Regulation of Adenylate Cyclase Activity by a GTP-Binding Peptida in Rat Liver.

A cytosolic peptide·GTP complex which stimulates iota-isoproterenol-responsive adenylate cyclase activity was identified in the rat liver.The peptide component was purified and characterized with regard to its interaction with GTP in the regulation of adenylate cyclase。The peptide was isolated as a complex form with GTP on a Sephadex G-25column in 1 mM NaHCO_3，and on the same column in 200 mM ammonium acetate it was purified as a dissociated form with Mr-3，000。The purified peptide alone displayed a markedly decreased stimulatory effect on adenylate cyclase activity，but its reassociated form with GTP clearly enhanced the effect of GTP on the enzyme activity。The isoproterenol competition curve using iota-[^3H]dihydroalprenolol(DHA)as an antagonist ligand shifted to lower affinity by the addition of the peptide reassociated with GTP(16.5-fold shift)，while the same concentration of GTP(1mu M)or the peptide alone had little or no effect(1.5-or 0.9-fold shift，respectively)。Furthermore，the peptide enhanced the GTP effect in the response to iota-isoproterenol but not in that to glucagon，prostaglandin E_1and fluoride。These results suggest that the peptide component of the cytosolic activator potentiates the effect of GTP on the agonist-beta-adrenergic receptor-stimulatory guanine nucleotide-binding regulatory component of adenylate cyclase(G_S)(GDP)ternary complex。

A cytosolic peptide ・ GTP complex which stimulates iota -isoproterenol- responsive adenylate cyclase activity was identified in the rat liver. The peptide component was purified and characterized with regard to its interaction with GTP in the regulation of adenylate cyclase. The peptide was isolated as a complex form with GTP on a Sephadex G-25 column in 1 mM NaHCO_3, and on the same column in 200 mM ammonium acetate it was purified as a dissociated form with Mr -3,000. The purified peptide alone displayed a markedly decreased stimulatory effect on adenylate cyclase activity, but its reassociated form with GTP clearly enhanced the effect of GTP on the enzyme activity. The isoproterenol competition curve using iota -[^3H]dihydroalprenolol (DHA) as an antagonist ligand shifted to lower affinity by the addition of the peptide reassociated with GTP (16.5-fold shift), while the same concentration of GTP (1 mu M) or the peptide alone had little or no effect (1.5- or 0.9-fold shift, respectively). Furthermore, the peptide enhanced the GTP effect in the response to iota -isoproterenol but not in that to glucagon, prostaglandin E_1 and fluoride. These results suggest that the peptide component of the cytosolic activator potentiates the effect of GTP on the agonist- beta -adrenergic receptor-stimulatory guanine nucleotide-binding regulatory component of adenylate cyclase (G_s) (GDP) ternary complex.