{"id":"af006bc3-aaf0-5824-b6ef-45aa3be0007a","stable_key":"1310afbd-6010-586e-805d-551d846da421:b6-transport-pdxk-k-na","predicate":"modulates","statement":"Human PDXK showed lower substrate Km with potassium than sodium, whereas sodium supported over twice the maximal activity.","claim_class":"mechanistic","status":"source_derived_draft","evidence_grade":"ungraded","direction":"context_dependent","is_public":true,"mechanism_event_id":"5859cd3a-b779-58f8-9bc6-513385670bcf","mechanism_event_label":"Potassium and sodium affect different kinetic properties.","subject":{"id":"5dd31e52-f51e-51f3-880e-240abcc0ab1d","slug":"potassium-ion","display_name":"Potassium ion","entity_type_key":"ion"},"object":{"id":"d2d46db7-13a4-595f-adaa-70ad6ca31a6c","slug":"pdxk","display_name":"Pyridoxal kinase / PDXK","entity_type_key":"protein"},"evidence_count":1,"mechanism_event":{"id":"5859cd3a-b779-58f8-9bc6-513385670bcf","stable_key":"1310afbd-6010-586e-805d-551d846da421:b6-transport-pdxk-k-na-event","event_type":"biochemical_relationship","label":"Potassium and sodium affect different kinetic properties.","description":"Human PDXK showed lower substrate Km with potassium than sodium, whereas sodium supported over twice the maximal activity.","status":"provisional","compartment":null,"participants":[{"entity":{"id":"5dd31e52-f51e-51f3-880e-240abcc0ab1d","slug":"potassium-ion","display_name":"Potassium ion","entity_type_key":"ion"},"role":"monovalent cation","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"38de8704-84db-5770-ac1d-242cd787e798","slug":"sodium-ion","display_name":"Sodium ion","entity_type_key":"ion"},"role":"comparator cation","stoichiometry":null,"state_label":"","sequence_order":1,"notes":""},{"entity":{"id":"24904faf-f4b4-5e5a-a2e6-3549fb7a2a2e","slug":"mg-atp","display_name":"Magnesium-ATP complex","entity_type_key":"chemical_species"},"role":"substrate complex","stoichiometry":null,"state_label":"","sequence_order":2,"notes":""},{"entity":{"id":"9bf6269d-9e01-553d-bd8b-11a0d613bfca","slug":"pyridoxal","display_name":"Pyridoxal","entity_type_key":"small_molecule"},"role":"substrate","stoichiometry":null,"state_label":"","sequence_order":3,"notes":""},{"entity":{"id":"d2d46db7-13a4-595f-adaa-70ad6ca31a6c","slug":"pdxk","display_name":"Pyridoxal kinase / PDXK","entity_type_key":"protein"},"role":"target","stoichiometry":null,"state_label":"","sequence_order":4,"notes":""}]},"contexts":[{"dimension":"cross_nutrient","value_text":"Potassium/sodium-B6 enzyme kinetics.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"evidence_location","value_text":"Full text: Metal binding and enzyme activity; Figure 1","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Purified recombinant human PDXK kinetics and crystallography.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"exposure","value_text":"Kinetic assays at pH 7.3.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"Lower Km is not a direct binding constant; results do not define dietary sodium/potassium effects.","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":"Potassium and sodium affect different kinetic properties.","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"primary_references","value_text":"[safo2007] Crystal Structure of human pyridoxal kinase: structural basis of M(+) and M(2+) activation. (2007). https://pubmed.ncbi.nlm.nih.gov/17766369/ DOI: 10.1110/ps.073022107","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"tissue_or_cell_type","value_text":"Purified human enzyme","comparator":null,"unit":null,"notes":"","entity":null}],"evidence":[{"id":"9a1d39c6-6c25-556b-bb7d-c2ebcba8451b","evidence_kind":"source_excerpt","locator":"Lines 203-215","start_line":203,"end_line":215,"excerpt":"### b6-transport-pdxk-k-na\nHuman PDXK showed lower substrate Km with potassium than sodium, whereas sodium supported over twice the maximal activity.\nCondition category: normal\nnutrient_topic: Vitamin B6 research collection; topical membership is not evidence of a direct dietary effect.\nplain_language: Potassium and sodium affect different kinetic properties.\norganism: Homo sapiens\ntissue_or_cell_type: Purified human enzyme\nexperimental_model: Purified recombinant human PDXK kinetics and crystallography.\nlimitations: Lower Km is not a direct binding constant; results do not define dietary sodium/potassium effects.\nexposure: Kinetic assays at pH 7.3.\nevidence_location: Full text: Metal binding and enzyme activity; Figure 1\ncross_nutrient: Potassium/sodium-B6 enzyme kinetics.\n[safo2007] Crystal Structure of human pyridoxal kinase: structural basis of M(+) and M(2+) activation. 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