Steroid 21-monooxygenase

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Steroid 21-monooxygenase (also called 21-hydroxylase, EC number 1.14.99.10) is 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. This condition is called 21-hydroxylase deficiency and causes congenital adrenal hyperplasia (type III).