Component

7,8-Dihydrobiopterin / BH2

7,8-Dihydrobiopterin / BH2. Species, exposure and limitations are retained in each linked claim.

4 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. BH4 oxidation accompanied eNOS uncoupling with increased ROS and reduced NO in hypertensive mouse aortas.

    7,8-Dihydrobiopterin / BH2 → Endothelial nitric oxide synthase uncoupling, model specified source_derived_draftungraded
    Experimental context and source evidence
    evidence_span
    {"source_cache": "artifacts/citrulline-research/12697739.abstract.txt", "locator": "Primary indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "d56604695c8c1bda167b76198a472d814d284a3c0c1e1e1eed8943cce31d0ad0", "start_char": 0, "end_char": 1474, "text_sha256": "d56604695c8c1bda167b76198a472d814d284a3c0c1e1e1eed8943cce31d0ad0"}
    experimental_model
    Hypertension and knockout mouse experiments
    exposure
    NADPH-oxidase/NOS genetic comparisons and BH4 treatment
    limitations
    Disease model; the exact response cannot be assumed in people taking citrulline.
    nutrient_topic
    Citrulline research collection; topical membership is not evidence of a direct dietary effect. · L-Citrulline
    organism
    Mouse DOCA-salt hypertension model
    plain_language
    Adding precursor is different from fixing a damaged cofactor system.
    primary_references
    [citrulline-p12697739] Oxidation of tetrahydrobiopterin leads to uncoupling of endothelial cell nitric oxide synthase in hypertension. (2003). https://pubmed.ncbi.nlm.nih.gov/12697739/ DOI: 10.1172/jci14172
    tissue_or_cell_type
    Aortic redox state and NO signaling

    Citrulline: arginine recycling, nitrogen disposal and nutrient connections (2026-09-17) · lines 801–812

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

    ### citrulline-bh4-oxidation BH4 oxidation accompanied eNOS uncoupling with increased ROS and reduced NO in hypertensive mouse aortas. Condition category: normal nutrient_topic: Citrulline research collection; topical membership is not evidence of a direct dietary effect. plain_language: Adding precursor is different from fixing a damaged cofactor system. organism: Mouse DOCA-salt hypertension model tissue_or_cell_type: Aortic redox state and NO signaling experimental_model: Hypertension and knockout mouse experiments limitations: Disease model; the exact response cannot be assumed in people taking citrulline. exposure: NADPH-oxidase/NOS genetic comparisons and BH4 treatment evidence_span: {"source_cache": "artifacts/citrulline-research/12697739.abstract.txt", "locator": "Primary indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "d56604695c8c1bda167b76198a472d814d284a3c0c1e1e1eed8943cce31d0ad0", "start_char": 0, "end_char": 1474, "text_sha256": "d56604695c8c1bda167b76198a472d814d284a3c0c1e1e1eed8943cce31d0ad0"} [citrulline-p12697739] Oxidation of tetrahydrobiopterin leads to uncoupling of endothelial cell nitric oxide synthase in hypertension. (2003). https://pubmed.ncbi.nlm.nih.gov/12697739/ DOI: 10.1172/jci14172
    Complete structured claim and evidence

Where it participates (unsigned role)

  1. The human TPH catalytic domain positioned tryptophan and a pterin analogue near its catalytic non-heme iron.

    Human tryptophan hydroxylase 1 / TPH1 → Ferrous iron source_derived_draftungraded
    Experimental context and source evidence
    evidence_span
    {"source_cache": "artifacts/melatonin-research/11747434.abstract.txt", "locator": "Primary indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "c98a1e028f9c3d7f749d37794a8e976c8c808e0ca9c5f08c394d9d29ae639e06", "start_char": 0, "end_char": 2063, "text_sha256": "c98a1e028f9c3d7f749d37794a8e976c8c808e0ca9c5f08c394d9d29ae639e06"}
    experimental_model
    NMR substrate/cofactor geometry and enzyme modeling
    exposure
    L-tryptophan and bound BH2 cofactor analogue
    limitations
    BH2 was a structural analogue in this experiment, not a demonstration that BH2 replaces physiological BH4. No clinical iron-deficiency threshold measured.
    nutrient_topic
    Melatonin research collection; topical membership is not evidence of a direct dietary effect. · Melatonin
    organism
    Recombinant human TPH1 catalytic domain
    plain_language
    The upstream hydroxylation machinery contains iron; giving more iron is not automatically a way to make more melatonin.
    primary_references
    [melatonin-p11747434] Conformation of the substrate and pterin cofactor bound to human tryptophan hydroxylase. Important role of Phe313 in substrate specificity. (2001). https://pubmed.ncbi.nlm.nih.gov/11747434/ DOI: 10.1021/bi015722x
    tissue_or_cell_type
    Non-heme iron active site

    Melatonin: synthesis, receptors, circadian timing and nutrient interactions (2026-09-17) · lines 162–173

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · NMR substrate/cofactor geometry and enzyme modeling · source_derived_draft · unverified_draft

    ### melatonin-tph1-iron The human TPH catalytic domain positioned tryptophan and a pterin analogue near its catalytic non-heme iron. Condition category: normal nutrient_topic: Melatonin research collection; topical membership is not evidence of a direct dietary effect. plain_language: The upstream hydroxylation machinery contains iron; giving more iron is not automatically a way to make more melatonin. organism: Recombinant human TPH1 catalytic domain tissue_or_cell_type: Non-heme iron active site experimental_model: NMR substrate/cofactor geometry and enzyme modeling limitations: BH2 was a structural analogue in this experiment, not a demonstration that BH2 replaces physiological BH4. No clinical iron-deficiency threshold measured. exposure: L-tryptophan and bound BH2 cofactor analogue evidence_span: {"source_cache": "artifacts/melatonin-research/11747434.abstract.txt", "locator": "Primary indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "c98a1e028f9c3d7f749d37794a8e976c8c808e0ca9c5f08c394d9d29ae639e06", "start_char": 0, "end_char": 2063, "text_sha256": "c98a1e028f9c3d7f749d37794a8e976c8c808e0ca9c5f08c394d9d29ae639e06"} [melatonin-p11747434] Conformation of the substrate and pterin cofactor bound to human tryptophan hydroxylase. Important role of Phe313 in substrate specificity. (2001). https://pubmed.ncbi.nlm.nih.gov/11747434/ DOI: 10.1021/bi015722x
    Complete structured claim and evidence

  2. DHFR knockdown decreased intracellular BH4 and increased BH2 in the cell systems.

    Mouse endothelial Dhfr knockdown → Endothelial BH4-to-BH2 ratio, model specified source_derived_draftungraded
    Experimental context and source evidence
    availability_state
    machinery_impairment Imported condition classification; unverified.
    evidence_span
    {"source_cache": "artifacts/citrulline-research/19666465.abstract.txt", "locator": "Primary indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "b1ef76ebbd312932011edd1b0f9f428026a4e4cdd53301bd66f99eaf543e77af", "start_char": 0, "end_char": 1716, "text_sha256": "b1ef76ebbd312932011edd1b0f9f428026a4e4cdd53301bd66f99eaf543e77af"}
    experimental_model
    DHFR knockdown/inhibition and controlled GTPCH-expression cell experiments
    exposure
    Methotrexate or RNA interference; comparison with GTPCH knockdown
    limitations
    Mouse models; DHFR also handles folate, but this study does not make folate and BH4 interchangeable.
    nutrient_topic
    Citrulline research collection; topical membership is not evidence of a direct dietary effect. · L-Citrulline
    organism
    Mouse endothelial and NIH-3T3-based experimental cell systems
    plain_language
    Recycling quality matters, not just the total amount of pterin.
    primary_references
    [citrulline-p19666465] Critical role for tetrahydrobiopterin recycling by dihydrofolate reductase in regulation of endothelial nitric-oxide synthase coupling: relative importance of the de novo biopterin synthesis versus salvage pathways. (2009). https://pubmed.ncbi.nlm.nih.gov/19666465/ DOI: 10.1074/jbc.m109.041483
    tissue_or_cell_type
    BH4/BH2 balance and NOS coupling
    trigger_kind
    machinery_impairment Imported condition classification; unverified.

    Citrulline: arginine recycling, nitrogen disposal and nutrient connections (2026-09-17) · lines 775–786

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · DHFR knockdown/inhibition and controlled GTPCH-expression cell experiments · source_derived_draft · unverified_draft

    ### citrulline-dhfr-ratio DHFR knockdown decreased intracellular BH4 and increased BH2 in the cell systems. Condition category: machinery_impairment nutrient_topic: Citrulline research collection; topical membership is not evidence of a direct dietary effect. plain_language: Recycling quality matters, not just the total amount of pterin. organism: Mouse endothelial and NIH-3T3-based experimental cell systems tissue_or_cell_type: BH4/BH2 balance and NOS coupling experimental_model: DHFR knockdown/inhibition and controlled GTPCH-expression cell experiments limitations: Mouse models; DHFR also handles folate, but this study does not make folate and BH4 interchangeable. exposure: Methotrexate or RNA interference; comparison with GTPCH knockdown evidence_span: {"source_cache": "artifacts/citrulline-research/19666465.abstract.txt", "locator": "Primary indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "b1ef76ebbd312932011edd1b0f9f428026a4e4cdd53301bd66f99eaf543e77af", "start_char": 0, "end_char": 1716, "text_sha256": "b1ef76ebbd312932011edd1b0f9f428026a4e4cdd53301bd66f99eaf543e77af"} [citrulline-p19666465] Critical role for tetrahydrobiopterin recycling by dihydrofolate reductase in regulation of endothelial nitric-oxide synthase coupling: relative importance of the de novo biopterin synthesis versus salvage pathways. (2009). https://pubmed.ncbi.nlm.nih.gov/19666465/ DOI: 10.1074/jbc.m109.041483
    Complete structured claim and evidence

  3. DHFR loss increased eNOS-dependent superoxide while reducing NO production.

    Mouse endothelial Dhfr knockdown → Endothelial nitric oxide synthase uncoupling, model specified source_derived_draftungraded
    Experimental context and source evidence
    availability_state
    machinery_impairment Imported condition classification; unverified.
    evidence_span
    {"source_cache": "artifacts/citrulline-research/19666465.abstract.txt", "locator": "Primary indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "b1ef76ebbd312932011edd1b0f9f428026a4e4cdd53301bd66f99eaf543e77af", "start_char": 0, "end_char": 1716, "text_sha256": "b1ef76ebbd312932011edd1b0f9f428026a4e4cdd53301bd66f99eaf543e77af"}
    experimental_model
    DHFR knockdown/inhibition and controlled GTPCH-expression cell experiments
    exposure
    Methotrexate or RNA interference; comparison with GTPCH knockdown
    limitations
    Mouse models; DHFR also handles folate, but this study does not make folate and BH4 interchangeable.
    nutrient_topic
    Citrulline research collection; topical membership is not evidence of a direct dietary effect. · L-Citrulline
    organism
    Mouse endothelial and NIH-3T3-based experimental cell systems
    plain_language
    A damaged cofactor balance can change the enzyme output.
    primary_references
    [citrulline-p19666465] Critical role for tetrahydrobiopterin recycling by dihydrofolate reductase in regulation of endothelial nitric-oxide synthase coupling: relative importance of the de novo biopterin synthesis versus salvage pathways. (2009). https://pubmed.ncbi.nlm.nih.gov/19666465/ DOI: 10.1074/jbc.m109.041483
    tissue_or_cell_type
    BH4/BH2 balance and NOS coupling
    trigger_kind
    machinery_impairment Imported condition classification; unverified.

    Citrulline: arginine recycling, nitrogen disposal and nutrient connections (2026-09-17) · lines 788–799

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · DHFR knockdown/inhibition and controlled GTPCH-expression cell experiments · source_derived_draft · unverified_draft

    ### citrulline-dhfr-uncoupling DHFR loss increased eNOS-dependent superoxide while reducing NO production. Condition category: machinery_impairment nutrient_topic: Citrulline research collection; topical membership is not evidence of a direct dietary effect. plain_language: A damaged cofactor balance can change the enzyme output. organism: Mouse endothelial and NIH-3T3-based experimental cell systems tissue_or_cell_type: BH4/BH2 balance and NOS coupling experimental_model: DHFR knockdown/inhibition and controlled GTPCH-expression cell experiments limitations: Mouse models; DHFR also handles folate, but this study does not make folate and BH4 interchangeable. exposure: Methotrexate or RNA interference; comparison with GTPCH knockdown evidence_span: {"source_cache": "artifacts/citrulline-research/19666465.abstract.txt", "locator": "Primary indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "b1ef76ebbd312932011edd1b0f9f428026a4e4cdd53301bd66f99eaf543e77af", "start_char": 0, "end_char": 1716, "text_sha256": "b1ef76ebbd312932011edd1b0f9f428026a4e4cdd53301bd66f99eaf543e77af"} [citrulline-p19666465] Critical role for tetrahydrobiopterin recycling by dihydrofolate reductase in regulation of endothelial nitric-oxide synthase coupling: relative importance of the de novo biopterin synthesis versus salvage pathways. (2009). https://pubmed.ncbi.nlm.nih.gov/19666465/ DOI: 10.1074/jbc.m109.041483
    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