Activation and deactivation of F0F1-ATPase in yeast mitochrondia

The regulation of membrane-bound proton F0F1 ATPase by the protonmotive for ce and nucleotides was studied in yeast mitochondria. Activation occurred i n whole mitochondria and the ATPase activity was measured just after disrup ting the membranes with Triton X-100. Deactivation occurred either in whole mitochondria uncoupled with FCCP, or in disrupted membranes. No effect of Triton X-100 on the ATPase was observed, except a slow reactivation observe d only in the absence of MgADP. Both AMPPNP and ATP increased the ATPase de activation rate, thus indicating that occupancy of nucleotidic sites by ATP is more decisive than catalytic turnover for this process. ADP was found t o stimulate the energy-dependent ATPase activation. ATPase deactivated at t he same rate in uncoupled and disrupted mitochondria This suggests that dea ctivation is not controlled by rebinding of some soluble factor, like IF1, but rather by the conversion of the F-1.IF1 complex into an inactive form.