{"id":"18d1a297-b58d-5abe-bbd4-9722783143ab","stable_key":"1310afbd-6010-586e-805d-551d846da421:b6-met-cbs-condensation","predicate":"catalyzes-formation-of","statement":"PLP-dependent human CBS condenses serine with homocysteine to produce cystathionine.","claim_class":"mechanistic","status":"source_derived_draft","evidence_grade":"ungraded","direction":"positive","is_public":true,"mechanism_event_id":"89055309-147a-5032-8a4f-c69d40126992","mechanism_event_label":"This B6-dependent step channels homocysteine into transsulfuration.","subject":{"id":"4688e32c-d7b6-5fca-9eb2-23307c29ae07","slug":"cbs","display_name":"Human cystathionine beta-synthase / CBS","entity_type_key":"protein"},"object":{"id":"ffc7d833-38ce-5224-82e0-19c0b87b45bf","slug":"cystathionine","display_name":"Cystathionine","entity_type_key":"small_molecule"},"evidence_count":1,"mechanism_event":{"id":"89055309-147a-5032-8a4f-c69d40126992","stable_key":"1310afbd-6010-586e-805d-551d846da421:b6-met-cbs-condensation-event","event_type":"biochemical_relationship","label":"This B6-dependent step channels homocysteine into transsulfuration.","description":"PLP-dependent human CBS condenses serine with homocysteine to produce cystathionine.","status":"provisional","compartment":null,"participants":[{"entity":{"id":"4688e32c-d7b6-5fca-9eb2-23307c29ae07","slug":"cbs","display_name":"Human cystathionine beta-synthase / CBS","entity_type_key":"protein"},"role":"enzyme","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"6b656ff5-9532-5da4-8eea-8ca163a48649","slug":"pyridoxal-phosphate","display_name":"PLP","entity_type_key":"small_molecule"},"role":"cofactor","stoichiometry":null,"state_label":"","sequence_order":1,"notes":""},{"entity":{"id":"c882cd0b-9d83-5b07-bd1c-fe4d45657dcb","slug":"l-serine","display_name":"L-Serine","entity_type_key":"small_molecule"},"role":"substrate","stoichiometry":null,"state_label":"","sequence_order":2,"notes":""},{"entity":{"id":"5b635b42-bc0d-5c54-aa94-9cf76cd0ed47","slug":"homocysteine","display_name":"Homocysteine","entity_type_key":"small_molecule"},"role":"substrate","stoichiometry":null,"state_label":"","sequence_order":3,"notes":""},{"entity":{"id":"ffc7d833-38ce-5224-82e0-19c0b87b45bf","slug":"cystathionine","display_name":"Cystathionine","entity_type_key":"small_molecule"},"role":"product","stoichiometry":null,"state_label":"","sequence_order":4,"notes":""},{"entity":{"id":"d31225b7-8e94-5857-9ea1-67ac794b1f15","slug":"water","display_name":"H2O","entity_type_key":"small_molecule"},"role":"product","stoichiometry":null,"state_label":"","sequence_order":5,"notes":""}]},"contexts":[{"dimension":"cross_nutrient","value_text":"Methionine-derived sulfur enters cysteine synthesis.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Recombinant truncated human CBS crystallography","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"Enzyme chemistry alone does not predict whole-body homocysteine during mild deficiency.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"nutrient_topic","value_text":"Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect.","comparator":null,"unit":null,"notes":"","entity":{"slug":"vitamin-b6","display_name":"Vitamin B6","entity_type_key":"chemical_species"}},{"dimension":"organism","value_text":"Homo sapiens","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"plain_language","value_text":"This B6-dependent step channels homocysteine into transsulfuration.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"[b6-cbs-2001] Structure of human cystathionine beta-synthase: a unique pyridoxal 5'-phosphate-dependent heme protein. (2001). https://pmc.ncbi.nlm.nih.gov/articles/PMC149156/ DOI: 10.1093/emboj/20.15.3910","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":"9f02468b-72cf-50e9-919f-1c892575f616","evidence_kind":"source_excerpt","locator":"Lines 517-527","start_line":517,"end_line":527,"excerpt":"### b6-met-cbs-condensation\nPLP-dependent human CBS condenses serine with homocysteine to produce cystathionine.\nCondition category: normal\nnutrient_topic: Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect.\nplain_language: This B6-dependent step channels homocysteine into transsulfuration.\norganism: Homo sapiens\ntissue_or_cell_type: Purified recombinant protein; no intact tissue\nexperimental_model: Recombinant truncated human CBS crystallography\nlimitations: Enzyme chemistry alone does not predict whole-body homocysteine during mild deficiency.\ncross_nutrient: Methionine-derived sulfur enters cysteine synthesis.\n[b6-cbs-2001] Structure of human cystathionine beta-synthase: a unique pyridoxal 5'-phosphate-dependent heme protein. (2001). https://pmc.ncbi.nlm.nih.gov/articles/PMC149156/ DOI: 10.1093/emboj/20.15.3910","model_system":"Recombinant truncated human CBS crystallography","directness":"author_interpretation","verification_status":"source_derived_draft","notes":"Exact curation-document quotation, not publisher quotation. Study references: [b6-cbs-2001] Structure of human cystathionine beta-synthase: a unique pyridoxal 5'-phosphate-dependent heme protein. (2001). https://pmc.ncbi.nlm.nih.gov/articles/PMC149156/ DOI: 10.1093/emboj/20.15.3910","relationship":"supports","weight":1.0,"link_notes":"","source":{"id":"251773bb-16f5-5903-b135-db4a61d9dec4","stable_key":"import-1310afbd-6010-586e-805d-551d846da421","title":"Vitamin B6: mechanisms, 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. 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