title: Physiological correlation between nucleoside-diphosphate kinases and the 21-kDa guanine-nucleotide binding proteins copurified with the enzymes from the cell membrane fractions of Ehrlich ascites tumor cells.
abstract: The physiological correlation between nucleoside-diphosphate kinases (NDP-kinases) and the 21-kDa guanine nucleotide-binding proteins (G1 and G2) which are copurified with the enzymes from the cell membrane fractions of Ehrlich ascites tumor cells has been biochemically investigated in vitro. We found that: incubation of the phosphoenzyme (enzyme-bound high-energy phosphate intermediate) of NDP-kinases (F-I and F-II) with one of the nucleoside 5'-diphosphates in the presence of 1 mM Mg2+ or 0.25 mM Ca2+ results in the rapid formation of nucleoside 5'-triphosphates without strict base specificity; GDP on the guanine nucleotide-binding proteins (G1, G2 and recombinant v-rasH p21) acts as a phosphate acceptor for the high-energy phosphates of the phosphoenzyme in the presence of 0.25 mM Ca2+; and [32P]GTP is preferentially formed from the 32P-labelled phosphoenzyme F-I and GDP-bound G1 or GDP-bound recombinant v-rasH p21 protein, even if any other nucleoside 5'-diphosphates are present in the reaction mixture. Although [32P]GTP formed was bound with the guanine nucleotide-binding proteins, it was immediately hydrolyzed by the proteins themselves in the presence of 5 mM Mg2+, but not in the presence of 0.25 mM Ca2+. Available evidence suggests that NDP-kinase may be responsible for the activation of the guanine nucleotide-binding proteins (G1, G2 and p21 proteins) through phosphate transfer by the enzyme.
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D051379:Mice; D009701:Nucleoside-Diphosphate Kinase / Q000378:metabolism*; D009711:Nucleotides / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism; D010770:Phosphotransferases / Q000378:metabolism*
chemical_list: D009711:Nucleotides; D010710:Phosphates; D006153:Guanosine Diphosphate; D000244:Adenosine Diphosphate; D006160:Guanosine Triphosphate; D010770:Phosphotransferases; D009701:Nucleoside-Diphosphate Kinase; D019204:GTP-Binding Proteins; D008274:Magnesium; D002118:Calcium