Isozyme specificity of testosterone 7 alpha-hydroxylation in rat hepatic microsomes: is cytochrome P-450a the sole catalyst?
In the present study we show that monospecific antibody against cytochrome P-450a completely inhibits testosterone 7 alpha-hydroxylation in hepatic microsomes of untreated male or female rats or rats of either sex treated with dexamethasone. These data are in contrast with those of K. Nagata et al. (1987, J. Biol. Chem. 262, 2787-2793) who recently reported that an antibody prepared against cytochrome P-450a completely inhibited testosterone 7 alpha-hydroxylase activity in microsomes from untreated or 3-methylcholanthrene-treated rats but only inhibited 50% of the activity in microsomes from dexamethasone-treated rats. They proposed that dexamethasone treatment of rats induced another testosterone 7 alpha-hydroxylase in rat liver. The discrepancy in the two sets of data was due, at least in part, to the use of a chromatography system by Nagata et al. that is incapable of resolving a number of testosterone metabolites. Dexamethasone treatment of rats leads to a marked increase in the production of several testosterone metabolites, including 15 beta-hydroxytestosterone which is cochromatographic with 7 alpha-hydroxytestosterone in their chromatography system. Our results indicate that cytochrome P-450a accounts for all of the testosterone 7 alpha-hydroxylase activity in microsomes from dexamethasone-treated rats, and that testosterone 7 alpha-hydroxylation continues to be a useful marker for monitoring cytochrome P-450a in rat hepatic microsomes.
Levin
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Department of Molecular Oncology, Roche Institute of Molecular Biology, Nutley, New Jersey 07110.
Thomas
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PE
Ryan
D E
DE
Wood
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AW
D000818:Animals; D000906:Antibodies; D000936:Antigen-Antibody Complex; D001189:Aryl Hydrocarbon Hydroxylases; D002851:Chromatography, High Pressure Liquid; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology; D006900:Hydroxylation; D007527:Isoenzymes / Q000378:metabolism*; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D013250:Steroid Hydroxylases / Q000378:metabolism*; D013739:Testosterone / Q000031:analogs & derivatives / Q000302:isolation & purification
D000906:Antibodies; D000936:Antigen-Antibody Complex; D007527:Isoenzymes; D013739:Testosterone; D003907:Dexamethasone; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; C022724:testosterone 7-alpha-hydroxylase, hamster