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. 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. COX7a2 (cytochrome c oxidase subunit VIIa polypeptide 2), also known as COX7AL or COX7AL1, is an 83 amino acid protein that localizes to the inner mitochondrial membrane and exists as a component of the COX complex, playing an important role in electron transport. Like COX7a2, COX7a3 (also known as COX7AP2 or COX7AL2) is a mitochondrial membrane protein that functions in conjunction with other COX proteins in the final steps of the respiratory chain.