InterPro domain: IPR002429

Cytochrome c oxidase ( 1.9.3.1 ) [ 1 , 2 ] is an oligomeric enzymatic complex which is a component of the respiratory chain and is involved in the transfer of electrons from cytochrome c to oxygen. In eukaryotes this enzyme complex is located in the mitochondrial inner membrane; in aerobic prokaryotes it is found in the plasma membrane. The number of polypeptides in the complex ranges from 3-4 (prokaryotes), up to 13(mammals). In Archaea, a cytochrome-c-type oxidase from Natronobacterium (cytochrome ba3) has been shown to consists of four subunits [ 3 ].

Subunit 2 (CO II) transfers the electrons from cytochrome c to the catalytic subunit 1. It contains two adjacent transmembrane regions in its N terminus and the major part of the protein is exposed to the periplasmic or to the mitochondrial intermembrane space, respectively. CO II provides the substrate-binding site and contains a copper centre called Cu(A), probably the primary acceptor in cytochrome c oxidase. An exception is the corresponding subunit of the cbb3-type oxidase which lacks the copper A redox-centre. Several bacterial CO II have a C-terminal extension that contains a covalently bound haem c.

It has been shown [ 4 , 5 ] that nitrous oxide reductase (gene nosZ) of Pseudomonas has sequence similarity in its C terminus to CO II. This enzyme is part of the bacterial respiratory system which is activated under anaerobic conditions in the presence of nitrate or nitrous oxide. NosZ is a periplasmic homodimer that contains a dinuclear copper centre, probably located in a 3-dimensional fold similar to the cupredoxin-like fold that has been suggested for the copper-binding site of CO II [ 6 ].

1. Structure of cytochrome c oxidase. Biochim. Biophys. Acta 726, 135-48
2. The superfamily of heme-copper respiratory oxidases. J. Bacteriol. 176, 5587-600
3. Cytochrome ba3 from Natronobacterium pharaonis--an archaeal four-subunit cytochrome-c-type oxidase. Eur. J. Biochem. 250, 332-41
4. Restoration of a lost metal-binding site: construction of two different copper sites into a subunit of the E. coli cytochrome o quinol oxidase complex. EMBO J. 11, 3209-17
5. Derived amino acid sequences of the nosZ gene (respiratory N2O reductase) from Alcaligenes eutrophus, Pseudomonas aeruginosa and Pseudomonas stutzeri reveal potential copper-binding residues. Implications for the CuA site of N2O reductase and cytochrome-c oxidase. Eur. J. Biochem. 208, 31-40