Effect of the ATPase inhibitor protein IF1 on H+ translocation in the mitochondrial ATP synthase complex.

The H(+) F(o)F(1)-ATP synthase complex of coupling membranes converts the proton-motive force into rotatory mechanical energy to drive ATP synthesis. The F(1) moiety of the complex protrudes at the inner side of the membrane, the F(o) sector spans the membrane reaching the outer side. The IF(1) component of the mitochondrial complex is a basic 10 kDa protein, which inhibits the F(o)F(1)-ATP hydrolase activity. The mitochondrial matrix pH is the critical factor for the inhibitory binding of the central segment of IF(1) (residue 42-58) to the F(1)-alpha/beta subunits. We have analyzed the effect of native purified IF(1) the IF(1)-(42-58) synthetic peptide and its mutants on proton conduction, driven by ATP hydrolysis or by [K(+)] gradients, in bovine heart inside-out submitochondrial particles and in liposome-reconstituted F(o)F(1) complex. The results show that IF(1), and in particular its central 42-58 segment, displays different inhibitory affinity for proton conduction from the F(1) to the F(o) side and in the opposite direction. Cross-linking of IF(1) to F(1)-alpha/beta subunits inhibits the ATP-driven H(+) translocation but enhances H(+) conduction in the reverse direction. These observation are discussed in terms of the rotary mechanism of the F(o)F(1) complex.