title: Properties of microsomal delta4-3-ketosteroid 5alpha-reductase in immature rat ovary. Inhibition by estradiol-17beta.
abstract: 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.
mesh_terms: D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D004958:Estradiol; D005260:Female; D007664:Ketosteroids; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology*; D010053:Ovary / Q000201:enzymology*; D010088:Oxidoreductases / Q000378:metabolism*; D051381:Rats; D013329:Structure-Activity Relationship
chemical_list: D007664:Ketosteroids; D004958:Estradiol; D010088:Oxidoreductases; D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase