This family consists of several NADH-ubiquinone oxidoreductase B18 subunit proteins from different eukaryotic organisms. Oxidative phosphorylation is the well-characterized process in which ATP, the principal carrier of chemical energy of individual cells, is produced due to a mitochondrial proton gradient formed by the transfer of electrons from NADH and FADH2 to molecular oxygen. The oxidative phosphorylation (OXPHOS) system is located in the mitochondrial inner membrane and consists of five multi-subunit enzyme complexes and two small electron carriers: coenzyme Q10 and cytochrome C. At least 70 structural proteins involved in the formation of the whole OXPHOS system are encoded by nuclear genes, whereas 13 structural proteins are encoded by the mitochondrial genome. Deficiency of NADH ubiquinone oxidoreductase, the first enzyme complex of the mitochondrial respiratory chain, is one of the most frequent causes of human mitochondrial encephalomyopathies.
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