Dihydroorotate dehydrogenase quinone（DHODH) is a member of the dihydroorotate dehydrogenase family. DHODH is a mitochondrial protein found on the outer surface of the inner mitochondrial membrane. DHODH catalyzes the 4th enzymatic step， the ubiquinone-mediated oxidation of dihydroorotate to orotate（with quinone as electron acceptor)， in de novo pyrimidine biosynthesis. DHODH gene defects cause the postaxial acrofacial dysostosis（POADS)， also known as Miller syndrome.
