Cytochrome c oxidase (EC 1.9.3.1) [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. In eukaryotes this enzyme complex is located in the mitochondrial inner membrane; in aerobic prokaryotes it is found in the plasma membrane. In addition to the three large subunits that form the catalytic center of the enzyme complex there are, in eukaryotes, 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 and a heart form. Only one form is found is fish [2].

A signature pattern for VIa was developed that is based on the best conserved part of the protein, a region located in its C-terminal section.