Cytochrome b5 Reductase 3 (CYB5R3)

The CYB5R3 gene encodes cytochrome b5 reductase-3, an enzyme that catalyzes the transfer of reducing equivalents from NADH to cytochrome b5 (CYB5A), which then acts as an electron donor. The membrane-bound isoform of CYB5R3 plays a role in physiologic processes, including cholesterol biosynthesis and fatty acid elongation and desaturation, whereas the soluble isoform of CYB5R3 is present in erythrocytes and functions to reduce methemoglobin to hemoglobin. There are 2 forms of NADH-cytochrome b5 reductase: a membrane-bound form in somatic cells and a soluble form in erythrocytes. The former exists mainly on the cytoplasmic side of the endoplasmic reticulum and functions in desaturation and elongation of fatty acids, in cholesterol biosynthesis, and in drug metabolism.