The possible role of disulfide bond reduction in transformation of the 10 S androgen receptor.
Dissociation of the 10 S androgen receptor to 8, 6, and 4.5 S forms was dependent on temperature, the reducing and ionic environment, and the binding of androgen. The [3H]dihydrotestosterone-labeled 10 S receptor was observed at low ionic strength using rat Dunning prostate tumor cytosol freshly prepared in the absence of an exogenous sulfhydryl reducing agent. Addition of mercaptoethanol caused 10 S receptor dissociation to 8 S following incubation at 0 degrees C for 30 min, to 6 S after a 30-min incubation at 23 degrees C at low ionic strength, and to 4.5 S at high ionic strength. Mercaptoethanol-induced dissociation required binding of [3H]dihydrotestosterone. Treatment with cupric phenanthroline, a disulfide-forming reagent, stabilized the 10 S receptor in 0.4 M KCl, but the receptor remained sensitive to dissociation by mercaptoethanol. Zn2+ (25 microM) and sodium molybdate (10 mM) also stabilized the 10 S receptor. A Stokes radius of 96 +/- 5 A was determined for the 10 S receptor by Sepharose-6B chromatography, with a calculated Mr of 396,000. The 10 S receptor was not retained by DNA-Sepharose, while dissociated forms displayed binding affinity for DNA. It is proposed that the 10 S receptor represents the nontransformed androgen receptor, composed of the 4.5 S steroid binding units plus a nonsteroid binding protein, perhaps in a tetrameric configuration. Binding of dihydrotestosterone appears to sensitize the 10 S receptor to disulfide bond reduction, resulting in transformation by subunit dissociation.