[Effect of C-terminal peptide of G-protein alfa(s)-subunit on regulation of adenylate cyclase and protein kinase A activities by biogenic amines and glucagon in mollusc and rat muscles].

The peptide synthesised by us: 387-394-amide (10(-7)-10(-4) M), in a dose dependent manner decreases activities of adenyl cyclase and proteinkinase A evoked by serotonine and glucagon in smooth muscles of the freshwater bivalve mollusc Anodonta cygnea and that evoked by beta-agonist isoproterenol--in the rat skeletal muscles. Even in concentration 10(-7) M, the peptide completely eliminates potentiation of the hormones' stimulating effect on adenylyl cyclase activity with the non-hydrolizable analogue of guanine nucleotides (Gpp[NH]p). At the same time, the peptide does not affect stimulation of the adenylyl cyclase activity with non-hormonal agents (NaF, Gpp[NH]p and forkolin). In the presence of the peptide, inhibiting effects of the hormones on activities of adenylyl cyclase and protein kinase A will be preserved. The findings reveal the importance of the G-protein alpha s-subunit's C-terminal regional of a stimulating type for its functional coupling with receptors of a serpentine type, and elucidate the molecular mechanisms of interaction between the G-protein and the receptor.