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Cytochrome c oxidase

Cytochrome c oxidase (CcO) catalyzes the final step of respiration - reduction of molecular oxygen. Reduction of one dioxygen to water requires four electrons that are supplied one-by-one from the water-soluble cytochrome c on the P-side, and four protons, taken up from the N-side of the membrane.

Scheme of cytochrome c oxidase. Only subunits I and II are shown.

Scheme of cytochrome c oxidase; only subunits I and II in a complex with electron donor cytochrome c are shown

The energy released in the reaction of oxygen reduction is conserved in the form of a transmembrane electrochemical gradient of protons across the membrane, ΔμH. Formation of ΔμH by CcO is based on two principles: vectorial chemistry and proton pumping. Since the protons and electrons for oxygen reduction to water are taken from the different sides of the membrane, the reaction results in net transfer of four charges across the membrane. At the same time, the enzyme is able not only to catalyze the oxygen reduction but also to utilize the released energy for proton pumping with stoichiometry 4H+/O2.


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