title: Effects of ions on the intrinsic activities of c-H-ras protein p21. A comparison with elongation factor Tu.
abstract: The influence of the ionic environment on the intrinsic GTPase activity and the guanine-nucleotide interaction of Ha-ras protein p21 were studied in various experimental conditions and compared with the behaviour of elongation factor (EF) Tu. To this purpose, nucleotide-free p21 was prepared, which is much more stable than by any other reported method. Specific differences between p21 and EF-Tu were found in the action of divalent anions which strongly enhance the dissociation rate of p21.GDP without affecting that of EF-Tu. Unlike EF-Tu, the GTPase activity of p21 is only slightly dependent on the presence and concentration of monovalent cations. The concentrations of Mg2+ influencing the dissociation rate of the p21.GDP complex are much higher than for the intrinsic GTPase activity, an effect also observed for EF-Tu. These results point to two distinct roles of Mg2+: as a conformational regulator of the interaction with the substrate and as a key element for the hydrolysis of GTP. The GTPase activity of p21 is not affected by changes in pH over the range 6-9.2, different from that of EF-Tu. However, stabilization by kirromycin confers a pH independence to the GTPase of EF-Tu in the pH range 6.5-10, suggesting that the bell-shaped behaviour of this activity in the absence of the antibiotic is due to denaturation. This implies similar properties in the catalytic mechanism of these two guanine-nucleotide-binding proteins.
authors.affiliation: Structure Diverse d'Interventions no. 61840 du CNRS, Laboratoire de Biochimie, Ecole Polytechnique, Palaiseau, France.
authors.forename: M Y
authors.initials: MY
authors.lastname: Mistou
authors.forename: R H
authors.initials: RH
authors.lastname: Cool
authors.forename: A
authors.initials: A
authors.lastname: Parmeggiani
mesh_terms: D000643:Ammonium Chloride / Q000494:pharmacology; D000645:Ammonium Sulfate / Q000494:pharmacology; D000838:Anions; D002413:Cations, Divalent; D002414:Cations, Monovalent; D020963:GTP Phosphohydrolase-Linked Elongation Factors / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007477:Ions; D015636:Magnesium Chloride / Q000494:pharmacology; D010444:Peptide Elongation Factor Tu / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism*
chemical_list: D000838:Anions; D002413:Cations, Divalent; D002414:Cations, Monovalent; D007477:Ions; D000643:Ammonium Chloride; D015636:Magnesium Chloride; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D020963:GTP Phosphohydrolase-Linked Elongation Factors; D010444:Peptide Elongation Factor Tu; D016283:Proto-Oncogene Proteins p21(ras); D000645:Ammonium Sulfate