{"id":"75080221-0b86-53b0-bd79-10d12abda8f0","stable_key":"b3c3f45a-50fb-5b79-98d7-5e5228df00db:cold-ascorbate-reductant","predicate":"is_required_in_assay_for","statement":"Ascorbate is the presumed in vivo reductant of dopamine beta-monooxygenase; the one-electron reductant ferrocyanide was nearly as kinetically competent, while dopamine as sole reductant reduced enzymic copper in a rate-limiting step 40-fold slower than with ascorbate, and the reductant binds at a site physically distinct from the substrate site.","claim_class":"mechanistic","status":"source_derived_draft","evidence_grade":"ungraded","direction":"positive","is_public":true,"mechanism_event_id":"b70d13e0-5834-56a3-a51a-b162f59b6464","mechanism_event_label":"Vitamin C is what hands the enzyme back its electrons, and without it the reaction crawls.","subject":{"id":"38d0c4d9-53d1-5239-bfe3-c1b5e9b79085","slug":"ascorbate","display_name":"L-Ascorbate","entity_type_key":"small_molecule"},"object":{"id":"485f2f39-c979-55f2-924e-7817830d1f53","slug":"dbh-catalysis","display_name":"Dopamine beta-hydroxylase catalytic turnover","entity_type_key":"cellular_process"},"evidence_count":1,"mechanism_event":{"id":"b70d13e0-5834-56a3-a51a-b162f59b6464","stable_key":"b3c3f45a-50fb-5b79-98d7-5e5228df00db:cold-ascorbate-reductant-event","event_type":"biochemical_relationship","label":"Vitamin C is what hands the enzyme back its electrons, and without it the reaction crawls.","description":"Ascorbate is the presumed in vivo reductant of dopamine beta-monooxygenase; the one-electron reductant ferrocyanide was nearly as kinetically competent, while dopamine as sole reductant reduced enzymic copper in a rate-limiting step 40-fold slower than with ascorbate, and the reductant binds at a site physically distinct from the substrate site.","status":"provisional","compartment":null,"participants":[{"entity":{"id":"9f0afdde-1ec1-5c8a-bb5e-f3b2b75f67f6","slug":"copper","display_name":"Copper","entity_type_key":"nutrient_element"},"role":"reduced_metal","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"d7386401-2b52-5cef-ba58-19edf9e96688","slug":"ferrocyanide","display_name":"Ferrocyanide, an alternative one-electron reductant","entity_type_key":"chemical_species"},"role":"alternative_reductant","stoichiometry":null,"state_label":"","sequence_order":1,"notes":""},{"entity":{"id":"9cca6209-0603-5ab7-96ad-2f3ae4b772d2","slug":"dopamine","display_name":"Dopamine","entity_type_key":"small_molecule"},"role":"substrate","stoichiometry":null,"state_label":"","sequence_order":2,"notes":""},{"entity":{"id":"da1a7137-08f2-5a36-8bb6-377fbd32e327","slug":"vitamin-c","display_name":"Vitamin C","entity_type_key":"chemical_species"},"role":"nutrient_source","stoichiometry":null,"state_label":"","sequence_order":3,"notes":""},{"entity":{"id":"38d0c4d9-53d1-5239-bfe3-c1b5e9b79085","slug":"ascorbate","display_name":"L-Ascorbate","entity_type_key":"small_molecule"},"role":"subject","stoichiometry":null,"state_label":"","sequence_order":4,"notes":""},{"entity":{"id":"485f2f39-c979-55f2-924e-7817830d1f53","slug":"dbh-catalysis","display_name":"Dopamine beta-hydroxylase catalytic turnover","entity_type_key":"cellular_process"},"role":"target","stoichiometry":null,"state_label":"","sequence_order":5,"notes":""}]},"contexts":[{"dimension":"evidence_span","value_text":"{\"source_cache\": \"artifacts/cold-research/3676254.abstract.txt\", \"locator\": \"Indexed abstract; zero-based, end-exclusive Unicode character offsets\", \"file_sha256\": \"e929132eed0f1c94ab0bdbef6e31bca7ecbed222cf9b585e17a1cfae7e93c82a\", \"start_char\": 0, \"end_char\": 1648, \"text_sha256\": \"e929132eed0f1c94ab0bdbef6e31bca7ecbed222cf9b585e17a1cfae7e93c82a\"}","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Steady-state kinetics of dopamine beta-monooxygenase with structurally distinct reductants","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"exposure","value_text":"Ascorbate, ferrocyanide or dopamine itself as the reducing agent, with deuterium isotope effects","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"A kinetic comparison identifying ascorbate as the presumed physiological reductant and locating a separate binding site for it. Truncated abstract; the reductant site is inferred from kinetics and modelling.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"nutrient_topic","value_text":"Cold water immersion research collection; topical membership is not evidence of a direct clinical effect, and a therapeutic exposure is not a dietary intake.","comparator":null,"unit":null,"notes":"","entity":{"slug":"cold-water-immersion","display_name":"Cold water immersion","entity_type_key":"drug"}},{"dimension":"organism","value_text":"Bovine enzyme","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"plain_language","value_text":"Vitamin C is what hands the enzyme back its electrons, and without it the reaction crawls.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"[cold-p3676254] Characterization of alternate reductant binding and electron transfer in the dopamine beta-monooxygenase reaction. (1987). https://pubmed.ncbi.nlm.nih.gov/3676254/ DOI: 10.1021/bi00391a013","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"tissue_or_cell_type","value_text":"Purified enzyme","comparator":null,"unit":null,"notes":"","entity":null}],"evidence":[{"id":"25787a2a-676e-5b7b-93c4-a9d394aa2f36","evidence_kind":"source_excerpt","locator":"Lines 585-596","start_line":585,"end_line":596,"excerpt":"### cold-ascorbate-reductant\nAscorbate is the presumed in vivo reductant of dopamine beta-monooxygenase; the one-electron reductant ferrocyanide was nearly as kinetically competent, while dopamine as sole reductant reduced enzymic copper in a rate-limiting step 40-fold slower than with ascorbate, and the reductant binds at a site physically distinct from the substrate site.\nCondition category: normal\nnutrient_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.\nplain_language: Vitamin C is what hands the enzyme back its electrons, and without it the reaction crawls.\norganism: Bovine enzyme\ntissue_or_cell_type: Purified enzyme\nexperimental_model: Steady-state kinetics of dopamine beta-monooxygenase with structurally distinct reductants\nlimitations: A kinetic comparison identifying ascorbate as the presumed physiological reductant and locating a separate binding site for it. Truncated abstract; the reductant site is inferred from kinetics and modelling.\nexposure: Ascorbate, ferrocyanide or dopamine itself as the reducing agent, with deuterium isotope effects\nevidence_span: {\"source_cache\": \"artifacts/cold-research/3676254.abstract.txt\", \"locator\": \"Indexed abstract; zero-based, end-exclusive Unicode character offsets\", \"file_sha256\": \"e929132eed0f1c94ab0bdbef6e31bca7ecbed222cf9b585e17a1cfae7e93c82a\", \"start_char\": 0, \"end_char\": 1648, \"text_sha256\": \"e929132eed0f1c94ab0bdbef6e31bca7ecbed222cf9b585e17a1cfae7e93c82a\"}\n[cold-p3676254] Characterization of alternate reductant binding and electron transfer in the dopamine beta-monooxygenase reaction. (1987). https://pubmed.ncbi.nlm.nih.gov/3676254/ DOI: 10.1021/bi00391a013","model_system":"Steady-state kinetics of dopamine beta-monooxygenase with structurally distinct reductants","directness":"author_interpretation","verification_status":"source_derived_draft","notes":"Exact curation-document quotation, not publisher quotation. Study references: [cold-p3676254] Characterization of alternate reductant binding and electron transfer in the dopamine beta-monooxygenase reaction. (1987). https://pubmed.ncbi.nlm.nih.gov/3676254/ DOI: 10.1021/bi00391a013","relationship":"supports","weight":1.0,"link_notes":"","source":{"id":"feeccadc-1392-573e-a0b5-0939ee5de6e2","stable_key":"import-b3c3f45a-50fb-5b79-98d7-5e5228df00db","title":"Cold water immersion: cold sensing, heat production, the catecholamine axis and what repeated exposure changes (2026-09-19)","document_type":"imported_text","citation_label":"AI-assisted literature curation; primary study URLs and scope retained in the document and extraction. Not publisher full text.","file_path":"","sha256":"557f074d372c49c502c34e648651aff7ebf2c8816305d2d2f08e338a7e96a5f0","revision_id":"ecc19e8d-40db-5b5d-b98e-0507f645976c","review_status":"unverified_draft","notes":""}}],"relations":[],"conflicts":[],"corrections":[],"research":null}