Comparison of 3α-hydroxysteroid dehydrogenase activities in the microsomal fractions of hyperplastic, malignant and normal human prostatic tissues

The conversion of dihydrotestosterone (DHT) to 3α-androstanediol (3α-adiol) was studied using the microsomal fractions of 15 hyperplastic, 5 malignant and 6 normal human prostatic tissues. Standard assay conditions were: 0.2 μ M DHT, 1.0 mM NADPH, 1.0 mM NADH, 2.0 mM EDTA and the microsomal fractions equivalent to 200 mg of prostatic tissue, in 0.1 M MES buffer, pH 6.5. Under the conditions of this assay, the back-conversion of 3α-adiol to DHT or the conversion of DHT to androstanediol were negligible. Optimum enzyme activity was achieved under standard assay conditions. In the absence of EDTA: enzyme activity was 65% of the standard assay; activity was diminished further by 2mM Ca 2+ and virtually eliminated by 2 mM Mg 2+ or 2 μM Zn 2+. Activity in the absence of either NADPH or NADH was only 50% of the activities seen in the presence of both cofactors. The pH optimum of the enzyme was between 6.0 and 6.5. The apparent K m values of the enzymes in hyperplastic, malignant and normal tissues were 0.03, 0.02 and 0.03μM, respectively. The V max values for these tissues were 6.0 ± 2.1, 1.6 ± 0.5 and 14.0 ± 3.0 pmol/mg protein/20 min incubation, respectively. The results of these experiments offer further explanation for the differences in DHT and 3α-adiol levels seen in the 3 prostatic tissues.