Dehydroxylation of a 7 beta-hydroxy-C27 plant sterol in rat liver.
(22R)-Cholest-5-ene-3 beta,7 alpha,22-triol and the isomeric (22R)-cholest-5-ene-3 beta,7 beta,2-triol were 7-dehydroxylated by rat liver microsomes, after addition of NAD+ to the incubations. The product from both sterols was identified as (22R)-22-hydroxycholesta-4,6-dien-3-one by gas chromatography-mass spectrometry. The overall conversion of the 7 alpha-compound had an apparent Vmax of 5 nmol/mg protein per h, about 3-times higher than that of the 7 beta-isomer. Km was about 0.018 mmol/l in both reactions. NAD+ was required for the 7-dehydroxylation to proceed, conceivably by serving as cofactor in formation of the intermediate 7 beta,2-dihydroxy-4-cholesten-3-one. EDTA had a stimulatory effect upon the product formation. 7 alpha-Dehydroxylation of the bile acid precursor 7 alpha-hydroxy-4-cholesten-3-one has been demonstrated in liver tissue, but a 7 beta-hydroxy-C27-steroid dehydroxylating enzyme has previously not been identified. The results are discussed in relation to the marked differences in effect on neoplastic growth by the two isomeric hydroxysterols.
Institute of Clinical Biochemistry, University of Oslo, Norway.
K M
KM
Boberg
A
A
Stabursvik
I
I
Björkhem
O
O
Stokke
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry; D006888:Hydroxycholesterols / Q000378:metabolism*; D006900:Hydroxylation; D066298:In Vitro Techniques; D008862:Microsomes, Liver / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013261:Sterols / Q000494:pharmacology
D006888:Hydroxycholesterols; D013261:Sterols; C060725:cholest-5-ene-3,7,22-triol