Physicochemical characterization of the cytosol glucocorticoid receptors in various lymphoid tissues

Cytosol glucocorticoid receptors of five different lymphoid tissues of chicken and rats were characterized and compared by physicochemical parameters. Binding specificity of receptors was found to be similar, except that cytosol receptors of chick tissues appeared slightly more specific for dexamethasone than those from rats. Association rate constants of the dexamethasone-receptor complex were higher by about one order of magnitude in the case of chicken thymus and bursa than in other cytosols. Dissociation of dexamethasone-receptor complex occurred in one step in rat tissues, whereas in case of chicken tissues two phases of dissociation were discernible. Differences between Ka and the ratio of the association and dissociation rate constants are explained by non-equilibrium conditions. The stability of receptors from the two species differed significantly, the chick receptor being more stable. Hormone-receptor complex from each tissue could be separated into two fractions by DE-52 chromatography. The peak eluted at the lower KCl concentration in the case of chick corresponded to the fast dissociating hormone-receptor complex. Kinetic analyses proved to be just as useful as ion-exchange chromatography for the characterization of, and distinguishing between, glucocorticoid receptors.