Physico-Chemical Studies of β-Adrenergic Receptors on Intact Cells
Kinetic studies were performed on intact murine cells using 3H-dihydroalprenolol as antagonist and 3H-hydroxybenzylisoproterenol as agonist radioligands for the β-adrenergic receptor. The binding specificity was tested by inhibition of binding of the radiolabeled antagonist by the agonist 1-isoproterenol and of the radiolabeled agonist by the antagonist dl-alprenolol.
The kinetics of the antagonist association are compatible with a diffusion-controlled process. Dissociation of the antagonist showed a biphasic Arrhenius plot with a low activation energy at temperatures under 20° and a 10-fold increase in activation energy above this temperature. The agonist did not bind specifically below 20°. Above 20° the binding kinetics reflect the need for a conformational change in the receptor before tight binding of agonist can occur.
KeywordsArrhenius Plot Binding Kinetic Agonist Binding Dissociation Rate Constant Association Rate Constant
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