Partial purification and characterization of two forms of phosphatidylinositol 4-phosphate 5-kinase from human platelet membrane.

The phosphatidylinositol 4-phosphate 5-kinase (PIP kinase) was isolated from the cholate extract of human platelet membranes. Two major activity peaks (PIP kinase I and PIP kinase II) were resolved by successive chromatographies on Fast Q-Sepharose, heparin-Sepharose, Mono Q and heparin-agarose columns. The PIP kinase I appears to be distinct from the PIP kinase II with regard to Mr (51 kDa and 47 kDa as determined by SDS-PAGE). The two forms of PIP kinase showed similarity in Km for ATP and Mg2+ dependency, but some differences were observed in effects of Mn2+ and phosphatidylethanolamine on the activity.