Transformation of the [3H]aldosterone-type I receptor complex to a DNA-binding species

For most steroid receptor complexes, the transformation to a DNA-binding species can be achieved readily in vitro by incubation at elevated temperatures and/or salt concentrations. Although the aldosterone-Type I receptor complex forms a clear exception to this generalization, a marked increase in its transformation can be achieved by incubation with the chaotropic anion, thiocyanate. Time and concentration-response analyses with brain cytosol revealed that over 40% of the complexes were retained in DNA-cellulose assays after a 15 min pre-incubation at 0 degree C with 100 mM thiocyanate. As expected, molybdate prevented this transformation; however, in contrast to results with heat- and/or salt-induced transformation of other steroid receptors, the molybdate effect was only partially removed by gel filtering the cytosol prior to thiocyanate addition. Thiocyanate-induced transformation should prove useful in the biochemical characterization and purification of non-transformed and transformed aldosterone-Type I receptor complexes.