Enzyminduktion bei Streptomyces hydrogenans, V. Charakterisierung der Testosteron-17β-Dehydrogenase und ihre Induktion durch Steroide

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Abstract
Testosterone 17.beta.-dehydrogenase can be enriched from S. hydrogenans. The enzyme dehydrogenizes testosterone with Km = 13 .mu.M and estradiol-17.beta. with Km = 21 .mu.M to the corresponding 17-ketoderivatives. NAD+ forms NADH with Km = 125 .mu.M. The enzyme is strongly inhibited by androstandione and 17.alpha.-methyltestosterone. The Ki for 17.alpha.-methyltestosterone is 18 .mu.M. The enzyme activity increases with increasing pH up to alkali-mediated denaturation at about pH 10. The optimum temperature is at 45.degree. C. If S. hydrogenans is cultivated in the absence of steroids, the specific activity of testosterone 17.beta.-dehydrogenase in the cytosol of the microorganisms amounts to 10 mU/mg protein, and increases up to 10-fold if the cells are cultivated in the presence of certain steroids. Testosterone, .alpha.-dihydrotestosterone, .beta.-dihydrotestosterone, estradiol-17.beta. and 17.alpha.-methyltestosterone are very effective inducers. Thus, for the 1st time, the ability of estradiol-17.beta. to induce an enzyme synthesis in a microorganism is shown. The steroid-dependent induction is inhibited by testosterone acetate and rifamycin SV. Cyproterone does not decrease the testosterone-dependent enzyme induction of testosterone 17.beta.-dehydrogenase.

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