The equilibrium between the mitochondrial ATPase (F 1) and its natural inhibitor in submitochondrial particles

Abstract

1. The reversible equilibrium between the mitochondrial ATPase (F 1) and its naturally occurring inhibitor in Mg-ATP submitochondrial particles has been studied under different conditions. 2. High ionic strength favours dissociation of the ATPase inhibitor as tested by ATPase and ATP-driven transhydrogenase activities. 3. Dissociation of the ATPase inhibitor results in an increased maximal velocity of the ATPase activity measured in the presence of uncoupler and an increased affinity for adenine nucleotides, in particular for ATP. 4. Association of the ATPase inhibitor with inhibitor-depleted Mg-ATP particles causes a slowing of the initial rate of succinate oxidation. 5. The antibiotic aurovertin stimulates the ATPase activity of Mg-ATP particles preinculbated in the presence of a supply of oxidative energy. Bound aurovertin impedes the association of inhibitor-deficient particles with ATPase inhibitor. 6. The fluorescence of aurovertin bound to inhibitor-containing particles is much less than that of aurovertin bound to inhibitor-depleted particles. 7. The oligomycin-sensitivity-conferring protein, added either alone or in the presence or absence of membranous components of the ATPase complex, has little or no effect on the fluorescence of the F 1-aurovertin complex. 8. It is suggested that the ATPase inhibitor brings F 1 in a conformation denoted ∗F 1 that binds aurovertin with a low quantum yield, a decreased affinity and an increased binding capacity.