Description_x000D_ General description_x000D_ Apolipoprotein E (ApoE) is an important constituent of all plasma lipoproteins. The concentration of Apo E in normal plasma is 5 mg/100mL. Significant quantities of ApoE are produced in liver and brain and to some extent in almost every organ. It exists in three major isoforms; E2, E3, and E4, which differ from one another by a single amino-acid substitution. The gene encoding this protein is localized on human chromosome 19q13.32._x000D_ Biochem/physiol Actions_x000D_ Apolipoprotein E (ApoE) serves as a ligand for low density receptors and participates in the transport and redistribution of cholesterol and other lipids. Other functions include immunoregulation, cell growth modulation and differentiation. Apo E is thought to be involved in tissue repair as increased amounts of the protein are found at sites of peripheral nerve injury and regeneration. A mutant form is associated with familial type III hyperlipoproteinemia. In addition to facilitating solubilization of lipids, these proteins help to maintain the structural integrity of lipoproteins, serve as ligands for lipoprotein receptors, and regulate the activity of enzymes involved in lipid metabolism. ApoE’s interaction with specific ApoE receptor enables uptake of chylomicron remnants by liver cells, which is an essential step during normal lipid metabolism. It also binds with the low-density lipoprotein (LDL) receptor (apo B/E)._x000D_ Physical form_x000D_ Frozen in 50 mM NH4HCO3, pH 8.0.