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EC number
Accepted name
cytochrome-c oxidase
4 ferrocytochrome c + O2 + 4 H+ = 4 ferricytochrome c + 2 H2O
Other name(s)
cytochrome aa3, cytochrome caa3, cytochrome bb3, cytochrome cbb3, cytochrome ba3, cytochrome a3, Warburg’s respiratory enzyme, indophenol oxidase, indophenolase, complex IV (mitochondrial electron transport), ferrocytochrome c oxidase, cytochrome oxidase (ambiguous), NADH cytochrome c oxidase (incorrect)
Systematic name
ferrocytochrome-c:oxygen oxidoreductase
CAS registry number
An oligomeric membrane heme-Cu:O2 reductase-type enzyme that terminates the respiratory chains of aerobic and facultative aerobic organisms. The reduction of O2 to water is accompanied by the extrusion of four protons. The cytochrome-aa3 enzymes of mitochondria and many bacterial species are the most abundant group, but other variations, such as the bacterial cytochrome-cbb3 enzymes, also exist. All of the variants have a conserved catalytic core subunit (subunit I) that contains a low-spin heme (of a- or b-type), a binuclear metal centre composed of a high-spin heme iron (of a-, o-, or b-type heme, referred to as a3, o3 or b3 heme), and a Cu atom (CuB). Besides subunit I, the enzyme usually has at least two other core subunits: subunit II is the primary electron acceptor; subunit III usually does not contain any cofactors, but in the case of cbb3-type enzymes it is a diheme c-type cytochrome. While most bacterial enzymes consist of only 3–4 subunits, the mitochondrial enzyme is much more complex and contains 14 subunits.
created 1961 as EC, modified 2000, transferred 2019 to EC