The conversion of androgens into estrogens involves removal of the angular methyl group at C-19 under the action of 19-aromatase (see Fig. 37.7). The A ring undergoes two dehydrogenations as part of the reaction, and the characteristic 1,3,5(10)-estratriene nucleus results. This aromatase enzyme is found most abundantly in the granulosa cells of the ovary, although it is worthy of note that an enzyme in adipose tissue can also convert some testosterone into estradiol. The biological actions of the steroid hormones are diverse and are best considered as part of the trophic hormone system to which they belong. This system is described in Chapter 37. Many genetic defects have been identified in the structure of the CYP enzymes leading to abnormal steroid biosynthesis and characteristic clinical disorders such as congenital adrenal hyperplasia. A genotype:phenotype relationship is becoming established in such conditions and genetic analysis may become routine in these disorders.
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