Isolation of 3 S androgen receptors from salt-resistant fractions and nuclear matrices of prostatic nuclei after mild trypsin digestion.

The physical properties of two types of androgen-binding sites in prostatic nuclei were compared and found to be identical. The first type was released from chromatin by micrococcal nuclease digestion and solution in 0.6 M NaCl; the second resisted such treatment and remained associated with nuclear structures. After in vivo administration of [1,2-3H]testosterone to 24-h castrated rats and sonication of purified nuclei, 90% of the nuclear radioactivity was extracted with nuclease/salt treatment and was found by sucrose density gradient analysis to be associated with a 3 S androgen receptor. If sonication was omitted, 50 to 60% of the nuclear radioactivity was recovered in the nuclease/salt-resistant pellets or bound to nuclear matrices. Mild digestion of either of these particulate fractions with trypsin resulted in the release of a 3 S androgen receptor. After in vitro isotope-exchange labeling with [1,2-3H]dihydrotestosterone, the sedimentation coefficient, steroid specificity, and dissociation constant of the androgen receptors released by trypsin digestion of nuclease/salt-resistant pellets or nuclear matrices were similar to those of the receptors extracted by nuclease/salt treatment. These results indicate first, that all androgen-binding sites in prostatic nuclei can be released, either with nuclease/salt or trypsin digestion procedures to yield a 3 S androgen receptor with uniform binding characteristics, and second, that the androgen receptors are distributed between two intra-nuclear pools--one containing about 10,000 molecules/nucleus sensitive to micrococcal nuclease digestion and salt and the other containing about 8,000 to 13,000 androgen receptors tightly bound to the nuclear matrix.