Activation of R-Ras GTPase by GTPase-activating proteins for Ras, Gap1(m), and p120GAP.
The enzymatic properties of Gap1(m) were characterized using three Ras and R-Ras proteins as substrates and were compared with those of p120GAP. Gap1(m) stimulated the GTPase of Ras better than that of R-Ras, in contrast to p120GAP which promoted the GTPase of R-Ras better than that of Ras. The EC50 values of Gap1(m) for Ha-Ras and R-Ras were 0.48 +/- 0.02 and 1.13 +/- 0.12 nM, respectively, whereas the EC50 values of p120GAP for Ha-Ras and R-Ras were 23.1 +/- 1.9 and 3.86 +/- 0.38 nM, respectively. The affinities of Gap1(m) and p120GAP to the substrates determined by competitive inhibition by using Ha-Ras.GTPgammaS (guanosine 5'-O-(3-thiotriphosphate)) or R-Ras.GTPgammaS as a competitor agreed well with the substrate specificities of these GTPase-activating proteins. The Km values of Gap1(m) for Ha-Ras and R-Ras were 1.53 +/- 0.27 and 3.38 +/- 0.53 microM, respectively, which were lower than that of p120GAP for Ha-Ras (145 +/- 11 microM) by almost 2 orders of magnitude. The high affinity of Gap1(m) to the substrates and its membrane localization suggest that Gap1(m) may act as a regulator of the basal activity of Ha-Ras and R-Ras.
Li
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Division of Biochemistry and Cellular Biology, National Institute of Neuroscience, National Center of Neurology and Psychiatry, 4-1-1 Kodaira, Tokyo 187, Japan.
Nakamura
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Hattori
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D004789:Enzyme Activation; D020558:GTP Phosphohydrolases / Q000187:drug effects*; D020690:GTPase-Activating Proteins; D007700:Kinetics; D025542:Neurofibromin 1; D011506:Proteins / Q000502:physiology*; D013379:Substrate Specificity; D020703:ras GTPase-Activating Proteins; D018631:ras Proteins / Q000378:metabolism*
D020690:GTPase-Activating Proteins; D025542:Neurofibromin 1; D011506:Proteins; D020703:ras GTPase-Activating Proteins; D020558:GTP Phosphohydrolases; D018631:ras Proteins