steroid 21-monooxygenase

ster·oid 21-mono·oxy·gen·ase (sterґoid mon″o-okґsə-jən-ās) [EC 1.14.99.10] an enzyme of the oxidoreductase class that catalyzes the NADPH-dependent hydroxylation of steroids at the 21 position. The enzyme is a microsomal cytochrome P-450, requires a flavoprotein for reducing equivalents, and is part of the steroid hormone synthesis system. Deficiency of the enzyme, an autosomal recessive trait, inhibits conversion of 17-hydroxyprogesterone to 11-deoxycortisol; it is called 21-hydroxylase deficiency (q.v.) and causes congenital adrenal hyperplasia (type III). Called also 21-hydroxylase.