PI System Another Second Messanger

The first part of PI consists of two fatty acids esterified to a glycerol. One of the fatty acids is the unsaturated fatty acid arachidonic acid (20 4), bound to carbon 2 of the glycerol. The other fatty acid is usually stearate (18 0). The combination of two fatty acids esterified to glycerol is called diacylglycerol, abbreviated DAG. 

Another component of PI is a carbohydrate, phosphoinositol, which a phosphate diester binds to the third position of the glycerol. The inositol is usually phosphorylated at two positions. 

Several types of signaling molecules are derived from PI. Hydrolysis of the glycerol-phosphate linkage by a phospholipase leads to the signaling molecule trisphosphoinositol, abbreviated IP3. 

The remaining part of the phosphoinositol, 1,2-diacylglycerol, is also a signaling molecule. 

Finally, the arachidonate that arises from cleavage of phos-phatidylinositol can serve as a precursor of prostaglandins. 

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