Differential subcellular distribution of rat prostatic steroid 5alpha-reductase isozyme activities

The rat prostate, a classical androgen-target tissue, contains both known isozymes of steroid 5alpha-reductase. i.e. type I and type II. So far, the role of the type I isozyme has been proposed as catabolic. The abundant expression of type I 5alpha-reductase in an androgen-target tissue is therefore puzzling. Assessment of the subcellular localization of 5alpha-reductase isozymes in rat prostate might contribute in elucidating their possibly distinct roles. After obtaining crude subcellular fractions by differential centrifugation, both isozyme activities were measured at neutral pH by plotting according to Eadie-Scatchard. The observations were extended by assessment of pH-dependent velocity ratios and type II 5alpha-reductase inhibitor sensitivities in these subcellular fractions. The results indicated a preferentially--although not exclusively--nuclear localization for the type I and a predominantly microsomal localization for the type II isozyme activity in the rat prostate. In conclusion, the nuclear localization of the type I isozyme seems not to concur with its proposed catabolic role.