title: ADP-ribosylation of Gs promotes the dissociation of its alpha and beta subunits.
abstract: We have utilized purified reactants and cofactors to examine the form of the stimulatory guanine nucleotide-binding regulatory component (Gs) of adenylate cyclase that serves as a substrate for ADP-ribosylation by cholera toxin; we have also investigated some of the consequences of that covalent modification. Activation of Gs with nonhydrolyzable analogs of GTP, which causes dissociation of its subunits, completely inhibits the toxin-catalyzed covalent modification. However, this effect cannot be explained by subunit dissociation, since activation of Gs by fluoride is not inhibitory and ADP ribosylation of the alpha (45,000-Da) subunit of Gs proceeds equally well in the presence and absence of the beta (35,000-Da) subunit. ADP-ribosylation of the alpha subunit of Gs decreases its apparent affinity for the beta subunit; however, the affinity of alpha and ADP-ribosyl-alpha for GTP appear to be approximately the same. ADP-ribosylation of Gs thus promotes the dissociation of its alpha and beta subunits. This effect may account for or contribute to the activation of adenylate cyclase by cholera toxin.
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism*; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D002772:Cholera Toxin / Q000494:pharmacology; D004789:Enzyme Activation; D019204:GTP-Binding Proteins; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D046911:Macromolecular Substances; D009702:Nucleoside Diphosphate Sugars / Q000378:metabolism*; D011817:Rabbits; D011956:Receptors, Cell Surface / Q000378:metabolism*
chemical_list: D046911:Macromolecular Substances; D009702:Nucleoside Diphosphate Sugars; D011956:Receptors, Cell Surface; D000246:Adenosine Diphosphate Ribose; D006160:Guanosine Triphosphate; D002772:Cholera Toxin; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases