Functional regions of the H(+)-ATPase inhibitory protein from ox heart mitochondria

Derivatives of the inhibitor protein (IF1) of the mitochondrial H(+)-ATP synthase, bearing deletions at the N- or C-terminal ends, were tested for their abilities (a) to bind to the synthase, (b) to inhibit its ATPase activity and (c) to respond to energisation of the mitochondrial membrane. Deletion of nine residues from its N-terminus, or ten from its C-terminus had little effect on any of these three properties of IF1. Further deletions from the N-terminus (up to residue 17) led to an increase in binding affinity but a reduced ability to inhibit ATPase activity and to form a stable ATPase-IF1 complex. Removal of five more residues from the N-terminus (up to residue 22) reduced these abilities further, but also decreased binding affinity by an order of magnitude. It was concluded that residues 10-17 of IF1 interact with F1 in a way which modulates the stability and function of the interaction between F1 and IF1.