Double-inhibitor and uncoupler-inhibitor titrations. 1. Analysis with a linear model of chemiosmotic energy coupling.

The results of double-inhibitor and uncoupler-inhibitor titrations have been simulated and analyzed with a linear model of delocalized protonic coupling using linear nonequilibrium thermodynamics. A detailed analysis of the changes of the intermediate delta muH induced by different combinations of inhibitors of the proton pumps has been performed. It is shown that with linear flow-force relationships the published experimental results of uncoupler-inhibitor titrations are not necessarily inconsistent with, and those of double-inhibitor titrations are inconsistent with, a delocalized chemiosmotic model of energy coupling in the presence of a negligible leak. Also shown and discussed are how the results are affected by a nonnegligible leak and to what extent the shape of the titration curves can be used to discriminate between localized and delocalized mechanisms of energy coupling.