phosphatidylinositol

Definition: Phosphatidylinositol (abbreviated PtdIns, or PI) is a minor phospholipid component in the cytosolic side of eukaryotic cell membranes. Being an amphiphile, this molecule possesses polymorphic behaviour.

Phosphatidylinositol (abbreviated PtdIns, or PI) is a negatively charged phospholipid and a minor component in the cytosolic side of eukaryotic cell membranes.

The inositol can be phosphorylated to form phosphatidylinositol phosphate (PIP), phosphatidylinositol bisphosphate (PIP2) and phosphatidylinositol trisphosphate (PIP3). PIP, PIP2 and PIP3 are collectively called phosphoinositides.

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.

Biosynthesis

The synthesis of phosphatidylinositol is catalyzed by phosphatidylinositol synthase and involves CDP-diacylglycerol and L-myo-inositol.

Phosphorylation

It is 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 seven different combinations.

Hydroxyl group two 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.

See also

 lipids