Partial characterization of [³H]methyltrienolone binding in rat prostate cytosol

³H-labelled R 1881 (methyltrienolone) was bound with high affinity (K_d, 2 · 10^-9 M) and low capacity (11-15 fmol/mg protein) in prostate cytosol from rats castrated 18 h earlier. The binding was inhibited by 5α-dihydrotosterone, testosterone, cyproterone acetate and LEO 1727, but not by estradiol-17β, R 5020 or corticosterone. The ³H-labelled R 1881-receptor complex was excluded from a Sephadex G-200 column, had a sedimentation coefficient of 3.5 S, was eluted from a DEAE-cellulose column at 0.2 M KCl concentration and precipitated between 20-40% of saturation of ammonium sulfate. 20% of specifically bound ³H-labelled R 1881 was retained by DNA-cellulose at low ionic strength. The fraction which was not bound to DNA-cellulose did not bind either, after rechromatography, not even following heating at 20°C for 20 min or following fractionation with ammonium sulphate. In summary, the results indicate that the ³H-labelled R 1881-receptor complex in rat prostate cytosol has characteristics similar to those of the 5μ-[³H]-dihydrotestosterone-receptor complex.