title: The effect of inorganic pyrophosphate on the activity and Pi-binding properties of mitochondrial F1-ATPase.
abstract: Interaction of F1-ATPase from beef heart mitochondria with PPi has been investigated. The presence of PPi in the ATPase assay medium does not affect the initial rate of ATP hydrolysis by F1-ATPase, but slows down the decrease of enzyme activity in the course of ATP hydrolysis and increases the steady-state rate of ATP hydrolysis. Being present in the ATPase assay medium, PPi accelerates the ATP-dependent reactivation of an inactive complex formed by F1-ATPase and ADP. This inactive complex is also reactivated after preincubation with PPi. F1-ATPase, preincubated with PPi, is inactivated by azide much more slowly than is the non-preincubated enzyme. PPi stimulates the binding of Pi to F1-ATPase by decreasing mainly the Kd for Pi and only slightly raising the stoichiometry of high-affinity Pi binding. It follows from the results obtained that PPi interacts with the non-catalytic site(s) of F1-ATPase.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001386:Azides / Q000494:pharmacology; D001665:Binding Sites / Q000187:drug effects; D002417:Cattle; D011756:Diphosphates / Q000378:metabolism / Q000494:pharmacology*; D006868:Hydrolysis; D008929:Mitochondria, Heart / Q000201:enzymology*; D010085:Oxidative Phosphorylation; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013447:Sulfites / Q000494:pharmacology
chemical_list: D001386:Azides; D011756:Diphosphates; D013447:Sulfites; D000255:Adenosine Triphosphate; D006180:Proton-Translocating ATPases