Phosphatidylinositol-5-Phosphate-4-Kinase Type II Gamma (PIP4K2C)

Phosphatidylinositol-4,5-bisphosphate (PtdIns-4,5-P2), a key molecule in the phosphoinositide signalling pathway, was thought to be synthesized exclusively by phosphorylation of PtdIns-4-P at the D-5 position of the inositol ring. The enzymes that produce PtdIns-4,5-P2 in vitro fall into two related subfamilies based on their enzymatic properties and sequence similarities'. As expected, the type I enzyme phosphorylates PtdIns-4-P at the D-5 position of the inositol ring. Surprisingly, the type II enzyme, which is abundant in some tissues, phosphorylates PtdIns-5-P at the D-4 position, and thus should be considered as a 4-OH kinase, or PIP(4)K.The earlier error in characterizing the activity of the type II enzyme is due to the presence of contaminating PtdIns-5-P in commercial preparations of PtdIns-4-P.