Activation of a complex of ATPase with the natural protein inhibitor in submitochondrial particles

Abstract

Almost all ATPase molecules in submitochondrial particles, isolated from beef heart mitochondria in the presence of MgATP, are in an inactive complex with the natural protein inhibitor (IF 1). In de-energized particles at high ionic strength a slow and irreversible ATPase activation is found to occur due to a dissociation of the enzyme-inhibitor complex. The pH-dependence of this process points out that deprotonation of IF 1 molecule is an essential step in the dissociation of the complex. Zn 2+ sharply accelerates ATPase activation, probably via binding with the deprotonated form of IF 1. ATPase activation is completely prevented by MgATP, indicating the formation of a transient enzyme-inhibitor complex retaining ATPase activity