Mitochondria have their own DNA (mtDNA, which is a 16.5-kb circular double-stranded DNA (dsDNA), encoding 13 polypeptides, 22 transfer RNA (tRNA), and two ribosomal RNA (rRNA). The 13 polypeptides are subunits of a series of large enzyme complexes located in the inner mitochondrial membrane necessary for ATP production via oxidative phosphorylation. The protein encoded by the MT-ATP8 gene belongs to the mitochondrial respiratory chain complex. The MT-ATP8 protein is one subunit of a large enzyme called ATP synthase, also known as complex V. This enzyme produces ATP from ADP in the presence of a proton gradient across the membrane which is generated by electron transport complexes of the respiratory chain.