5-Methyltetrahydrofolate

evidence_access

Primary abstract

experimental_model

Rat liver GNMT crystallography and binding experiments.

limitations

Rat enzyme and defined ligand conditions; not a demonstrated human supplement interaction.

nutrient_topic

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

plain_language

Folate can regulate methyl-group disposal through glycine.

primary_references

5-methyltetrahydrofolate is bound in intersubunit areas of rat liver folate-binding protein glycine N-methyltransferase. · 2007 · https://pubmed.ncbi.nlm.nih.gov/17158459/ · DOI 10.1074/jbc.M610384200

L-Methionine: transport, methylation, sulfur metabolism and cross-nutrient mechanisms (2026-09-19) · lines 212–218

AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Rat liver GNMT crystallography and binding experiments. · source_derived_draft · unverified_draft

## methionine-gnmt-folate-structure Folate can regulate methyl-group disposal through glycine. Rat GNMT structures located two folate-binding sites between subunits; occupancy restricts the N-terminal movements needed for substrate access. Model: Rat liver GNMT crystallography and binding experiments. Limitations: Rat enzyme and defined ligand conditions; not a demonstrated human supplement interaction. Evidence access: Primary abstract 5-methyltetrahydrofolate is bound in intersubunit areas of rat liver folate-binding protein glycine N-methyltransferase. · 2007 · https://pubmed.ncbi.nlm.nih.gov/17158459/ · DOI 10.1074/jbc.M610384200

availability_state

machinery_impairment Imported condition classification; unverified.

cross_nutrient

Folate binding can stabilize a B2-derived cofactor interaction.

evidence_location

Results: FAD loss; Figs 1-3

experimental_model

Baculovirus-produced purified human wild-type, Ala222Val, Glu429Ala and double-mutant MTHFR; dilution/cofactor-release assays.

exposure

Purified-enzyme assay

limitations

Protein-stability assay; clinical folate or riboflavin treatment effects were not tested here.

nutrient_topic

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

organism

Homo sapiens

plain_language

Folate product helped the variant retain FAD in vitro.

primary_references

[yamada2001] Effects of common polymorphisms on the properties of recombinant human methylenetetrahydrofolate reductase. (2001). https://pubmed.ncbi.nlm.nih.gov/11742092/ DOI: 10.1073/pnas.261469998

tissue_or_cell_type

Purified recombinant enzyme; no intact tissue

trigger_kind

machinery_impairment Imported condition classification; unverified.

Riboflavin: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 1052–1064

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Baculovirus-produced purified human wild-type, Ala222Val, Glu429Ala and double-mutant MTHFR; dilution/cofactor-release assays. · source_derived_draft · unverified_draft

### b2-methylfolate-mthfr-retention Methyltetrahydrofolate slowed FAD loss from diluted Ala222Val MTHFR in the tested concentration series. Condition category: machinery_impairment nutrient_topic: Riboflavin research collection; topical membership is not evidence of a direct dietary effect. plain_language: Folate product helped the variant retain FAD in vitro. organism: Homo sapiens tissue_or_cell_type: Purified recombinant enzyme; no intact tissue experimental_model: Baculovirus-produced purified human wild-type, Ala222Val, Glu429Ala and double-mutant MTHFR; dilution/cofactor-release assays. limitations: Protein-stability assay; clinical folate or riboflavin treatment effects were not tested here. exposure: Purified-enzyme assay cross_nutrient: Folate binding can stabilize a B2-derived cofactor interaction. evidence_location: Results: FAD loss; Figs 1-3 [yamada2001] Effects of common polymorphisms on the properties of recombinant human methylenetetrahydrofolate reductase. (2001). https://pubmed.ncbi.nlm.nih.gov/11742092/ DOI: 10.1073/pnas.261469998

evidence_span

{"source_cache": "artifacts/citrulline-research/16940192.abstract.txt", "locator": "Primary indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "42c07dd0bbacfc1ff44f78d6ce69810a58946e53c76bf5d3bf8385db5278ba8b", "start_char": 0, "end_char": 1942, "text_sha256": "42c07dd0bbacfc1ff44f78d6ce69810a58946e53c76bf5d3bf8385db5278ba8b"}

experimental_model

Ex-vivo vessel exposure and randomized pre-harvest infusion

exposure

5-MTHF ex vivo 1-100 micromolar; intravenous 5-MTHF or placebo in a separate subset

limitations

Uses 5-MTHF and acute vessel endpoints; cannot be generalized to all folic-acid doses or combination supplements.

nutrient_topic

Citrulline research collection; topical membership is not evidence of a direct dietary effect. · L-Citrulline

organism

Human, vessels from 117 CABG patients

plain_language

A folate form affected availability of the NO-synthase cofactor.

primary_references

[citrulline-p16940192] 5-methyltetrahydrofolate rapidly improves endothelial function and decreases superoxide production in human vessels: effects on vascular tetrahydrobiopterin availability and endothelial nitric oxide synthase coupling. (2006). https://pubmed.ncbi.nlm.nih.gov/16940192/ DOI: 10.1161/circulationaha.106.612325

tissue_or_cell_type

Saphenous veins and internal mammary arteries

Citrulline: arginine recycling, nitrogen disposal and nutrient connections (2026-09-17) · lines 736–747

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Ex-vivo vessel exposure and randomized pre-harvest infusion · source_derived_draft · unverified_draft

### citrulline-folate-bh4 5-MTHF increased vascular BH4 and its proportion of total biopterin in human vessel experiments. Condition category: normal nutrient_topic: Citrulline research collection; topical membership is not evidence of a direct dietary effect. plain_language: A folate form affected availability of the NO-synthase cofactor. organism: Human, vessels from 117 CABG patients tissue_or_cell_type: Saphenous veins and internal mammary arteries experimental_model: Ex-vivo vessel exposure and randomized pre-harvest infusion limitations: Uses 5-MTHF and acute vessel endpoints; cannot be generalized to all folic-acid doses or combination supplements. exposure: 5-MTHF ex vivo 1-100 micromolar; intravenous 5-MTHF or placebo in a separate subset evidence_span: {"source_cache": "artifacts/citrulline-research/16940192.abstract.txt", "locator": "Primary indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "42c07dd0bbacfc1ff44f78d6ce69810a58946e53c76bf5d3bf8385db5278ba8b", "start_char": 0, "end_char": 1942, "text_sha256": "42c07dd0bbacfc1ff44f78d6ce69810a58946e53c76bf5d3bf8385db5278ba8b"} [citrulline-p16940192] 5-methyltetrahydrofolate rapidly improves endothelial function and decreases superoxide production in human vessels: effects on vascular tetrahydrobiopterin availability and endothelial nitric oxide synthase coupling. (2006). https://pubmed.ncbi.nlm.nih.gov/16940192/ DOI: 10.1161/circulationaha.106.612325

evidence_span

{"source_cache": "artifacts/citrulline-research/16940192.abstract.txt", "locator": "Primary indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "42c07dd0bbacfc1ff44f78d6ce69810a58946e53c76bf5d3bf8385db5278ba8b", "start_char": 0, "end_char": 1942, "text_sha256": "42c07dd0bbacfc1ff44f78d6ce69810a58946e53c76bf5d3bf8385db5278ba8b"}

experimental_model

Ex-vivo vessel exposure and randomized pre-harvest infusion

exposure

5-MTHF ex vivo 1-100 micromolar; intravenous 5-MTHF or placebo in a separate subset

limitations

Uses 5-MTHF and acute vessel endpoints; cannot be generalized to all folic-acid doses or combination supplements.

nutrient_topic

Citrulline research collection; topical membership is not evidence of a direct dietary effect. · L-Citrulline

organism

Human, vessels from 117 CABG patients

plain_language

The enzyme used its electron supply more productively under the tested conditions.

primary_references

[citrulline-p16940192] 5-methyltetrahydrofolate rapidly improves endothelial function and decreases superoxide production in human vessels: effects on vascular tetrahydrobiopterin availability and endothelial nitric oxide synthase coupling. (2006). https://pubmed.ncbi.nlm.nih.gov/16940192/ DOI: 10.1161/circulationaha.106.612325

tissue_or_cell_type

Saphenous veins and internal mammary arteries

Citrulline: arginine recycling, nitrogen disposal and nutrient connections (2026-09-17) · lines 749–760

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Ex-vivo vessel exposure and randomized pre-harvest infusion · source_derived_draft · unverified_draft

### citrulline-folate-coupling 5-MTHF improved eNOS coupling and increased its dimer-to-monomer ratio and activity in the human vessel study. Condition category: normal nutrient_topic: Citrulline research collection; topical membership is not evidence of a direct dietary effect. plain_language: The enzyme used its electron supply more productively under the tested conditions. organism: Human, vessels from 117 CABG patients tissue_or_cell_type: Saphenous veins and internal mammary arteries experimental_model: Ex-vivo vessel exposure and randomized pre-harvest infusion limitations: Uses 5-MTHF and acute vessel endpoints; cannot be generalized to all folic-acid doses or combination supplements. exposure: 5-MTHF ex vivo 1-100 micromolar; intravenous 5-MTHF or placebo in a separate subset evidence_span: {"source_cache": "artifacts/citrulline-research/16940192.abstract.txt", "locator": "Primary indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "42c07dd0bbacfc1ff44f78d6ce69810a58946e53c76bf5d3bf8385db5278ba8b", "start_char": 0, "end_char": 1942, "text_sha256": "42c07dd0bbacfc1ff44f78d6ce69810a58946e53c76bf5d3bf8385db5278ba8b"} [citrulline-p16940192] 5-methyltetrahydrofolate rapidly improves endothelial function and decreases superoxide production in human vessels: effects on vascular tetrahydrobiopterin availability and endothelial nitric oxide synthase coupling. (2006). https://pubmed.ncbi.nlm.nih.gov/16940192/ DOI: 10.1161/circulationaha.106.612325

evidence_span

{"source_cache": "artifacts/citrulline-research/16940192.abstract.txt", "locator": "Primary indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "42c07dd0bbacfc1ff44f78d6ce69810a58946e53c76bf5d3bf8385db5278ba8b", "start_char": 0, "end_char": 1942, "text_sha256": "42c07dd0bbacfc1ff44f78d6ce69810a58946e53c76bf5d3bf8385db5278ba8b"}

experimental_model

Ex-vivo vessel exposure and randomized pre-harvest infusion

exposure

5-MTHF ex vivo 1-100 micromolar; intravenous 5-MTHF or placebo in a separate subset

limitations

Uses 5-MTHF and acute vessel endpoints; cannot be generalized to all folic-acid doses or combination supplements.

nutrient_topic

Citrulline research collection; topical membership is not evidence of a direct dietary effect. · L-Citrulline

organism

Human, vessels from 117 CABG patients

plain_language

The experiment distinguished this effect from simply lowering homocysteine.

primary_references

[citrulline-p16940192] 5-methyltetrahydrofolate rapidly improves endothelial function and decreases superoxide production in human vessels: effects on vascular tetrahydrobiopterin availability and endothelial nitric oxide synthase coupling. (2006). https://pubmed.ncbi.nlm.nih.gov/16940192/ DOI: 10.1161/circulationaha.106.612325

tissue_or_cell_type

Saphenous veins and internal mammary arteries

Citrulline: arginine recycling, nitrogen disposal and nutrient connections (2026-09-17) · lines 762–773

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Ex-vivo vessel exposure and randomized pre-harvest infusion · source_derived_draft · unverified_draft

### citrulline-folate-superoxide 5-MTHF reduced vascular superoxide; the effect was not explained by direct superoxide scavenging or changed plasma homocysteine. Condition category: normal nutrient_topic: Citrulline research collection; topical membership is not evidence of a direct dietary effect. plain_language: The experiment distinguished this effect from simply lowering homocysteine. organism: Human, vessels from 117 CABG patients tissue_or_cell_type: Saphenous veins and internal mammary arteries experimental_model: Ex-vivo vessel exposure and randomized pre-harvest infusion limitations: Uses 5-MTHF and acute vessel endpoints; cannot be generalized to all folic-acid doses or combination supplements. exposure: 5-MTHF ex vivo 1-100 micromolar; intravenous 5-MTHF or placebo in a separate subset evidence_span: {"source_cache": "artifacts/citrulline-research/16940192.abstract.txt", "locator": "Primary indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "42c07dd0bbacfc1ff44f78d6ce69810a58946e53c76bf5d3bf8385db5278ba8b", "start_char": 0, "end_char": 1942, "text_sha256": "42c07dd0bbacfc1ff44f78d6ce69810a58946e53c76bf5d3bf8385db5278ba8b"} [citrulline-p16940192] 5-methyltetrahydrofolate rapidly improves endothelial function and decreases superoxide production in human vessels: effects on vascular tetrahydrobiopterin availability and endothelial nitric oxide synthase coupling. (2006). https://pubmed.ncbi.nlm.nih.gov/16940192/ DOI: 10.1161/circulationaha.106.612325

availability_state

machinery_impairment Imported condition classification; unverified.

cross_nutrient

Demonstrates a formate-to-folate consequence downstream of a mitochondrial flavin-supply defect, not dietary folate deficiency.

evidence_spans

[{"source_bundle": "artifacts/riboflavin_metabolism_sources.json", "source_key": "PMC11072207", "locator": "HTML article p", "paragraph_index": 38, "char_start": 0, "char_end": 1062, "evidence_access": "full-text"}]

experimental_model

Slc25a32-null embryos and missense knock-in mice, isolated mitochondria and skeletal-muscle enzyme assays.

exposure

Dams received 0.1 mol/L sodium formate in drinking water; experimental context only.

limitations

Analyzed responder subgroup; does not prove normal folate metabolism or bypass every effect of Slc25a32 loss.

nutrient_topic

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

organism

Mus musculus

plain_language

Supplying a missing one-carbon donor changed the downstream folate profile.

primary_references

[peng-2022-slc25a32] Mitochondrial FAD shortage in SLC25A32 deficiency affects folate-mediated one-carbon metabolism (2022). https://pubmed.ncbi.nlm.nih.gov/35727412/ DOI: 10.1007/s00018-022-04404-0

tissue_or_cell_type

Whole E11.5 embryos

trigger_kind

machinery_impairment Imported condition classification; unverified.

Riboflavin: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 902–914

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Slc25a32-null embryos and missense knock-in mice, isolated mitochondria and skeletal-muscle enzyme assays. · source_derived_draft · unverified_draft

### b2-met-formate-embryo-folate-rescue Maternal sodium formate supplementation increased embryo CH3-THF in Slc25a32-null offspring that completed neural tube closure. Condition category: machinery_impairment nutrient_topic: Riboflavin research collection; topical membership is not evidence of a direct dietary effect. plain_language: Supplying a missing one-carbon donor changed the downstream folate profile. organism: Mus musculus tissue_or_cell_type: Whole E11.5 embryos experimental_model: Slc25a32-null embryos and missense knock-in mice, isolated mitochondria and skeletal-muscle enzyme assays. limitations: Analyzed responder subgroup; does not prove normal folate metabolism or bypass every effect of Slc25a32 loss. exposure: Dams received 0.1 mol/L sodium formate in drinking water; experimental context only. cross_nutrient: Demonstrates a formate-to-folate consequence downstream of a mitochondrial flavin-supply defect, not dietary folate deficiency. evidence_spans: [{"source_bundle": "artifacts/riboflavin_metabolism_sources.json", "source_key": "PMC11072207", "locator": "HTML article p", "paragraph_index": 38, "char_start": 0, "char_end": 1062, "evidence_access": "full-text"}] [peng-2022-slc25a32] Mitochondrial FAD shortage in SLC25A32 deficiency affects folate-mediated one-carbon metabolism (2022). https://pubmed.ncbi.nlm.nih.gov/35727412/ DOI: 10.1007/s00018-022-04404-0

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.

experimental_model

N2O-treated HeLa cells and cblG patient fibroblasts.

limitations

Fig. 2A reports folate-species percentages, not absolute amounts; one disease/control cell-line comparison.

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

Genetic MTR loss shifted the measured folate mixture toward methylfolate.

primary_references

[palmer-2017] Folate rescues vitamin B12 depletion-induced inhibition of nuclear thymidylate biosynthesis and genome instability (2017). https://pubmed.ncbi.nlm.nih.gov/28461497/ DOI: 10.1073/pnas.1619582114

tissue_or_cell_type

Patient fibroblasts

trigger_kind

machinery_impairment Imported condition classification; unverified.

Folate and folic acid: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 555–564

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · N2O-treated HeLa cells and cblG patient fibroblasts. · source_derived_draft · unverified_draft

### folate-methyl-cblg-methyl-trap The fraction of measured intracellular folate present as 5-methyl-THF was 2.5-fold higher in cblG WG4215 fibroblasts than in control MCH058 fibroblasts. Condition category: machinery_impairment nutrient_topic: Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. plain_language: Genetic MTR loss shifted the measured folate mixture toward methylfolate. organism: Homo sapiens tissue_or_cell_type: Patient fibroblasts experimental_model: N2O-treated HeLa cells and cblG patient fibroblasts. limitations: Fig. 2A reports folate-species percentages, not absolute amounts; one disease/control cell-line comparison. [palmer-2017] Folate rescues vitamin B12 depletion-induced inhibition of nuclear thymidylate biosynthesis and genome instability (2017). https://pubmed.ncbi.nlm.nih.gov/28461497/ DOI: 10.1073/pnas.1619582114

availability_state

machinery_impairment Imported condition classification; unverified.

cross_nutrient

Methylfolate does not remove the B12-dependent MTR requirement.

evidence_location

Ghergurovich 2021 Fig. 3A; physiological folate experiments Fig. 2 and Extended Data Fig. 2.

experimental_model

Isotope tracing in tumour cells, mouse tissues and xenografts.

exposure

CRISPR MTR deletion; folic acid or 5-methyl-THF medium; physiological folate-mixture experiments

limitations

Nutrient environment matters.

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

Methylfolate still needs MTR for reuse.

primary_references

[ghergurovich-2021] Methionine synthase supports tumour tetrahydrofolate pools (2021). https://pubmed.ncbi.nlm.nih.gov/34799699/ DOI: 10.1038/s42255-021-00465-w

tissue_or_cell_type

HCT116 human colorectal cancer cells (folate profiling)

trigger_kind

machinery_impairment Imported condition classification; unverified.

Folate and folic acid: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 517–529

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Isotope tracing in tumour cells, mouse tissues and xenografts. · source_derived_draft · unverified_draft

### folate-methyl-mtr-ko-trap MTR knockout in tumour cells using physiological extracellular folates caused trapping and limited assimilation into other folate forms. Condition category: machinery_impairment nutrient_topic: Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. plain_language: Methylfolate still needs MTR for reuse. organism: Homo sapiens tissue_or_cell_type: HCT116 human colorectal cancer cells (folate profiling) experimental_model: Isotope tracing in tumour cells, mouse tissues and xenografts. limitations: Nutrient environment matters. cross_nutrient: Methylfolate does not remove the B12-dependent MTR requirement. exposure: CRISPR MTR deletion; folic acid or 5-methyl-THF medium; physiological folate-mixture experiments evidence_location: Ghergurovich 2021 Fig. 3A; physiological folate experiments Fig. 2 and Extended Data Fig. 2. [ghergurovich-2021] Methionine synthase supports tumour tetrahydrofolate pools (2021). https://pubmed.ncbi.nlm.nih.gov/34799699/ DOI: 10.1038/s42255-021-00465-w

availability_state

machinery_impairment Imported condition classification; unverified.

experimental_model

Mtrr gene-trap hypomorphic mice and controls.

limitations

Abstract-level tissue aggregate; no universal fold change.

nutrient_topic

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

organism

Mus musculus

plain_language

Reduced reductase function altered folate distribution.

primary_references

[elmore-2007] Metabolic derangement of methionine and folate metabolism in mice deficient in methionine synthase reductase (2007). https://pubmed.ncbi.nlm.nih.gov/17369066/ DOI: 10.1016/j.ymgme.2007.02.001

tissue_or_cell_type

Tissue extracts

trigger_kind

machinery_impairment Imported condition classification; unverified.

Folate and folic acid: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 599–608

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Mtrr gene-trap hypomorphic mice and controls. · source_derived_draft · unverified_draft

### folate-methyl-mtrr-mouse-methylfolate Mtrr gt/gt mice showed increased tissue methyltetrahydrofolate. Condition category: machinery_impairment nutrient_topic: Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. plain_language: Reduced reductase function altered folate distribution. organism: Mus musculus tissue_or_cell_type: Tissue extracts experimental_model: Mtrr gene-trap hypomorphic mice and controls. limitations: Abstract-level tissue aggregate; no universal fold change. [elmore-2007] Metabolic derangement of methionine and folate metabolism in mice deficient in methionine synthase reductase (2007). https://pubmed.ncbi.nlm.nih.gov/17369066/ DOI: 10.1016/j.ymgme.2007.02.001

availability_state

machinery_impairment Imported condition classification; unverified.

cross_nutrient

B12 function controls usable folate.

experimental_model

N2O-treated HeLa cells and cblG patient fibroblasts.

limitations

Fig. 2 reports percentages of measured folate species, not absolute concentrations; chemical/culture impairment is not a dietary threshold.

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 nuclear folate mixture shifted toward methylfolate.

primary_references

[palmer-2017] Folate rescues vitamin B12 depletion-induced inhibition of nuclear thymidylate biosynthesis and genome instability (2017). https://pubmed.ncbi.nlm.nih.gov/28461497/ DOI: 10.1073/pnas.1619582114

tissue_or_cell_type

HeLa nuclear fractions

trigger_kind

machinery_impairment Imported condition classification; unverified.

Folate and folic acid: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 543–553

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · N2O-treated HeLa cells and cblG patient fibroblasts. · source_derived_draft · unverified_draft

### folate-methyl-nuclear-methyl-trap In B12-impaired HeLa nuclei, the fraction of measured nuclear folate present as 5-methyl-THF increased over fourfold, while the THF fraction fell approximately 50%, versus replete controls. Condition category: machinery_impairment nutrient_topic: Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. plain_language: The nuclear folate mixture shifted toward methylfolate. organism: Homo sapiens tissue_or_cell_type: HeLa nuclear fractions experimental_model: N2O-treated HeLa cells and cblG patient fibroblasts. limitations: Fig. 2 reports percentages of measured folate species, not absolute concentrations; chemical/culture impairment is not a dietary threshold. cross_nutrient: B12 function controls usable folate. [palmer-2017] Folate rescues vitamin B12 depletion-induced inhibition of nuclear thymidylate biosynthesis and genome instability (2017). https://pubmed.ncbi.nlm.nih.gov/28461497/ DOI: 10.1073/pnas.1619582114

experimental_model

Portal/peripheral isotope crossover in six TIPSS patients

exposure

500 nmol labeled 6S-5-formylTHF; four comparator participants

limitations

Does not show superiority for clinical outcomes.

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 gut readily processed the reduced folate in this comparison.

primary_references

[patanwala2014] Folic acid handling by the human gut: implications for food fortification and supplementation (2014). https://pubmed.ncbi.nlm.nih.gov/24944062/ DOI: 10.3945/ajcn.113.080507

tissue_or_cell_type

Hepatic portal blood

Folate and folic acid: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 399–409

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Portal/peripheral isotope crossover in six TIPSS patients · source_derived_draft · unverified_draft

### folate-portal-formyl-to-methyl-conversion After oral labeled 6S-5-formylTHF, portal folate was predominantly labeled 5-MTHF at 15 minutes; unchanged formylTHF was 4 ± 18%. Condition category: normal nutrient_topic: Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. plain_language: The gut readily processed the reduced folate in this comparison. organism: Homo sapiens tissue_or_cell_type: Hepatic portal blood experimental_model: Portal/peripheral isotope crossover in six TIPSS patients limitations: Does not show superiority for clinical outcomes. exposure: 500 nmol labeled 6S-5-formylTHF; four comparator participants [patanwala2014] Folic acid handling by the human gut: implications for food fortification and supplementation (2014). https://pubmed.ncbi.nlm.nih.gov/24944062/ DOI: 10.3945/ajcn.113.080507

experimental_model

Human SLC19A1 structures and HEK293F uptake assays

exposure

5-MTHF-bound cryo-EM complex

limitations

Static inward-facing structure does not itself measure a complete transport 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

RFC directly recognizes methylfolate.

primary_references

[dang2022] Molecular mechanism of substrate recognition by folate transporter SLC19A1 (2022). https://pubmed.ncbi.nlm.nih.gov/36575193/ DOI: 10.1038/s41421-022-00508-w

tissue_or_cell_type

Purified transporter and HEK293F cells

Folate and folic acid: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 155–165

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Human SLC19A1 structures and HEK293F uptake assays · source_derived_draft · unverified_draft

### folate-rfc-methylfolate-binding Cryo-EM resolved 5-methyltetrahydrofolate in the central substrate pocket of human SLC19A1. Condition category: normal nutrient_topic: Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. plain_language: RFC directly recognizes methylfolate. organism: Homo sapiens tissue_or_cell_type: Purified transporter and HEK293F cells experimental_model: Human SLC19A1 structures and HEK293F uptake assays limitations: Static inward-facing structure does not itself measure a complete transport cycle. exposure: 5-MTHF-bound cryo-EM complex [dang2022] Molecular mechanism of substrate recognition by folate transporter SLC19A1 (2022). https://pubmed.ncbi.nlm.nih.gov/36575193/ DOI: 10.1038/s41421-022-00508-w

availability_state

machinery_impairment Imported condition classification; unverified.

cross_nutrient

Connects a B2-related machinery defect to folate-dependent development through one-carbon availability.

evidence_spans

[{"source_bundle": "artifacts/riboflavin_metabolism_sources.json", "source_key": "PMC11072207", "locator": "HTML article p", "paragraph_index": 38, "char_start": 0, "char_end": 1062, "evidence_access": "full-text"}]

experimental_model

Slc25a32-null embryos and missense knock-in mice, isolated mitochondria and skeletal-muscle enzyme assays.

exposure

0.1 mol/L sodium formate in dam drinking water; 73 total embryos, nine litters.

limitations

Small animal intervention; incomplete rescue and no human treatment inference.

nutrient_topic

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

organism

Mus musculus

plain_language

One-carbon supplementation partly bypassed a developmental consequence in this mouse model.

primary_references

[peng-2022-slc25a32] Mitochondrial FAD shortage in SLC25A32 deficiency affects folate-mediated one-carbon metabolism (2022). https://pubmed.ncbi.nlm.nih.gov/35727412/ DOI: 10.1007/s00018-022-04404-0

tissue_or_cell_type

E11.5 embryos

trigger_kind

machinery_impairment Imported condition classification; unverified.

Riboflavin: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 916–928

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Slc25a32-null embryos and missense knock-in mice, isolated mitochondria and skeletal-muscle enzyme assays. · source_derived_draft · unverified_draft

### b2-met-formate-embryo-neural-tube After maternal sodium formate treatment, 14 of 16 Slc25a32-null embryos completed neural tube closure in the reported nine-litter experiment. Condition category: machinery_impairment nutrient_topic: Riboflavin research collection; topical membership is not evidence of a direct dietary effect. plain_language: One-carbon supplementation partly bypassed a developmental consequence in this mouse model. organism: Mus musculus tissue_or_cell_type: E11.5 embryos experimental_model: Slc25a32-null embryos and missense knock-in mice, isolated mitochondria and skeletal-muscle enzyme assays. limitations: Small animal intervention; incomplete rescue and no human treatment inference. exposure: 0.1 mol/L sodium formate in dam drinking water; 73 total embryos, nine litters. cross_nutrient: Connects a B2-related machinery defect to folate-dependent development through one-carbon availability. evidence_spans: [{"source_bundle": "artifacts/riboflavin_metabolism_sources.json", "source_key": "PMC11072207", "locator": "HTML article p", "paragraph_index": 38, "char_start": 0, "char_end": 1062, "evidence_access": "full-text"}] [peng-2022-slc25a32] Mitochondrial FAD shortage in SLC25A32 deficiency affects folate-mediated one-carbon metabolism (2022). https://pubmed.ncbi.nlm.nih.gov/35727412/ DOI: 10.1007/s00018-022-04404-0

cross_nutrient

B2 flavins support reactivation of B12-dependent folate/homocysteine metabolism.

evidence_location

Abstract

experimental_model

Recombinant human MTRR purification, flavin analysis, NADPH spectroscopy and methionine-synthase reconstitution.

exposure

Purified-enzyme assay

limitations

Reconstituted biochemistry; the accessible abstract identifies human MTRR but not the target MTR species. No dietary B2/B12 synergy was tested.

nutrient_topic

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

organism

Homo sapiens

plain_language

The flavin reductase helps restore an enzyme that uses B12 and methylfolate.

primary_references

[olteanu2001] Human methionine synthase reductase, a soluble P-450 reductase-like dual flavoprotein, is sufficient for NADPH-dependent methionine synthase activation. (2001). https://pubmed.ncbi.nlm.nih.gov/11466310/ DOI: 10.1074/jbc.m103707200

tissue_or_cell_type

Purified recombinant enzyme; no intact tissue

Riboflavin: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 1122–1134

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Recombinant human MTRR purification, flavin analysis, NADPH spectroscopy and methionine-synthase reconstitution. · source_derived_draft · unverified_draft

### b2-mtrr-mtr-reactivation Reconstituted assays showed human MTRR sufficient to support NADPH-dependent activity of cobalamin-dependent methionine synthase. Condition category: normal nutrient_topic: Riboflavin research collection; topical membership is not evidence of a direct dietary effect. plain_language: The flavin reductase helps restore an enzyme that uses B12 and methylfolate. organism: Homo sapiens tissue_or_cell_type: Purified recombinant enzyme; no intact tissue experimental_model: Recombinant human MTRR purification, flavin analysis, NADPH spectroscopy and methionine-synthase reconstitution. limitations: Reconstituted biochemistry; the accessible abstract identifies human MTRR but not the target MTR species. No dietary B2/B12 synergy was tested. exposure: Purified-enzyme assay cross_nutrient: B2 flavins support reactivation of B12-dependent folate/homocysteine metabolism. evidence_location: Abstract [olteanu2001] Human methionine synthase reductase, a soluble P-450 reductase-like dual flavoprotein, is sufficient for NADPH-dependent methionine synthase activation. (2001). https://pubmed.ncbi.nlm.nih.gov/11466310/ DOI: 10.1074/jbc.m103707200

availability_state

machinery_impairment Imported condition classification; unverified.

experimental_model

Children with FOLR1 variants and patient fibroblasts

exposure

Inherited compound-heterozygous genotype

limitations

Observations in two siblings; does not generalize to common folate variation.

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

Normal blood folate did not exclude impaired brain delivery.

primary_references

[steinfeld2009] Folate receptor alpha defect causes cerebral folate transport deficiency: a treatable neurodegenerative disorder associated with disturbed myelin metabolism (2009). https://pubmed.ncbi.nlm.nih.gov/19732866/ DOI: 10.1016/j.ajhg.2009.08.005

tissue_or_cell_type

CSF, plasma and erythrocytes

trigger_kind

machinery_impairment Imported condition classification; unverified.

Folate and folic acid: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 231–241

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Children with FOLR1 variants and patient fibroblasts · source_derived_draft · unverified_draft

### folate-folr1-csf-peripheral-dissociation Two siblings with FOLR1 Q118X/C175X variants had severe CSF folate depletion despite unremarkable plasma and erythrocyte folate. Condition category: machinery_impairment nutrient_topic: Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. plain_language: Normal blood folate did not exclude impaired brain delivery. organism: Homo sapiens tissue_or_cell_type: CSF, plasma and erythrocytes experimental_model: Children with FOLR1 variants and patient fibroblasts limitations: Observations in two siblings; does not generalize to common folate variation. exposure: Inherited compound-heterozygous genotype [steinfeld2009] Folate receptor alpha defect causes cerebral folate transport deficiency: a treatable neurodegenerative disorder associated with disturbed myelin metabolism (2009). https://pubmed.ncbi.nlm.nih.gov/19732866/ DOI: 10.1016/j.ajhg.2009.08.005

cross_nutrient

Folate methyl transfer requires B12.

experimental_model

Human MTR/MTRR expressed in insect cells; purified enzymes and extracts.

limitations

Chemistry, not dietary response.

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

B12-dependent MTR recycles both homocysteine and folate.

primary_references

[yamada-2006] Human methionine synthase reductase is a molecular chaperone for human methionine synthase (2006). https://pubmed.ncbi.nlm.nih.gov/16769880/ DOI: 10.1073/pnas.0603694103

tissue_or_cell_type

Purified protein

Folate and folic acid: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 482–492

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Human MTR/MTRR expressed in insect cells; purified enzymes and extracts. · source_derived_draft · unverified_draft

### folate-methyl-mtr-methyl-transfer Reconstituted human MTR transfers methylfolate-derived methyl groups through cobalamin to homocysteine, producing methionine and THF. Condition category: normal nutrient_topic: Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. plain_language: B12-dependent MTR recycles both homocysteine and folate. organism: Homo sapiens tissue_or_cell_type: Purified protein experimental_model: Human MTR/MTRR expressed in insect cells; purified enzymes and extracts. limitations: Chemistry, not dietary response. cross_nutrient: Folate methyl transfer requires B12. [yamada-2006] Human methionine synthase reductase is a molecular chaperone for human methionine synthase (2006). https://pubmed.ncbi.nlm.nih.gov/16769880/ DOI: 10.1073/pnas.0603694103

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

B1-folate: phosphorylated thiamine and folates share RFC recognition; exclusive physiological counter-substrate status remains unproven.

experimental_model

Human SLC19A1 structures and HEK293F uptake assays

exposure

Binding assays and extracellular competition

limitations

Supports shared recognition; does not prove dietary B1 deficiency blocks folate delivery.

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

A vitamin B1 cofactor can occupy the folate carrier.

primary_references

[dang2022] Molecular mechanism of substrate recognition by folate transporter SLC19A1 (2022). https://pubmed.ncbi.nlm.nih.gov/36575193/ DOI: 10.1038/s41421-022-00508-w

tissue_or_cell_type

Purified transporter and HEK293F cells

Folate and folic acid: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 167–178

AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Human SLC19A1 structures and HEK293F uptake assays · source_derived_draft · unverified_draft

### folate-rfc-thdp-shared-pocket Human SLC19A1 bound thiamine diphosphate in the same pocket as 5-MTHF; thiamine diphosphate inhibited methotrexate uptake with IC50 about 19 micromolar. Condition category: normal nutrient_topic: Folate and folic acid research collection; topical membership is not evidence of a direct dietary effect. plain_language: A vitamin B1 cofactor can occupy the folate carrier. organism: Homo sapiens tissue_or_cell_type: Purified transporter and HEK293F cells experimental_model: Human SLC19A1 structures and HEK293F uptake assays limitations: Supports shared recognition; does not prove dietary B1 deficiency blocks folate delivery. exposure: Binding assays and extracellular competition cross_nutrient: B1-folate: phosphorylated thiamine and folates share RFC recognition; exclusive physiological counter-substrate status remains unproven. [dang2022] Molecular mechanism of substrate recognition by folate transporter SLC19A1 (2022). https://pubmed.ncbi.nlm.nih.gov/36575193/ DOI: 10.1038/s41421-022-00508-w