5,10-Methylenetetrahydrofolate

evidence_access

Primary full text, Figure 1 and metabolic-labeling experiments

experimental_model

Human HeLa metabolic labeling plus biochemical reconstitution.

limitations

A folate connection is not evidence for a benefit from folic acid supplementation in replete people.

nutrient_topic

Taurine collection; molecular form, preparation, species, exposure and manipulation remain explicit. · Taurine

plain_language

Folate chemistry contributes part of the RNA mark; taurine supplies a different part.

primary_references

Metabolic and chemical regulation of tRNA modification associated with taurine deficiency and human disease. · 2018 · https://pubmed.ncbi.nlm.nih.gov/29390138/ · DOI 10.1093/nar/gky068

Taurine: synthesis, transport, mitochondrial decoding and nutrient interactions (2026-09-19) · lines 209–215

AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Human HeLa metabolic labeling plus biochemical reconstitution. · source_derived_draft · unverified_draft

## taurine-folate-carbon-donor Folate chemistry contributes part of the RNA mark; taurine supplies a different part. Isotope tracing supported the beta-carbon of serine entering the methylene group of mitochondrial taurine-modified uridine through 5,10-methylene-THF. Model: Human HeLa metabolic labeling plus biochemical reconstitution. Limitations: A folate connection is not evidence for a benefit from folic acid supplementation in replete people. Evidence access: Primary full text, Figure 1 and metabolic-labeling experiments Metabolic and chemical regulation of tRNA modification associated with taurine deficiency and human disease. · 2018 · https://pubmed.ncbi.nlm.nih.gov/29390138/ · DOI 10.1093/nar/gky068

cross_nutrient

B6-dependent GLDC precedes lipoyl-carrier transfer and folate-dependent AMT chemistry.

experimental_model

Purified human AMT structures and mutational analyses

limitations

AMT is the directly examined human enzyme; this study did not test dietary B6 depletion or the entire pathway flux.

nutrient_topic

Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. · Vitamin B6

organism

Homo sapiens

plain_language

Glycine cleavage connects its B6-dependent first step to a separate folate-dependent step.

primary_references

[b6-amt-2005] Crystal structure of human T-protein of glycine cleavage system at 2.0 A resolution and its implication for understanding non-ketotic hyperglycinemia. (2005). https://pubmed.ncbi.nlm.nih.gov/16051266/ DOI: 10.1016/j.jmb.2005.06.056

tissue_or_cell_type

Purified recombinant protein; no intact tissue

Vitamin B6: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 682–692

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Purified human AMT structures and mutational analyses · source_derived_draft · unverified_draft

### b6-met-amt-onecarbon Human AMT transfers the aminomethyl-lipoyl intermediate's carbon to tetrahydrofolate, yielding 5,10-methylene-THF, ammonia and reduced H-protein. Condition category: normal nutrient_topic: Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. plain_language: Glycine cleavage connects its B6-dependent first step to a separate folate-dependent step. organism: Homo sapiens tissue_or_cell_type: Purified recombinant protein; no intact tissue experimental_model: Purified human AMT structures and mutational analyses limitations: AMT is the directly examined human enzyme; this study did not test dietary B6 depletion or the entire pathway flux. cross_nutrient: B6-dependent GLDC precedes lipoyl-carrier transfer and folate-dependent AMT chemistry. [b6-amt-2005] Crystal structure of human T-protein of glycine cleavage system at 2.0 A resolution and its implication for understanding non-ketotic hyperglycinemia. (2005). https://pubmed.ncbi.nlm.nih.gov/16051266/ DOI: 10.1016/j.jmb.2005.06.056

cross_nutrient

PLP (B6) and THF (folate) cooperate in one reaction.

experimental_model

Purified human SHMT1 and SHMT2; structures and solution oligomerization

limitations

Reaction is reversible; assembly assays do not establish flux in every cell.

nutrient_topic

Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. · Vitamin B6

organism

Homo sapiens

plain_language

The enzyme connects B6-dependent amino-acid chemistry to folate chemistry.

primary_references

[b6-shmt-2015] How pyridoxal 5'-phosphate differentially regulates human cytosolic and mitochondrial serine hydroxymethyltransferase oligomeric state (2015). https://febs.onlinelibrary.wiley.com/doi/10.1111/febs.13211 DOI: 10.1111/febs.13211

tissue_or_cell_type

Purified recombinant protein; no intact tissue

Vitamin B6: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 602–612

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Purified human SHMT1 and SHMT2; structures and solution oligomerization · source_derived_draft · unverified_draft

### b6-met-shmt1-onecarbon Human SHMT1 uses PLP to couple serine-to-glycine conversion with transfer of a one-carbon unit to tetrahydrofolate. Condition category: normal nutrient_topic: Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. plain_language: The enzyme connects B6-dependent amino-acid chemistry to folate chemistry. organism: Homo sapiens tissue_or_cell_type: Purified recombinant protein; no intact tissue experimental_model: Purified human SHMT1 and SHMT2; structures and solution oligomerization limitations: Reaction is reversible; assembly assays do not establish flux in every cell. cross_nutrient: PLP (B6) and THF (folate) cooperate in one reaction. [b6-shmt-2015] How pyridoxal 5'-phosphate differentially regulates human cytosolic and mitochondrial serine hydroxymethyltransferase oligomeric state (2015). https://febs.onlinelibrary.wiley.com/doi/10.1111/febs.13211 DOI: 10.1111/febs.13211

cross_nutrient

PLP (B6) and THF (folate) cooperate in one reaction.

experimental_model

Purified human SHMT1 and SHMT2; structures and solution oligomerization

limitations

Reaction is reversible; assembly assays do not establish flux in every cell.

nutrient_topic

Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. · Vitamin B6

organism

Homo sapiens

plain_language

The enzyme connects B6-dependent amino-acid chemistry to folate chemistry.

primary_references

[b6-shmt-2015] How pyridoxal 5'-phosphate differentially regulates human cytosolic and mitochondrial serine hydroxymethyltransferase oligomeric state (2015). https://febs.onlinelibrary.wiley.com/doi/10.1111/febs.13211 DOI: 10.1111/febs.13211

tissue_or_cell_type

Purified recombinant protein; no intact tissue

Vitamin B6: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 614–624

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Purified human SHMT1 and SHMT2; structures and solution oligomerization · source_derived_draft · unverified_draft

### b6-met-shmt2-onecarbon Human SHMT2 uses PLP to couple serine-to-glycine conversion with transfer of a one-carbon unit to tetrahydrofolate. Condition category: normal nutrient_topic: Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. plain_language: The enzyme connects B6-dependent amino-acid chemistry to folate chemistry. organism: Homo sapiens tissue_or_cell_type: Purified recombinant protein; no intact tissue experimental_model: Purified human SHMT1 and SHMT2; structures and solution oligomerization limitations: Reaction is reversible; assembly assays do not establish flux in every cell. cross_nutrient: PLP (B6) and THF (folate) cooperate in one reaction. [b6-shmt-2015] How pyridoxal 5'-phosphate differentially regulates human cytosolic and mitochondrial serine hydroxymethyltransferase oligomeric state (2015). https://febs.onlinelibrary.wiley.com/doi/10.1111/febs.13211 DOI: 10.1111/febs.13211

evidence_span

{"source_cache": "artifacts/choline-research/24858690.abstract.txt", "locator": "Primary indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "e00bbb8f1c2c805e9d7261c286bace5758abd277bc95b3e0a830bd9cdb82a34f", "start_char": 0, "end_char": 1506, "text_sha256": "e00bbb8f1c2c805e9d7261c286bace5758abd277bc95b3e0a830bd9cdb82a34f"}

experimental_model

Rat DMGDH crystallography and enzyme characterization

exposure

Dimethylglycine turnover and THF-bound structures

limitations

Pathway chemistry interpreted with rat enzyme structures; not proof that dietary folate rescue restores every human choline-dependent function.

nutrient_topic

Choline research collection; topical membership is not evidence of a direct dietary effect. · Choline

organism

Rat recombinant enzyme

plain_language

Choline-derived methyl metabolism feeds the folate pool.

primary_references

[choline-p24858690] Folate in demethylation: the crystal structure of the rat dimethylglycine dehydrogenase complexed with tetrahydrofolate. (2014). https://pubmed.ncbi.nlm.nih.gov/24858690/ DOI: 10.1016/j.bbrc.2014.05.064

tissue_or_cell_type

Mitochondrial-enzyme preparation

Choline: metabolism, signaling and nutrient connections (2026-09-17) · lines 685–696

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Rat DMGDH crystallography and enzyme characterization · source_derived_draft · unverified_draft

### choline-dmgdh-one-carbon In the THF-coupled DMGDH pathway, a removed one-carbon unit is captured as 5,10-methylenetetrahydrofolate rather than released as free formaldehyde. Condition category: normal nutrient_topic: Choline research collection; topical membership is not evidence of a direct dietary effect. plain_language: Choline-derived methyl metabolism feeds the folate pool. organism: Rat recombinant enzyme tissue_or_cell_type: Mitochondrial-enzyme preparation experimental_model: Rat DMGDH crystallography and enzyme characterization limitations: Pathway chemistry interpreted with rat enzyme structures; not proof that dietary folate rescue restores every human choline-dependent function. exposure: Dimethylglycine turnover and THF-bound structures evidence_span: {"source_cache": "artifacts/choline-research/24858690.abstract.txt", "locator": "Primary indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "e00bbb8f1c2c805e9d7261c286bace5758abd277bc95b3e0a830bd9cdb82a34f", "start_char": 0, "end_char": 1506, "text_sha256": "e00bbb8f1c2c805e9d7261c286bace5758abd277bc95b3e0a830bd9cdb82a34f"} [choline-p24858690] Folate in demethylation: the crystal structure of the rat dimethylglycine dehydrogenase complexed with tetrahydrofolate. (2014). https://pubmed.ncbi.nlm.nih.gov/24858690/ DOI: 10.1016/j.bbrc.2014.05.064

cross_nutrient

ATP and NADPH support folate-mediated carbon use.

experimental_model

Localization and folate-pathway experiments

exposure

Assay conditions described in the linked primary study.

limitations

Compartmental flux varies with cell cycle.

nutrient_topic

Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. · Folate (vitamin B9)

organism

Homo sapiens

plain_language

Formate can feed DNA-base production inside the nucleus.

primary_references

[field-2014] Nuclear enrichment of folate cofactors and methylenetetrahydrofolate dehydrogenase 1 (MTHFD1) protect de novo thymidylate biosynthesis during folate deficiency (2014). https://pubmed.ncbi.nlm.nih.gov/25213861/ DOI: 10.1074/jbc.m114.599589

tissue_or_cell_type

HeLa and MCF7 cells

Folate and folic acid: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 936–947

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Localization and folate-pathway experiments · source_derived_draft · unverified_draft

### mthfd1-formate-nuclear-carbon Nuclear MTHFD1 supplies formate-derived one-carbon units for thymidylate synthesis through its folate-interconversion activities. Condition category: normal nutrient_topic: Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. plain_language: Formate can feed DNA-base production inside the nucleus. organism: Homo sapiens tissue_or_cell_type: HeLa and MCF7 cells experimental_model: Localization and folate-pathway experiments limitations: Compartmental flux varies with cell cycle. exposure: Assay conditions described in the linked primary study. cross_nutrient: ATP and NADPH support folate-mediated carbon use. [field-2014] Nuclear enrichment of folate cofactors and methylenetetrahydrofolate dehydrogenase 1 (MTHFD1) protect de novo thymidylate biosynthesis during folate deficiency (2014). https://pubmed.ncbi.nlm.nih.gov/25213861/ DOI: 10.1074/jbc.m114.599589

experimental_model

Purified short isoform

exposure

Assay conditions described in the linked primary study.

limitations

Negative activity result is assay-specific; full-length MTHFD1L has synthetase activity.

nutrient_topic

Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. · Folate (vitamin B9)

organism

Homo sapiens

plain_language

This short isoform cannot be assumed to replace MTHFD2.

primary_references

[prasannan-2009] Human mitochondrial C1-tetrahydrofolate synthase: submitochondrial localization of the full-length enzyme and characterization of a short isoform (2009). https://pubmed.ncbi.nlm.nih.gov/18996079/ DOI: 10.1016/j.abb.2008.10.028

tissue_or_cell_type

Cell-free

Folate and folic acid: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 887–897

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Purified short isoform · source_derived_draft · unverified_draft

### mthfd1l-short-no-dehydrogenase The purified short human MTHFD1L isoform lacked detectable methylene-THF dehydrogenase activity. Condition category: normal nutrient_topic: Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. plain_language: This short isoform cannot be assumed to replace MTHFD2. organism: Homo sapiens tissue_or_cell_type: Cell-free experimental_model: Purified short isoform limitations: Negative activity result is assay-specific; full-length MTHFD1L has synthetase activity. exposure: Assay conditions described in the linked primary study. [prasannan-2009] Human mitochondrial C1-tetrahydrofolate synthase: submitochondrial localization of the full-length enzyme and characterization of a short isoform (2009). https://pubmed.ncbi.nlm.nih.gov/18996079/ DOI: 10.1016/j.abb.2008.10.028

cross_nutrient

Nicotinamide cofactors connect folate chemistry to redox metabolism.

experimental_model

Purified recombinant enzyme

exposure

Assay conditions described in the linked primary study.

limitations

Cellular cofactor partition is not quantified.

nutrient_topic

Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. · Folate (vitamin B9)

organism

Homo sapiens

plain_language

This mitochondrial enzyme extracts electrons from folate-bound carbon.

primary_references

[shin-2017] Human mitochondrial MTHFD2 is a dual redox cofactor-specific methylenetetrahydrofolate dehydrogenase/methenyltetrahydrofolate cyclohydrolase (2017). https://pubmed.ncbi.nlm.nih.gov/29225823/ DOI: 10.1186/s40170-017-0173-0

tissue_or_cell_type

Cell-free

Folate and folic acid: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 812–823

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Purified recombinant enzyme · source_derived_draft · unverified_draft

### mthfd2-nad-oxidation Purified human MTHFD2 oxidizes 5,10-methylene-THF using NAD+ to form methenyl-THF and NADH. Condition category: normal nutrient_topic: Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. plain_language: This mitochondrial enzyme extracts electrons from folate-bound carbon. organism: Homo sapiens tissue_or_cell_type: Cell-free experimental_model: Purified recombinant enzyme limitations: Cellular cofactor partition is not quantified. exposure: Assay conditions described in the linked primary study. cross_nutrient: Nicotinamide cofactors connect folate chemistry to redox metabolism. [shin-2017] Human mitochondrial MTHFD2 is a dual redox cofactor-specific methylenetetrahydrofolate dehydrogenase/methenyltetrahydrofolate cyclohydrolase (2017). https://pubmed.ncbi.nlm.nih.gov/29225823/ DOI: 10.1186/s40170-017-0173-0

experimental_model

Purified recombinant rat protein

exposure

Assay conditions described in the linked primary study.

limitations

Human ortholog flux was not measured.

nutrient_topic

Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. · Folate (vitamin B9)

organism

Rattus norvegicus

plain_language

A second mitochondrial enzyme can use either electron carrier.

primary_references

[shin-2014] Mitochondrial MTHFD2L is a dual redox cofactor-specific methylenetetrahydrofolate dehydrogenase/methenyltetrahydrofolate cyclohydrolase expressed in both adult and embryonic tissues (2014). https://pubmed.ncbi.nlm.nih.gov/24733394/ DOI: 10.1074/jbc.m114.555573

tissue_or_cell_type

Cell-free

Folate and folic acid: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 838–848

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Purified recombinant rat protein · source_derived_draft · unverified_draft

### rat-mthfd2l-oxidation Rat MTHFD2L catalyzes methylene-THF oxidation with either NAD+ or NADP+. Condition category: normal nutrient_topic: Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. plain_language: A second mitochondrial enzyme can use either electron carrier. organism: Rattus norvegicus tissue_or_cell_type: Cell-free experimental_model: Purified recombinant rat protein limitations: Human ortholog flux was not measured. exposure: Assay conditions described in the linked primary study. [shin-2014] Mitochondrial MTHFD2L is a dual redox cofactor-specific methylenetetrahydrofolate dehydrogenase/methenyltetrahydrofolate cyclohydrolase expressed in both adult and embryonic tissues (2014). https://pubmed.ncbi.nlm.nih.gov/24733394/ DOI: 10.1074/jbc.m114.555573

availability_state

nutrient_deficiency Imported condition classification; unverified.

cross_nutrient

B6-dependent glycine cleavage supplies folate one-carbon chemistry.

experimental_model

Thirteen healthy adults (seven men, six women; ages 20–39); glycine and leucine stable-isotope infusion.

exposure

Moderate dietary B6 restriction; plasma PLP55±4 to 23±1 nmol/L.

limitations

Whole-body kinetics do not resolve separate organs or prove severe deficiency harmless.

nutrient_topic

Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. · Vitamin B6

organism

Homo sapiens

plain_language

This folate-linked carbon supply remained measurable despite lower blood B6.

primary_references

[b6-lamers2009] Moderate dietary vitamin B-6 restriction raises plasma glycine and cystathionine concentrations while minimally affecting the rates of glycine turnover and glycine cleavage in healthy men and women (2009). https://pubmed.ncbi.nlm.nih.gov/19158217/ DOI: 10.3945/jn.108.099184

tissue_or_cell_type

Human blood and whole-body measurements

trigger_kind

nutrient_deficiency Imported condition classification; unverified.

Vitamin B6: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 1397–1408

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Thirteen healthy adults (seven men, six women; ages 20–39); glycine and leucine stable-isotope infusion. · source_derived_draft · unverified_draft

### b6-glycine-cleavage-resilience Restriction did not significantly change glycine cleavage or serine synthesis from GCS-derived one-carbon units. Condition category: nutrient_deficiency nutrient_topic: Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. plain_language: This folate-linked carbon supply remained measurable despite lower blood B6. organism: Homo sapiens tissue_or_cell_type: Human blood and whole-body measurements experimental_model: Thirteen healthy adults (seven men, six women; ages 20–39); glycine and leucine stable-isotope infusion. limitations: Whole-body kinetics do not resolve separate organs or prove severe deficiency harmless. exposure: Moderate dietary B6 restriction; plasma PLP55±4 to 23±1 nmol/L. cross_nutrient: B6-dependent glycine cleavage supplies folate one-carbon chemistry. [b6-lamers2009] Moderate dietary vitamin B-6 restriction raises plasma glycine and cystathionine concentrations while minimally affecting the rates of glycine turnover and glycine cleavage in healthy men and women (2009). https://pubmed.ncbi.nlm.nih.gov/19158217/ DOI: 10.3945/jn.108.099184

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary full text, Figure 1F

experimental_model

Chinese hamster ovary Mft mutant cells.

limitations

Compartment-specific transport failure is different from low total blood folate.

nutrient_topic

Taurine collection; molecular form, preparation, species, exposure and manipulation remain explicit. · Taurine

plain_language

Getting folate into the mitochondrial compartment matters.

primary_references

Metabolic and chemical regulation of tRNA modification associated with taurine deficiency and human disease. · 2018 · https://pubmed.ncbi.nlm.nih.gov/29390138/ · DOI 10.1093/nar/gky068

trigger_kind

machinery_impairment Imported condition classification; unverified.

Taurine: synthesis, transport, mitochondrial decoding and nutrient interactions (2026-09-19) · lines 225–231

AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Chinese hamster ovary Mft mutant cells. · source_derived_draft · unverified_draft

## taurine-folate-carrier-mutation Getting folate into the mitochondrial compartment matters. Mitochondrial folate-transporter-mutant CHO cells showed reduced taurine modification of mitochondrial tRNA. Model: Chinese hamster ovary Mft mutant cells. Limitations: Compartment-specific transport failure is different from low total blood folate. Evidence access: Primary full text, Figure 1F Metabolic and chemical regulation of tRNA modification associated with taurine deficiency and human disease. · 2018 · https://pubmed.ncbi.nlm.nih.gov/29390138/ · DOI 10.1093/nar/gky068

evidence_access

Primary full text, in-vitro reconstitution methods and results

experimental_model

Human enzyme-complex reconstitution and mass spectrometry.

limitations

The reaction mixture also contained GTP, ATP, FAD, NADH, NADPH and magnesium; their presence alone does not demonstrate each is individually limiting.

nutrient_topic

Taurine collection; molecular form, preparation, species, exposure and manipulation remain explicit. · Taurine

plain_language

Two proteins join taurine and a folate-derived carbon unit onto mitochondrial tRNA.

primary_references

Metabolic and chemical regulation of tRNA modification associated with taurine deficiency and human disease. · 2018 · https://pubmed.ncbi.nlm.nih.gov/29390138/ · DOI 10.1093/nar/gky068

Taurine: synthesis, transport, mitochondrial decoding and nutrient interactions (2026-09-19) · lines 201–207

AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · Human enzyme-complex reconstitution and mass spectrometry. · source_derived_draft · unverified_draft

## taurine-mto1-gtpbp3 Two proteins join taurine and a folate-derived carbon unit onto mitochondrial tRNA. Reconstituting the human MTO1-GTPBP3 complex with hypomodified mitochondrial tRNA, taurine and 5,10-methylene-THF produced the taurine-containing U34 modification. Model: Human enzyme-complex reconstitution and mass spectrometry. Limitations: The reaction mixture also contained GTP, ATP, FAD, NADH, NADPH and magnesium; their presence alone does not demonstrate each is individually limiting. Evidence access: Primary full text, in-vitro reconstitution methods and results Metabolic and chemical regulation of tRNA modification associated with taurine deficiency and human disease. · 2018 · https://pubmed.ncbi.nlm.nih.gov/29390138/ · DOI 10.1093/nar/gky068

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary full text, Figure 1F

experimental_model

CHO mutant-cell mass spectrometry.

limitations

This species-specific machinery defect is not a B6 or folate deprivation experiment.

nutrient_topic

Taurine collection; molecular form, preparation, species, exposure and manipulation remain explicit. · Taurine

plain_language

One-carbon supply can affect the same RNA mark even when the taurine molecule is present.

primary_references

Metabolic and chemical regulation of tRNA modification associated with taurine deficiency and human disease. · 2018 · https://pubmed.ncbi.nlm.nih.gov/29390138/ · DOI 10.1093/nar/gky068

trigger_kind

machinery_impairment Imported condition classification; unverified.

Taurine: synthesis, transport, mitochondrial decoding and nutrient interactions (2026-09-19) · lines 217–223

AI-assisted research curation; primary-abstract references and experimental limitations individually identified. Not publisher full text. · supports · CHO mutant-cell mass spectrometry. · source_derived_draft · unverified_draft

## taurine-shmt2-mutation One-carbon supply can affect the same RNA mark even when the taurine molecule is present. Shmt2-mutant Chinese hamster ovary cells showed reduced mitochondrial tRNA taurine modification compared with wild type. Model: CHO mutant-cell mass spectrometry. Limitations: This species-specific machinery defect is not a B6 or folate deprivation experiment. Evidence access: Primary full text, Figure 1F Metabolic and chemical regulation of tRNA modification associated with taurine deficiency and human disease. · 2018 · https://pubmed.ncbi.nlm.nih.gov/29390138/ · DOI 10.1093/nar/gky068

cross_nutrient

B2-FAD, folate and nicotinamide-containing NADPH participate in one reaction.

evidence_location

Results: kinetics, FAD occupancy and SAM inhibition; Table 1; Figs 2-4, 6

experimental_model

Recombinant human MTHFR expressed in Sf9 cells; mass spectrometry, 2.5-A structure, HPLC activity assays.

exposure

Purified-enzyme assay

limitations

Biochemical evidence does not establish a dietary threshold or supplementation benefit.

nutrient_topic

Riboflavin research collection; topical membership is not evidence of a direct dietary effect. · Riboflavin (vitamin B2)

organism

Homo sapiens

plain_language

The enzyme makes the methylfolate used in homocysteine recycling.

primary_references

[froese2018] Structural basis for the regulation of human 5,10-methylenetetrahydrofolate reductase by phosphorylation and S-adenosylmethionine inhibition. (2018). https://pubmed.ncbi.nlm.nih.gov/29891918/ DOI: 10.1038/s41467-018-04735-2

tissue_or_cell_type

Purified recombinant enzyme; no intact tissue

Riboflavin: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 1010–1022

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Recombinant human MTHFR expressed in Sf9 cells; mass spectrometry, 2.5-A structure, HPLC activity assays. · source_derived_draft · unverified_draft

### b2-mthfr-methylfolate-production HPLC assays measured human MTHFR reduction of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate using NADPH. Condition category: normal nutrient_topic: Riboflavin research collection; topical membership is not evidence of a direct dietary effect. plain_language: The enzyme makes the methylfolate used in homocysteine recycling. organism: Homo sapiens tissue_or_cell_type: Purified recombinant enzyme; no intact tissue experimental_model: Recombinant human MTHFR expressed in Sf9 cells; mass spectrometry, 2.5-A structure, HPLC activity assays. limitations: Biochemical evidence does not establish a dietary threshold or supplementation benefit. exposure: Purified-enzyme assay cross_nutrient: B2-FAD, folate and nicotinamide-containing NADPH participate in one reaction. evidence_location: Results: kinetics, FAD occupancy and SAM inhibition; Table 1; Figs 2-4, 6 [froese2018] Structural basis for the regulation of human 5,10-methylenetetrahydrofolate reductase by phosphorylation and S-adenosylmethionine inhibition. (2018). https://pubmed.ncbi.nlm.nih.gov/29891918/ DOI: 10.1038/s41467-018-04735-2

availability_state

machinery_impairment Imported condition classification; unverified.

evidence_access

Primary abstract

experimental_model

Human SHMT2 knockout and mitochondrial ribosome profiling.

limitations

The methyl-donor route was mechanistically inferred alongside measured modification and translation defects.

nutrient_topic

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

plain_language

Serine-linked folate chemistry helps mitochondria read particular codons.

primary_references

Mitochondrial translation requires folate-dependent tRNA methylation. · 2018 · https://pubmed.ncbi.nlm.nih.gov/29364879/ · DOI 10.1038/nature25460

trigger_kind

machinery_impairment Imported condition classification; unverified.

L-Serine: synthesis, one-carbon metabolism, lipids 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 · Human SHMT2 knockout and mitochondrial ribosome profiling. · source_derived_draft · unverified_draft

## l-serine-shmt2-translation Serine-linked folate chemistry helps mitochondria read particular codons. Catalytic SHMT2 loss in human cells impaired mitochondrial tRNA modification and caused preferential ribosome stalling at AAG lysine and UUG leucine codons. Model: Human SHMT2 knockout and mitochondrial ribosome profiling. Limitations: The methyl-donor route was mechanistically inferred alongside measured modification and translation defects. Evidence access: Primary abstract Mitochondrial translation requires folate-dependent tRNA methylation. · 2018 · https://pubmed.ncbi.nlm.nih.gov/29364879/ · DOI 10.1038/nature25460

cross_nutrient

Folate reduction uses nicotinamide reducing equivalents.

experimental_model

Recombinant human MTHFR; kinetics and structures.

limitations

Affinity does not quantify cellular flux.

nutrient_topic

Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. · Folate (vitamin B9)

organism

Homo sapiens

plain_language

MTHFR strongly preferred NADPH in this assay.

primary_references

[froese-2018] Structural basis for the regulation of human 5,10-methylenetetrahydrofolate reductase by phosphorylation and S-adenosylmethionine inhibition (2018). https://pubmed.ncbi.nlm.nih.gov/29891918/ DOI: 10.1038/s41467-018-04735-2

tissue_or_cell_type

Purified protein

Folate and folic acid: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 435–445

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Recombinant human MTHFR; kinetics and structures. · source_derived_draft · unverified_draft

### folate-methyl-nadph-preference Purified full-length human MTHFR had apparent Km values of 35.5 micromolar for NADPH and 3760 micromolar for NADH. Condition category: normal nutrient_topic: Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. plain_language: MTHFR strongly preferred NADPH in this assay. organism: Homo sapiens tissue_or_cell_type: Purified protein experimental_model: Recombinant human MTHFR; kinetics and structures. limitations: Affinity does not quantify cellular flux. cross_nutrient: Folate reduction uses nicotinamide reducing equivalents. [froese-2018] Structural basis for the regulation of human 5,10-methylenetetrahydrofolate reductase by phosphorylation and S-adenosylmethionine inhibition (2018). https://pubmed.ncbi.nlm.nih.gov/29891918/ DOI: 10.1038/s41467-018-04735-2

cross_nutrient

Folate polyglutamylation changes nicotinamide-cofactor use.

experimental_model

Purified recombinant enzyme

exposure

Mono- versus pentaglutamate folate substrates; controlled NAD(P)+ assays.

limitations

Kinetics do not establish dominant in vivo NADPH production.

nutrient_topic

Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. · Folate (vitamin B9)

organism

Homo sapiens

plain_language

The folate tail affects which electron carrier the enzyme uses.

primary_references

[shin-2017] Human mitochondrial MTHFD2 is a dual redox cofactor-specific methylenetetrahydrofolate dehydrogenase/methenyltetrahydrofolate cyclohydrolase (2017). https://pubmed.ncbi.nlm.nih.gov/29225823/ DOI: 10.1186/s40170-017-0173-0

tissue_or_cell_type

Cell-free

Folate and folic acid: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 825–836

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Purified recombinant enzyme · source_derived_draft · unverified_draft

### mthfd2-nadp-polyglutamate Human MTHFD2 also uses NADP+ with methylene-THF pentaglutamate; NADP-linked activity increases relative to the monoglutamate assay. Condition category: normal nutrient_topic: Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. plain_language: The folate tail affects which electron carrier the enzyme uses. organism: Homo sapiens tissue_or_cell_type: Cell-free experimental_model: Purified recombinant enzyme limitations: Kinetics do not establish dominant in vivo NADPH production. exposure: Mono- versus pentaglutamate folate substrates; controlled NAD(P)+ assays. cross_nutrient: Folate polyglutamylation changes nicotinamide-cofactor use. [shin-2017] Human mitochondrial MTHFD2 is a dual redox cofactor-specific methylenetetrahydrofolate dehydrogenase/methenyltetrahydrofolate cyclohydrolase (2017). https://pubmed.ncbi.nlm.nih.gov/29225823/ DOI: 10.1186/s40170-017-0173-0

cross_nutrient

Links existing B6-dependent SHMT chemistry to folate flux direction.

experimental_model

Stable-isotope tracing

exposure

Assay conditions described in the linked primary study.

limitations

Not a universal direction across tissues or nutrition states.

nutrient_topic

Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. · Folate (vitamin B9)

organism

Homo sapiens

plain_language

SHMT1 can consume one-carbon units instead of producing them.

primary_references

[ducker-2016] Reversal of Cytosolic One-Carbon Flux Compensates for Loss of the Mitochondrial Folate Pathway (2016). https://pubmed.ncbi.nlm.nih.gov/27211901/ DOI: 10.1016/j.cmet.2016.04.016

tissue_or_cell_type

HEK293T and HCT116 cells

Folate and folic acid: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 923–934

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Stable-isotope tracing · source_derived_draft · unverified_draft

### shmt1-reverse-flux-replete In nutrient-replete HEK293T and HCT116 cells, isotope tracing showed net SHMT1 flux toward serine synthesis. Condition category: normal nutrient_topic: Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. plain_language: SHMT1 can consume one-carbon units instead of producing them. organism: Homo sapiens tissue_or_cell_type: HEK293T and HCT116 cells experimental_model: Stable-isotope tracing limitations: Not a universal direction across tissues or nutrition states. exposure: Assay conditions described in the linked primary study. cross_nutrient: Links existing B6-dependent SHMT chemistry to folate flux direction. [ducker-2016] Reversal of Cytosolic One-Carbon Flux Compensates for Loss of the Mitochondrial Folate Pathway (2016). https://pubmed.ncbi.nlm.nih.gov/27211901/ DOI: 10.1016/j.cmet.2016.04.016

experimental_model

Purified human TYMS reaction assays

exposure

Assay conditions described in the linked primary study.

limitations

Purified-enzyme chemistry does not specify cellular flux.

nutrient_topic

Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. · Folate (vitamin B9)

organism

Homo sapiens

plain_language

Folate supplies the carbon and reducing power to make a DNA base.

primary_references

[islam-2018] Bacterial versus human thymidylate synthase: Kinetics and functionality (2018). https://pubmed.ncbi.nlm.nih.gov/29715278/ DOI: 10.1371/journal.pone.0196506

tissue_or_cell_type

Cell-free

Folate and folic acid: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 973–983

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Purified human TYMS reaction assays · source_derived_draft · unverified_draft

### tyms-dump-methylation Human TYMS uses 5,10-methylene-THF to convert dUMP to dTMP, producing dihydrofolate. Condition category: normal nutrient_topic: Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. plain_language: Folate supplies the carbon and reducing power to make a DNA base. organism: Homo sapiens tissue_or_cell_type: Cell-free experimental_model: Purified human TYMS reaction assays limitations: Purified-enzyme chemistry does not specify cellular flux. exposure: Assay conditions described in the linked primary study. [islam-2018] Bacterial versus human thymidylate synthase: Kinetics and functionality (2018). https://pubmed.ncbi.nlm.nih.gov/29715278/ DOI: 10.1371/journal.pone.0196506