Component

L-3,4-Dihydroxyphenylalanine

L-3,4-Dihydroxyphenylalanine

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

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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.

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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 acts on it

  1. Human cytosolic and mitochondrial phenylalanyl-tRNA synthetases could mischarge L-DOPA in biochemical assays; cytosolic editing hydrolyzed L-DOPA- and tyrosine-mischarged tRNA, whereas the mitochondrial system discriminated less effectively.

    Human cytosolic FARSA/FARSB phenylalanyl-tRNA synthetase → L-3,4-Dihydroxyphenylalanine source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    In-vitro human cytosolic and mitochondrial synthetase assays.
    limitations
    Assay mischarging does not establish clinical proteotoxicity from a usual phenylalanine intake.
    nutrient_topic
    L-Phenylalanine collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Phenylalanine
    plain_language
    Similar-looking molecules can challenge protein-building accuracy.
    primary_references
    Bacterial and eukaryotic phenylalanyl-tRNA synthetases catalyze misaminoacylation of tRNA(Phe) with 3,4-dihydroxy-L-phenylalanine. · 2011 · https://pubmed.ncbi.nlm.nih.gov/22035791/ · DOI 10.1016/j.chembiol.2011.08.008

    L-Phenylalanine: transport, protein synthesis, cofactor recycling and cross-nutrient mechanisms (2026-09-19) · lines 134–140

    AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · In-vitro human cytosolic and mitochondrial synthetase assays. · source_derived_draft · unverified_draft

    ## l-phenylalanine-charging-fidelity Similar-looking molecules can challenge protein-building accuracy. Human cytosolic and mitochondrial phenylalanyl-tRNA synthetases could mischarge L-DOPA in biochemical assays; cytosolic editing hydrolyzed L-DOPA- and tyrosine-mischarged tRNA, whereas the mitochondrial system discriminated less effectively. Model: In-vitro human cytosolic and mitochondrial synthetase assays. Limitations: Assay mischarging does not establish clinical proteotoxicity from a usual phenylalanine intake. Evidence access: Primary abstract Bacterial and eukaryotic phenylalanyl-tRNA synthetases catalyze misaminoacylation of tRNA(Phe) with 3,4-dihydroxy-L-phenylalanine. · 2011 · https://pubmed.ncbi.nlm.nih.gov/22035791/ · DOI 10.1016/j.chembiol.2011.08.008
    Complete structured claim and evidence

  2. Human tyrosine hydroxylase catalyzes BH4-dependent tyrosine hydroxylation to L-DOPA, a downstream step in dopamine biosynthesis.

    Human tyrosine hydroxylase → L-3,4-Dihydroxyphenylalanine source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Human TH variant study; established enzyme reaction described in the abstract.
    limitations
    This is a downstream connection, not evidence that oral phenylalanine predictably raises brain dopamine.
    nutrient_topic
    L-Phenylalanine collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Phenylalanine
    plain_language
    Producing tyrosine is only the first part of the route toward dopamine.
    primary_references
    Tyrosine hydroxylase variants influence protein expression, cellular localization, stability, enzymatic activity and the physical interaction between tyrosine hydroxylase and GTP cyclohydrolase 1. · 2024 · https://pubmed.ncbi.nlm.nih.gov/38084654/ · DOI 10.1002/jimd.12690

    L-Phenylalanine: transport, protein synthesis, cofactor recycling and cross-nutrient mechanisms (2026-09-19) · lines 118–124

    AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human TH variant study; established enzyme reaction described in the abstract. · source_derived_draft · unverified_draft

    ## l-phenylalanine-tyrosine-next-step Producing tyrosine is only the first part of the route toward dopamine. Human tyrosine hydroxylase catalyzes BH4-dependent tyrosine hydroxylation to L-DOPA, a downstream step in dopamine biosynthesis. Model: Human TH variant study; established enzyme reaction described in the abstract. Limitations: This is a downstream connection, not evidence that oral phenylalanine predictably raises brain dopamine. Evidence access: Primary abstract Tyrosine hydroxylase variants influence protein expression, cellular localization, stability, enzymatic activity and the physical interaction between tyrosine hydroxylase and GTP cyclohydrolase 1. · 2024 · https://pubmed.ncbi.nlm.nih.gov/38084654/ · DOI 10.1002/jimd.12690
    Complete structured claim and evidence

  3. Bacterial tyrosine decarboxylases converted levodopa to dopamine despite competing tyrosine or human decarboxylase inhibitors.

    Enterococcus faecalis tyrosine decarboxylase → L-3,4-Dihydroxyphenylalanine source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Bacterial enzyme experiments, human PD associations and proximal-intestinal rat studies.
    limitations
    Patient abundance associations and rat plasma effects are not proof that changing dietary tyrosine improves levodopa response.
    nutrient_topic
    L-Tyrosine collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Tyrosine
    plain_language
    Blocking the human enzyme may leave a microbial route active.
    primary_references
    Gut bacterial tyrosine decarboxylases restrict levels of levodopa in the treatment of Parkinson's disease. · 2019 · https://pubmed.ncbi.nlm.nih.gov/30659181/ · DOI 10.1038/s41467-019-08294-y

    L-Tyrosine: catecholamines, thyroid chemistry, pigment, metabolism and cross-nutrient mechanisms (2026-09-19) · lines 340–346

    AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Bacterial enzyme experiments, human PD associations and proximal-intestinal rat studies. · source_derived_draft · unverified_draft

    ## l-tyrosine-bacterial-drug Blocking the human enzyme may leave a microbial route active. Bacterial tyrosine decarboxylases converted levodopa to dopamine despite competing tyrosine or human decarboxylase inhibitors. Model: Bacterial enzyme experiments, human PD associations and proximal-intestinal rat studies. Limitations: Patient abundance associations and rat plasma effects are not proof that changing dietary tyrosine improves levodopa response. Evidence access: Primary abstract Gut bacterial tyrosine decarboxylases restrict levels of levodopa in the treatment of Parkinson's disease. · 2019 · https://pubmed.ncbi.nlm.nih.gov/30659181/ · DOI 10.1038/s41467-019-08294-y
    Complete structured claim and evidence

  4. Purified recombinant human tyrosinase showed monophenolase activity with L-tyrosine, the initial hydroxylation step toward pigment.

    Human tyrosinase / TYR → L-3,4-Dihydroxyphenylalanine source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary full text; Results and catalytic assays
    experimental_model
    Human intramelanosomal domain expressed in insect cells; activity assays.
    limitations
    Same metabolite identity as L-DOPA in catecholamine synthesis, but different enzyme and compartment.
    nutrient_topic
    L-Tyrosine collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Tyrosine
    plain_language
    A different enzyme uses the same amino acid for pigment chemistry.
    primary_references
    Albinism-causing mutations in recombinant human tyrosinase alter intrinsic enzymatic activity. · 2014 · https://pubmed.ncbi.nlm.nih.gov/24392141/ · DOI 10.1371/journal.pone.0084494

    L-Tyrosine: catecholamines, thyroid chemistry, pigment, metabolism and cross-nutrient mechanisms (2026-09-19) · lines 148–154

    AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Human intramelanosomal domain expressed in insect cells; activity assays. · source_derived_draft · unverified_draft

    ## l-tyrosine-tyr-dopa A different enzyme uses the same amino acid for pigment chemistry. Purified recombinant human tyrosinase showed monophenolase activity with L-tyrosine, the initial hydroxylation step toward pigment. Model: Human intramelanosomal domain expressed in insect cells; activity assays. Limitations: Same metabolite identity as L-DOPA in catecholamine synthesis, but different enzyme and compartment. Evidence access: Primary full text; Results and catalytic assays Albinism-causing mutations in recombinant human tyrosinase alter intrinsic enzymatic activity. · 2014 · https://pubmed.ncbi.nlm.nih.gov/24392141/ · DOI 10.1371/journal.pone.0084494
    Complete structured claim and evidence

Where it participates (unsigned role)

  1. Expressed human DDC decarboxylated L-DOPA; added PLP enhanced the measured activity.

    Human aromatic L-amino acid decarboxylase / DDC → Dopamine source_derived_draftungraded
    Experimental context and source evidence
    experimental_model
    Human DDC expressed in monkey COS cells; enzyme assays
    exposure
    PLP addition to transfected COS-cell enzyme incubations.
    limitations
    An expression-system response is not proof that supplements increase brain monoamines.
    nutrient_topic
    Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. · Vitamin B6
    organism
    Human DDC expressed in monkey COS cells
    plain_language
    B6 cofactor supports this monoamine-producing step.
    primary_references
    [sumi-1990-ddc] Characterization of recombinant human aromatic L-amino acid decarboxylase expressed in COS cells (1990). https://doi.org/10.1111/j.1471-4159.1990.tb04601.x DOI: 10.1111/j.1471-4159.1990.tb04601.x
    tissue_or_cell_type
    COS-cell expression system

    Vitamin B6: mechanisms, deficiency and nutrient interactions (2026-09-17) · lines 999–1009

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Human DDC expressed in monkey COS cells; enzyme assays · source_derived_draft · unverified_draft

    ### b6-neuro-ddc-dopamine Expressed human DDC decarboxylated L-DOPA; added PLP enhanced the measured activity. Condition category: normal nutrient_topic: Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect. plain_language: B6 cofactor supports this monoamine-producing step. organism: Human DDC expressed in monkey COS cells tissue_or_cell_type: COS-cell expression system experimental_model: Human DDC expressed in monkey COS cells; enzyme assays limitations: An expression-system response is not proof that supplements increase brain monoamines. exposure: PLP addition to transfected COS-cell enzyme incubations. [sumi-1990-ddc] Characterization of recombinant human aromatic L-amino acid decarboxylase expressed in COS cells (1990). https://doi.org/10.1111/j.1471-4159.1990.tb04601.x DOI: 10.1111/j.1471-4159.1990.tb04601.x
    Complete structured claim and evidence

  2. Gut bacterial tyrosine decarboxylase accepts tyrosine and also decarboxylates levodopa.

    Enterococcus faecalis tyrosine decarboxylase → Tyramine source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary abstract
    experimental_model
    Gut bacterial enzyme/substrate characterization.
    limitations
    This is bacterial metabolism, distinct from human DDC. Tyramine exposure from food is not equivalent to free tyrosine intake.
    nutrient_topic
    L-Tyrosine collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Tyrosine
    plain_language
    Microbes can divert the amino acid into a bioactive amine.
    primary_references
    Gut bacterial tyrosine decarboxylases restrict levels of levodopa in the treatment of Parkinson's disease. · 2019 · https://pubmed.ncbi.nlm.nih.gov/30659181/ · DOI 10.1038/s41467-019-08294-y

    L-Tyrosine: catecholamines, thyroid chemistry, pigment, metabolism and cross-nutrient mechanisms (2026-09-19) · lines 332–338

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

    ## l-tyrosine-bacterial-tyramine Microbes can divert the amino acid into a bioactive amine. Gut bacterial tyrosine decarboxylase accepts tyrosine and also decarboxylates levodopa. Model: Gut bacterial enzyme/substrate characterization. Limitations: This is bacterial metabolism, distinct from human DDC. Tyramine exposure from food is not equivalent to free tyrosine intake. Evidence access: Primary abstract Gut bacterial tyrosine decarboxylases restrict levels of levodopa in the treatment of Parkinson's disease. · 2019 · https://pubmed.ncbi.nlm.nih.gov/30659181/ · DOI 10.1038/s41467-019-08294-y
    Complete structured claim and evidence

  3. Recombinant human tyrosinase also showed diphenol oxidase activity with L-DOPA, supporting the next oxidation toward dopaquinone.

    Human tyrosinase / TYR → Dopaquinone source_derived_draftungraded
    Experimental context and source evidence
    evidence_access
    Primary full text; Results and catalytic assays
    experimental_model
    Purified human enzyme; L-DOPA colorimetric assays.
    limitations
    A colorimetric enzyme rate does not establish whole-body melanin output.
    nutrient_topic
    L-Tyrosine collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Tyrosine
    plain_language
    The pigment route includes a separate oxidation step.
    primary_references
    Albinism-causing mutations in recombinant human tyrosinase alter intrinsic enzymatic activity. · 2014 · https://pubmed.ncbi.nlm.nih.gov/24392141/ · DOI 10.1371/journal.pone.0084494

    L-Tyrosine: catecholamines, thyroid chemistry, pigment, metabolism and cross-nutrient mechanisms (2026-09-19) · lines 156–162

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

    ## l-tyrosine-tyr-quinone The pigment route includes a separate oxidation step. Recombinant human tyrosinase also showed diphenol oxidase activity with L-DOPA, supporting the next oxidation toward dopaquinone. Model: Purified human enzyme; L-DOPA colorimetric assays. Limitations: A colorimetric enzyme rate does not establish whole-body melanin output. Evidence access: Primary full text; Results and catalytic assays Albinism-causing mutations in recombinant human tyrosinase alter intrinsic enzymatic activity. · 2014 · https://pubmed.ncbi.nlm.nih.gov/24392141/ · DOI 10.1371/journal.pone.0084494
    Complete structured claim and evidence

  4. Human TYR R422Q and R422W variants had lower activity and temperature sensitivity compared with wild type.

    Human tyrosinase / TYR → Human TYR R422Q/R422W pigment-enzyme activity source_derived_draftungraded
    Experimental context and source evidence
    availability_state
    machinery_impairment Imported condition classification; unverified.
    evidence_access
    Primary abstract
    experimental_model
    Purified human intramelanosomal domains expressed in insect cells.
    limitations
    These variants retain activity; they should not be conflated with all albinism variants.
    nutrient_topic
    L-Tyrosine collection; species, compartment, exposure, co-substrates and manipulation remain explicit. · L-Tyrosine
    plain_language
    Reduced pigment synthesis can reflect enzyme structure rather than low tyrosine.
    primary_references
    Albinism-causing mutations in recombinant human tyrosinase alter intrinsic enzymatic activity. · 2014 · https://pubmed.ncbi.nlm.nih.gov/24392141/ · DOI 10.1371/journal.pone.0084494
    trigger_kind
    machinery_impairment Imported condition classification; unverified.

    L-Tyrosine: catecholamines, thyroid chemistry, pigment, metabolism and cross-nutrient mechanisms (2026-09-19) · lines 164–170

    AI-assisted research curation; primary references, access levels and experimental limitations individually identified. Not publisher full text. · supports · Purified human intramelanosomal domains expressed in insect cells. · source_derived_draft · unverified_draft

    ## l-tyrosine-tyr-variants Reduced pigment synthesis can reflect enzyme structure rather than low tyrosine. Human TYR R422Q and R422W variants had lower activity and temperature sensitivity compared with wild type. Model: Purified human intramelanosomal domains expressed in insect cells. Limitations: These variants retain activity; they should not be conflated with all albinism variants. Evidence access: Primary abstract Albinism-causing mutations in recombinant human tyrosinase alter intrinsic enzymatic activity. · 2014 · https://pubmed.ncbi.nlm.nih.gov/24392141/ · DOI 10.1371/journal.pone.0084494
    Complete structured claim and evidence

  5. Tyrosine hydroxylase is a non-heme iron enzyme that uses molecular oxygen to hydroxylate tyrosine to L-DOPA and tetrahydrobiopterin to 4a-hydroxybiopterin in the rate-limiting step of the catecholamine biosynthetic pathway.

    Iron → Human tyrosine hydroxylase source_derived_draftungraded
    Experimental context and source evidence
    evidence_span
    {"source_cache": "artifacts/cold-research/9753429.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "3c76ec6d5dadb463c0a044175d5a78fbd02df4da7c339029c8c232e8878175b9", "start_char": 0, "end_char": 1695, "text_sha256": "3c76ec6d5dadb463c0a044175d5a78fbd02df4da7c339029c8c232e8878175b9"}
    experimental_model
    Crystal structure of rat tyrosine hydroxylase with a cofactor analogue and iron at 2.3 angstrom
    exposure
    Bound 7,8-dihydrobiopterin and iron
    limitations
    Structural chemistry of the rate-limiting step. It is a rat enzyme structure with a cofactor analogue, not a measurement of iron status in an animal.
    nutrient_topic
    Cold water immersion research collection; topical membership is not evidence of a direct clinical effect, and a therapeutic exposure is not a dietary intake. · Cold water immersion
    organism
    Rat enzyme
    plain_language
    The first and slowest step of making noradrenaline needs an iron atom and a molecule of oxygen.
    primary_references
    [cold-p9753429] Crystal structure of tyrosine hydroxylase with bound cofactor analogue and iron at 2.3 A resolution: self-hydroxylation of Phe300 and the pterin-binding site. (1998). https://pubmed.ncbi.nlm.nih.gov/9753429/ DOI: 10.1021/bi981462g
    tissue_or_cell_type
    Purified catalytic and tetramerization domains

    Cold water immersion: cold sensing, heat production, the catecholamine axis and what repeated exposure changes (2026-09-19) · lines 533–544

    AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text. · supports · Crystal structure of rat tyrosine hydroxylase with a cofactor analogue and iron at 2.3 angstrom · source_derived_draft · unverified_draft

    ### cold-th-iron-oxygen-pterin Tyrosine hydroxylase is a non-heme iron enzyme that uses molecular oxygen to hydroxylate tyrosine to L-DOPA and tetrahydrobiopterin to 4a-hydroxybiopterin in the rate-limiting step of the catecholamine biosynthetic pathway. Condition category: normal nutrient_topic: Cold water immersion research collection; topical membership is not evidence of a direct clinical effect, and a therapeutic exposure is not a dietary intake. plain_language: The first and slowest step of making noradrenaline needs an iron atom and a molecule of oxygen. organism: Rat enzyme tissue_or_cell_type: Purified catalytic and tetramerization domains experimental_model: Crystal structure of rat tyrosine hydroxylase with a cofactor analogue and iron at 2.3 angstrom limitations: Structural chemistry of the rate-limiting step. It is a rat enzyme structure with a cofactor analogue, not a measurement of iron status in an animal. exposure: Bound 7,8-dihydrobiopterin and iron evidence_span: {"source_cache": "artifacts/cold-research/9753429.abstract.txt", "locator": "Indexed abstract; zero-based, end-exclusive Unicode character offsets", "file_sha256": "3c76ec6d5dadb463c0a044175d5a78fbd02df4da7c339029c8c232e8878175b9", "start_char": 0, "end_char": 1695, "text_sha256": "3c76ec6d5dadb463c0a044175d5a78fbd02df4da7c339029c8c232e8878175b9"} [cold-p9753429] Crystal structure of tyrosine hydroxylase with bound cofactor analogue and iron at 2.3 A resolution: self-hydroxylation of Phe300 and the pterin-binding site. (1998). https://pubmed.ncbi.nlm.nih.gov/9753429/ DOI: 10.1021/bi981462g
    Complete structured claim and evidence

In the sources

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