Partial Characterization of the Nuclear Reduced Nicotinamide Adenine Dinucleotide Phosphate: Δ4-3-Ketosteroid 5α-Oxidoreductase of Rat Prostate

The 5α-reductase enzyme that converts testosterone to 17β-hydroxy-5α-androstan-3-one has been investigated in the rat ventral prostate by utilizing a thin layer chromatographic assay system and 3H-labeled substrates. First, it was demonstrated that approximately half of the enzyme is located in the nuclei, the remainder being found in a cytoplasmic fraction presumed to be endoplasmic reticulum. As is the case for previously described Δ4-3-ketosteroid 5α-oxidoreductases, it was not possible to solubilize the nuclear 5α-reductase, and as a result the subsequent studies were performed either on the nuclei themselves or on NaCl extracts of these nuclei. The enzyme was shown to have a pH optimum of around 6.6, to exhibit an apparent absolute requirement for NADPH as the source of the reducing hydrogen, and to be stable to freezing for long periods but unstable at 37°. The enzyme is potently inhibited by some divalent cations, particularly Hg++, Cu++, and Zn++. The substrate specificity of the enzyme for a variety of Δ4-3-ketosteroids and the ability of these steroids to inhibit the reduction of testosterone-1,2-3H were also investigated, and it was shown that the ability of these steroids to serve as substrates was paralleled by their ability to inhibit the reduction of testosterone-1,2-3H. It was concluded that in contrast to the situation in liver the nucleus of the rat prostate probably contains a single 5α-reductase enzyme and that this enzyme has a rather broad specificity for Δ4-3-ketosteroids that do not contain substitutions on the 11-carbon of the steroid molecule.