KINETIC-ANALYSIS OF ADP-DEPENDENT AND MG-2+-DEPENDENT INACTIVATION OF CF1-ATPASE

Addition of the soluble chloroplast ATPase (CF1-ATPase) to a reaction mixture containing ADP and Mg2+ produced a slow conversion of the enzyme from the unstable active state into the stable low-activity state. With the active CF1-ATPase, the reciprocal of reaction rate was linearly dependent on the reciprocal of ATP concentration, and ADP competitively inhibited the reaction. This dependence ceased to be linear during enzyme inactivation. With a low ATP concentration, ADP became a non-competitive inhibitor of the reaction. The increasing ATP concentration made the inhibition weaker and promoted the CF1-ATPase activation. Oxyanions induced a similar action. Thus when the CF1-ATPase was in the unstable active state, its catalytic sites had similar kinetic characteristics. The reversible ADP- and Mg2+-dependent inactivation of these sites was accompanied by a variation in their properties: one of them demonstrated a growing affinity and specificity for ADP, another for ATP, while the third one was characterized by a sharp decrease in affinity and specificity for nucleotides.