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  • Title: Conditions associated with the appearance of guanine nucleotide-dependent adenylate cyclase activity in turkey erythrocyte membranes.
    Author: Morris SA, Bilezikian JP.
    Journal: Biochem Pharmacol; 1982 Sep 01; 31(17):2783-90. PubMed ID: 7138573.
    Abstract:
    The mechanisms involved in the activation of adenylate cyclase in turkey erythrocyte membranes may include the release of inhibitory nucleotides from the guanine nucleotide regulatory protein (N) and the subsequent formation of an active GTP-N complex. We have studied the conditions required for the appearance of guanine nucleotide-dependent adenylate cyclase activity in turkey erythrocyte membranes in an effort to understand further the mechanisms involved in its activation. Turkey erythrocyte membranes, whose adenylate cyclase enzyme is usually poorly responsive to the direct actions of GTP or its analogue, Gpp(NH)p, became markedly responsive after previous exposure to isoproterenol in a sucrose-containing buffer. Without sucrose, isoproterenol alone did not lead to Gpp(NH)p responsiveness. Maximum expression of Gpp(NH)p-dependent adenylate cyclase activity required prior incubation with both GMP and isoproterenol. The requirement for sucrose when isoproterenol was used without GMP was lost when GMP was present. With or without GMP, isoproterenol induced a half-maximum effect after 5 min at 37 degrees. The development and maintenance of Gpp(NH)p-dependent adenylate cyclase activity was mediated, in part, by beta-adrenergic receptors. Following a 10-min incubation period with isoproterenol and GMP, the addition of the beta-adrenergic inhibitor, propranolol, for 4 additional min completely reversed the stimulation produced by isoproterenol and GMP. In addition, high-affinity agonist binding to beta-receptors was necessary, but not sufficient, for the development of Gpp(NH)p responsiveness.
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