title: The binding and release of the inhibitor protein are governed independently by ATP and membrane potential in ox-heart submitochondrial vesicles.
abstract: (1) The effects of membrane potential (delta psi) and nucleotides on the interaction between the F1-ATP synthase and its natural inhibitor protein (IF1) are studied in ox-heart submitochondrial vesicles. (2) Membrane potential causes displacement of IF1 from submitochondrial vesicles, as shown by measuring both delta psi-dependent stimulation of ATPase capacity and release of 125I-labelled IF1 from the vesicles. These effects are abolished if ATP is included in the incubation. (3) There is a linear increase in the steady-state ATPase capacity of oxidising vesicles as delta psi is increased from 100 mV to 135 mV. Increasing delta psi above 140 mV leads to no further change. (4) At a constant membrane potential, ATP suppresses the increase in ATPase capacity, with a concentration for half maximal effect of 140 microM. This value is close to the Km for ATP hydrolysis by membrane-bound F1. This suppression is related to ATP concentration rather than to delta Gp or ATP/ADP ratio. (5) The unidirectional on- and off-rates of IF1 were measured separately. The off-rate of IF1 is increased by membrane potential but unaffected by ATP. The on-rate, conversely, is increased by ATP. Thus, the suppression of the potential-dependent net release of IF1 from submitochondrial vesicles by ATP results from an increase of the IF1 on-rate above the off-rate.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002417:Cattle; D004789:Enzyme Activation / Q000187:drug effects; D008297:Male; D008564:Membrane Potentials; D008929:Mitochondria, Heart / Q000378:metabolism*; D011485:Protein Binding; D011506:Proteins / Q000378:metabolism*; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013386:Succinates / Q000494:pharmacology; D019802:Succinic Acid; D000097795:ATPase Inhibitory Protein
chemical_list: D000255:Adenosine Triphosphate; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D011506:Proteins; D006180:Proton-Translocating ATPases; D013386:Succinates; D019802:Succinic Acid; D000097795:ATPase Inhibitory Protein