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Bacterially synthesized c-Ha-ras protein (Ras) was incubated with guanosine triphosphatase (GTPase) activating (GA) protein in the presence of various phospholipids. The stimulation of Ras GTPase activity by GA protein was inhibited in some cases. Among the lipids most active in blocking GA protein activity were lipids that show altered metabolism during mitogenic stimulation. These included phosphatidic acid (containing arachidonic acid), phosphatidylinositol phosphates, and arachidonic acid. Other lipids, including phosphatidic acid with long, saturated side chains, diacylglycerols, and many other common phospholipids, were unable to alter GA protein activity. The interaction of lipids with GA protein might be important in the regulation of Ras activity during mitogenic stimulation.
Tsai et al. (Fri,) studied this question.