Initial characterizations of nontransformed and transformed [3H ]aldosterone-type I receptor complexes in brain cytosol

Incubation of [3H]aldosterone-type I receptor complexes in mouse brain cytosol with the chaotropic anion thiocyanate increased the fraction of receptors retained by DNA-cellulose from less than 10% to over 40%, whereas it decreased the fraction retained by protamine sulfate from more than 90% to less than 10%. Thiocyanate-induced transformation to the DNA-binding species was also accompanied by a 2.1-fold decrease in the rate of [3H]aldosterone dissociation from type I receptors as well as by an increase in the apparent positive charge and hydrophobicity of the surface of these receptors, as revealed by DEAE Bio-Gel ion exchange and pentyl agarose hydrophobic interaction chromatography. Sucrose density gradient sedimentation and Sephacryl S-300 gel exclusion chromatography revealed a reduction in the sedimentation coefficient and Stokes radius of the steroid-receptor complex from 9.6S and 8.0 nm before to 4.7S and 6.1 nm after transformation, respectively. These changes in hydrodynamic parameters were found to correspond to a 2.8-fold reduction in the apparent molecular mass from 331,000 before to 120,000 after transformation. In view of these various findings as well as the known differential affinity of protamine sulfate for the 90K heat shock protein, we suggest that thiocyanate-induced transformation is initiated by the dissociation of two molecules of heat shock protein from each steroid/DNA-binding type I receptor subunit.