Inhibitory and anchoring domains in the ATPase inhibitor protein IF1 of bovine heart mitochondrial ATP synthase

The inhibitor protein IF1 is a basic protein of 84 residues which inhibits the ATPase activity of the mitochondrial F0F1-ATP synthase complex without having any effect on ATP synthesis. Results of cross-linking and limited proteolysis experiments are presented showing that in the intact F0F1 complex "in situ," in the inner membrane of bovine heart mitochondria, the central segment of IF1 (residues 42-58) binds to the alpha and beta subunits of F-1 in a pH dependent process, and inhibits the ATPase activity. The C-terminal region of IF1 binds, simultaneously, to the OSCP subunit of F-0 in a pH-independent process. This binding keeps IF1 anchored to the complex, both under inhibitory conditions, at acidic pH, and noninhibitory conditions at alkaline pH.