Steroid 21-hydroxylase (or steroid 21-monooxygenase or 21α-Hydroxylase; EC 1.14.99.10) is a cytochrome P450 enzyme which is involved with the biosynthesis of the steroid hormones aldosterone and cortisol.

The CAS number is 9029-68-9.

21-Hydroxylase is encoded by the gene CYP21B.

[edit] Reaction

It catalyses the hydroxylation of the carbon atom 21 in steroids (adding an "–OH"), which is necessary with the formation of these hormones.

Progesterone

11-deoxycorticosterone

Steroid numbering - #21 is near center top

[edit] Pathway

Corticosteroid biosynthetic pathway in rat

Steroidogenesis, showing both reactions of 21-Hydroxylase at center top.

[edit] Clinical significance

A defect within the CYP21B 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 account for many cases of steroid 21-hydroxylase deficiency.^[1]

[edit] References

[edit] Further reading

[edit] External links

• Synthesis of Desoxycorticosterone from Progesterone through 21-Hydroxylase (Image)
• MeSH Steroid+21-Hydroxylase