IUBMB Enzyme Nomenclature


Accepted name: steroid 21-monooxygenase

Reaction: a C21 steroid + [reduced NADPH—hemoprotein reductase] + O2 = a 21-hydroxy-C21-steroid + [oxidized NADPH—hemoprotein reductase] + H2O

Other name(s): steroid 21-hydroxylase; 21-hydroxylase; P450c21; CYP21A2 (gene name)

Systematic name: steroid,NADPH—hemoprotein reductase:oxygen oxidoreductase (21-hydroxylating)

Comments: A P-450 heme-thiolate protein responsible for the conversion of progesterone and 17α-hydroxyprogesterone to their respective 21-hydroxylated derivatives, 11-deoxycorticosterone and 11-deoxycortisol. Involved in the biosynthesis of the hormones aldosterone and cortisol. The electron donor is EC, NADPH—hemoprotein reductase.

Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number:


1. Hayano, M. and Dorfman, R.I. The action of adrenal homogenates on progesterone, 17-hydroxyprogesterone and 21-desoxycortisone. Arch. Biochem. Biophys. 36 (1952) 237-239. [PMID: 14934270]

2. Plager, J.E. and Samuels, L.T. Synthesis of C14-17-hydroxy-11-desoxycorticosterone and 17-hydroxycorticosterone by fractionated extracts of adrenal homogenates. Arch. Biochem. Biophys. 42 (1953) 477-478. [PMID: 13031650]

3. Ryan, K.J. and Engel, L.L. Hydroxylation of steroids at carbon 21. J. Biol. Chem. 225 (1957) 103-114. [PMID: 13416221]

4. Kominami, S., Ochi, H., Kobayashi, Y. and Takemori, S. Studies on the steroid hydroxylation system in adrenal cortex microsomes. Purification and characterization of cytochrome P-450 specific for steroid C-21 hydroxylation. J. Biol. Chem. 255 (1980) 3386-3394. [PMID: 6767716]

5. Martineau, I., Belanger, A., Tchernof, A. and Tremblay, Y. Molecular cloning and expression of guinea pig cytochrome P450c21 cDNA (steroid 21-hydroxylase) isolated from the adrenals. J. Steroid Biochem. Mol. Biol. 86 (2003) 123-132. [PMID: 14568563]

6. Arase, M., Waterman, M.R. and Kagawa, N. Purification and characterization of bovine steroid 21-hydroxylase (P450c21) efficiently expressed in Escherichia coli. Biochem. Biophys. Res. Commun. 344 (2006) 400-405. [PMID: 16597434]

[EC created 1961 as EC, transferred 1965 to EC, transferred 1972 to EC, modified 2013]

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