Studies of the human testis. VIII. Product activation of 17beta-hydroxysteroid oxidoreductase for testosterone.
Cell-free homogenates prepared from human testis tissue were incubated with either 1.3 x 10(-5)M[4-14C]testosterone and 2 x 10(-4)M NADP or 1.3 x 10(-5) [4-14C]nadrostenedione and 2 x 10(-4)M NADPH. Addition of non-radioactive androstenedione and testosterone to the incubation medium increased the formation of [14C]androstenedione from [4-14C]testosterone and [14C]testosterone from [4-14C]androstenedione, respectively, while addition of product nucleotide NADPH or NADP, respectively, decreased the conversions. The addition of androstenedione to the incubation medium changed the apparent optimal pH of 17beta-hydroxysteroid oxidoreductase for testosterone from 8.6 to 8.0. It appears likely that in a cell-free system human testicular 17beta-hydroxysteroid oxidoreductase not solubilized and still attached to membrane is activated by the product of the reaction catalyzed by the enzyme.
D015067:17-Hydroxysteroid Dehydrogenases / Q000378:metabolism*; D000368:Aged; D000735:Androstenedione / Q000096:biosynthesis / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008861:Microsomes / Q000201:enzymology; D008875:Middle Aged; D009249:NADP / Q000494:pharmacology; D013737:Testis / Q000201:enzymology*; D013739:Testosterone / Q000096:biosynthesis* / Q000494:pharmacology
D013739:Testosterone; D000735:Androstenedione; D009249:NADP; D015067:17-Hydroxysteroid Dehydrogenases