The Binding Characteristics and Number of β-Adrenergic Receptors on the Turkey Erythrocyte

Turkey erythrocyte ghosts (empty membranes) possess a class of receptors that can bind both L-[3 H]isoproterenol and DL-[3 H]propranolol. The binding of [3 H]isoproterenol to these receptors occurs with a dissociation constant of 0.15 μM and can be fully inhibited by 1 μM propranolol. The binding of [3 H]propranolol occurs with a dissociation constant of 2.5 nM and can be fully inhibited by 0.2 mM DL-isoproterenol. Ligand binding is sensitive to sonication, boiling, and 8 M urea. The cells possess 500 to 1000 β-adrenergic receptors per cell. Binding of propranolol to the β-receptor was found to be stereospecific for the L stereoisomer. If one assumed a 1:1 relationship between β-adrenergic receptors and adenylate cyclase, the turnover number of this adenylate cyclase would be close to 100 min-1 .