Phosphatidylinositol synthase from mammalian tissues.

Phosphatidylinositol synthase (CDP-diacylglycerol:myo-inositol 3-phosphatidyl-transferase, EC 2.7.8.11) is a 24-kDa membrane-bound enzyme. It is present in all mammalian cells and is localized predominantly to the endoplasmic reticulum. The enzyme performs the last step in the de novo biosynthesis of the phospholipid phosphatidylinositol by catalyzing the condensation of CDP-diacylglycerol and myo-inositol to form the products phosphatidylinositol and CMP. Phosphatidylinositol, apart from being an essential membrane phospholipid, is involved in protein membrane anchoring and is the precursor for the second messengers inositol-tri-phosphate and diacylglycerol.