Direct measurement of proton release by cytochrome c oxidase in solution during the F-->O transition.

The mechanism by which electron transfer is coupled to proton pumping in cytochrome c oxidase is a major unsolved problem in molecular bioenergetics. In this work it is shown that, at least under some conditions, proton release from the enzyme occurs before proton uptake upon electron transfer to the heme/Cu active site of the enzyme. This sequence is similar to that of proton release and uptake observed for the light-activated proton pump bacteriorhodopsin. In the case of cytochrome c oxidase, this observation means that both the ejected proton and the proton required for the chemistry at the enzyme active site must come from an internal proton pool.