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Phosphatidylinositol (abbreviated PtdIns, or PI) is a negatively charged phospholipid and a minor component in the cytosolic side of eukaryotic cell membranes. PI has a polar and non-polar region, making the lipid an amphiphile. Amphiphatic lipids demonstrate polymorphic behavior, a current academic research topic. Phosphatidylinositol is classified as a glycerophospholipid that contains a glycerol backbone, two non-polar fatty acid tails, a Phosphate group substituted with an inositol polar head group. The inositol can be phosphorylated to form Phosphatidylinositol phosphate (PIP) andPhosphatidylinositol bisphosphate (PIP2). PI, PIP, and PIP2 are collectively called phosphoinositides. The most common fatty acids of phosphoinositides are the 18:0 in the SN1 position and 20:4, Arachidonic acid, in the SN2 position. Hydrolysis of phosphoinositides yield one mole of glycerol, two moles of fatty acids, one mole of inositol and one, two, or three moles of phosphoric acids, depending on the number of phosphates on the inositol rings. Phosphoinositides are regarded as the most acidic phospholipid.

Biosynthesis and Phosphorylation


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

Phosphatidylinositol plays important rolls in Lipid signaling and cell signaling. As previously mentioned, the inositol ring can be phosphorylated by a variety of kinases on the three, four and five hydroxyl groups in seven different combinations. However, the two and six hydroxyl group is typically not phosphorylated due to steric hindrance.

All seven variations of phosphorylated inositols have been found in animals, but only six variations are found in plant cells (not phosphatidylinositol (3,4,5)-trisphosphate}..

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