{"id":"79aafff6-d28c-5798-a5c3-ecc88c362f2b","stable_key":"252872b9-233f-5692-b72b-c8930ba0cfb7:sil-two-thousand-fold-over-substrate","predicate":"binds","statement":"Sildenafil and zaprinast are both competitive inhibitors of PDE5 and double-inhibition analysis shows they interact with the catalytic site in a mutually exclusive manner, with inhibition constants of 1 nanomolar for sildenafil, 5 nanomolar for UK-122764 and 130 nanomolar for zaprinast, and the affinity of each of these inhibitors for the enzyme is much higher than that of cyclic GMP itself whose Michaelis constant is 2000 nanomolar.","claim_class":"mechanistic","status":"source_derived_draft","evidence_grade":"ungraded","direction":"negative","is_public":true,"mechanism_event_id":"ba463b4c-8a2b-5384-962b-cb15a11d1d1d","mechanism_event_label":"The drug holds the working part of the enzyme about two thousand times more tightly than the molecule the enzyme is meant to destroy.","subject":{"id":"fe62cf8d-5f89-5e19-bc36-03ad3c9063b7","slug":"sildenafil","display_name":"Sildenafil","entity_type_key":"drug"},"object":{"id":"681fc093-5976-515a-822c-abff6329a0b9","slug":"pde5-catalytic-site","display_name":"The catalytic site of phosphodiesterase type 5","entity_type_key":"protein_state"},"evidence_count":1,"mechanism_event":{"id":"ba463b4c-8a2b-5384-962b-cb15a11d1d1d","stable_key":"252872b9-233f-5692-b72b-c8930ba0cfb7:sil-two-thousand-fold-over-substrate-event","event_type":"biochemical_relationship","label":"The drug holds the working part of the enzyme about two thousand times more tightly than the molecule the enzyme is meant to destroy.","description":"Sildenafil and zaprinast are both competitive inhibitors of PDE5 and double-inhibition analysis shows they interact with the catalytic site in a mutually exclusive manner, with inhibition constants of 1 nanomolar for sildenafil, 5 nanomolar for UK-122764 and 130 nanomolar for zaprinast, and the affinity of each of these inhibitors for the enzyme is much higher than that of cyclic GMP itself whose Michaelis constant is 2000 nanomolar.","status":"provisional","compartment":null,"participants":[{"entity":{"id":"6d2f509b-3a5b-5a38-b3e7-b148581edec9","slug":"cgmp","display_name":"Cyclic guanosine monophosphate","entity_type_key":"small_molecule"},"role":"displaced_substrate","stoichiometry":null,"state_label":"","sequence_order":0,"notes":""},{"entity":{"id":"9381d4a4-dd83-5d06-8ae4-f3a17ecbda8e","slug":"zaprinast","display_name":"Zaprinast","entity_type_key":"chemical_species"},"role":"comparator_inhibitor","stoichiometry":null,"state_label":"","sequence_order":1,"notes":""},{"entity":{"id":"3d39054f-649d-5b50-ba42-92d743e23824","slug":"cgmp-hydrolysis","display_name":"Hydrolysis of cyclic GMP to 5-guanosine monophosphate","entity_type_key":"cellular_process"},"role":"blocked_reaction","stoichiometry":null,"state_label":"","sequence_order":2,"notes":""},{"entity":{"id":"fe62cf8d-5f89-5e19-bc36-03ad3c9063b7","slug":"sildenafil","display_name":"Sildenafil","entity_type_key":"drug"},"role":"subject","stoichiometry":null,"state_label":"","sequence_order":3,"notes":""},{"entity":{"id":"681fc093-5976-515a-822c-abff6329a0b9","slug":"pde5-catalytic-site","display_name":"The catalytic site of phosphodiesterase type 5","entity_type_key":"protein_state"},"role":"target","stoichiometry":null,"state_label":"","sequence_order":4,"notes":""}]},"contexts":[{"dimension":"evidence_span","value_text":"{\"source_cache\": \"artifacts/sildenafil-research/10385692.abstract.txt\", \"locator\": \"Indexed abstract; zero-based, end-exclusive Unicode character offsets\", \"file_sha256\": \"9ce2e7f3f2d22246734a6f998124d7a57cc0eded673f321bbc47586fd2ea3bcf\", \"start_char\": 0, \"end_char\": 1888, \"text_sha256\": \"9ce2e7f3f2d22246734a6f998124d7a57cc0eded673f321bbc47586fd2ea3bcf\"}","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"experimental_model","value_text":"Kinetic and site-directed mutagenesis analysis of inhibitor interaction with the phosphodiesterase type 5 catalytic domain","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"exposure","value_text":"Sildenafil, UK-122764 and zaprinast against wild-type enzyme and 23 conserved catalytic-domain point mutants","comparator":null,"unit":null,"notes":"","entity":null},{"dimension":"limitations","value_text":"Places the drug at the catalytic site by competition and by a mutant series, and gives the comparison with the natural substrate that makes the affinity meaningful. 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Recombinant enzyme.\nexposure: Sildenafil, UK-122764 and zaprinast against wild-type enzyme and 23 conserved catalytic-domain point mutants\nevidence_span: {\"source_cache\": \"artifacts/sildenafil-research/10385692.abstract.txt\", \"locator\": \"Indexed abstract; zero-based, end-exclusive Unicode character offsets\", \"file_sha256\": \"9ce2e7f3f2d22246734a6f998124d7a57cc0eded673f321bbc47586fd2ea3bcf\", \"start_char\": 0, \"end_char\": 1888, \"text_sha256\": \"9ce2e7f3f2d22246734a6f998124d7a57cc0eded673f321bbc47586fd2ea3bcf\"}\n[sil-p10385692] Inhibition of cyclic GMP-binding cyclic GMP-specific phosphodiesterase (Type 5) by sildenafil and related compounds. 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