Apolipoproteins :

      Apolipoproteins are either peripheral (can be transferred between different lipoproteins) or integral (cannot be removed). All apolipoproteins are mainly synthesized in liver, but small quantites are produced from almost all organs.

Functions of Apolipoproteins :

     Apart from solubilizing the lipid part, the protein components have specific functions:

1. Structural role: Apo B48 is an important component of chylomicrons.
2. Activation of enzymes: Apo C11 is an activator of lipoprotein lipase.  Apo A1 present in HDL activates lecithin cholesterol acyl transferase (LCAT) enzyme.
3. Ligands for interaction with lipoprotein in tissue:  Apo A1 is the ligand for HDL receptor. ApoB100 and apo E for LDL receptor.

     Apo E is the hepatic ligand for the chylomicron remnants.