Pumping of protons from the mitochondrial matrix by cytochrome oxidase.

The stoichiometry and mechanism of redox-linked proton translocation by the mitochondrial respiratory chain is a major issue of debate in membrane bioenergetics. The function of cytochrome oxidase is a focal point of disagreement. In 1977 it was suggested that the terminal component of the respiratory chain, cytochrome oxidase, functions as a redox-linked proton pump. That and subsequent studies were based mainly on measurements of proton ejection from mitochondria or from vesicles reconstituted with isolated cytochrome oxidase, or on measurements of translocation of electrical charge equivalents across mitochondrial and vesicle membranes. This proton-translocating function of cytochrome oxidase is confirmed here by a quantitative determination of proton uptake from the inside (matrix) of intact mitochondria.