  We propose a simple model of cytochrome c oxidase, including four redox
centers and four protonable sites, to study the time evolution of
electrostatically coupled electron and proton transfers initiated by the
injection of a single electron into the enzyme. We derive a system of master
equations for electron and proton state probabilities and show that an
efficient pumping of protons across the membrane can be obtained for a
reasonable set of parameters. All four experimentally observed kinetic phases
appear naturally from our model. We also calculate the dependence of the
pumping efficiency on the transmembrane voltage at different temperatures and
discuss a possible mechanism of the redox-driven proton translocation.
