page_title: 21-Hydroxylase
section_title: Pathway
hierarchical_section_title: 21-Hydroxylase / Pathway
caption_attribution_description: Corticosteroid biosynthetic pathway rat
context_page_description: Steroid 21-hydroxylase, also called steroid 21-monooxygenase, 21α-hydroxylase, P45021A2, and, less commonly, 21β-hydroxylase, is a cytochrome P450 enzyme that is involved with the biosynthesis of the steroid hormones aldosterone and cortisol. These syntheses take place in the adrenal cortex. Specifically, 21-hydroxylase converts progesterone and 17α-hydroxyprogesterone into 11-deoxycorticosterone and 11-deoxycortisol, respectively, by hydroxylating at the C21 position. The products of the conversions then continue through their appropriate pathways towards creation of aldosterone and cortisol.
  A defect in the CYP21A2 gene causes a disturbance of the development of the enzyme, which leads to congenital adrenal hyperplasia due to 21-hydroxylase deficiency. A related pseudogene is located near this gene; gene conversion events involving the functional gene and the pseudogene are thought to account for many cases of steroid 21-hydroxylase deficiency. Both genes are located on chromosome 6, in the major histocompatibility complex, and the pseudogene, CYP21A1, retains 98% exonic sequence identity with the functional gene.
caption: Corticosteroid biosynthetic pathway in the rat.
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