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HIROYUKI OSHIMA, LISA PARASKA, KEN-ICHIRO YOSHIDA, PHILIP TROEN, Studies of the Human Testis. VIII. Product Activation of 17β-Hydroxysteroid Oxidoreductase for Testosterone, The Journal of Clinical Endocrinology & Metabolism, Volume 45, Issue 5, 1 November 1977, Pages 1097–1099, https://doi.org/10.1210/jcem-45-5-1097
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Abstract
Cell-free homogenates prepared from human testis tissue were incubated with either 1.3 × 10−5m[4-14C]testosteroneand 2× 10−4m NADP or 1.3 × 10−5 [4-14C]androstenedione and 2 × 10−4m 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 17β-hydroxysteroid oxidoreductase for testosterone from 8.6 to 8.0.
It appears likely that in a cell-free system human testicular 17β-hydroxysteroid oxidoreductase not solubilized and still attached to membrane is activated by the product of the reaction catalyzed by the enzyme.
