تسجيل الدخول

تسجيل

11β-Hydroxylase

المؤلف:  Norman, A. W., & Henry, H. L.

المصدر:  Hormones

الجزء والصفحة:  3rd edition , p44

2026-06-18

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The 11β-hydroxylase (P450c11) is still another example of one enzyme that can catalyze more than one enzymatic reaction. In cattle there is one P450 gene with one protein that has 11β-hydroxylase, 18-hydroxylase, and 18-methyl oxidase activities (entry #4 in Table 1; see Fig. 1). However, in man there are two separate genes CYP11B1 and CYP11B2 that produce two separate enzymes, P450c11β (11β-hydroxylase) and P450c11AS (aldosterone synthase), respectively. Both of these enzymes are present in the inner mitochondrial membrane (IMM) and donate electrons to ferredoxin and ferredoxin reductase. The existence of two genes is consistent with known human clinical deficiency states associated with congenital adrenal hyperplasia.

Table1. ^a Key Human Enzymes Concerned with the Production of Steroid Hormones

Fig1. Adrenal cortex pathways for production of three classes of steroid hormones. Cholesterol and the presence of the cholesterol side chain cleavage enzyme are the starting point of separate steroid hormone(s) biosynthesis for the three classes. The zona glomerulosa (mineralocorticoids) produces aldosterone. A structural hallmark of aldosterone is the presence of both a C-11 hydroxyl and a C-18 aldehyde. The C-18 aldehyde can form either a five member hemiacetal ring, which uses the C-11 hydroxyl group or a six member hemiacetal ring, which uses the C-21 hydroxyl group. These are reminiscent of carbohydrate chemistry. The zona fasciculata (glucocorticoids) produces both cortisol and corticosterone. The zona reticularis produces limited amounts (represented by the dashed arrow) of the androgens, dehydroepiandrosterone (DHEA), androst-4-ene-3,17-dione and testosterone. DHEA can be converted to DHEA-sulfate via a sulfotransferase, which forms a mixed ester with the 3β-hydroxyl group. For each of the steroid enzyme transformations, the 3-7 letter/number acronymn is shown in magenta next to the arrow. The enzyme’s full name for each acronymn is tabulated in Table 1.