These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Kinetic analysis of the hydrolysis of GTP by p21N-ras. The basal GTPase mechanism.
    Author: Neal SE, Eccleston JF, Hall A, Webb MR.
    Journal: J Biol Chem; 1988 Dec 25; 263(36):19718-22. PubMed ID: 2848838.
    Abstract:
    The rate constants have been determined for elementary steps in the basal GTPase mechanism of normal p21N-ras (Gly-12) and an oncogenic mutant (Asp-12): namely GTP binding, hydrolysis, phosphate release, and GDP release. By extrapolation from data at lower temperatures, the GTP association rate constant at 37 degrees C is 1.4 x 10(8) M-1 s-1 for the normal protein and 4.8 x 10(8) M-1 s-1 for the mutant. Other rate constants were measured directly at 37 degrees C, and three processes have similar slow values. GTP dissociation is at 1.0 x 10(-4) s-1 (normal) and 5.0 x 10(-4) s-1 (mutant). The hydrolysis step is at 3.4 x 10(-4) s-1 (normal) and 1.5 x 10(-4) s-1 (mutant). GDP dissociates at 4.2 x 10(-4) s-1 (normal) and 2.0 x 10(-4) s-1 (mutant). GDP association rate constants are similar to those for GTP, 0.5 x 10(8) M-1 s-1 for normal and 0.7 x 10(8) M-1 s-1 for mutant. Both hydrolysis and GDP release therefore contribute to rate limitation of the basal GTPase activity. There are distinct differences (up to 5-fold) between rate constants for the normal and mutant proteins at a number of steps. The values are consistent with the reduced GTPase activity for this mutant and suggest little difference between normal and mutant proteins in the relative steady-state concentrations of GTP and GDP complexes that may represent active and inactive states. The results are discussed in terms of the likely role of p21ras in transmembrane signalling.
    [Abstract] [Full Text] [Related] [New Search]