Dimerization of bovine F-1-ATPase by binding the inhibitor protein, IF1

In mitochondria, the hydrolytic activity of ATP synthase is regulated by a natural inhibitor protein, IF1. The binding of IF1 to ATP synthase depends on pH values, and below neutrality, IF1 forms a stable complex with the enz yme. Bovine IF1 has two oligomeric states, dimer and tetramer, depending on pH values. At pH 6.5, where it is active, IF1 dimerizes by formation of an antiparallel alpha-helical coiled-coil in its C-terminal region. This arra ngement places the inhibitory N-terminal regions in opposition, implying th at active dimeric IF1 can bind two F-1 domains simultaneously. Evidence of dimerization of F-1-ATPase by binding to IF1 is provided by gel filtration chromatography, analytical ultracentrifugation, and electron microscopy. At present, it is not known whether IF1 can bring about the dimerization of t he F1F0-ATPase complex.