Ligand specificity and characteristics of the β-adrenergic receptor in turkey erythrocyte plasma membranes

Detailed kinetic studies of adenylate cyclase activation by catecholamines in turkey erythrocyte plasma membranes were carried out in order to characterize the ligand specificity of the β-adrenergic receptor. A general kinetic method was used to evaluate the affinity of the β-receptor towards full-agonists, partial agonists and antagonists. This method allowed us to study ligands that bind with high affinity as well as ligands that bind with low affinity. Direct binding studies of [³H]propranolol to the β-receptor were used to study the ligand specificity and the modulation of that specificity by regulatory ligands known to activate or inhibit adenylate cyclase stimulation by l-catecholamines. A very close correspondence between the binding constants obtained by the kinetic method and the binding method was found. It was found that the allosteric activator of adenylate cyclase, guanylylimidodiphosphate, and the allosteric inhibitor, Ca²⁺, do not affect propranolol binding.