Phosphatidylinositol-4-phosphate 5-kinase isozymes catalyze the synthesis of 3-phosphate-containing phosphatidylinositol signaling molecules.

Phosphatidylinositol-4-phosphate 5-kinases (PIP5Ks) utilize phosphatidylinositols containing D-3-position phosphates as substrates to form phosphatidylinositol 3,4-bisphosphate. In addition, type I PIP5Ks phosphorylate phosphatidylinositol 3, 4-bisphosphate to phosphatidylinositol 3,4,5-trisphosphate, while type II kinases have less activity toward this substrate. Remarkably, these kinases can convert phosphatidylinositol 3-phosphate to phosphatidylinositol 3,4,5-trisphosphate in a concerted reaction. Kinase activities toward the 3-position phosphoinositides are comparable with those seen with phosphatidylinositol 4-phosphate as the substrate. Therefore, the PIP5Ks can synthesize phosphatidylinositol 4,5-bisphosphate and two 3-phosphate-containing polyphosphoinositides. These unexpected activities position the PIP5Ks as potential participants in the generation of all polyphosphoinositide signaling molecules.