[20] Phosphatidylinositol 4-kinase from yeast

Phosphatidylinositol 4-kinase (1-phosphatidylinositol kinase) catalyzes the reaction of phosphatidylinositol with ATP to form phosphatidylinositol 4-phosphate. Phosphatidylinositol 4-kinase (ATP:1-phosphatidyl-lD-myo-inositol 4-phosphotransferase) is the first enzyme in the phosphorylation sequence of phosphatidylinositol leading to the formation of phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate in Saccharomyces cerevisiae (S. cerevisiae). The synthesis and turnover of the polyphosphoinositides in S. cerevisiae and in higher eukaryotes play an important role in cell growth. Phosphatidylinositol 4-kinase is associated with the microsomal, plasma membrane, and cytosolic fractions of S. cerevisiae. Phosphatidylinositol 4-kinase has been purified to near homogeneity from the microsomal fraction of S. cerevisiae by standard protein purification procedures. The chapter describes the purification and properties of the enzyme. The properties of phosphatidylinositol 4-kinase are also discussed. Pure phosphatidylinositol 4-kinase can be used to synthesize radiolabeled phosphatidylinositol 4-phosphate.