Studies of the cytosol 3α-hydroxysteroid dehydrogenase of human prostatic tissue: Comparison of enzyme activities in hyperplastic, malignant and normal tissues

The conversion of dihydrotestosterone (DHT) to 3α-androstanediol (3α-Adiol) was studied using the cytosol fractions of hyperplastic [20], malignant [15] and normal [1] human prostatic tissues. Standard assay conditions for the 3α-hydroxysteroid dehydrogenase in hyperplastic tissue were: 0.5 μM DHT, 2.0 mM EDTA and the cytosol fraction equivalent to 200 mg of prostatic tissue, in 0.1 M HEPES buffer, pH 7.4. Under the conditions of this assay, 3α-Adiol was the major metabolite of DHT. The conversion of 3α-Adiol to DHT was negligible. Optimum enzyme activity was achieved under standard assay conditions. In the absence of EDTA: enzyme activity was 60% of the standard assay; 2 mM Ca 2+, 2 mM Mg 2+ or 2 μM Zn 2+ raised enzyme activity to that of the standard assay; 2 mM Zn 2+ diminished activity to 65% of the standard assay. If NADPH were omitted, 3α-hydroxysteroid dehydrogenase activity was 10% of the standard assay activity. NADH (0.4 mM) could not be substituted for NADPH to obtain maximum enzyme activity. The pH optimum of the enzyme was between pH 6.8 and 7.8. The K m of the enzyme in hyperplastic tissue was 0.2 μM. The V max was 2.1 ± 1.0 pmol/mg protein/30 min incubation. Using the assay conditions found to be optimal for hyperplastic tissue, the K m of the enzyme in malignant prostatic tissue was 0.3 μM. The V max was 12 ± 4.8 pmol/mg protein/30 min incubation. The K m of the enzyme in the normal tissue was 0.2 μM. The V max was 14.5 pmol/mg protein/30 min incubation. The results of these experiments would suggest that differences in the conversion of DHT to 3α-Adiol may explain, at least in part, the higher DHT and lower 3α-Adiol levels seen in hyperplastic prostatic tissue than in either the normal or malignant prostate.