Phosphatidylinositol

] Phosphatidylinositol (abbreviated PtdIns, or PI) is a minor phospholipid component in the cytosolic side of eukaryotic cell membranes. Phosphatidylinositol is a class of phospholipid, which is made up of glycerol, fatty acid and the base is replaced by a hexahydric alcohol namely inositol. This hexahydric alcohol exists as its stereoisomer - myo-inositol. Upon hydrolysis, they yield 1 mole of glycerol, 2 moles of fatty acid, 1 mole of inositol and 1, 2, or 3 moles of phosphoric acids. They are regarded to be the most acidic of all the phospholipids. It is however the substrate for a large number of enzymes which are involved in cell signaling because it can be phosphorylated by a variety of kinases on the hydroxyl groups 3, 4 and 5 on the inositol ring in in seven different combinations. Hydroxyl group one and six can probably not be phosphoroylated because of steric hindrance. All seven variations have been found in animals but only six in plant cells (not phosphatidylinositol (3,4,5)-trisphosphate..