Properties of microsomal delta4-3-ketosteroid 5alpha-reductase in immature rat ovary. Inhibition by estradiol-17beta.
The subcellular distribution of immature rat ovarian 5alpha-reductase has been studied by utilizing 20alpha-hydroxypregn-4-en-3-one as substrate. The main enzyme activity was found to be associated with the microsomal fraction, with lower activities in the 1000 X g and 10 000 X g fractions. The enzyme activity associated with the microsomes exhibited an apparent Km of 3.0 +/- 1.1 micrometer for 20alpha-hydroxypregn-4-en-3-one and 36.3 +/- 6.7 micrometer for testosterone as substrate. Progesterone and testosterone competitively inhibited the 5alpha-reduction of 20alpha-hydroxypregn-4-en-3-one; estradiol-17beta was found to be a noncompetitive inhibitor of this reaction. A concentration of estradiol-17beta as low as 1 micrometer when added to 25 micrometer concentration of 20alpha-hydroxypregn-4-en-3-one exerted a significant inhibition of 5alpha-reductase activity.[1]References
- Properties of microsomal delta4-3-ketosteroid 5alpha-reductase in immature rat ovary. Inhibition by estradiol-17beta. Eckstein, B., Nimrod, A. Biochim. Biophys. Acta (1977) [Pubmed]
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