Differential inhibition of dehydrogenase and 5-ene----4-ene isomerase activities of purified 3 beta-hydroxysteroid dehydrogenase. Evidence for two distinct sites.
The success in synthesis of [3H]5-androstene-3,17-dione, the intermediate product in the transformation of DHEA to 4-androstenedione by 3 beta-hydroxysteroid dehydrogenase/5-ene----4-ene isomerase (3 beta-HSD) offers the opportunity to determine whether or not the two activities reside in one active site or in two closely related active sites. The finding that N,N-dimethyl-4-methyl-3-oxo-4-aza-5 alpha-androstane-17 beta-carboxamide (4-MA) inhibits competitively and specifically the dehydrogenase activity whereas a non-competitive inhibition type with a Ki value 1000 fold higher was observed for the isomerase activity, indicated that dehydrogenase and isomerase activities belong to separate sites. Using 5 alpha-dihydro-testosterone and 5 alpha-androstane-3 beta, 17 beta-diol, exclusive substrates for dehydrogenase activity, it was shown that dehydrogenase is reversible and strongly inhibited by 4-MA and that thus the irreversible step in the transformation of DHEA to 4-androstenedione is due to the isomerase activity.
Luu-The
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MRC Group in Molecular Endocrinology, CHUL Research Center, Quebec, Canada.
Takahashi
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Labrie
F
F
D015096:3-Hydroxysteroid Dehydrogenases / Q000037:antagonists & inhibitors*; D000735:Androstenedione / Q000378:metabolism; D001378:Azasteroids / Q000494:pharmacology; D001665:Binding Sites; D003687:Dehydroepiandrosterone / Q000378:metabolism; D013196:Dihydrotestosterone / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics
D001378:Azasteroids; D013196:Dihydrotestosterone; D000735:Androstenedione; D003687:Dehydroepiandrosterone; C003528:5-androstene-3,17-dione; C031563:17-N,N-diethylcarbamoyl-4-methyl-4-azaandrostane-3-one; D015096:3-Hydroxysteroid Dehydrogenases; C009954:trilostane