11β-hydroxylase is a steroidogenic enzyme, i.e. the enzyme involved in the metabolism of steroids. The enzyme is primarily localized in the zona glomerulosa and zona fasciculata of the adrenal cortex. The enzyme functions by introducing a hydroxyl group at carbon position 11β on the steroid nucleus, thereby facilitating the conversion of certain steroids.
Humans have two isozymes with 11β-hydroxylase activity: CYP11B1 and CYP11B2.
CYP11B1 (11β-hydroxylase) is expressed at high levels and is regulated by ACTH, while CYP11B2 (aldosterone synthase) is usually expressed at low levels and is regulated by angiotensin II. In addition to the 11β-hydroxylase activity, both isozymes have 18-hydroxylase activity. The CYP11B1 isozyme has strong 11β-hydroxylase activity, but the activity of 18-hydroxylase is only one-tenth of CYP11B2. The weak 18-hydroxylase activity of CYP11B1 explains why an adrenal with suppressed CYP11B2 expression continues to synthesize 18-hydroxycorticosterone.
Here are some of the steroids, grouped by catalytic activity of the CYP11B1 isozyme:
* strong activity:
** 11-deoxycortisol to cortisol,
** 11-deoxycorticosterone to corticosterone;
* medium activity:
** progesterone to 11β-hydroxyprogesterone,
** 17α-hydroxyprogesterone to 21-deoxycortisol,
** androstenedione to 11β-hydroxyandrostenedione;
** testosterone to 11β-hydroxytestosterone,
* weak activity:
** corticosterone to 18-hydroxycorticosterone,
** cortisol to 18-hydroxycortisol.