(or steroid 21-monooxygenase
; ) is a cytochrome P450 enzyme
which is involved with the biosynthesis
of the steroid hormones aldosterone
The CAS number is 9029-68-9.
21-Hydroxylase is encoded by the gene CYP21B.
of the carbon
atom 21 in steroids
(adding an "–OH"), which is necessary with the formation of these hormones
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.