Prominent protein constituents of plasma VLDL, chylomicrons, and a subfraction of HDL as well as of remnant lipoproteins which are derived from the lipoprotein lipase-mediated intravascular catabolism of triglyceride-rich lipoproteins; recognized by the LDL receptor and Apo E receptor; any defect in the Apo E metabolism leads to increased plasma Apo E levels; a strong association has been found between high levels of Apo E and type III hyperlipoproteinemia.

A class of protein components which can be found in several lipoproteins including HIGH-DENSITY LIPOPROTEINS; VERY-LOW-DENSITY LIPOPROTEINS; and CHYLOMICRONS. Synthesized in most organs, Apo E is important in the global transport of lipids and cholesterol throughout the body. Apo E is also a ligand for LDL receptors (RECEPTORS, LDL) that mediates the binding, internalization, and catabolism of lipoprotein particles in cells. There are several allelic isoforms (such as E2, E3, and E4). Deficiency or defects in Apo E are causes of HYPERLIPOPROTEINEMIA TYPE III.