2-Bromo- and 16-bromo-estrogens and related compounds: potential inhibitors for both estradiol 2- and 16 alpha-hydroxylases in rat liver microsomes.
Kinetic studies of inhibition of estradiol 2- and 16 alpha-hydroxylase activities in male rat liver microsomes with 2-bromoestrogens, 4-bromo-estrone (4-BrE1), 16 alpha- and 16 beta-bromoestrones and 16 beta-acetylthioestrone (16-AcSE1) were carried out. 2-Bromoestrogens and 4-BrE1 nonspecifically blocked the two enzyme activities in a competitive manner, and 2-bromo-estradiol (2-BrE2) was the most potent inhibitor for the two hydroxylases among the 2- and 4-bromo steroids. Kinetic data, the apparent Ki's for the inhibitors and the apparent Km's for the substrate E2 in the assay, demonstrate that the A-ring bromo steroids are potent inhibitors for the two enzymes (Ki/Km ranging from 0.28 to 0.48 for the 2-hydroxylation and ranging from 0.26 to 0.49 for the 16 alpha-hydroxylation). In contrast, 16-bromoestrones and 16-AcSE1 non-competitively inhibited the 2-hydroxylation (Ki = ca. 70 microM) while the other was competitively blocked by them (Ki/Km ranging from 0.24 to 0.30). These 16-substituted steroids were very potent inhibitors for the 16 alpha-hydroxylase rather than the 2-hydroxylase and preferentially blocked the former.
Tohoku College of Pharmacy, Sendai, Japan.
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M
Numazawa
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S
Satoh
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D001667:Binding, Competitive; D001966:Bromine; D019363:Cytochrome P-450 CYP1A1; D000072467:Cytochrome P450 Family 2; D004965:Estrogen Antagonists / Q000138:chemical synthesis / Q000494:pharmacology*; D007202:Indicators and Reagents; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D039181:Steroid 16-alpha-Hydroxylase; D013250:Steroid Hydroxylases / Q000037:antagonists & inhibitors*
D004965:Estrogen Antagonists; D007202:Indicators and Reagents; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; C450279:CYP2C11 protein, rat; D019363:Cytochrome P-450 CYP1A1; D000072467:Cytochrome P450 Family 2; D039181:Steroid 16-alpha-Hydroxylase; C020120:estrogen 2-hydroxylase; D001966:Bromine