Solubilization of a mammalian ?-adrenergic receptor

Abstract
Binding sites for iodohydroxybenzylpindolol with characteristics of a β2-adrenergic receptor have been identified in a crude membrane fraction from guinea-pig lung. The binding sites could be solubilized by treatment of the membrane fraction with digitonin. Upon solubilization receptors retain their β2-adrenergic type as indicated by the rank order of potencies of agonists in binding-inhibition experiments. The solubilized receptors demonstrate a marked increase in affinity for agonists compared with particulate receptors whereas antagonist affinity remains unchanged. Solubilized receptors are insensitive to divalent cations (Mg2+, Mn2+, Ca2+) which increase the potency of agonists for particulate receptors. The effects of Mg2+ can be reversed by Gpp(NH)p in particulate preparations; Gpp(NH)p is ineffective for the solubilized preparation. These experiments establish that β-adrenergic receptors can be solubilized even from crude mammalian membrane preparations. They also show that the mammalian β-adrenergic receptor in situ is under constraints with respect to agonist affinity and is modulated by divalent cations and guanyl nucleotides in the intact membrane.

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