Activation of ATPase of spinach coupling factor 1. Release of tightly bound ADP from the soluble enzyme

Several seemingly unrelated procedures used to elicit the latent ATPase activity of soluble spinach coupling factor 1 can be correlated to the release of tightly-bound ADP from the uncoupled enzyme. This ADP release is further enhanced by the presence of medium nucleotides, especially substrate ATP, and may or may not involve release from the catalytic site itself. Similarly, the light/dithiothreitol activation of membrane-bound CF1 ATPase is reported to be accompanied by energy-dependent ADP dissociation. Further indication that ADP release is involved in the ATPase activation mechanism is the observation that a pyruvate kinase phosphoenolpyruvate trap for ADP released during light/dithiothreitol treatment greatly retards the decay of membrane-bound ATPase activity that occurs in the dark, presumably by preventing reassociation of ADP. The time course of CF1 reactivation by light, after light/dithiothreitol activation followed by dark decay, allows a distinction to be made between the apparently rate-limiting dithiol modification and the more rapid dissociation of tightly bound ADP.