The phosphatidylinositol 3-kinases (PI 3-kinases), which play a pivotal role in cellular signaling, represent a family of enzymes that phosphorylate phosphoinositides on the 3-position of the inositol ring (1 ). PtdIns(3,4,5)P3 (phosphatidylinositol(3,4,5)trisphosphate) is one of the principle products of this reaction and has been suggested to be a second messenger involved in many physiological phenomena.
