Component

Pyridoxine 5-prime-phosphate oxidase / PNPO

FMN-dependent oxidase of phosphorylated pyridoxine and pyridoxamine. Measured process or biological entity; consult each linked claim for the experimental scope.

13 recorded relationships. Experimental role, claim status and evidence remain attached to each record.

Read recorded mechanisms Open recursive mind map

How nutrients influence it

Every nutrient with a recorded effect on this component, credited to the nutrient that acted rather than the chapter that recorded it. Open a nutrient to see the findings and the conditions they were measured under.

How nutrients reach it in more than one step

Chains of two or more recorded steps that end here, grouped by the nutrient they start from. Each step is a separate finding, so a chain is a route a mechanism could take, not proof that it does.

Tracing routes…

What it does

Every recorded relationship this component is part of, grouped by its role. Plain wording comes first; the technical statement follows.

Recorded relationships

What it acts on

  1. Human PNPO also converted PMP to PLP, with a turnover number of 0.20 per second at 37 C.

    Pyridoxine 5-prime-phosphate oxidase / PNPO → Pyridoxamine 5-prime-phosphate source_derived_draftungraded
    Experimental context and source evidence
    cross_nutrient
    A second B6 precursor depends on the FMN enzyme.
    evidence_location
    Results: kinetic properties; Table 1; FMN-binding structure
    experimental_model
    Recombinant human PNPO expressed in E. coli; crystallography and purified-enzyme kinetics at 37 C.
    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
    Phosphorylated pyridoxamine enters the same activation enzyme.
    primary_references
    [musayev2003] Structure and properties of recombinant human pyridoxine 5'-phosphate oxidase. (2003). https://pubmed.ncbi.nlm.nih.gov/12824491/ DOI: 10.1110/ps.0356203
    tissue_or_cell_type
    Purified recombinant enzyme; no intact tissue

    Riboflavin: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 1164–1176

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Recombinant human PNPO expressed in E. coli; crystallography and purified-enzyme kinetics at 37 C. · source_derived_draft · unverified_draft

    ### b2-pnpo-pmp-oxidation Human PNPO also converted PMP to PLP, with a turnover number of 0.20 per second at 37 C. Condition category: normal nutrient_topic: Riboflavin research collection; topical membership is not evidence of a direct dietary effect. plain_language: Phosphorylated pyridoxamine enters the same activation enzyme. organism: Homo sapiens tissue_or_cell_type: Purified recombinant enzyme; no intact tissue experimental_model: Recombinant human PNPO expressed in E. coli; crystallography and purified-enzyme kinetics at 37 C. limitations: Biochemical evidence does not establish a dietary threshold or supplementation benefit. exposure: Purified-enzyme assay cross_nutrient: A second B6 precursor depends on the FMN enzyme. evidence_location: Results: kinetic properties; Table 1; FMN-binding structure [musayev2003] Structure and properties of recombinant human pyridoxine 5'-phosphate oxidase. (2003). https://pubmed.ncbi.nlm.nih.gov/12824491/ DOI: 10.1110/ps.0356203
    Complete structured claim and evidence

  2. Purified human PNPO converted PNP to PLP with a turnover number of 0.19 per second at 37 C.

    Pyridoxine 5-prime-phosphate oxidase / PNPO → Pyridoxine 5-prime-phosphate source_derived_draftungraded
    Experimental context and source evidence
    cross_nutrient
    B2-dependent oxidation activates one B6 precursor.
    evidence_location
    Results: kinetic properties; Table 1; FMN-binding structure
    experimental_model
    Recombinant human PNPO expressed in E. coli; crystallography and purified-enzyme kinetics at 37 C.
    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
    PNPO changes phosphorylated pyridoxine into active B6.
    primary_references
    [musayev2003] Structure and properties of recombinant human pyridoxine 5'-phosphate oxidase. (2003). https://pubmed.ncbi.nlm.nih.gov/12824491/ DOI: 10.1110/ps.0356203
    tissue_or_cell_type
    Purified recombinant enzyme; no intact tissue

    Riboflavin: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 1150–1162

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Recombinant human PNPO expressed in E. coli; crystallography and purified-enzyme kinetics at 37 C. · source_derived_draft · unverified_draft

    ### b2-pnpo-pnp-oxidation Purified human PNPO converted PNP to PLP with a turnover number of 0.19 per second at 37 C. Condition category: normal nutrient_topic: Riboflavin research collection; topical membership is not evidence of a direct dietary effect. plain_language: PNPO changes phosphorylated pyridoxine into active B6. organism: Homo sapiens tissue_or_cell_type: Purified recombinant enzyme; no intact tissue experimental_model: Recombinant human PNPO expressed in E. coli; crystallography and purified-enzyme kinetics at 37 C. limitations: Biochemical evidence does not establish a dietary threshold or supplementation benefit. exposure: Purified-enzyme assay cross_nutrient: B2-dependent oxidation activates one B6 precursor. evidence_location: Results: kinetic properties; Table 1; FMN-binding structure [musayev2003] Structure and properties of recombinant human pyridoxine 5'-phosphate oxidase. (2003). https://pubmed.ncbi.nlm.nih.gov/12824491/ DOI: 10.1110/ps.0356203
    Complete structured claim and evidence

What acts on it

  1. The human PNPO IVS3-1G>A splice-site construct had no detectable PNPO activity in the reported CHO expression assay.

    Human PNPO IVS3-1G>A splice genotype → Pyridoxine 5-prime-phosphate oxidase / PNPO source_derived_draftungraded
    Experimental context and source evidence
    availability_state
    machinery_impairment Imported condition classification; unverified.
    evidence_location
    Indexed abstract: CHO expression studies
    experimental_model
    Five affected patients and human PNPO constructs expressed in CHO cells.
    exposure
    Construct expression, not nutrient withdrawal.
    limitations
    Cannot generalize to every PNPO variant or vitamer treatment response.
    nutrient_topic
    Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. · Vitamin B6
    organism
    Homo sapiens protein expressed in Cricetulus griseus cells
    plain_language
    This variant prevented measured B6 activation.
    primary_references
    [mills2005] Neonatal epileptic encephalopathy caused by mutations in the PNPO gene encoding pyridox(am)ine 5'-phosphate oxidase. (2005). https://pubmed.ncbi.nlm.nih.gov/15772097/ DOI: 10.1093/hmg/ddi120
    tissue_or_cell_type
    CHO expression system
    trigger_kind
    machinery_impairment Imported condition classification; unverified.

    Vitamin B6: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 361–372

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Five affected patients and human PNPO constructs expressed in CHO cells. · source_derived_draft · unverified_draft

    ### b6-transport-pnpo-splice The human PNPO IVS3-1G>A splice-site construct had no detectable PNPO activity in the reported CHO expression assay. Condition category: machinery_impairment nutrient_topic: Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. plain_language: This variant prevented measured B6 activation. organism: Homo sapiens protein expressed in Cricetulus griseus cells tissue_or_cell_type: CHO expression system experimental_model: Five affected patients and human PNPO constructs expressed in CHO cells. limitations: Cannot generalize to every PNPO variant or vitamer treatment response. exposure: Construct expression, not nutrient withdrawal. evidence_location: Indexed abstract: CHO expression studies [mills2005] Neonatal epileptic encephalopathy caused by mutations in the PNPO gene encoding pyridox(am)ine 5'-phosphate oxidase. (2005). https://pubmed.ncbi.nlm.nih.gov/15772097/ DOI: 10.1093/hmg/ddi120
    Complete structured claim and evidence

  2. The human PNPO X262Q stop-loss construct had no detectable PNPO activity in the reported CHO expression assay.

    Human PNPO stop262Gln genotype → Pyridoxine 5-prime-phosphate oxidase / PNPO source_derived_draftungraded
    Experimental context and source evidence
    availability_state
    machinery_impairment Imported condition classification; unverified.
    evidence_location
    Indexed abstract: CHO expression studies
    experimental_model
    Five affected patients and human PNPO constructs expressed in CHO cells.
    exposure
    Construct expression, not nutrient withdrawal.
    limitations
    Cannot generalize to every PNPO variant or vitamer treatment response.
    nutrient_topic
    Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. · Vitamin B6
    organism
    Homo sapiens protein expressed in Cricetulus griseus cells
    plain_language
    This variant prevented measured B6 activation.
    primary_references
    [mills2005] Neonatal epileptic encephalopathy caused by mutations in the PNPO gene encoding pyridox(am)ine 5'-phosphate oxidase. (2005). https://pubmed.ncbi.nlm.nih.gov/15772097/ DOI: 10.1093/hmg/ddi120
    tissue_or_cell_type
    CHO expression system
    trigger_kind
    machinery_impairment Imported condition classification; unverified.

    Vitamin B6: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 374–385

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Five affected patients and human PNPO constructs expressed in CHO cells. · source_derived_draft · unverified_draft

    ### b6-transport-pnpo-stoploss The human PNPO X262Q stop-loss construct had no detectable PNPO activity in the reported CHO expression assay. Condition category: machinery_impairment nutrient_topic: Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. plain_language: This variant prevented measured B6 activation. organism: Homo sapiens protein expressed in Cricetulus griseus cells tissue_or_cell_type: CHO expression system experimental_model: Five affected patients and human PNPO constructs expressed in CHO cells. limitations: Cannot generalize to every PNPO variant or vitamer treatment response. exposure: Construct expression, not nutrient withdrawal. evidence_location: Indexed abstract: CHO expression studies [mills2005] Neonatal epileptic encephalopathy caused by mutations in the PNPO gene encoding pyridox(am)ine 5'-phosphate oxidase. (2005). https://pubmed.ncbi.nlm.nih.gov/15772097/ DOI: 10.1093/hmg/ddi120
    Complete structured claim and evidence

  3. PLP competitively inhibited purified human PNPO in the reported kinetic assays.

    PLP → Pyridoxine 5-prime-phosphate oxidase / PNPO source_derived_draftungraded
    Experimental context and source evidence
    cross_nutrient
    B6-product feedback regulates a B2-dependent enzyme.
    evidence_location
    Results: kinetic properties; Table 1; FMN-binding structure
    experimental_model
    Recombinant human PNPO expressed in E. coli; crystallography and purified-enzyme kinetics at 37 C.
    exposure
    Purified-enzyme assay
    limitations
    The paper did not establish free PLP pools or inhibition magnitude in intact mammalian tissues.
    nutrient_topic
    Riboflavin research collection; topical membership is not evidence of a direct dietary effect. · Riboflavin (vitamin B2)
    organism
    Homo sapiens
    plain_language
    The active B6 product can slow its own formation in vitro.
    primary_references
    [musayev2003] Structure and properties of recombinant human pyridoxine 5'-phosphate oxidase. (2003). https://pubmed.ncbi.nlm.nih.gov/12824491/ DOI: 10.1110/ps.0356203
    tissue_or_cell_type
    Purified recombinant enzyme; no intact tissue

    Riboflavin: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 1178–1190

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Recombinant human PNPO expressed in E. coli; crystallography and purified-enzyme kinetics at 37 C. · source_derived_draft · unverified_draft

    ### b2-pnp-product-inhibition PLP competitively inhibited purified human PNPO in the reported kinetic assays. Condition category: normal nutrient_topic: Riboflavin research collection; topical membership is not evidence of a direct dietary effect. plain_language: The active B6 product can slow its own formation in vitro. organism: Homo sapiens tissue_or_cell_type: Purified recombinant enzyme; no intact tissue experimental_model: Recombinant human PNPO expressed in E. coli; crystallography and purified-enzyme kinetics at 37 C. limitations: The paper did not establish free PLP pools or inhibition magnitude in intact mammalian tissues. exposure: Purified-enzyme assay cross_nutrient: B6-product feedback regulates a B2-dependent enzyme. evidence_location: Results: kinetic properties; Table 1; FMN-binding structure [musayev2003] Structure and properties of recombinant human pyridoxine 5'-phosphate oxidase. (2003). https://pubmed.ncbi.nlm.nih.gov/12824491/ DOI: 10.1110/ps.0356203
    Complete structured claim and evidence

  4. The human PNPO structure localized tightly bound FMN at the conserved catalytic site of the homodimer.

    Flavin mononucleotide → Pyridoxine 5-prime-phosphate oxidase / PNPO source_derived_draftungraded
    Experimental context and source evidence
    cross_nutrient
    B2-FMN is a cofactor for B6 activation.
    evidence_location
    Results: kinetic properties; Table 1; FMN-binding structure
    experimental_model
    Recombinant human PNPO expressed in E. coli; crystallography and purified-enzyme kinetics at 37 C.
    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
    PNPO uses the FMN form of vitamin B2.
    primary_references
    [musayev2003] Structure and properties of recombinant human pyridoxine 5'-phosphate oxidase. (2003). https://pubmed.ncbi.nlm.nih.gov/12824491/ DOI: 10.1110/ps.0356203
    tissue_or_cell_type
    Purified recombinant enzyme; no intact tissue

    Riboflavin: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 1136–1148

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Recombinant human PNPO expressed in E. coli; crystallography and purified-enzyme kinetics at 37 C. · source_derived_draft · unverified_draft

    ### b2-pnpo-fmn-binding The human PNPO structure localized tightly bound FMN at the conserved catalytic site of the homodimer. Condition category: normal nutrient_topic: Riboflavin research collection; topical membership is not evidence of a direct dietary effect. plain_language: PNPO uses the FMN form of vitamin B2. organism: Homo sapiens tissue_or_cell_type: Purified recombinant enzyme; no intact tissue experimental_model: Recombinant human PNPO expressed in E. coli; crystallography and purified-enzyme kinetics at 37 C. limitations: Biochemical evidence does not establish a dietary threshold or supplementation benefit. exposure: Purified-enzyme assay cross_nutrient: B2-FMN is a cofactor for B6 activation. evidence_location: Results: kinetic properties; Table 1; FMN-binding structure [musayev2003] Structure and properties of recombinant human pyridoxine 5'-phosphate oxidase. (2003). https://pubmed.ncbi.nlm.nih.gov/12824491/ DOI: 10.1110/ps.0356203
    Complete structured claim and evidence

Where it participates (unsigned role)

  1. Polarized Caco-2 cells supplied apically with PM generated PL and released more PL basolaterally than apically.

    Pyridoxamine → Pyridoxal source_derived_draftungraded
    Experimental context and source evidence
    evidence_location
    Results: Incubation with pyridoxamine; Figure 4
    experimental_model
    Polarized human Caco-2 monolayers; human intestinal lysates.
    exposure
    100 or 1000 nM PM; 6-48 h.
    limitations
    Vitamer measurements establish net conversion; individual enzyme fluxes were not separately perturbed.
    nutrient_topic
    Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. · Vitamin B6
    organism
    Homo sapiens
    plain_language
    Enterocytes can process a precursor before releasing pyridoxal.
    primary_references
    [albersen2013] The intestine plays a substantial role in human vitamin B6 metabolism: a Caco-2 cell model. (2013). https://pubmed.ncbi.nlm.nih.gov/23342087/ DOI: 10.1371/journal.pone.0054113
    tissue_or_cell_type
    Polarized Caco-2 monolayers

    Vitamin B6: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 137–148

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Polarized human Caco-2 monolayers; human intestinal lysates. · source_derived_draft · unverified_draft

    ### b6-transport-enterocyte-pm-to-pl Polarized Caco-2 cells supplied apically with PM generated PL and released more PL basolaterally than apically. Condition category: normal nutrient_topic: Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. plain_language: Enterocytes can process a precursor before releasing pyridoxal. organism: Homo sapiens tissue_or_cell_type: Polarized Caco-2 monolayers experimental_model: Polarized human Caco-2 monolayers; human intestinal lysates. limitations: Vitamer measurements establish net conversion; individual enzyme fluxes were not separately perturbed. exposure: 100 or 1000 nM PM; 6-48 h. evidence_location: Results: Incubation with pyridoxamine; Figure 4 [albersen2013] The intestine plays a substantial role in human vitamin B6 metabolism: a Caco-2 cell model. (2013). https://pubmed.ncbi.nlm.nih.gov/23342087/ DOI: 10.1371/journal.pone.0054113
    Complete structured claim and evidence

  2. Polarized Caco-2 cells supplied apically with PN generated PL and released more PL basolaterally than apically.

    Pyridoxine → Pyridoxal source_derived_draftungraded
    Experimental context and source evidence
    evidence_location
    Results: Incubation with pyridoxine; Figure 4
    experimental_model
    Polarized human Caco-2 monolayers; human intestinal lysates.
    exposure
    100 or 1000 nM PN; 6-48 h.
    limitations
    Vitamer measurements establish net conversion; individual enzyme fluxes were not separately perturbed.
    nutrient_topic
    Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. · Vitamin B6
    organism
    Homo sapiens
    plain_language
    Enterocytes can process a precursor before releasing pyridoxal.
    primary_references
    [albersen2013] The intestine plays a substantial role in human vitamin B6 metabolism: a Caco-2 cell model. (2013). https://pubmed.ncbi.nlm.nih.gov/23342087/ DOI: 10.1371/journal.pone.0054113
    tissue_or_cell_type
    Polarized Caco-2 monolayers

    Vitamin B6: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 124–135

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Polarized human Caco-2 monolayers; human intestinal lysates. · source_derived_draft · unverified_draft

    ### b6-transport-enterocyte-pn-to-pl Polarized Caco-2 cells supplied apically with PN generated PL and released more PL basolaterally than apically. Condition category: normal nutrient_topic: Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. plain_language: Enterocytes can process a precursor before releasing pyridoxal. organism: Homo sapiens tissue_or_cell_type: Polarized Caco-2 monolayers experimental_model: Polarized human Caco-2 monolayers; human intestinal lysates. limitations: Vitamer measurements establish net conversion; individual enzyme fluxes were not separately perturbed. exposure: 100 or 1000 nM PN; 6-48 h. evidence_location: Results: Incubation with pyridoxine; Figure 4 [albersen2013] The intestine plays a substantial role in human vitamin B6 metabolism: a Caco-2 cell model. (2013). https://pubmed.ncbi.nlm.nih.gov/23342087/ DOI: 10.1371/journal.pone.0054113
    Complete structured claim and evidence

  3. After a 100 nM D3-PN pulse, labeled PLP appeared in whole cells but scarcely in SLC25A38-null mitochondria.

    Human SLC25A38 knockout genotype → PLP source_derived_draftungraded
    Experimental context and source evidence
    availability_state
    machinery_impairment Imported condition classification; unverified.
    evidence_location
    Figure 4A-B
    experimental_model
    Human K562 knockout cells, Mito-IP, LC-MS and isotope tracing.
    exposure
    100 nM D3-PN, one-hour tracing after 10 nM PN conditioning.
    limitations
    Import, retention and indirect regulation remain alternatives.
    nutrient_topic
    Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. · Vitamin B6
    organism
    Homo sapiens
    plain_language
    Synthesis persisted while mitochondrial accumulation failed.
    primary_references
    [pena2025] SLC25A38 is required for mitochondrial pyridoxal 5'-phosphate (PLP) accumulation. (2025). https://pubmed.ncbi.nlm.nih.gov/39856062/ DOI: 10.1038/s41467-025-56130-3
    tissue_or_cell_type
    K562 cells
    trigger_kind
    machinery_impairment Imported condition classification; unverified.

    Vitamin B6: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 465–476

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Human K562 knockout cells, Mito-IP, LC-MS and isotope tracing. · source_derived_draft · unverified_draft

    ### b6-transport-slc25a38-tracer After a 100 nM D3-PN pulse, labeled PLP appeared in whole cells but scarcely in SLC25A38-null mitochondria. Condition category: machinery_impairment nutrient_topic: Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. plain_language: Synthesis persisted while mitochondrial accumulation failed. organism: Homo sapiens tissue_or_cell_type: K562 cells experimental_model: Human K562 knockout cells, Mito-IP, LC-MS and isotope tracing. limitations: Import, retention and indirect regulation remain alternatives. exposure: 100 nM D3-PN, one-hour tracing after 10 nM PN conditioning. evidence_location: Figure 4A-B [pena2025] SLC25A38 is required for mitochondrial pyridoxal 5'-phosphate (PLP) accumulation. (2025). https://pubmed.ncbi.nlm.nih.gov/39856062/ DOI: 10.1038/s41467-025-56130-3
    Complete structured claim and evidence

  4. In G6PD-deficient erythrocytes, glutathione reductase was usually already FAD-saturated despite evidence of low FMN-dependent oxidase activity.

    Glucose-6-phosphate dehydrogenase / G6PD → Erythrocyte glutathione reductase activation coefficient / EGRAC source_derived_draftungraded
    Experimental context and source evidence
    availability_state
    biomarker_context Imported condition classification; unverified.
    cross_nutrient
    G6PD genotype and distinct flavin pools alter interpretation of B2/B6-linked assays.
    experimental_model
    Human erythrocytes from G6PD deficiency, heterozygous beta-thalassemia and controls.
    exposure
    In-vitro FAD stimulation of glutathione reductase and PNP oxidase activity, with oral-riboflavin response observations.
    limitations
    Human red-cell observation; the proposed faster FMN-to-FAD flux was an interpretation, not a directly measured universal mechanism.
    nutrient_topic
    Riboflavin research collection; topical membership is not evidence of a direct dietary effect. · Riboflavin (vitamin B2)
    organism
    Homo sapiens
    plain_language
    A red-cell FAD saturation test can look adequate while another B2-dependent enzyme system is poorly supplied.
    primary_references
    [b2-anderson1987] Glutathione reductase activity and its relationship to pyridoxine phosphate activity in G6PD deficiency (1987). https://pubmed.ncbi.nlm.nih.gov/3582603/ DOI: 10.1111/j.1600-0609.1987.tb01417.x
    tissue_or_cell_type
    Human clinical setting
    trigger_kind
    biomarker_context Imported condition classification; unverified.

    Riboflavin: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 1666–1677

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Human erythrocytes from G6PD deficiency, heterozygous beta-thalassemia and controls. · source_derived_draft · unverified_draft

    ### b2-g6pd-fad-assay-limit In G6PD-deficient erythrocytes, glutathione reductase was usually already FAD-saturated despite evidence of low FMN-dependent oxidase activity. Condition category: biomarker_context nutrient_topic: Riboflavin research collection; topical membership is not evidence of a direct dietary effect. plain_language: A red-cell FAD saturation test can look adequate while another B2-dependent enzyme system is poorly supplied. organism: Homo sapiens tissue_or_cell_type: Human clinical setting experimental_model: Human erythrocytes from G6PD deficiency, heterozygous beta-thalassemia and controls. limitations: Human red-cell observation; the proposed faster FMN-to-FAD flux was an interpretation, not a directly measured universal mechanism. exposure: In-vitro FAD stimulation of glutathione reductase and PNP oxidase activity, with oral-riboflavin response observations. cross_nutrient: G6PD genotype and distinct flavin pools alter interpretation of B2/B6-linked assays. [b2-anderson1987] Glutathione reductase activity and its relationship to pyridoxine phosphate activity in G6PD deficiency (1987). https://pubmed.ncbi.nlm.nih.gov/3582603/ DOI: 10.1111/j.1600-0609.1987.tb01417.x
    Complete structured claim and evidence

  5. Low FMN-dependent PNP oxidase activity in many G6PD-deficient participants responded to oral riboflavin despite the contrasting FAD-saturated GSR pattern.

    Riboflavin (vitamin B2) → Erythrocyte pyridoxamine/pyridoxine phosphate oxidase activity source_derived_draftungraded
    Experimental context and source evidence
    availability_state
    biomarker_context Imported condition classification; unverified.
    cross_nutrient
    B2 cofactor supply affects a B6-activation assay.
    experimental_model
    Human erythrocytes from G6PD deficiency, heterozygous beta-thalassemia and controls.
    exposure
    In-vitro FAD stimulation of glutathione reductase and PNP oxidase activity, with oral-riboflavin response observations.
    limitations
    No isolated whole-body B6 flux or clinical seizure/neuropathy outcome was established.
    nutrient_topic
    Riboflavin research collection; topical membership is not evidence of a direct dietary effect. · Riboflavin (vitamin B2)
    organism
    Homo sapiens
    plain_language
    FMN and FAD should not be treated as one interchangeable vitamin pool.
    primary_references
    [b2-anderson1987] Glutathione reductase activity and its relationship to pyridoxine phosphate activity in G6PD deficiency (1987). https://pubmed.ncbi.nlm.nih.gov/3582603/ DOI: 10.1111/j.1600-0609.1987.tb01417.x
    tissue_or_cell_type
    Human clinical setting
    trigger_kind
    biomarker_context Imported condition classification; unverified.

    Riboflavin: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 1679–1690

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Human erythrocytes from G6PD deficiency, heterozygous beta-thalassemia and controls. · source_derived_draft · unverified_draft

    ### b2-g6pd-fmn-oxidase-response Low FMN-dependent PNP oxidase activity in many G6PD-deficient participants responded to oral riboflavin despite the contrasting FAD-saturated GSR pattern. Condition category: biomarker_context nutrient_topic: Riboflavin research collection; topical membership is not evidence of a direct dietary effect. plain_language: FMN and FAD should not be treated as one interchangeable vitamin pool. organism: Homo sapiens tissue_or_cell_type: Human clinical setting experimental_model: Human erythrocytes from G6PD deficiency, heterozygous beta-thalassemia and controls. limitations: No isolated whole-body B6 flux or clinical seizure/neuropathy outcome was established. exposure: In-vitro FAD stimulation of glutathione reductase and PNP oxidase activity, with oral-riboflavin response observations. cross_nutrient: B2 cofactor supply affects a B6-activation assay. [b2-anderson1987] Glutathione reductase activity and its relationship to pyridoxine phosphate activity in G6PD deficiency (1987). https://pubmed.ncbi.nlm.nih.gov/3582603/ DOI: 10.1111/j.1600-0609.1987.tb01417.x
    Complete structured claim and evidence

  6. R229W PNPO had an FMN dissociation constant approximately 50-fold higher than wild type in apoenzyme fluorescence titrations.

    PNPO Arg229Trp protein → Flavin mononucleotide source_derived_draftungraded
    Experimental context and source evidence
    availability_state
    machinery_impairment Imported condition classification; unverified.
    cross_nutrient
    A B6-activation disorder directly disrupts B2-cofactor binding.
    evidence_location
    Results: Table 3 and Fig 1; Table 2 and Fig 2
    experimental_model
    Recombinant human wild-type and R229W PNPO; fluorescence titration, kinetics and 2.5-A mutant structure.
    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 genetic substitution weakens FMN binding.
    primary_references
    [musayev2009] Molecular basis of reduced pyridoxine 5'-phosphate oxidase catalytic activity in neonatal epileptic encephalopathy disorder. (2009). https://pubmed.ncbi.nlm.nih.gov/19759001/ DOI: 10.1074/jbc.m109.038372
    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 1206–1218

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Recombinant human wild-type and R229W PNPO; fluorescence titration, kinetics and 2.5-A mutant structure. · source_derived_draft · unverified_draft

    ### b2-pnpo-r229w-fmn-affinity R229W PNPO had an FMN dissociation constant approximately 50-fold higher than wild type in apoenzyme fluorescence titrations. Condition category: machinery_impairment nutrient_topic: Riboflavin research collection; topical membership is not evidence of a direct dietary effect. plain_language: The genetic substitution weakens FMN binding. organism: Homo sapiens tissue_or_cell_type: Purified recombinant enzyme; no intact tissue experimental_model: Recombinant human wild-type and R229W PNPO; fluorescence titration, kinetics and 2.5-A mutant structure. limitations: Biochemical evidence does not establish a dietary threshold or supplementation benefit. exposure: Purified-enzyme assay cross_nutrient: A B6-activation disorder directly disrupts B2-cofactor binding. evidence_location: Results: Table 3 and Fig 1; Table 2 and Fig 2 [musayev2009] Molecular basis of reduced pyridoxine 5'-phosphate oxidase catalytic activity in neonatal epileptic encephalopathy disorder. (2009). https://pubmed.ncbi.nlm.nih.gov/19759001/ DOI: 10.1074/jbc.m109.038372
    Complete structured claim and evidence

  7. Erythrocyte PPO activity and its activation coefficient responded to B2 supplementation and correlated with EGRAC; enzyme activity showed a dose response.

    Riboflavin (vitamin B2) → Erythrocyte pyridoxamine/pyridoxine phosphate oxidase activity source_derived_draftungraded
    Experimental context and source evidence
    availability_state
    biomarker_context Imported condition classification; unverified.
    cross_nutrient
    A B6-activation enzyme provides a B2-sensitive functional assay.
    experimental_model
    Assay-development study using hemolysates from the RIBOFEM riboflavin intervention; same trial registration ISRCTN35811298.
    exposure
    Erythrocyte PPO activity with/without flavin activation; 2 and 4 mg/day supplementation arms. Not independent replication of RIBOFEM.
    limitations
    Assay-development analysis shares samples with RIBOFEM; not independent replication. Proposed utility in G6PD deficiency requires population-specific validation.
    nutrient_topic
    Riboflavin research collection; topical membership is not evidence of a direct dietary effect. · Riboflavin (vitamin B2)
    organism
    Homo sapiens
    plain_language
    An enzyme used to activate B6 can also reveal aspects of B2 status because it needs an FMN cofactor.
    primary_references
    [b2-mushtaq2009] Erythrocyte pyridoxamine phosphate oxidase activity: a potential biomarker of riboflavin status? (2009). https://pubmed.ncbi.nlm.nih.gov/19740970/ DOI: 10.3945/ajcn.2009.28338
    tissue_or_cell_type
    Human clinical setting
    trigger_kind
    biomarker_context Imported condition classification; unverified.

    Riboflavin: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 1653–1664

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Assay-development study using hemolysates from the RIBOFEM riboflavin intervention; same trial registration ISRCTN35811298. · source_derived_draft · unverified_draft

    ### b2-ppo-biomarker-response Erythrocyte PPO activity and its activation coefficient responded to B2 supplementation and correlated with EGRAC; enzyme activity showed a dose response. Condition category: biomarker_context nutrient_topic: Riboflavin research collection; topical membership is not evidence of a direct dietary effect. plain_language: An enzyme used to activate B6 can also reveal aspects of B2 status because it needs an FMN cofactor. organism: Homo sapiens tissue_or_cell_type: Human clinical setting experimental_model: Assay-development study using hemolysates from the RIBOFEM riboflavin intervention; same trial registration ISRCTN35811298. limitations: Assay-development analysis shares samples with RIBOFEM; not independent replication. Proposed utility in G6PD deficiency requires population-specific validation. exposure: Erythrocyte PPO activity with/without flavin activation; 2 and 4 mg/day supplementation arms. Not independent replication of RIBOFEM. cross_nutrient: A B6-activation enzyme provides a B2-sensitive functional assay. [b2-mushtaq2009] Erythrocyte pyridoxamine phosphate oxidase activity: a potential biomarker of riboflavin status? (2009). https://pubmed.ncbi.nlm.nih.gov/19740970/ DOI: 10.3945/ajcn.2009.28338
    Complete structured claim and evidence

In the sources

Preserved passages that mention this component, quoted exactly. Open one to read it in context.

    This is a research prototype built from draft material. It is not medical advice, and its statements still await verification against the original studies.

    Evidence, AI assistance and curation standards