Apolipoprotein

Lipoprotein is composed of lipids and proteins. The protein constituent is called apolipoprotein. Apolipoprotein AI (Apo AI) and apolipoprotein AII (Apo AII) comprise approximately 70% and 20%, respectively, of high-density lipoprotein (HDL). Apo AI activates Lecithin:cholesterol acyltransferase (LCAT). Apo AII has been shown to activate hepatic lipase and inhibit LCAT. As the concentration of Apo AI and Apo AII are independent, each must be assayed separately.

Apolipoprotein B (Apo B) is the major protein component of low density lipoprotein (LDL). Apo B is an integral component of the four major atherogenic lipoproteins: very low-density lipoprotein (VLDL), intermediate density lipoprotein (IDL), low density lipoprotein (LDL), and lipoprotein (a) (Lp(a)). Apo B plays a major role in the recognition of cellular receptors for the catabolism of LDL.

Apolipoprotein E (Apo E), a 34,000 dalton plasma protein, is found primarily in chylomicrons, chylomicron remnants, VLDL, IDL and HDL. Apo E serves as a ligand for lipoprotein receptors. Through its interaction with these receptors, Apo E is involved in the transport and metabolism of cholesterol and other lipids in the body.