Stereospecific binding of propranolol and catecholamines to the β adrenergic receptor

The stereospecificity of the β adrenergic receptor of turkey erythrocyte ghosts was studied. Binding of the specific β 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 [³H]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, the authors were able to calculate the dissociation constants for l epinephrine, l norepinephrine, and l isoproterenol from the β 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.