Information on EC 1.9.3.1 - cytochrome-c oxidase

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 aa₃-type enzymes of mitochondria and many bacterial species are the most abundant group, but other variations, such as the bacterial 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 center composed of a high spin heme (of a-, o-, or b-type heme, referred to as a₃, o₃ or b₃)-iron, 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.