JBC, Vol. 250, Issue 9, 3451-3458, May, 1975
Regulation and substrate specificity of a steroid sulfate-specific hydroxylase system in female rat liver microsomes
J. A. Gustafsson and M. Ingelman-Sunberg
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..
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