Type I phosphatidylinositol 4-phosphate 5-kinase isoforms are specifically stimulated by phosphatidic acid.

A phosphatidylinositol 4-phosphate (PIP) kinase was isolated and purified to near homogeneity from bovine erythrocyte membranes. The PIP kinase was extracted from bovine erythrocyte membranes with a high salt wash, followed by phosphocellulose and phenyl-Sepharose chromatography. The predominant protein after phenyl-Sepharose purification had a molecular size of 68 kDa. Renaturation of PIP kinase activity after SDS-PAGE showed that a 68-kDa protein was able to phosphorylate PIP. An antibody developed against the 68-kDa protein Western blots the 68-kDa protein and is able to immunoprecipitate the 68-kDa protein and PIP kinase activity from membrane extracts. Based on functional studies, the 68-kDa protein is indistinguishable from the type I PIP kinase previously characterized from human erythrocyte membranes (Bazenet, C. E., Ruano, A.R., Brockman, J.L., and Anderson, R.A. (1990) J. Biol. Chem. 265, 18012-18022). These studies also show that the type I PIP kinases, but not the type II PIP kinase, are stimulated by phosphatidic acid, suggesting alternative roles for these enzymes. Two immunoreactive isoforms of the type I PIP kinase, of 68 and 90 kDa, were identified in rat brain and partially purified. Both of these isoforms are also stimulated by phosphatidic acid.