InterPro domain: IPR001349

Cytochrome c oxidase ( 1.9.3.1 ) is an oligomeric enzymatic complex which is a component of the respiratory chain complex and is involved in the transfer of electrons from cytochrome c to oxygen [ 1 ]. In eukaryotes this enzyme complex is located in the mitochondrial inner membrane; in aerobic prokaryotes it is found in the plasma membrane.

In eukaryotes, in addition to the three large subunits, I, II and III, that form the catalytic centre of the enzyme complex, there are a variable number of small polypeptidic subunits. One of these subunits is known as VIa in vertebrates and fungi. Mammals have two tissue-specific isoforms of VIa, a liver (VIa-L) and a heart and skeletal muscle isoform (VIa-H). Mammalian VIa-H induces a slip in CcO (decrease in proton/electron stoichiometry) at high intramitochondrial ATP/ADP ratios, while VIa-L induces a permanent slip in CcO, depending on the presence of cardiolipin and palmitate [ 2 ]. Only one form is found in fish [ 3 ].

1. Structure of cytochrome c oxidase. Biochim. Biophys. Acta 726, 135-48
2. A third isoform of cytochrome c oxidase subunit VIII is present in mammals. Gene 312, 95-102
3. The cDNA sequences of cytochrome c oxidase subunit VIa from carp and rainbow trout suggest the absence of isoforms in fishes. Biochim. Biophys. Acta 1319, 14-8