Comparison of nuclear 5α-reductase activities in the stromal and epithelial fractions of human prostatic tissue

The nuclear conversion of testosterone (T) to dihydrotestosterone (DHT) was compared in the separated stromal and epithelial fractions of hyperplastic ( n = 20), malignant ( n = 5) and normal ( n = 1) prostatic tissues. Standard assay conditions were: 1 μM testosterone, plus 4–6 × 10 5DPM [ 3H]T, 1.0 mM NADPH, 2.0 mM EDTA and 0.5–1.0mg nuclear protein in a total volume of 1.1 ml HEPES buffer, pH 7.4 (stroma) or MES buffer, pH 6.5 (epithelium). The apparent K m values for the stromal enzyme were 0.2, 0.2 and 0.3 μM, respectively, for the enzymes in hyperplastic, malignant and normal tissues. The V max values were 26 ± 4.2, 2.8 ± 0.6 and 4.1 pmol/mg protein/30 min incubation, respectively, for these same tissues. The apparent K m values for the epithelial enzymes, from the same tissues, were 0.03, 0.07 and 0.08 μM. The V max values for the epithelial enzymes were 4.8 ± 1.2, 0.69 ± 0.08 and 1.1 pmol/mg protein/30 min incubation. The pH optimum for the stromal enzyme lay between pH 6.5 and 7.5, whereas the pH optimum for the epithelial enyme lay between 5.5 and 6.5. Enzymatic activity in both fractions revealed a biphasic response to zinc. In the absence of EDTA, μM quantities of zinc enhanced enzymatic activity while mM quantities inhibited this activity. These results would suggest that differences in the conversion of T to DHT help to explain, at least in part, the higher DHT levels seen in hyperplastic tissue and the higher T levels seen in the malignant prostate.