Journal of Lipid Research, Vol 19, 933-944, Copyright © 1978 by Lipid Research, Inc.
7-Hydroxylation of 3-oxygenated C27-, C28-, and C29-steroids in rat liver 18,000 g supernate
L Aringer
Structurally closely related steroids have been tested as substrates for
the NADPH-dependent cholesterol-and cholestanol-7 alpha- hydroxylase(s)
considered to be the rate-limiting enzyme(s) in bile acid biosynthesis. Of
the steroids tested, 5-cholesten-3 alpha-0l, 5 alpha-cholestan-3 alpha-ol,
5 beta-cholestan-3 alpha-ol, 5 beta- cholestan-3 beta-ol, 4-cholesten-3
alpha-ol, 4-cholesten-3 beta-ol, 5 alpha-cholestan-3-one, 5
beta-cholestan-3-one, 24 alpha- methylcholesterol and the 24 alpha-ethyl
derivatives of cholestanol, 5 beta-cholestan-3 alpha-ol, 5 beta-cholestan-3
beta-ol, and 4-cholesten- 3-one, only 4-cholesten-3 beta-ol was 7
alpha-hydroxylated to a significant extent (approximately 1/5 of the
conversion of exogenous cholesterol). This suggests that the 7
alpha-hydroxylase(s) is sensitive to the structure of the side chain, and
that it requires a rather flat steroid nucleus (delta4-, delta5-, or 5
alpha-steroid) and an equatorial or quasiequatorial hydroxyl group at C3.
The nature of the 7 alpha-hydroxylation is discussed and the importance of
the beta- side of the steroid molecule is emphasized. Minute amounts of the
7 beta-hydroxy derivatives were formed from 4-cholesten-3 beta-ol, 5 beta-
cholestan-3 alpha-ol, 24 alpha-ethyl-5 beta-cholestan-3 alpha-ol and,
probably, from 5 beta-cholestan-3 beta-ol and 24 alpha-ethyl-5 beta-
cholestan-3 beta-ol.
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