Steroid 11β-Hydroxylase Isozymes (CYP11B1 and CYP11B2)

Cortisol is synthesized from cholesterol in the zona fasciculata of the adrenal cortex under the control of corticotropin (ACTH) (reviewed in New et al. 1989). Synthesis of Cortisol requires five enzymatic steps (Fig. 1): cleavage of the cholesterol side-chain to yield pregnenolone, 3β-dehydrogenation to progesterone, and successive hydroxylations at the 17α, 21 and 11β positions which are mediated by three distinct cytochrome P450 enzymes. A 17-deoxy pathway is also active in the zona fasciculata, in which 17α-hydroxylation does not occur, and the final product is normally corticosterone.