<p>Cytochrome c oxidase (<db_xref db="EC" dbkey="1.9.3.1"/>) is an oligomeric enzymatic complex that is a component of the respiratory chain complex and is involved in the transfer of electrons from cytochrome c to oxygen [<cite idref="PUB00000581"/>]. In eukaryotes this enzyme complex is located in the mitochondrial inner membrane; in aerobic prokaryotes it is found in the plasma membrane.</p><p>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 polypeptide subunits. One of these subunits is the potentially haem-binding subunit, VIb, which is encoded in the nucleus [<cite idref="PUB00014035"/>]. </p>