Considerations on the kinetics of an electrochemical model of oxidative phosphorylation

Abstract

Proton translocation is proposed to be caused by the difference in dissociation equilibria of consecutive reaction partners. This mechanism, which was given earlier for redox-linked proton transfer, is extended to the phosphorylation process. Interfacial ion transfers, regarded separately on either side of the membrane and with respect to individual intramembrane chemical reactions, are treated from the kinetic point of view. On the basis of the theory of interfacial charge transfer, equations are derived according to which interfacial as well as transmembrane fluxes of protons are exponential functions of the difference in electrochemical potential of the proton. As far as mass transport is concerned, the exponential relationships become sigmoidal. From this, the parallelism between electrochemical and biological energy conversion is elucidated. In both cases, the driving forces vary as a function of charge flow. In oxidative phosphorylation the driving force is regarded to be the difference in electrochemical potential of the proton, the same as in the original version of the chemiosmotic theory (proton-motive force). By contrast to the latter, the present theory considers the biological energy conversion machinery as a dynamic rather than a static system. Therefore it is considered to be a step beyond the chemiosmotic theory.