Relative binding properties of microsomal and cytosolic androgen receptor species of the ventral prostate.

A comparison between a microsomal and a cytosolic source of receptor-like androgen-binding activity was made in the rat ventral prostate. Microsomal binders remain in solution at 90% saturation with (NH4)2SO4 and display equal affinity for 5 alpha-dihydrotestosterone (DHT) and mibolerone. They have a half-life of dissociation of steroid-receptor complexes of 96 +/- 11 h and a 5S sedimentation coefficient for the untransformed moiety, with the appearance of a 3.5S species after incubation at 24 C for 30 min. They do not acquire DNA-binding capability after heat- or salt-attempted activation. Cytosol binders precipitate upon 90% saturation with (NH4)SO4 and have higher affinity for DHT than mibolerone. The half-life for dissociation of complexes is 85 +/- 14 h, and the complex sediments as an 8S moiety which is able to transform to a 4.4S form after heat activation correlated with increased DNA-binding ability of these species. Unactivated cytosol steroid-receptor complexes are also able to bind to DNA in the presence of molybdate. Salt-induced activation of cytosol moieties only occurred in the absence of molybdate. Microsomal androgen receptor is more stable than cytosol androgen receptor independently of the presence of hormone or partial purification of the moieties; the inactivation rates of the two forms of complexes differ 3-fold. Results indicate that androgen-binding sites associated with the microsomal and cytosolic fractions of the prostate are distinct entities.