A common coupling mechanism for A-type heme-copper oxidases from bacteria to mitochondria.

Abstract

Mitochondria metabolize almost all the oxygen that we consume, reducing it to water by cytochrome <i>c</i> oxidase (C<i>c</i>O). C<i>c</i>O maximizes energy capture into the protonmotive force by pumping protons across the mitochondrial inner membrane. Forty years after the H⁺/e^- stoichiometry was established, a consensus has yet to be reached on the route taken by pumped protons to traverse C<i>c</i>O's hydrophobic core and on whether bacterial and mitochondrial C<i>c</i>Os operate via the same coupling mechanism. To resolve this, we exploited the unique amenability to mitochondrial DNA mutagenesis of the yeast <i>Saccharomyces cerevisiae</i> to introduce single point mutations in the hydrophilic pathways of C<i>c</i>O to test function. From adenosine diphosphate to oxygen ratio measurements on preparations of intact mitochondria, we definitely established that the D-channel, and not the H-channel, is the proton pump of the yeast mitochondrial enzyme, supporting an identical coupling mechanism in all forms of the enzyme.