{"id":"30f220b3-a515-51a5-83a7-2cb22a00ec64","stable_key":"a9dd23c6-978a-5755-8bd8-f29bd1fe0cda:b3-pre-tdo-reaction","predicate":"catalyzes-production-of","statement":"Human TDO2 substrate and product structures support oxidative conversion of L-tryptophan and oxygen to N-formylkynurenine.","claim_class":"mechanistic","status":"source_derived_draft","evidence_grade":"ungraded","direction":"positive","is_public":true,"mechanism_event_id":"7b6be18b-15e3-5647-87f3-0c050311c26d","mechanism_event_label":"TDO2 opens the tryptophan ring at the beginning of the kynurenine route.","subject":{"id":"069155e2-e27b-55c2-85e3-b4a96bc91876","slug":"tdo2","display_name":"Human tryptophan 2,3-dioxygenase / TDO2","entity_type_key":"protein"},"object":{"id":"540784df-850e-5eac-a71c-22556535e471","slug":"n-formylkynurenine","display_name":"N-Formyl-L-kynurenine","entity_type_key":"small_molecule"},"evidence_count":1,"mechanism_event":{"id":"7b6be18b-15e3-5647-87f3-0c050311c26d","stable_key":"a9dd23c6-978a-5755-8bd8-f29bd1fe0cda:b3-pre-tdo-reaction-event","event_type":"biochemical_relationship","label":"TDO2 opens the tryptophan ring at the beginning of the kynurenine route.","description":"Human TDO2 substrate and product structures support oxidative conversion of L-tryptophan and oxygen to N-formylkynurenine.","status":"provisional","compartment":null,"participants":[{"entity":{"id":"069155e2-e27b-55c2-85e3-b4a96bc91876","slug":"tdo2","display_name":"Human tryptophan 2,3-dioxygenase / TDO2","entity_type_key":"protein"},"role":"enzyme","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"769339cb-213b-559e-acc0-07ed00368b94","slug":"l-tryptophan","display_name":"L-Tryptophan","entity_type_key":"small_molecule"},"role":"substrate","stoichiometry":null,"state_label":"","sequence_order":1,"notes":""},{"entity":{"id":"899c7ab0-6f81-5b38-a6bd-fbb33d66ac8d","slug":"oxygen","display_name":"Molecular oxygen","entity_type_key":"small_molecule"},"role":"substrate","stoichiometry":null,"state_label":"","sequence_order":2,"notes":""},{"entity":{"id":"540784df-850e-5eac-a71c-22556535e471","slug":"n-formylkynurenine","display_name":"N-Formyl-L-kynurenine","entity_type_key":"small_molecule"},"role":"product","stoichiometry":null,"state_label":"","sequence_order":3,"notes":""}]},"contexts":[{"dimension":"cross_nutrient","value_text":"Tryptophan provides the carbon framework entering the de novo niacin pathway; downstream steps remain necessary.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"evidence_span","value_text":"{\"source_cache\": \"artifacts/niacin-precursors-sources/tdo2016.paragraphs.txt\", \"locator\": \"Normalized full-text paragraphs 9–9 (0-based)\", \"start_char\": 8003, \"end_char\": 9136, \"file_sha256\": \"3f91886745b8ff9fb808232c839dd346b03605dd025d5fa682a3de4f81338ec5\", \"text_sha256\": \"b39e2ce5d405e5eb8fde25aec369c306954365d7ec2b448fe5a5689e89785e2a\"}","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Purified human TDO2 crystallography and spectroscopy; substrate/product complexes","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"exposure","value_text":"Biochemical or structural assay; no dietary intervention","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"Purified-enzyme evidence does not establish dietary intake requirements or clinical outcomes.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"nutrient_topic","value_text":"Niacin research collection; topical membership is not evidence of a direct dietary effect.","comparator":null,"unit":null,"notes":"","entity":{"slug":"niacin","display_name":"Niacin (vitamin B3)","entity_type_key":"nutrient_element"}},{"dimension":"organism","value_text":"Homo sapiens","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"plain_language","value_text":"TDO2 opens the tryptophan ring at the beginning of the kynurenine route.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"[b3-pre-tdo2016] Molecular basis for catalysis and substrate-mediated cellular stabilization of human tryptophan 2,3-dioxygenase. (2016). https://pubmed.ncbi.nlm.nih.gov/27762317/ DOI: 10.1038/srep35169","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"tissue_or_cell_type","value_text":"Purified recombinant protein; no intact tissue","comparator":null,"unit":null,"notes":"","entity":null}],"evidence":[{"id":"ce2a18ac-4ad6-5e0f-8528-1ae96aab3d9c","evidence_kind":"source_excerpt","locator":"Lines 479-491","start_line":479,"end_line":491,"excerpt":"### b3-pre-tdo-reaction\nHuman TDO2 substrate and product structures support oxidative conversion of L-tryptophan and oxygen to N-formylkynurenine.\nCondition category: normal\nnutrient_topic: Niacin research collection; topical membership is not evidence of a direct dietary effect.\nplain_language: TDO2 opens the tryptophan ring at the beginning of the kynurenine route.\norganism: Homo sapiens\ntissue_or_cell_type: Purified recombinant protein; no intact tissue\nexperimental_model: Purified human TDO2 crystallography and spectroscopy; substrate/product complexes\nlimitations: Purified-enzyme evidence does not establish dietary intake requirements or clinical outcomes.\nexposure: Biochemical or structural assay; no dietary intervention\ncross_nutrient: Tryptophan provides the carbon framework entering the de novo niacin pathway; downstream steps remain necessary.\nevidence_span: {\"source_cache\": \"artifacts/niacin-precursors-sources/tdo2016.paragraphs.txt\", \"locator\": \"Normalized full-text paragraphs 9–9 (0-based)\", \"start_char\": 8003, \"end_char\": 9136, \"file_sha256\": \"3f91886745b8ff9fb808232c839dd346b03605dd025d5fa682a3de4f81338ec5\", \"text_sha256\": \"b39e2ce5d405e5eb8fde25aec369c306954365d7ec2b448fe5a5689e89785e2a\"}\n[b3-pre-tdo2016] Molecular basis for catalysis and substrate-mediated cellular stabilization of human tryptophan 2,3-dioxygenase. (2016). https://pubmed.ncbi.nlm.nih.gov/27762317/ DOI: 10.1038/srep35169","model_system":"Purified human TDO2 crystallography and spectroscopy; substrate/product complexes","directness":"author_interpretation","verification_status":"source_derived_draft","notes":"Exact curation-document quotation, not publisher quotation. Study references: [b3-pre-tdo2016] Molecular basis for catalysis and substrate-mediated cellular stabilization of human tryptophan 2,3-dioxygenase. (2016). https://pubmed.ncbi.nlm.nih.gov/27762317/ DOI: 10.1038/srep35169","relationship":"supports","weight":1.0,"link_notes":"","source":{"id":"a62b7b5b-786a-57e9-85e9-67c6912a5054","stable_key":"import-a9dd23c6-978a-5755-8bd8-f29bd1fe0cda","title":"Niacin: NAD metabolism, deficiency and nutrient interactions (2026-09-17)","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":"a8cac59639322f74812ce12eef338c2f6c385c04cc4af6ab511fc7c972f0c2e6","revision_id":"bec8fc45-12e7-5f75-a814-5d72ed015d01","review_status":"unverified_draft","notes":""}}],"relations":[],"conflicts":[],"corrections":[],"research":null}