F1I, the specific ATPase inhibitor protein, and the chromium(III) analogs of ATP and ADP, CrATP and CrADP, were used to study the inhibition of Pi goes to and comes from ATP exchange reaction catalyzed by beef heart submitochondrial particles. F1I was found to be an uncompetitive inhibitor of the exchange reaction. CrATP and CrADP, both competitive inhibitors of ATP hydrolysis in isolated F1 (Schuster, S. M., Ebel, R. E., and Lardy, H. A. (1975) ARch. Biochem. Biophys. 171, 656-661) were shown to be competitive and noncompetitive inhibitors of Pi goes to and comes from ATP exchange, respectively. Dual inhibitor studies were done using combinations of F1I and the chromium nucleotides, or the nucleotide analogs in combination. All cases show sets of intersecting Dixon plots indicative of interacting inhibitors. Upward curvature is also evident on some of the plots. This phenomenon was explained using the concept of multiple synergistic binding of the inhibitors. Binding mechanisms and their relevant kinetic equations were postulated to explain the results of the dual inhibitor studies. They support the notion that in addition to the catalytic site, there are two types of regulatory binding sites on F1, one specific for nucleotides and one specific for F1I. When one of these sites is occupied, other sites are either opened or other inhibitors become more potent.