Characterization of the glucocorticoid receptor in rat skin

Using an exchange assay to measure occupied and unoccupied binding sites the interaction between [3H]triamcinolone acetonide and rat skin cytosol proteins was studied. A binding site with a high affinity (dissociation constant = 7 x 10(-10) mol/l) and a low capacity (400-600 fmol/mg protein) for triamcinolone acetonide was detected. The binding was specific to corticosteroids; fluorinated steroids showed a higher affinity than natural steroids. Non-corticosteroids, with the exception of progesterone, had little or no affinity for the binding site. At 0 degrees C the second-order rate constant of association was 2.23 x 10(6) mol/l per min and the first-order rate constant of dissociation was 1.6 x 10(-4) per min. In the absence of dithiothreitol and molybdate the specific binding was rapidly abolished. The binding was also labile to heating and proteolytic enzymes. One day after adrenalectomy there was a significant increase in the number of assayable binding sites in the cytosol. The results are consistent with the binding protein being the physiological glucocorticoid receptor in rat skin.