Beta-Adrenergic receptors: solubilization of (-)(3H)alprenolol binding sites from frog erythrocyte membranes.

The β-adrenergic receptors ((?)³H]alprenolol binding sites) present in a purified preparation of frog erythrocyte membranes have been solubilized with digitonin and assayed by equilibrium dialysis with (?)³H]alprenolol. At a concentration of 0.5–1% the detergent solubilizes about 80% of the receptor binding activity. The soluble receptor sites are not sedimented at centrifugal forces up to 105,000 xg for two hours, pass freely through Millipore filters of 0.22 μ pore size and fractionate on Sepharose 6B gel with an apparent molecular weight of 130–150,000 in the presence of digitonin. The soluble receptor sites retain all of the binding characteristics of the membrane-bound receptors. β-adrenergic agonists and antagonists compete with (?)³H]alprenolol for occupancy of the soluble sites with affinities which are directly related to their β-adrenergic potency on membrane-bound adenylate cyclase.