Representation and quantitation of the binding interaction between prednisone, prednisolone and corticosteroid binding globulin.

The interaction between prednisone and prednisolone (0-500 ng ml-1) for binding sites on corticosteroid binding globulin (CBG) in rabbit plasma has been investigated. The fraction unbound of each steroid rose markedly with increasing concentration at low concentrations (250 ng ml-1), tending to a plateau (0.29 prednisone, 0.15 prednisolone) at the higher concentrations (250-500 ng ml-1), indicating both saturation of CBG and the importance of binding to albumin in higher concentrations. A method is proposed of representing graphically the prednisone-prednisolone-protein interaction in three dimensions.