5α-Androstane-3β,17β-diol hydroxylase (3β-diol OHase), a form of cytochrome P-450 whose main function is thought to be the elimination of dihydrotestosterone (DHT) from its target tissues, was found in the central nervous system (CNS) of both male and female rats at a level which is at least 300-fold higher than any other P-450 catalyzed steroid hydroxylase in the brain. In order to gain some insight into the physiological function of this enzyme we have studied its distribution throughout the CNS as well as the effects of age and hormonal manipulations of rats. We have also partially purified the enzyme from the brain and compared it with the 3β-diol OHase in the prostate. 3β-Diol OHase activity was distributed throughout the CNS of adult male and female rats with levels between 70-153 nmol products formed/g tissue·h. The products were identified as 5α-androstane-3β,7β,17β-triol,5α-androstane-3β,6α,17β-triol and 5α-androstane-3β,7α,17β-triol. The ratio of these three triols was 1:9:3. Catalytic activity was not affected by castration or adrenalectomy of male rats, or during late pregnancy or lactation in females. In the brains of 14-day-old fetuses and 2-day-old rats, the level of 3β-diol OHase was 30% of that of adults and it increased to adult levels by day 28. Cytochrome P-450 was partially purified from microsomes of whole brain, hypothalamus, and prostate and 3β-diol OHase activity reconstituted. On the basis of the ratios of the three triols formed from 3β-diol, it can be concluded that the 3β-diol OHase in the brain is similar to that in the prostate. From a comparison of the turnover numbers in reconstituted systems with P-450 prepared from the prostate, brain, and hypothalamus, it can be estimated that up to 50% of the P-450 in the hypothalamus and 10% in whole brain is 3β-diol OHase. Supportive evidence for this relative distribution of 3β-diol OHase in the hypothalamus was obtained by comparing the sodium dodecyl sulfate electrophoretic profiles of P-450 obtained from the hypothalamus and prostate microsomes.
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