Localization of the Reduced Nicotinamide Adenine Dinucleotide Phosphate: Δ4-3-Ketosteroid 5α-Oxidoreductase in the Nuclear Membrane of the Rat Ventral Prostate

The intranuclear localization of the 5α-reductase that converts testosterone to dihydrotestosterone in rat ventral prostate has been investigated in nuclei purified by sedimentation through 2.2 m sucrose. First, as the result of chemical analyses of the isolated nuclei, light microscopy studies, and an investigation of the subcellular distribution of several marker enzymes in this tissue, it was concluded that the nuclei prepared in this manner were free from major contamination with other cytoplasmic constituents. In keeping with previous studies of the enzyme approximately half the enzyme activity in rat prostate was found in the nucleus. Second, the nuclei were fragmented by exposure to sonic oscillation and subjected to centrifugation in previously formed cesium chloride density gradients. Under these conditions, all the enzyme activity was found to coincide with a visible band of turbidity at approximately d 1.23 to 1.27. On the basis of the buoyant density, the chemical composition of the fraction, and similar flotation patterns of NADH-cytochrome c reductase, a known enzyme of the nuclear membrane, it was concluded that the 5α-reductase in prostatic nuclei is located in a nuclear membrane. In the isolation of this nuclear membrane fraction a 90-fold purification of the enzyme has been achieved.