β-Adrenoceptor is Required for Activation of Avian Erythrocyte GS by Guanine Nucleotides
During catecholamine-induced activation of turkey erythrocyte adenylate cyclase, hormone binding to the β-adrenoceptor (R) increases affinity of the latter for the stimulatory guanine nucleotide binding protein Gs. Exchange of GDP for GTP at the level of the Gsα subunit then occurs, leading to Gs activation and increased conversion of ATP to cAMP via activation of the catalytic unit of adenylate cyclase C. While guanine nucleotide analogues such as Gpp(NH)p have been reported to cause marked cyclase stimulation in frog erythrocytes in the absence of hormone , the turkey system has been said to be refractory to such stimulation . We now demonstrate that in both chicken and turkey erythrocyte membranes, Gpp(NH)p is a significant stimulant of adenylate cyclase activity and that this stimulation is abolished stereoselectivity by the β-adrenoceptor antagonist (+-) — propranolol. Furthermore we show that hormone-independent activation of Gs in a reconstituted system requires the simultaneous presence of R and we propose therefore that the target species for guanine nucleotide activation in avian erythrocytes is an R-Gs complex which exists in equilibrium with free R and GS.
KeywordsAdenylate Cyclase Erythrocyte Membrane Guanine Nucleotide Adenylate Cyclase Activity Reconstituted System
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