Cytochrome c oxidase subunit VIIc. Cytochrome c oxidase (CcO), the terminal oxidase in the respiratory chains of eukaryotes and most bacteria, is a multi-chain transmembrane protein located in the inner membrane of mitochondria and the cell membrane of prokaryotes. It catalyzes the reduction of O2 and simultaneously pumps protons across the membrane. The number of subunits varies from three to five in bacteria and up to 13 in mammalian mitochondria. Subunits I, II, and III of mammalian CcO are encoded within the mitochondrial genome and the remaining 10 subunits are encoded within the nuclear genome. The VIIc subunit is found only in eukaryotes and its specific function remains unclear. Peroxide inactivation of bovine CcO coincides with the direct oxidation of tryptophan (W19) within subunit VIIc, along with other structural changes in other subunits.
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