page_title: Cytochrome c oxidase
section_title: Extramitochondrial and subcellular localizations
hierarchical_section_title: Cytochrome c oxidase / Extramitochondrial and subcellular localizations
context_page_description: The enzyme cytochrome c oxidase or Complex IV, EC 1.9.3.1, is a large transmembrane protein complex found in bacteria, archaea, and the mitochondria of eukaryotes.
  It is the last enzyme in the respiratory electron transport chain of cells located in the membrane. It receives an electron from each of four cytochrome c molecules, and transfers them to one dioxygen molecule, converting the molecular oxygen to two molecules of water. In this process it binds four protons from the inner aqueous phase to make two water molecules, and translocates another four protons across the membrane, increasing the transmembrane difference of proton electrochemical potential which the ATP synthase then uses to synthesize ATP.
context_section_description: Cytochrome c oxidase has 3 subunits which are encoded by mitochondrial DNA (cytochrome c oxidase subunit I, subunit II, and subunit III). Of these 3 subunits encoded by mitochondrial DNA, two have been identified in extramitochondrial locations. In pancreatic acinar tissue, these subunits were found in zymogen granules. Additionally, in the anterior pituitary, relatively high amounts of these subunits were found in growth hormone secretory granules. The extramitochondrial function of these cytochrome c oxidase subunits has not yet been characterized. Besides cytochrome c oxidase subunits, extramitochondrial localization has also been observed for large numbers of other mitochondrial proteins. This raises the possibility about existence of yet unidentified specific mechanisms for protein translocation from mitochondria to other cellular destinations.
caption: Location of the 3 cytochrome c oxidase subunit genes in the human mitochondrial genome: COXI, COXII, and COXIII (orange boxes).