Kinetic properties of F0F1-ATPases. Theoretical predictions from alternating-site models.

We present an analysis of models based on current structural concepts of the F0F1 synthases, accounting for coupling between proton transport and ATP synthesis. It is assumed that each of the three alpha beta-subunits of the synthase can exist in three different conformational states E, Eo and E*. Proton translocation is coupled to cyclic interconversion of the conformations of the alpha beta-subunits. The conformational changes of these subunits are assumed to be coordinated so that all three interconvert simultaneously, in a rate-limiting transition. Binding and release of the ligands ATP, ADP, Pi, and protons are assumed to be equilibrium steps. In one family of models, interconversion of the alpha beta-subunits of F1 is coupled to the translocation event in F0 acting as a proton carrier. In a second family of models, protons combine with F0F1 and are translocated during the interconversion step in a chemiport. Kinetic tests involving the mutual effects of [ATP], [ADP], H+', and H+" are described, allowing us to make a distinction between the different models and submodels.