Heterologous desensitization of turkey erythrocyte β-adrenoceptors correlates with receptor phosphorylation and impaired receptor-Gs coupling, as assessed by fusion of purified desensitized receptors with X. laevis erythrocytes [(1984) Science 225, 837-840]. We have purified β-receptors from desensitized and untreated turkey erythrocytes and have compared the abilities of these two receptors to couple with pure turkey erythrocyte Gs in a reconstituted system. Functional receptor-Gs coupling was assessed by measuring hormone-dependent (i) Gs, activation by GTPγS and (ii) GTPase activity. While in membranes prepared from desensitized cells, receptor-Gs, coupling was clearly reduced, this effect was absent when coupling of purified desensitized receptor was measured. We conclude that covalent modification by phosphorylation does not fully explain the functional uncoupling at the membrane level.
