Activation and deactivation of F0F1-ATPase in yeast mitochondria.

The regulation of membrane-bound proton F0F1 ATPase by the protonmotive force and nucleotides was studied in yeast mitochondria. Activation occurred in whole mitochondria and the ATPase activity was measured just after disrupting 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 observed only in the absence of MgADP. Both AMPPNP and ATP increased the ATPase deactivation rate, thus indicating that occupancy of nucleotidic sites by ATP is more decisive than catalytic turnover for this process. ADP was found to stimulate the energy-dependent ATPase activation. ATPase deactivated at the same rate in uncoupled and disrupted mitochondria This suggests that deactivation is not controlled by rebinding of some soluble factor, like IF1, but rather by the conversion of the F1.IF1 complex into an inactive form.