Binding of an intrinsic ATPase inhibitor to the F(1)FoATPase in phosphorylating conditions of yeast mitochondria

Yeast mitochondrial ATP synthase has three regulatory proteins; ATPase inhi bitor, 9K protein, and 15K protein A mutant yeast lacking these three regul atory factors was constructed by gene disruption. Rates of ATP synthesis of both wild-type and the mutant yeast mitochondria decreased with decrease o f respiration, while their membrane potential was maintained at 170-160 mV under various respiration rates, When mitochondrial respiration was blocked by antimycin A, the membrane potential of both types of mitochondria was m aintained at about 160 mV by ATP hydrolysis. ATP hydrolyzing activity of F( 1)FoATPase solubilized from normal mitochondria decreased in proportion to the rate of ATP synthesis, while the activity of the mutant F(1)FoATPase wa s constant regardless of changes in the rate of phosphorylation, These obse rvations strongly suggest that F(1)FoATPase in the phosphorylating mitochon dria is a mixture of two types of enzyme, phosphorylating and non-phosphory lating enzymes, whose ratio is determined by the rate of respiration and th at the ATPase inhibitor binds preferentially to the non-phosphorylating enz yme.