title: The protein cofactor necessary for ADP-ribosylation of Gs by cholera toxin is itself a GTP binding protein.
abstract: A membrane-bound protein cofactor (ARF) is required for the cholera toxin-dependent ADP-ribosylation of the stimulatory regulatory component (Gs) of adenylate cyclase. Improved methods for the purification of ARF from bovine brain are described. ARF has a high-affinity binding site for guanine nucleotides. Binding of GTP or GTP gamma S to ARF is necessary for the activity of the cofactor; GDP X ARF does not support ADP-ribosylation of Gs. Although the protein as purified contains stoichiometric amounts of GDP, GTPase activity of isolated ARF was not detected. Cholera toxin-dependent activation of adenylate cyclase thus requires two guanine nucleotide binding proteins.
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism*; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002772:Cholera Toxin / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D007700:Kinetics; D009702:Nucleoside Diphosphate Sugars / Q000378:metabolism*; D013873:Thionucleotides / Q000378:metabolism
chemical_list: D009702:Nucleoside Diphosphate Sugars; D013873:Thionucleotides; D000246:Adenosine Diphosphate Ribose; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; D002772:Cholera Toxin; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases