Oct 21, 1976

Distinct testicular 17-ketosteroid reductases, one in interstitial tissue and one in seminiferous tubules. Differential modulation by testosterone and metabolites of testosterone

Biochimica Et Biophysica Acta
E P Murono, A H Payne


The final step in the biosynthesis of testosterone is the reduction of androstenedione, which is catalyzed by the microsomal enzyme 17-ketosteroid reductase. Evidence is presented which suggests that there are two distinct 17-ketosteroid reductases in rat testes, one in interstitial tissue and one in seminiferous tubules. The two enzymes have different pH optima, 5.6 for the one from interstitial tissue and 6.5 for the one from seminiferous tubules. At the optimum pH, a 70-fold difference in Km values was observed, 17 muM for the interstitial tissue enzyme and 0.25 muM for the enzyme from seminiferous tubules. Testosterone and metabolites of testosterone have very different effects of each of these enzyme activities. The interstitial tissue enzyme activity is inhibited by testosterone and several 5alpha-reduced metabolites of testosterone and by estrogens. The most potent inhibitor of the steroids investigated was 5alpha-androstane-3alpha, 17beta-diol, followed by 17beta-estradiol approximately equal to dihydrotestosterone greater than testosterone greater than estrone greater than estriol. 5alpha-Androstane-3alpha, 17beta-diol and 17beta-estradiol were shown to act by competitive inhibition with apparent Ki values of 2.2 and 3...Continue Reading

Mentioned in this Paper

Estriol Measurement
Testosterone Measurement
Estrone Measurement
Androgen Effect
Dihydrotestosterone Assay
17-Hydroxysteroid Dehydrogenases
Enzymes, antithrombotic
Androstenedione Measurement
Structure of Interstitial Cell of Leydig

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