human ALDH4A1 S352L disease-associated variant abolished catalytic activity and NAD+ binding, with a major rearrangement of the catalytic loop. Model: Recombinant human mutant/wild-type structures and kinetic analysis. Limitations: This tests one inherited variant and does not establish a nutrient-addition rescue. Evidence access: Primary abstract The three-dimensional structural basis of type II hyperprolinemia. · 2012 · https://pubmed.ncbi.nlm.nih.gov/22516612/ · DOI 10.1016/j.jmb.2012.04.010

evidence_access

Primary abstract

experimental_model

Human enzyme structures and kinetics; mouse enzyme complexes supplied high-resolution ligand views.

limitations

P5C and glutamate semialdehyde interconvert; the aldehyde is the oxidation substrate. Mouse ligand structures are not relabeled as human complexes.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

A second enzyme turns the breakdown intermediate into glutamate.

primary_references

The three-dimensional structural basis of type II hyperprolinemia. · 2012 · https://pubmed.ncbi.nlm.nih.gov/22516612/ · DOI 10.1016/j.jmb.2012.04.010

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 102–108

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human enzyme structures and kinetics; mouse enzyme complexes supplied high-resolution ligand views. · source_derived_draft · unverified_draft

## l-proline-aldh4-oxidation A second enzyme turns the breakdown intermediate into glutamate. ALDH4A1 catalyzes NAD+-dependent oxidation of glutamate semialdehyde to glutamate, completing the second enzymatic stage of proline catabolism. Model: Human enzyme structures and kinetics; mouse enzyme complexes supplied high-resolution ligand views. Limitations: P5C and glutamate semialdehyde interconvert; the aldehyde is the oxidation substrate. Mouse ligand structures are not relabeled as human complexes. Evidence access: Primary abstract The three-dimensional structural basis of type II hyperprolinemia. · 2012 · https://pubmed.ncbi.nlm.nih.gov/22516612/ · DOI 10.1016/j.jmb.2012.04.010

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary full text

experimental_model

Mouse genetic deletion with extracellular amino-acid measurements and electrophysiology.

limitations

This does not show that oral proline treats NMDAR dysfunction in humans. Correction record: Author correction PMID 39242973 / DOI 10.1038/s44321-024-00125-y corrects the human embryonic stem-cell neuron protocol IRB approval number to KH2017-109 from KA2018-61 and KH2020-55. It does not report a change to experimental results. https://link.springer.com/article/10.1038/s44321-024-00125-y

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Changing a proline-sharing transporter can change glycine-dependent brain signaling.

primary_references

SLC6A20 transporter: a novel regulator of brain glycine homeostasis and NMDAR function. · 2021 · https://pubmed.ncbi.nlm.nih.gov/33428810/ · DOI 10.15252/emmm.202012632

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 206–212

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Mouse genetic deletion with extracellular amino-acid measurements and electrophysiology. · source_derived_draft · unverified_draft

## l-proline-brain-transporter-loss Changing a proline-sharing transporter can change glycine-dependent brain signaling. Slc6a20a-knockout mice had higher extracellular brain glycine and increased NMDA-receptor currents. Model: Mouse genetic deletion with extracellular amino-acid measurements and electrophysiology. Limitations: This does not show that oral proline treats NMDAR dysfunction in humans. Correction record: Author correction PMID 39242973 / DOI 10.1038/s44321-024-00125-y corrects the human embryonic stem-cell neuron protocol IRB approval number to KH2017-109 from KA2018-61 and KH2020-55. It does not report a change to experimental results. https://link.springer.com/article/10.1038/s44321-024-00125-y Evidence access: Primary full text SLC6A20 transporter: a novel regulator of brain glycine homeostasis and NMDAR function. · 2021 · https://pubmed.ncbi.nlm.nih.gov/33428810/ · DOI 10.15252/emmm.202012632

evidence_access

Primary full text

experimental_model

Human fibroblast cultures; 2 mM labeled glutamine for 72 hours in the collagen-peptide experiment.

limitations

Atom tracing does not show that dietary glutamine or proline is the limiting substrate in a person. Correction record: Author correction PMID 35927357 / DOI 10.1038/s42255-022-00632-7 corrects the author surname Riero-Domingo to Riera-Domingo. It does not report a change to the experimental results. https://www.nature.com/articles/s42255-022-00632-7

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Collagen-building cells can make their own proline from glutamine.

primary_references

Cancer-associated fibroblasts require proline synthesis by PYCR1 for the deposition of pro-tumorigenic extracellular matrix. · 2022 · https://pubmed.ncbi.nlm.nih.gov/35760868/ · DOI 10.1038/s42255-022-00582-0

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 246–252

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human fibroblast cultures; 2 mM labeled glutamine for 72 hours in the collagen-peptide experiment. · source_derived_draft · unverified_draft

## l-proline-collagen-carbon Collagen-building cells can make their own proline from glutamine. Carbon-13 glutamine tracing in human mammary cancer-associated fibroblasts demonstrated incorporation of newly synthesized proline into COL1A1 peptides. Model: Human fibroblast cultures; 2 mM labeled glutamine for 72 hours in the collagen-peptide experiment. Limitations: Atom tracing does not show that dietary glutamine or proline is the limiting substrate in a person. Correction record: Author correction PMID 35927357 / DOI 10.1038/s42255-022-00632-7 corrects the author surname Riero-Domingo to Riera-Domingo. It does not report a change to the experimental results. https://www.nature.com/articles/s42255-022-00632-7 Evidence access: Primary full text Cancer-associated fibroblasts require proline synthesis by PYCR1 for the deposition of pro-tumorigenic extracellular matrix. · 2022 · https://pubmed.ncbi.nlm.nih.gov/35760868/ · DOI 10.1038/s42255-022-00582-0

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary full text

experimental_model

Human CAF knockdown and matrix measurements; xenograft experiments separately examined tumor consequences.

limitations

This is a tumor-associated fibroblast model, not a trial of ordinary wound healing. Correction record: Author correction PMID 35927357 / DOI 10.1038/s42255-022-00632-7 corrects the author surname Riero-Domingo to Riera-Domingo. It does not report a change to the experimental results. https://www.nature.com/articles/s42255-022-00632-7

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Endogenous synthesis can limit matrix production in activated fibroblasts.

primary_references

Cancer-associated fibroblasts require proline synthesis by PYCR1 for the deposition of pro-tumorigenic extracellular matrix. · 2022 · https://pubmed.ncbi.nlm.nih.gov/35760868/ · DOI 10.1038/s42255-022-00582-0

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 254–260

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human CAF knockdown and matrix measurements; xenograft experiments separately examined tumor consequences. · source_derived_draft · unverified_draft

## l-proline-collagen-pycr1 Endogenous synthesis can limit matrix production in activated fibroblasts. Reducing PYCR1 in human mammary cancer-associated fibroblasts lowered proline supply for collagen production and decreased collagen deposition. Model: Human CAF knockdown and matrix measurements; xenograft experiments separately examined tumor consequences. Limitations: This is a tumor-associated fibroblast model, not a trial of ordinary wound healing. Correction record: Author correction PMID 35927357 / DOI 10.1038/s42255-022-00632-7 corrects the author surname Riero-Domingo to Riera-Domingo. It does not report a change to the experimental results. https://www.nature.com/articles/s42255-022-00632-7 Evidence access: Primary full text Cancer-associated fibroblasts require proline synthesis by PYCR1 for the deposition of pro-tumorigenic extracellular matrix. · 2022 · https://pubmed.ncbi.nlm.nih.gov/35760868/ · DOI 10.1038/s42255-022-00582-0

evidence_access

Primary full text

experimental_model

Purified human EPRS/ProRS biochemical assays.

limitations

tRNA charging and collagen hydroxylation are separate enzyme steps.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

A protein-building block must first be loaded onto the correct tRNA.

primary_references

Halofuginone and other febrifugine derivatives inhibit prolyl-tRNA synthetase. · 2012 · https://pubmed.ncbi.nlm.nih.gov/22327401/ · DOI 10.1038/nchembio.790

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 222–228

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Purified human EPRS/ProRS biochemical assays. · source_derived_draft · unverified_draft

## l-proline-eprs-charging A protein-building block must first be loaded onto the correct tRNA. The prolyl-tRNA synthetase domain of human EPRS attaches proline to its cognate tRNA in an ATP-dependent aminoacylation reaction. Model: Purified human EPRS/ProRS biochemical assays. Limitations: tRNA charging and collagen hydroxylation are separate enzyme steps. Evidence access: Primary full text Halofuginone and other febrifugine derivatives inhibit prolyl-tRNA synthetase. · 2012 · https://pubmed.ncbi.nlm.nih.gov/22327401/ · DOI 10.1038/nchembio.790

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary full text

experimental_model

Biochemical charging assays and mammalian-cell experiments.

limitations

This is pharmacological machinery inhibition, not a claim that halofuginone physically removes all cellular proline.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Blocking the loading enzyme can mimic a shortage even while proline is present.

primary_references

Halofuginone and other febrifugine derivatives inhibit prolyl-tRNA synthetase. · 2012 · https://pubmed.ncbi.nlm.nih.gov/22327401/ · DOI 10.1038/nchembio.790

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 230–236

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Biochemical charging assays and mammalian-cell experiments. · source_derived_draft · unverified_draft

## l-proline-eprs-inhibition Blocking the loading enzyme can mimic a shortage even while proline is present. Halofuginone inhibited the prolyl-tRNA synthetase activity of EPRS by competing with proline; added proline or enzyme reversed inhibition in the tested systems. Model: Biochemical charging assays and mammalian-cell experiments. Limitations: This is pharmacological machinery inhibition, not a claim that halofuginone physically removes all cellular proline. Evidence access: Primary full text Halofuginone and other febrifugine derivatives inhibit prolyl-tRNA synthetase. · 2012 · https://pubmed.ncbi.nlm.nih.gov/22327401/ · DOI 10.1038/nchembio.790

evidence_access

Primary abstract

experimental_model

Truncated purified human HYPDH; quinone analogue and oxygen comparisons.

limitations

CoQ10 as the physiological acceptor is inferred, not directly measured in intact human tissues; this does not demonstrate benefit from CoQ10 supplements.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Hydroxyproline breakdown can feed a quinone electron-transfer route.

primary_references

Proline dehydrogenase 2 (PRODH2) is a hydroxyproline dehydrogenase (HYPDH) and molecular target for treating primary hyperoxaluria. · 2015 · https://pubmed.ncbi.nlm.nih.gov/25697095/ · DOI 10.1042/BJ20141159

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 286–292

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Truncated purified human HYPDH; quinone analogue and oxygen comparisons. · source_derived_draft · unverified_draft

## l-proline-hypdh-electrons Hydroxyproline breakdown can feed a quinone electron-transfer route. Quinone acceptors including CoQ1 reacted more efficiently than oxygen during purified human HYPDH turnover, supporting a dehydrogenase mechanism. Model: Truncated purified human HYPDH; quinone analogue and oxygen comparisons. Limitations: CoQ10 as the physiological acceptor is inferred, not directly measured in intact human tissues; this does not demonstrate benefit from CoQ10 supplements. Evidence access: Primary abstract Proline dehydrogenase 2 (PRODH2) is a hydroxyproline dehydrogenase (HYPDH) and molecular target for treating primary hyperoxaluria. · 2015 · https://pubmed.ncbi.nlm.nih.gov/25697095/ · DOI 10.1042/BJ20141159

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary abstract

experimental_model

Genetic mouse models, including Grhpr knockout and a 1% hydroxyproline diet.

limitations

Hydroxyproline loading is not equivalent to free proline intake; human efficacy of pathway inhibition was not established.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

A collagen-derived amino acid can feed an oxalate-producing pathway under specific conditions.

primary_references

The effects of the inactivation of Hydroxyproline dehydrogenase on urinary oxalate and glycolate excretion in mouse models of primary hyperoxaluria. · 2020 · https://pubmed.ncbi.nlm.nih.gov/31821850/ · DOI 10.1016/j.bbadis.2019.165633

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 294–300

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Genetic mouse models, including Grhpr knockout and a 1% hydroxyproline diet. · source_derived_draft · unverified_draft

## l-proline-hypdh-oxalate A collagen-derived amino acid can feed an oxalate-producing pathway under specific conditions. Prodh2 deletion reduced urinary oxalate in mouse hyperoxaluria models; combined Grhpr/Prodh2 deletion prevented kidney calcium-oxalate deposition during a 1% hydroxyproline diet. Model: Genetic mouse models, including Grhpr knockout and a 1% hydroxyproline diet. Limitations: Hydroxyproline loading is not equivalent to free proline intake; human efficacy of pathway inhibition was not established. Evidence access: Primary abstract The effects of the inactivation of Hydroxyproline dehydrogenase on urinary oxalate and glycolate excretion in mouse models of primary hyperoxaluria. · 2020 · https://pubmed.ncbi.nlm.nih.gov/31821850/ · DOI 10.1016/j.bbadis.2019.165633

evidence_access

Primary abstract

experimental_model

Human recombinant catalytic core, residues 157–515; substrate kinetics.

limitations

PRODH2 is not simply a second interchangeable proline oxidase.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Hydroxyproline uses a related but distinct breakdown enzyme.

primary_references

Proline dehydrogenase 2 (PRODH2) is a hydroxyproline dehydrogenase (HYPDH) and molecular target for treating primary hyperoxaluria. · 2015 · https://pubmed.ncbi.nlm.nih.gov/25697095/ · DOI 10.1042/BJ20141159

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 278–284

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human recombinant catalytic core, residues 157–515; substrate kinetics. · source_derived_draft · unverified_draft

## l-proline-hypdh-specificity Hydroxyproline uses a related but distinct breakdown enzyme. Purified truncated human PRODH2/HYPDH contained one FAD and showed approximately twelvefold higher catalytic efficiency for hydroxyproline than proline. Model: Human recombinant catalytic core, residues 157–515; substrate kinetics. Limitations: PRODH2 is not simply a second interchangeable proline oxidase. Evidence access: Primary abstract Proline dehydrogenase 2 (PRODH2) is a hydroxyproline dehydrogenase (HYPDH) and molecular target for treating primary hyperoxaluria. · 2015 · https://pubmed.ncbi.nlm.nih.gov/25697095/ · DOI 10.1042/BJ20141159

evidence_access

Primary abstract

experimental_model

Anaerobic C. difficile culture in limiting medium; selenite supplementation and radiolabeled selenium protein analysis.

limitations

This bacterial growth mechanism does not establish that dietary selenium causes or prevents infection.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Selenium also supports some microbial amino-acid fermentation pathways.

primary_references

Analysis of proline reduction in the nosocomial pathogen Clostridium difficile. · 2006 · https://pubmed.ncbi.nlm.nih.gov/17041035/ · DOI 10.1128/JB.01370-06

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 414–420

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Anaerobic C. difficile culture in limiting medium; selenite supplementation and radiolabeled selenium protein analysis. · source_derived_draft · unverified_draft

## l-proline-microbial-selenium Selenium also supports some microbial amino-acid fermentation pathways. Selenium supplementation was required for the increased bacterial growth yield seen with the tested Stickland amino-acid pairs; proline-related acceptors induced selenoenzyme expression. Model: Anaerobic C. difficile culture in limiting medium; selenite supplementation and radiolabeled selenium protein analysis. Limitations: This bacterial growth mechanism does not establish that dietary selenium causes or prevents infection. Evidence access: Primary abstract Analysis of proline reduction in the nosocomial pathogen Clostridium difficile. · 2006 · https://pubmed.ncbi.nlm.nih.gov/17041035/ · DOI 10.1128/JB.01370-06

evidence_access

Primary abstract

experimental_model

Purified bacterial reductase and substrate tests.

limitations

L-proline-linked fermentation requires stereochemical processing; this enzyme is not a human PRODH isoform.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Gut bacteria can use a different form of proline with different machinery.

primary_references

Analysis of proline reduction in the nosocomial pathogen Clostridium difficile. · 2006 · https://pubmed.ncbi.nlm.nih.gov/17041035/ · DOI 10.1128/JB.01370-06

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 406–412

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Purified bacterial reductase and substrate tests. · source_derived_draft · unverified_draft

## l-proline-microbial-stereospecificity Gut bacteria can use a different form of proline with different machinery. Purified C. difficile proline reductase contained PrdA and selenocysteine-containing PrdB and used D-proline; its stereospecific activity is distinct from human L-proline oxidation. Model: Purified bacterial reductase and substrate tests. Limitations: L-proline-linked fermentation requires stereochemical processing; this enzyme is not a human PRODH isoform. Evidence access: Primary abstract Analysis of proline reduction in the nosocomial pathogen Clostridium difficile. · 2006 · https://pubmed.ncbi.nlm.nih.gov/17041035/ · DOI 10.1128/JB.01370-06

evidence_access

Primary abstract

experimental_model

Purified bacterial-enzyme assays.

limitations

No safe or effective intestinal zinc intervention is established by the enzyme experiment.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

A mineral can inhibit this microbial enzyme rather than serve as its cofactor.

primary_references

Analysis of proline reduction in the nosocomial pathogen Clostridium difficile. · 2006 · https://pubmed.ncbi.nlm.nih.gov/17041035/ · DOI 10.1128/JB.01370-06

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 422–428

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Purified bacterial-enzyme assays. · source_derived_draft · unverified_draft

## l-proline-microbial-zinc A mineral can inhibit this microbial enzyme rather than serve as its cofactor. Zinc strongly inhibited purified C. difficile D-proline reductase, which did not require added divalent cations for its measured activity. Model: Purified bacterial-enzyme assays. Limitations: No safe or effective intestinal zinc intervention is established by the enzyme experiment. Evidence access: Primary abstract Analysis of proline reduction in the nosocomial pathogen Clostridium difficile. · 2006 · https://pubmed.ncbi.nlm.nih.gov/17041035/ · DOI 10.1128/JB.01370-06

evidence_access

Primary abstract

experimental_model

Mouse breast-cancer models, complemented by three-dimensional culture and human tumor-expression comparisons.

limitations

This does not establish that dietary proline causes metastasis or that proline restriction is a proven treatment.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

A proline-consuming pathway can support growth in a metastatic setting.

primary_references

Proline metabolism supports metastasis formation and could be inhibited to selectively target metastasizing cancer cells. · 2017 · https://pubmed.ncbi.nlm.nih.gov/28492237/ · DOI 10.1038/ncomms15267

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 382–388

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Mouse breast-cancer models, complemented by three-dimensional culture and human tumor-expression comparisons. · source_derived_draft · unverified_draft

## l-proline-mouse-metastatic-catabolism A proline-consuming pathway can support growth in a metastatic setting. Pharmacological inhibition of Prodh impaired lung-metastasis formation in orthotopic 4T1 and EMT6.5 mouse breast-cancer models. Model: Mouse breast-cancer models, complemented by three-dimensional culture and human tumor-expression comparisons. Limitations: This does not establish that dietary proline causes metastasis or that proline restriction is a proven treatment. Evidence access: Primary abstract Proline metabolism supports metastasis formation and could be inhibited to selectively target metastasizing cancer cells. · 2017 · https://pubmed.ncbi.nlm.nih.gov/28492237/ · DOI 10.1038/ncomms15267

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary abstract

experimental_model

Mammalian NADK2-deletion cell models; primary abstract.

limitations

Detailed model and exposure differences remain distinct; the two publications are not duplicate evidence records from one experiment.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

A second research group found the same synthesis vulnerability.

primary_references

Mitochondrial NADP+ is essential for proline biosynthesis during cell growth. · 2021 · https://pubmed.ncbi.nlm.nih.gov/33833463/ · DOI 10.1038/s42255-021-00374-y

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 78–84

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Mammalian NADK2-deletion cell models; primary abstract. · source_derived_draft · unverified_draft

## l-proline-nadk2-independent-study A second research group found the same synthesis vulnerability. A separate study found NADK2 loss depleted mitochondrial NADPH, limited P5C generation and made tested mammalian cells dependent on exogenous proline for growth. Model: Mammalian NADK2-deletion cell models; primary abstract. Limitations: Detailed model and exposure differences remain distinct; the two publications are not duplicate evidence records from one experiment. Evidence access: Primary abstract Mitochondrial NADP+ is essential for proline biosynthesis during cell growth. · 2021 · https://pubmed.ncbi.nlm.nih.gov/33833463/ · DOI 10.1038/s42255-021-00374-y

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary full text

experimental_model

Human DLD1 cells; immunopurified mitochondrial fractions and enzyme-cycling assays.

limitations

A compartment-specific genetic manipulation is not equivalent to dietary niacin deficiency.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

The cofactor pool inside mitochondria can fail even when a whole-cell measurement looks adequate.

primary_references

Mitochondrial NADP(H) generation is essential for proline biosynthesis. · 2021 · https://pubmed.ncbi.nlm.nih.gov/33888598/ · DOI 10.1126/science.abd5491

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 54–60

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human DLD1 cells; immunopurified mitochondrial fractions and enzyme-cycling assays. · source_derived_draft · unverified_draft

## l-proline-nadk2-pool The cofactor pool inside mitochondria can fail even when a whole-cell measurement looks adequate. CRISPR deletion of NADK2 in human DLD1 cells reduced mitochondrial NADP(H) by more than 80% while whole-cell NADP(H) was not similarly depleted. Model: Human DLD1 cells; immunopurified mitochondrial fractions and enzyme-cycling assays. Limitations: A compartment-specific genetic manipulation is not equivalent to dietary niacin deficiency. Evidence access: Primary full text Mitochondrial NADP(H) generation is essential for proline biosynthesis. · 2021 · https://pubmed.ncbi.nlm.nih.gov/33888598/ · DOI 10.1126/science.abd5491

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary full text

experimental_model

Human cell models; ROS probes, targeted redox sensors and serine isotope tracing.

limitations

The authors do not exclude effects during other physiological stresses; this is not a universal claim that mitochondrial NADPH is irrelevant to antioxidant defense.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Losing this cofactor pool did not shut down every pathway that might be connected to it.

primary_references

Mitochondrial NADP(H) generation is essential for proline biosynthesis. · 2021 · https://pubmed.ncbi.nlm.nih.gov/33888598/ · DOI 10.1126/science.abd5491

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 86–92

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human cell models; ROS probes, targeted redox sensors and serine isotope tracing. · source_derived_draft · unverified_draft

## l-proline-nadk2-redox-boundary Losing this cofactor pool did not shut down every pathway that might be connected to it. Under the tested culture conditions, NADK2 deletion did not increase measured mitochondrial oxidative stress or disrupt mitochondrial folate pathway activity despite reduced proline synthesis. Model: Human cell models; ROS probes, targeted redox sensors and serine isotope tracing. Limitations: The authors do not exclude effects during other physiological stresses; this is not a universal claim that mitochondrial NADPH is irrelevant to antioxidant defense. Evidence access: Primary full text Mitochondrial NADP(H) generation is essential for proline biosynthesis. · 2021 · https://pubmed.ncbi.nlm.nih.gov/33888598/ · DOI 10.1126/science.abd5491

evidence_access

Primary abstract

experimental_model

Cell-free NMR, chromatography and mass-spectrometry experiments motivated by hyperprolinemia type II.

limitations

This demonstrates chemistry under the tested conditions, not B6 depletion from an ordinary proline-containing meal.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

An accumulating proline intermediate can chemically trap active vitamin B6.

primary_references

Pyridoxal phosphate de-activation by pyrroline-5-carboxylic acid. Increased risk of vitamin B6 deficiency and seizures in hyperprolinemia type II. · 2001 · https://pubmed.ncbi.nlm.nih.gov/11134058/ · DOI 10.1074/jbc.M010860200

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 118–124

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Cell-free NMR, chromatography and mass-spectrometry experiments motivated by hyperprolinemia type II. · source_derived_draft · unverified_draft

## l-proline-p5c-b6-trapping An accumulating proline intermediate can chemically trap active vitamin B6. P5C reacted with pyridoxal phosphate at pH 7.4 and 310 K to form three characterized adducts through condensation involving the PLP aldehyde group. Model: Cell-free NMR, chromatography and mass-spectrometry experiments motivated by hyperprolinemia type II. Limitations: This demonstrates chemistry under the tested conditions, not B6 depletion from an ordinary proline-containing meal. Evidence access: Primary abstract Pyridoxal phosphate de-activation by pyrroline-5-carboxylic acid. Increased risk of vitamin B6 deficiency and seizures in hyperprolinemia type II. · 2001 · https://pubmed.ncbi.nlm.nih.gov/11134058/ · DOI 10.1074/jbc.M010860200

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary abstract

experimental_model

Human index-case context combined with in-vitro chemical mechanism.

limitations

Contribution to seizures is an interpretation; the paper does not establish controlled efficacy or a universal treatment dose.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

A breakdown disorder can create a secondary cofactor problem.

primary_references

Pyridoxal phosphate de-activation by pyrroline-5-carboxylic acid. Increased risk of vitamin B6 deficiency and seizures in hyperprolinemia type II. · 2001 · https://pubmed.ncbi.nlm.nih.gov/11134058/ · DOI 10.1074/jbc.M010860200

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 126–132

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human index-case context combined with in-vitro chemical mechanism. · source_derived_draft · unverified_draft

## l-proline-p5c-clinical-link A breakdown disorder can create a secondary cofactor problem. The study was prompted by B6 deficiency and seizures in a child with hyperprolinemia type II; the adduct experiments support P5C-mediated cofactor inactivation as a contributing mechanism. Model: Human index-case context combined with in-vitro chemical mechanism. Limitations: Contribution to seizures is an interpretation; the paper does not establish controlled efficacy or a universal treatment dose. Evidence access: Primary abstract Pyridoxal phosphate de-activation by pyrroline-5-carboxylic acid. Increased risk of vitamin B6 deficiency and seizures in hyperprolinemia type II. · 2001 · https://pubmed.ncbi.nlm.nih.gov/11134058/ · DOI 10.1074/jbc.M010860200

evidence_access

Primary full text

experimental_model

Human PDAC culture and tracer experiments under limited fuel availability.

limitations

Collagen uptake, peptide digestion and proline oxidation are distinct steps; no effect of oral collagen supplements is demonstrated.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

A tissue matrix can become a nutrient reservoir for cells.

primary_references

Collagen-derived proline promotes pancreatic ductal adenocarcinoma cell survival under nutrient limited conditions. · 2017 · https://pubmed.ncbi.nlm.nih.gov/28685754/ · DOI 10.1038/ncomms16031

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 374–380

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human PDAC culture and tracer experiments under limited fuel availability. · source_derived_draft · unverified_draft

## l-proline-pdac-collagen-fuel A tissue matrix can become a nutrient reservoir for cells. Human pancreatic cancer cells took up collagen fragments and used collagen-derived proline in metabolism under nutrient-limited culture conditions. Model: Human PDAC culture and tracer experiments under limited fuel availability. Limitations: Collagen uptake, peptide digestion and proline oxidation are distinct steps; no effect of oral collagen supplements is demonstrated. Evidence access: Primary full text Collagen-derived proline promotes pancreatic ductal adenocarcinoma cell survival under nutrient limited conditions. · 2017 · https://pubmed.ncbi.nlm.nih.gov/28685754/ · DOI 10.1038/ncomms16031

evidence_access

Primary abstract and linked primary deposited structure 5M4G

experimental_model

Human enzyme crystal structures, including deposited structure 5M4G at 1.48 angstroms.

limitations

Structural metal dependence does not establish that adding manganese improves recycling when manganese is already adequate.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

A mineral is part of the machinery that recycles proline from dipeptides.

primary_references

Substrate specificity and reaction mechanism of human prolidase. · 2017 · https://pubmed.ncbi.nlm.nih.gov/28677335/ · DOI 10.1111/febs.14158

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 270–276

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human enzyme crystal structures, including deposited structure 5M4G at 1.48 angstroms. · source_derived_draft · unverified_draft

## l-proline-pepd-manganese A mineral is part of the machinery that recycles proline from dipeptides. Human prolidase structures contain a binuclear manganese active site associated with the hydrolytic reaction; the study proposes hydroxide as the attacking catalytic species. Model: Human enzyme crystal structures, including deposited structure 5M4G at 1.48 angstroms. Limitations: Structural metal dependence does not establish that adding manganese improves recycling when manganese is already adequate. Evidence access: Primary abstract and linked primary deposited structure 5M4G Substrate specificity and reaction mechanism of human prolidase. · 2017 · https://pubmed.ncbi.nlm.nih.gov/28677335/ · DOI 10.1111/febs.14158

evidence_access

Primary full text; background reaction distinguished from new experiments

experimental_model

Established reaction described in a primary mitochondrial proline-oxidation study.

limitations

The reaction description is biochemical background, distinct from the paper-specific ROS-site experiments.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Breaking proline down starts with a flavin-dependent mitochondrial enzyme.

primary_references

Sources of superoxide/H2O2 during mitochondrial proline oxidation. · 2014 · https://pubmed.ncbi.nlm.nih.gov/25184115/ · DOI 10.1016/j.redox.2014.07.003

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 94–100

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Established reaction described in a primary mitochondrial proline-oxidation study. · source_derived_draft · unverified_draft

## l-proline-prodh-oxidation Breaking proline down starts with a flavin-dependent mitochondrial enzyme. Mitochondrial PRODH catalyzes the FAD-dependent oxidation of proline to P5C, linking proline breakdown to mitochondrial electron transfer. Model: Established reaction described in a primary mitochondrial proline-oxidation study. Limitations: The reaction description is biochemical background, distinct from the paper-specific ROS-site experiments. Evidence access: Primary full text; background reaction distinguished from new experiments Sources of superoxide/H2O2 during mitochondrial proline oxidation. · 2014 · https://pubmed.ncbi.nlm.nih.gov/25184115/ · DOI 10.1016/j.redox.2014.07.003

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary abstract

experimental_model

Human genetic families and patient fibroblasts.

limitations

The clinical disorder is not shown to be an isolated dietary proline deficiency or reliably corrected by proline supplementation. Correction record: Author correction PMID 35064218 / DOI 10.1038/s41588-022-01013-2 adds an omitted funding acknowledgment for Hulya Kayserili (TUBITAK SBAG-108S418). The notice does not report a change to the mechanism results. https://www.nature.com/articles/s41588-022-01013-2

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

An enzyme defect can affect connective tissue and cellular stress handling together.

primary_references

Mutations in PYCR1 cause cutis laxa with progeroid features. · 2009 · https://pubmed.ncbi.nlm.nih.gov/19648921/ · DOI 10.1038/ng.413

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 150–156

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human genetic families and patient fibroblasts. · source_derived_draft · unverified_draft

## l-proline-pycr1-genetic An enzyme defect can affect connective tissue and cellular stress handling together. Fibroblasts from people with PYCR1-related cutis laxa showed altered mitochondrial morphology and membrane potential and greater apoptosis during oxidative stress. Model: Human genetic families and patient fibroblasts. Limitations: The clinical disorder is not shown to be an isolated dietary proline deficiency or reliably corrected by proline supplementation. Correction record: Author correction PMID 35064218 / DOI 10.1038/s41588-022-01013-2 adds an omitted funding acknowledgment for Hulya Kayserili (TUBITAK SBAG-108S418). The notice does not report a change to the mechanism results. https://www.nature.com/articles/s41588-022-01013-2 Evidence access: Primary abstract Mutations in PYCR1 cause cutis laxa with progeroid features. · 2009 · https://pubmed.ncbi.nlm.nih.gov/19648921/ · DOI 10.1038/ng.413

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary full text

experimental_model

Human cancer-cell PYCR1 depletion/knockout and xenograft experiments.

limitations

This is a context-specific vulnerability and is not proof of systemic proline deficiency.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

A cell may need the synthesis reaction itself, not merely a measured pool of the final amino acid.

primary_references

Proline synthesis through PYCR1 is required to support cancer cell proliferation and survival in oxygen-limiting conditions. · 2022 · https://pubmed.ncbi.nlm.nih.gov/35108535/ · DOI 10.1016/j.celrep.2022.110320

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 358–364

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human cancer-cell PYCR1 depletion/knockout and xenograft experiments. · source_derived_draft · unverified_draft

## l-proline-pycr1-hypoxic-loss A cell may need the synthesis reaction itself, not merely a measured pool of the final amino acid. PYCR1 loss increased hypoxia-associated cell death in three-dimensional cancer cultures and tumors in vivo. Model: Human cancer-cell PYCR1 depletion/knockout and xenograft experiments. Limitations: This is a context-specific vulnerability and is not proof of systemic proline deficiency. Evidence access: Primary full text Proline synthesis through PYCR1 is required to support cancer cell proliferation and survival in oxygen-limiting conditions. · 2022 · https://pubmed.ncbi.nlm.nih.gov/35108535/ · DOI 10.1016/j.celrep.2022.110320

evidence_access

Primary full text

experimental_model

Human cancer-cell hypoxia experiments and three-dimensional/xenograft models.

limitations

A benefit to tumor-cell survival is not a health benefit of supplementation; proline production is part of the reaction that consumes NADH.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Making proline can also help rebalance mitochondrial reducing power.

primary_references

Proline synthesis through PYCR1 is required to support cancer cell proliferation and survival in oxygen-limiting conditions. · 2022 · https://pubmed.ncbi.nlm.nih.gov/35108535/ · DOI 10.1016/j.celrep.2022.110320

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 350–356

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human cancer-cell hypoxia experiments and three-dimensional/xenograft models. · source_derived_draft · unverified_draft

## l-proline-pycr1-hypoxic-redox Making proline can also help rebalance mitochondrial reducing power. In hypoxic cancer models, increased PYCR1-dependent proline synthesis oxidized NADH and helped sustain TCA-cycle activity. Model: Human cancer-cell hypoxia experiments and three-dimensional/xenograft models. Limitations: A benefit to tumor-cell survival is not a health benefit of supplementation; proline production is part of the reaction that consumes NADH. Evidence access: Primary full text Proline synthesis through PYCR1 is required to support cancer cell proliferation and survival in oxygen-limiting conditions. · 2022 · https://pubmed.ncbi.nlm.nih.gov/35108535/ · DOI 10.1016/j.celrep.2022.110320

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary abstract

experimental_model

Human families, variant-expression studies and CRISPR-modified human cells.

limitations

This does not prove that low circulating proline is the disease mechanism or that extra substrate rescues it.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

A related enzyme has a distinct neurological disease pattern.

primary_references

Mutations in PYCR2, Encoding Pyrroline-5-Carboxylate Reductase 2, Cause Microcephaly and Hypomyelination. · 2015 · https://pubmed.ncbi.nlm.nih.gov/25865492/ · DOI 10.1016/j.ajhg.2015.03.003

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 158–164

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human families, variant-expression studies and CRISPR-modified human cells. · source_derived_draft · unverified_draft

## l-proline-pycr2-genetic A related enzyme has a distinct neurological disease pattern. PYCR2 variants in two families were associated with microcephaly and hypomyelination; engineered PYCR2 loss in HEK293FT cells lowered mitochondrial membrane potential and increased oxidative-stress-induced apoptosis. Model: Human families, variant-expression studies and CRISPR-modified human cells. Limitations: This does not prove that low circulating proline is the disease mechanism or that extra substrate rescues it. Evidence access: Primary abstract Mutations in PYCR2, Encoding Pyrroline-5-Carboxylate Reductase 2, Cause Microcephaly and Hypomyelination. · 2015 · https://pubmed.ncbi.nlm.nih.gov/25865492/ · DOI 10.1016/j.ajhg.2015.03.003

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary abstract

experimental_model

Human RPE culture with pharmacological catabolism inhibition and metabolite measurements.

limitations

Pharmacological specificity and culture conditions limit inference; no human blood-proline threshold is established.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

A block in proline use can affect antioxidant production indirectly.

primary_references

Proline mediates metabolic communication between retinal pigment epithelial cells and the retina. · 2019 · https://pubmed.ncbi.nlm.nih.gov/31110046/ · DOI 10.1074/jbc.RA119.007983

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 318–324

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human RPE culture with pharmacological catabolism inhibition and metabolite measurements. · source_derived_draft · unverified_draft

## l-proline-rpe-catabolism-block A block in proline use can affect antioxidant production indirectly. Blocking proline catabolism in human RPE impaired glucose metabolism and glutathione production. Model: Human RPE culture with pharmacological catabolism inhibition and metabolite measurements. Limitations: Pharmacological specificity and culture conditions limit inference; no human blood-proline threshold is established. Evidence access: Primary abstract Proline mediates metabolic communication between retinal pigment epithelial cells and the retina. · 2019 · https://pubmed.ncbi.nlm.nih.gov/31110046/ · DOI 10.1074/jbc.RA119.007983

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary final published full text

experimental_model

Mouse Prodh mutant tissue and isotope-transfer experiments, supported by coculture and in-vivo tracing.

limitations

Mouse compartmental transfer is not proof that oral proline prevents human retinal degeneration.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

The retina depends on processing in a neighboring support tissue.

primary_references

Proline provides a nitrogen source in the retinal pigment epithelium to synthesize and export amino acids for the neural retina. · 2023 · https://pubmed.ncbi.nlm.nih.gov/37741457/ · DOI 10.1016/j.jbc.2023.105275

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 334–340

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Mouse Prodh mutant tissue and isotope-transfer experiments, supported by coculture and in-vivo tracing. · source_derived_draft · unverified_draft

## l-proline-rpe-retina-nitrogen The retina depends on processing in a neighboring support tissue. Prodh loss blocked proline nitrogen utilization by mouse RPE and diminished delivery of proline-derived amino-acid nitrogen to the retina. Model: Mouse Prodh mutant tissue and isotope-transfer experiments, supported by coculture and in-vivo tracing. Limitations: Mouse compartmental transfer is not proof that oral proline prevents human retinal degeneration. Evidence access: Primary final published full text Proline provides a nitrogen source in the retinal pigment epithelium to synthesize and export amino acids for the neural retina. · 2023 · https://pubmed.ncbi.nlm.nih.gov/37741457/ · DOI 10.1016/j.jbc.2023.105275

evidence_access

Primary full text

experimental_model

Purified human ACE2-SIT1 complex; pipecolate is a proline-related ligand, not proline itself.

limitations

ACE2 partnership does not establish that proline intake changes susceptibility to viral infection.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

A transporter can use a partner protein and still have its own distinct transport mechanism.

primary_references

Structure and function of the SIT1 proline transporter in complex with the COVID-19 receptor ACE2. · 2024 · https://pubmed.ncbi.nlm.nih.gov/38951531/ · DOI 10.1038/s41467-024-48921-x

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 182–188

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Purified human ACE2-SIT1 complex; pipecolate is a proline-related ligand, not proline itself. · source_derived_draft · unverified_draft

## l-proline-sit1-ace2 A transporter can use a partner protein and still have its own distinct transport mechanism. Cryo-EM resolved human SIT1 in complex with ACE2, with pipecolate-bound and substrate-free conformations identifying the cytoplasmic gate and substrate-release changes. Model: Purified human ACE2-SIT1 complex; pipecolate is a proline-related ligand, not proline itself. Limitations: ACE2 partnership does not establish that proline intake changes susceptibility to viral infection. Evidence access: Primary full text Structure and function of the SIT1 proline transporter in complex with the COVID-19 receptor ACE2. · 2024 · https://pubmed.ncbi.nlm.nih.gov/38951531/ · DOI 10.1038/s41467-024-48921-x

evidence_access

Primary full text

experimental_model

Human SIT1 in Xenopus oocytes; 1 mM substrates at pH 7.4 and -60 mV.

limitations

Failure of glycine to stabilize purified SIT1 thermally did not rule out its transport; binding-proxy and transport assays measure different things.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

This transporter has overlapping amino-acid routes with unequal efficiency.

primary_references

Structure and function of the SIT1 proline transporter in complex with the COVID-19 receptor ACE2. · 2024 · https://pubmed.ncbi.nlm.nih.gov/38951531/ · DOI 10.1038/s41467-024-48921-x

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 190–196

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human SIT1 in Xenopus oocytes; 1 mM substrates at pH 7.4 and -60 mV. · source_derived_draft · unverified_draft

## l-proline-sit1-glycine This transporter has overlapping amino-acid routes with unequal efficiency. Human SIT1 produced glycine-evoked current about 18% of the proline response in the reported substrate comparison; sarcosine current was about 83%. Model: Human SIT1 in Xenopus oocytes; 1 mM substrates at pH 7.4 and -60 mV. Limitations: Failure of glycine to stabilize purified SIT1 thermally did not rule out its transport; binding-proxy and transport assays measure different things. Evidence access: Primary full text Structure and function of the SIT1 proline transporter in complex with the COVID-19 receptor ACE2. · 2024 · https://pubmed.ncbi.nlm.nih.gov/38951531/ · DOI 10.1038/s41467-024-48921-x

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary full text

experimental_model

Human SIT1 variant expressed in Xenopus oocytes with structural interpretation.

limitations

The proposed packing mechanism is an interpretation informed by structure, while reduced current was measured.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

A transporter can reach the assay system yet move substrate less efficiently.

primary_references

Structure and function of the SIT1 proline transporter in complex with the COVID-19 receptor ACE2. · 2024 · https://pubmed.ncbi.nlm.nih.gov/38951531/ · DOI 10.1038/s41467-024-48921-x

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 198–204

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human SIT1 variant expressed in Xenopus oocytes with structural interpretation. · source_derived_draft · unverified_draft

## l-proline-sit1-variant A transporter can reach the assay system yet move substrate less efficiently. SIT1 T199M reduced maximal proline-induced transport current about threefold, supporting a defect in gate dynamics implicated in iminoglycinuria. Model: Human SIT1 variant expressed in Xenopus oocytes with structural interpretation. Limitations: The proposed packing mechanism is an interpretation informed by structure, while reduced current was measured. Evidence access: Primary full text Structure and function of the SIT1 proline transporter in complex with the COVID-19 receptor ACE2. · 2024 · https://pubmed.ncbi.nlm.nih.gov/38951531/ · DOI 10.1038/s41467-024-48921-x

evidence_access

Primary abstract

experimental_model

Mouse embryonic stem-cell model; reversible phenotype and histone-mark measurements.

limitations

The result does not establish a supplement ratio, a clinical methylation imbalance, or vitamin C depletion by ordinary proline intake.

nutrient_topic

L-Proline collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Proline

plain_language

Vitamin C and proline intersect in this experimental epigenetic response.

primary_references

L-Proline induces a mesenchymal-like invasive program in embryonic stem cells by remodeling H3K9 and H3K36 methylation. · 2013 · https://pubmed.ncbi.nlm.nih.gov/24319666/ · DOI 10.1016/j.stemcr.2013.09.001

L-Proline: synthesis, collagen processing, redox metabolism and cross-nutrient mechanisms (2026-09-19) · lines 398–404

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Mouse embryonic stem-cell model; reversible phenotype and histone-mark measurements. · source_derived_draft · unverified_draft

## l-proline-stem-cell-vitamin-c Vitamin C and proline intersect in this experimental epigenetic response. Ascorbic-acid addition or proline withdrawal reversed the reported proline-induced stem-cell state and reduced the associated H3K9/H3K36 methylation pattern. Model: Mouse embryonic stem-cell model; reversible phenotype and histone-mark measurements. Limitations: The result does not establish a supplement ratio, a clinical methylation imbalance, or vitamin C depletion by ordinary proline intake. Evidence access: Primary abstract L-Proline induces a mesenchymal-like invasive program in embryonic stem cells by remodeling H3K9 and H3K36 methylation. · 2013 · https://pubmed.ncbi.nlm.nih.gov/24319666/ · DOI 10.1016/j.stemcr.2013.09.001

evidence_access

Primary abstract

experimental_model

Six pigs; isolated loops perfused for 120 minutes with an amino-acid mixture and labeled phenylalanine incorporation.

limitations

An acute local dose response is distinct from chronic whole-diet excess.

nutrient_topic

L-Threonine collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Threonine

plain_language

The local amino-acid supply can change how quickly mucus protein is made.

primary_references

Luminal threonine concentration acutely affects intestinal mucosal protein and mucin synthesis in piglets. · 2008 · https://pubmed.ncbi.nlm.nih.gov/18567751/ · DOI 10.1093/jn/138.7.1298

L-Threonine: translation, intestinal barrier, metabolism and cross-nutrient mechanisms (2026-09-19) · lines 210–216

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Six pigs; isolated loops perfused for 120 minutes with an amino-acid mixture and labeled phenylalanine incorporation. · source_derived_draft · unverified_draft

## l-threonine-gut-local-synthesis The local amino-acid supply can change how quickly mucus protein is made. Increasing luminal threonine across 0, 21 and 56 mg/g total amino acids raised measured mucin synthesis in perfused intestinal loops. Model: Six pigs; isolated loops perfused for 120 minutes with an amino-acid mixture and labeled phenylalanine incorporation. Limitations: An acute local dose response is distinct from chronic whole-diet excess. Evidence access: Primary abstract Luminal threonine concentration acutely affects intestinal mucosal protein and mucin synthesis in piglets. · 2008 · https://pubmed.ncbi.nlm.nih.gov/18567751/ · DOI 10.1093/jn/138.7.1298

evidence_access

Full-text results, Figures 2 and 6, Europe PMC PMC5075284; primary abstract.

experimental_model

Primary human activated T cells; isotope tracing and functional assays.

limitations

Flux is model-specific; not evidence of clinical wound healing.

nutrient_topic

L-Arginine collection; tissue, species, dose and formulation distinctions retained. · L-Arginine

plain_language

Arginine fed more than the NO pathway.

primary_references

L-Arginine Modulates T Cell Metabolism and Enhances Survival and Anti-tumor Activity. · 2016 · https://pubmed.ncbi.nlm.nih.gov/27745970/ · DOI 10.1016/j.cell.2016.09.031

L-Arginine: transport, metabolic branches, nutrient interactions, availability and discovery questions (2026-09-18) · lines 222–228

AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Primary human activated T cells; isotope tracing and functional assays. · source_derived_draft · unverified_draft

## arg-tcell-carbon Arginine fed more than the NO pathway. Tracer carbon appeared in putrescine and proline; arginase inhibition reduced these labeled products. Model: Primary human activated T cells; isotope tracing and functional assays. Limitations: Flux is model-specific; not evidence of clinical wound healing. Evidence access: Full-text results, Figures 2 and 6, Europe PMC PMC5075284; primary abstract. L-Arginine Modulates T Cell Metabolism and Enhances Survival and Anti-tumor Activity. · 2016 · https://pubmed.ncbi.nlm.nih.gov/27745970/ · DOI 10.1016/j.cell.2016.09.031