{"id":"91cbf388-2881-504f-b992-89e05b9d0387","stable_key":"7fc92b9e-9cbf-556e-8719-6b5244625250:b12-abs-haptocorrin-affinity","predicate":"binds","statement":"Human salivary R protein bound cobalamin with 50-fold higher affinity than human intrinsic factor at pH 2 and threefold higher affinity at pH 8.","claim_class":"mechanistic","status":"source_derived_draft","evidence_grade":"ungraded","direction":"positive","is_public":true,"mechanism_event_id":"0f520b35-db40-5554-8ba5-a7bab952b4a0","mechanism_event_label":"Haptocorrin outcompeted intrinsic factor, especially in acid.","subject":{"id":"21f01bdf-1da9-59c3-af35-c67281e89dd4","slug":"tcn1","display_name":"Human haptocorrin / TCN1","entity_type_key":"protein"},"object":{"id":"b6d9b937-895d-5e0a-8cc5-0454a0b7d373","slug":"vitamin-b12","display_name":"Vitamin B12 (cobalamins)","entity_type_key":"chemical_species"},"evidence_count":1,"mechanism_event":{"id":"0f520b35-db40-5554-8ba5-a7bab952b4a0","stable_key":"7fc92b9e-9cbf-556e-8719-6b5244625250:b12-abs-haptocorrin-affinity-event","event_type":"biochemical_relationship","label":"Haptocorrin outcompeted intrinsic factor, especially in acid.","description":"Human salivary R protein bound cobalamin with 50-fold higher affinity than human intrinsic factor at pH 2 and threefold higher affinity at pH 8.","status":"provisional","compartment":null,"participants":[{"entity":{"id":"b6d9b937-895d-5e0a-8cc5-0454a0b7d373","slug":"vitamin-b12","display_name":"Vitamin B12 (cobalamins)","entity_type_key":"chemical_species"},"role":"nutrient","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"490161eb-b7f8-56b6-82bc-77c8c0bdc1ca","slug":"gif","display_name":"Human gastric intrinsic factor / GIF","entity_type_key":"protein"},"role":"comparator","stoichiometry":null,"state_label":"","sequence_order":1,"notes":""},{"entity":{"id":"21f01bdf-1da9-59c3-af35-c67281e89dd4","slug":"tcn1","display_name":"Human haptocorrin / TCN1","entity_type_key":"protein"},"role":"subject","stoichiometry":null,"state_label":"","sequence_order":2,"notes":""}]},"contexts":[{"dimension":"cross_nutrient","value_text":"false","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Purified human salivary R protein and gastric intrinsic factor in vitro","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"exposure","value_text":"pH 2 or 8; purified protein competition","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"Reconstituted binding/protease conditions; measured competition does not quantify absorption in an intact person. Individual protease isoforms and reagent species not resolved in abstract.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"nutrient_topic","value_text":"Vitamin B12 research collection; topical membership is not evidence of a direct dietary effect.","comparator":null,"unit":null,"notes":"","entity":{"slug":"vitamin-b12","display_name":"Vitamin B12 (cobalamins)","entity_type_key":"chemical_species"}},{"dimension":"organism","value_text":"Homo sapiens","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"plain_language","value_text":"Haptocorrin outcompeted intrinsic factor, especially in acid.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"[allen-1978-proteases] Effect of proteolytic enzymes on the binding of cobalamin to R protein and intrinsic factor. In vitro evidence that a failure to partially degrade R protein is responsible for cobalamin malabsorption in pancreatic insufficiency. (1978). https://pubmed.ncbi.nlm.nih.gov/22556/ DOI: 10.1172/jci108924","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"tissue_or_cell_type","value_text":"Salivary/gastric and intestinal luminal binding models","comparator":null,"unit":null,"notes":"","entity":null}],"evidence":[{"id":"c202612f-5d36-5977-85f6-c7ac52e4c4c4","evidence_kind":"source_excerpt","locator":"Lines 153-164","start_line":153,"end_line":164,"excerpt":"### b12-abs-haptocorrin-affinity\nHuman salivary R protein bound cobalamin with 50-fold higher affinity than human intrinsic factor at pH 2 and threefold higher affinity at pH 8.\nCondition category: normal\nnutrient_topic: Vitamin B12 research collection; topical membership is not evidence of a direct dietary effect.\nplain_language: Haptocorrin outcompeted intrinsic factor, especially in acid.\norganism: Homo sapiens\ntissue_or_cell_type: Salivary/gastric and intestinal luminal binding models\nexperimental_model: Purified human salivary R protein and gastric intrinsic factor in vitro\nlimitations: Reconstituted binding/protease conditions; measured competition does not quantify absorption in an intact person. Individual protease isoforms and reagent species not resolved in abstract.\nexposure: pH 2 or 8; purified protein competition\ncross_nutrient: false\n[allen-1978-proteases] Effect of proteolytic enzymes on the binding of cobalamin to R protein and intrinsic factor. In vitro evidence that a failure to partially degrade R protein is responsible for cobalamin malabsorption in pancreatic insufficiency. (1978). https://pubmed.ncbi.nlm.nih.gov/22556/ DOI: 10.1172/jci108924","model_system":"Purified human salivary R protein and gastric intrinsic factor in vitro","directness":"author_interpretation","verification_status":"source_derived_draft","notes":"Exact curation-document quotation, not publisher quotation. Study references: [allen-1978-proteases] Effect of proteolytic enzymes on the binding of cobalamin to R protein and intrinsic factor. In vitro evidence that a failure to partially degrade R protein is responsible for cobalamin malabsorption in pancreatic insufficiency. (1978). https://pubmed.ncbi.nlm.nih.gov/22556/ DOI: 10.1172/jci108924","relationship":"supports","weight":1.0,"link_notes":"","source":{"id":"73145023-2982-5848-aff2-8d8875d6b9c5","stable_key":"import-7fc92b9e-9cbf-556e-8719-6b5244625250","title":"Vitamin B12: 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. Not publisher full text.","file_path":"","sha256":"ad5b3a51d36e856aa7fdfd1cc23f690b094689bad87d28e1a621a54675a01c92","revision_id":"118bd616-0c13-549f-bfeb-bc439715b89c","review_status":"unverified_draft","notes":""}}],"relations":[],"conflicts":[],"corrections":[],"research":null}