| Abstract: | The product of the protooncogenic ras gene (p21N ras) exhibits a weak GTPase activity. A significant increase in the GTPase activity associated with p21N ras protein was obtained by using glycerol in the assay mixture. Of the several metal ions tested, only Mg++ and Mn++ are effective divalent cations that support the GTPase activity of p21N ras protein. p21N ras protein exhibits higher GTPase activity and yields higher 3H] GDP binding in the presence of MnCl2 than with MgCl2. Optimal GTPase and 3H] GDP binding are obtained at micromolar concentrations of MgCl2 or MnCl2. Concentrations in the millimolar range of either MgCl2 or MnCl2 are inhibitory to the GTPase activity, whereas 3H] GDP binding was not affected. |
