title: A kinetic study of the interaction between mitochondrial F1 adenosine triphosphatase and adenylyl imidodiphosphate and guanylyl imidodiphosphate.
abstract: 1. The presence of 5'-adenylyl imidodiphosphate, a non-hydrolysable analogue of ATP, in the solution used to assay the soluble bovine heart mitochondrial F1-ATPase produced slow competitive inhibition. If the enzyme was preincubated with the inhibitor before the substrate, MgATP, was added, a partial re-activation was obtained. 2. The slow inhibitory process showed first-order rate kinetics, and therefore it seems likely that a conformational change of the enzyme occurs following a faster binding process. A reaction scheme is suggested. At pH 7.8 the rate constant for the inhibition reaction was calculated to be 6.7 X 10(-2)s-1 and that for the re-activation 3.8 X 10(-3)s-1, with Keq. 17.6, indicating that the inhibited enzyme-inhibitor complex will be favoured over the non-inhibited enzyme-inhibitor complex. 3. The presence of 5'-guanylyl imidodiphosphate in the solution used to assay F1-ATPase produced rapid competitive inhibition, which was then slowly reversed until a steady state was reached. This might be explained by a rapid but reversible shift of the inhibition pathway induced by this non-hydrolysable analogue of ATP. A complex rate constant for the displacement of the inhibitor by the substrate of 7.6 X 10(-3)s-1 was calculated. 4. The results are discussed in the light of other recent observations about binding of 5'-adenylyl imidodiphosphate to F1-ATPase and with reference to the binding-site-change mechanism of hydrolysis of ATP by F1-ATPase.
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives*; D000266:Adenylyl Imidodiphosphate / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives*; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology*; D007700:Kinetics; D008929:Mitochondria, Heart / Q000201:enzymology*; D008956:Models, Chemical; D006180:Proton-Translocating ATPases / Q000037:antagonists & inhibitors*
chemical_list: D000266:Adenylyl Imidodiphosphate; D006165:Guanylyl Imidodiphosphate; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D006180:Proton-Translocating ATPases