Apolipoprotein E (Apo-E), is a member of the apolipoprotein A1/A4/E family. ApoE is a major protein component of serum LDL, VLDL, HDL, and chylomicrons. APOE may function in mediating the binding, internalization, and catabolism of lipoprotein particles. It can serve as a ligand for the LDL (apo B/E) receptor and for the specific apo-E receptor (chylomicron remnant) of hepatic tissues. APOE is usually secreted in plasma. Phosphorylation sites are present in the extracellular medium.