[Role of guanyl nucleotides in regulation of activity of heart adenylate cyclase by chloride ions].

Guanyl nucleotides enhance the activating effect of chloride ions on adenylate cyclase of rabbit heart sarcolemma. Chloride ions decrease the lag period in the effect of guanyl-5'-ylimidodiphosphate (Gpp(NH)p), the non-hydrolyzed analog of GTP, on adenylate cyclase. Guanyl nucleotides and chloride ions exert a synergistic effect on the enzyme activation. The adenylate cyclase activity in the presence of Gpp(NH)p is increased by other anions as well. The activating effect of chloride ions on the enzyme is enhanced by GTP, as well as by GDP. On the contrast, GDP completely inhibits the enzyme activation by isoproterenol. It was assumed that chloride ions favour the formation of a complex between the adenylate cyclase catalytic subunit and the regulatory protein irrespective of the type of guanyl nucleotide, i.e. GTP, Gpp(NH)p or GDP, present in the nucleotide binding site of the regulatory protein.