Stimulation of mammalian adenylate cyclase activity with guanosine 5′-tetraphosphate and other guanine nucleotides

Abstract

Guanosine 5′-tetraphosphate (GTP 4) stimulated mammalian adenylate cyclase activity at concentrations down to 1 μM. Greater stimulatory activity was apparent with lung than with heart, brain or liver from the rat. At a concentration of 0.1 mM, GTP 4 stimulated lung adenylate cyclase activity from rat, guinea pig and mouse about four-fold. Other guanine nucleotides such as GTP, GDP, GMP, guanosine 3′, 5′-monophosphate and 5′-guanylylimidodiphosphate (GMP · PNP) also stimulated mammalian adenylate cyclase activity. GMP · PNP irreversibly activated, whereas GTP 4 and GTP reversibly activated adenylate cyclase. Adenosine 5′-tetraphosphate (ATP 4) stimulated rat lung and liver but inhibited rat heart and brain adenylate cyclase activities. Lung from guinea pig and mouse were not affected by ATP 4. The formation of cyclic AMP by GTP 4-stimulated rat lung adenylate cyclase was verified by Dowex-50 (H +), Dowex 1-formate and polyethyleneimine cellulose column chromatography. GTP 4 was at least three times more potent than 1-isoproterenol in stimulating rat lung adenylate cyclase activity. The β-adrenergic receptor antagonist propranolol blocked the effect of 1-isoproterenol but not that of GTP 4, thus, suggesting that GTP 4 and β-adrenergic agonists interact with different receptor sites on membrane-bound adenylate cyclase. Stimulation of rat lung and liver adenylate cyclase activities with 1-isoproterenol was potentiated by either GTP 4 or GMP. PNP, thus indicating that GTP 4 resembles other guanine nucleotides in their capacity to increase the sensitivity of adenylate cyclase to β-adrenergic agonists. Stimulation of adenylate cyclase activity by guanine derivatives requires one or more free phosphate moieties on the 5 position of ribose, as no effect was elicited with guanine, guanosine, guanosine 2′-monophosphate, guanosine 3′-monophosphate or guanosine 2′,5′-monophosphate. Ribose, ribose 5-phosphate, phosphate and pyrophosphate were inactive. Pyrimidine nucleoside mono-, di-, tri- and tetraphosphates elicited negligible effects on mammalian adenylate cyclase activity.