A cytoplasmic receptor for testosterone (T) was characterized in Sertoli cell-enriched (SCE) testes from hypophysectomized (hypex) rats. Receptor binding was also measured in tubules isolated from SCE testes and primary cultures of Sertoli cells (33 fmol\106 cells). Receptor labeled at 0 C with [3H]T ± excess unlabeled T was precipitated with ammonium sulfate and specific binding was measured by gel filtration. Specific binding reached equilibrium within 2 h and maximum binding was achieved at 3–6 nM [3H]T. Scatchard analysis revealed a Kd, of 7.6 × 1010M which was similar to receptor preparations from non-irradiated hypex rats (6.8 × 1010M). However, the specific activity of receptors in non-irradiated hypex testis (12.7 fmol/mg prot) was greater than that in SCE hypex testis (9.6 fmol/mg prot). The receptor could be precipitated quantitatively at 40% ammonium sulfate, thereby separating ABP which precipitated at 50% and albumin which precipitated between 60 and 80%. The receptor was labile to heat, charcoal and sulfhydryl reagents. It had a t of several days, was excluded by Sephadex G-200, and migrated slower than ABP during polyacrylamide gel electrophoresis. Relative affinities for steroids were T >DHT, 5αandrostane-3α, 17β-diol > cyproterone acetate, 5αandrostane-3β, 17β-diol androstenedione, dehydroepiandrosterone, cortdsol.
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