The generation of the proton electrochemical potential and its role in energy transduction

The evidence that all energy transducing membranes can generate a proton electrochemical potential difference, Δ $\tilde \mu $ _H, across the membrane and that this potential can be used to transfer energy among energy transducing units and to generate ATP, has increased the interest for the view that Δ $\tilde \mu $ _H plays an obligatory role in energy transduction and ATP synthesis. In the present article we shall concentrate on two experimental questions related with the generation and role of Δ $\tilde \mu $ _H: (a) the charge/site ratio; (b) the relation between the proton electrochemical potential on one side and the cation electrochemical potential, the phosphate potential and the redox potential on the other. We shall then discuss the view that energy transduction corresponds to a molecular energy machine rather than to a fuel cell.