Characterization of [3H] corticosterone binding activity in adrenal incubation media

Glucocorticoid-binding activity in adrenal incubation media was investigated with regard to characterization of a protein-like ligand. Scatchard analysis of corticosterone binding activity indicated the presence of a single non-interacting protein with a dissociation constant (Kd) of 8.81 X 10(-10) M (0 degrees C), a value which is different from that of plasma and cytoplasmic glucocorticoid binding proteins. In addition, an observed lack of affinity of the protein for dexamethasone distinguishes the protein from Type II cytoplasmic receptor proteins. Thus our data suggest a glucocorticoid-binding protein which is distinct from the two known groups of glucocorticoid-binding proteins, corticosteroid-binding globulin (CBG) and cytoplasmic receptors.