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Studies of the human testis. VIII. Product activation of 17beta-hydroxysteroid oxidoreductase for testosterone

Oshima H, Paraska L, Yoshida KI, Troen P

The Journal of clinical endocrinology and metabolism, 1977

Abstract

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.

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