The cytochrome c oxidase (COX) family of proteins function as the final electron donor in the respiratory chain to drive a proton gradient across the inner mitochondrial membrane, ultimately resulting in the production of water and ATP. The mammalian COX apoenzyme is a dimer, with each monomer consisting of 13 subunits, some of which are mitochondrial and some of which are nuclear. The COX8 (cytochrome c oxidase subunit VIII) subunits are nuclear and have muscle and non-muscle-specific isoforms. COX8 exists as three isoforms: COX8a, a liver and heart isoform, Cox8b, a heart-specific isoform, and Cox8c, whose expression pattern has yet to be elucidated. All three Cox8 isoforms exists as components of the COX complex and play an important role in electron transport.