POR (Cytochrome P450 Oxidoreductase, also known as CYPOR) is a Protein Coding gene. The POR gene, located on 7q11.23, is conserved in chimpanzee, Rhesus monkey, dog, and cow, etc. CYPOR is a microsomal electron-transferring enzyme containing both FAD and FMN as co-factors, which provides the reducing equivalents to various redox partners, such as cytochromes P450 (CYPs), heme oxygenase (HO), cytochrome b(5), and squalene monooxygenase. Human patients with severe forms of CYPOR mutation show bone defects such as cranio- and humeroradial synostoses and long bone fractures, known as Antley-Bixler-like Syndrome (ABS). CYPOR is essential for electron donation to microsomal cytochrome P450-mediated monooxygenation in such diverse physiological processes as drug metabolism (approximately 85-90% of therapeutic drugs), steroid biosynthesis, and bioactive metabolite production (vitamin D and retinoic acid metabolites).

P450 (cytochrome) oxidoreductase