Modulation by divalent metal ions of the autocatalytic reactivity of adenosinetriphosphatase from chloroplasts.
A nonlinear, pre-steady-state initial rate of ATP hydrolysis is obtained on the addition of a divalent metal ion--ATP complex to a heat-activated coupling factor 1 isolated from chloroplasts. The acceleration of the initial rate follows first-order kinetics. The observed first-order kinetic constant (kobsd) changes with the concentration of the substrate, reaching half-maximal value at the Km for ATP hydrolysis. Preincubation of the enzyme with divalent metal ions decreases the kobsd from 1 to 0.04 s-1. Saturation of the divalent metal ion effect was obtained at the micromolar range. It is suggested that the autocatalysis is a result of early stages in ATP hydrolysis which induce conformational changes in the enzyme. Binding of divalent metal ions in the absence of ATP slows down this change.
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000266:Adenylyl Imidodiphosphate / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology; D002413:Cations, Divalent / Q000494:pharmacology*; D002736:Chloroplasts / Q000201:enzymology*; D006868:Hydrolysis; D006180:Proton-Translocating ATPases
D002413:Cations, Divalent; D000266:Adenylyl Imidodiphosphate; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D006180:Proton-Translocating ATPases; D002118:Calcium