Regulation and substrate specificity of a steroid sulfate-specific hydroxylase system in female rat liver microsomes.

Abstract

The sulfate-specific hydroxylase system in liver microsomes from rats has been investigated with respect to its substrate specificity. Eighteen different C18, C19, C21, and C27 steroid sulfates and the coresponding free steroids have been incubated with microsomal preparations from male and female rats. The sulfate-specific system was only present in preparations from female rats and primarily catalyzed hydroxylation in position 15beta but also in position 7beta. In contrast to this, male liver microsomes were more efficient than female liver microsomes in hydroxylating free steroids; these were hydroxylated in positions 2alpha,2beta,6alpha,6beta,7alpha,7beta,16alpha, and 18. The sulfate-specific hydroxylase system in female liver microsomes was found to have rigid requirements c concerning the structure of ring D in the substrate molecule; only 17beta-sulfates (C18 and C19 steroids) and 21-sulfates (C21 steroids) were hydroxylated. Less rigid criteria, however, exist concerning the structure of ring A. The following K-m values were determined for microsomal 15beta-hydroxylation: 5alpha-androstane-3alpha,17beta-diol disulfate, 17.2 muM; 5beta-androstane-3alpha,17beta-diol disulfate, 16muM;5alpha-androstane-3alpha,17beta-diol 17-sulfate, 26 muM; and estradiol 17-sulfate, 181 muM. Some of the regulatory mechanism controlling the activity of the sex-specific 15beta-hydroxylase system also have been studied and compared to the mechanism controlling the activities of the less specific 2alpha-, 7alpha-, and 18-hydroxylase systems active on 5alpha-[4-14C]androstane-3alpha,17beta-diol. Biliary drainage did not affect the 15beta-hydroxylase activity, whereas the 2alpha- and 7alpha-hydroxylase activities decreased..