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The phosphorylation of vinculin by a highly purified tyrosine-specific protein kinase was enhanced more than 10-fold by anionic phospholipids: the phosphorylation of casein, actin, and alpha-actinin was inhibited. The effect of phospholipid was dependent on the divalent cation used. Stimulation was observed by phosphatidylinositol or phosphatidylglycerol in the presence of either 0.5 mM Mn2+ of 5 mM Mg2+; with either phospholipid, more enzyme activity was observed with Mn2+. Maximal stimulation by phosphatidylinositol was observed at about 400 micrograms/ml. In contrast, marked stimulation by phosphatidylserine was observed only with Mn2+ and marked stimulation by phosphatidic acid was observed only with Mg2+. These results raise the possibility that phospholipids modulate vinculin phosphorylation in Rous sarcoma virus-transformed cells.
Ito et al. (Sun,) studied this question.