. . "CYP21A2 encodes a member of the cytochrome P450 superfamily of heme containing membrane associated enzymes. These proteins function as monooxygenases utilizing NADPH for the reduction of molecular oxygen via a membrane bound microsomal electron transfer system. CYP21A2 localizes to the endoplasmic reticulum membrane and catalyzes the conversion of both progesterone and 17α-hydroxyprogesterone into 11-deoxycorticosterone and 11-deoxycortisol, respectively |CITS: [3487786]|. In these reactions the electrons are transferred from NADPH to the two flavin molecules of cytochrome p450 oxidoreductase protein, from flavinadenine dinucleotide to flavin mononucleotide, to CYP21A2 and finally to activate the oxygen substrate. CYP21A2 is expressed only in the adrenal cortex and C21 hydroxylation is the catalytic step that determines synthesis of adrenal steroid hormones. Mutations in this gene cause \"salt wasting disease\" or congenital adrenal hyperplasia type 3 |CITS: [3038528]|. A related pseudogene (CYP21A1P) from an ancient duplication event is located near this gene |CITS: [3486422]| Gene conversion events involving the functional gene and the pseudogene are thought to account for many cases of steroid 21-hydroxylase deficiency |CITS: [3267225]|."^^ . . . . . . . . . . . . . . . . . . . . . . . . "CYP21A2"^^ . "cytochrome P450, family 21, subfamily A, polypeptide 2"^^ . "steroid 21-monooxygenase"^^ . "P450-C21B"^^ . "cytochrome P450, subfamily XXIA (steroid 21-hydroxylase, congenital adrenal hyperplasia), polypeptide 2"^^ . "STEROID 21-HYDROXYLASE"^^ . . "CYP21A2"^^ .