Stereospecific Binding of Propranolol and Catecholamines to the β-Adrenergic Receptor

The stereospecificity of the beta-adrenergic receptor of turkey erythrocyte ghosts was studied. Binding of the specific beta-adrenergic antagonist, propranolol, was found to occur exclusively with the l-stereoisomer. The stereospecificity of catecholamine binding was determined by assaying the ability of the catecholamines to displace [(3)H]propranolol. Binding of the catecholamines was also found to be stereospecific for the l-stereoisomers. Furthermore, the d-stereoisomers do not compete with the l form for binding. Using this displacement technique, we were able to calculate the dissociation constants for l-epinephrine, l-norepinephrine, and l-isoproterenol from the beta-receptor and compare these values to the apparent dissociation constants obtained from the direct activation of adenylate cyclase (EC 4.6.1.1) by these catecholamines.