Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
Apolipoproteins are lipid-binding proteins which are the constituents of the plasma lipoproteins, sub-microscopic spherical particles that transport dietary lipids through the bloodstream from the intestine to the liver, and endogenously synthesized lipids from the liver to tissues that can store them (adipocytes), metabolize them (muscle, heart, lung), or secrete them (breast). The amphipathic detergent-like properties of apolipoproteins solubilize the hydrophobic lipid constituents of lipoproteins. In addition, apolipoproteins also serve as enzyme co-factors, receptor ligands, and lipid transfer carriers that regulate the intravascular metabolism of lipoproteins and their ultimate tissue uptake.
|Apolipoprotein||Predominant lipoprotein||Minor lipoproteins||Plasma concentration (mg/dL)||Role||Molecular Weight (kDa)||Chromosome|
|ApoA-II||HDL||Chylomicrons||25–45||Hepatic Lipase (HL) activation||17||1q21-23|
|ApoA-IV||HDL||10-20||LCAT and lipoprotein lipase (LPL) activation||45||11q23|
|ApoA-V||VLDL, HDL||Metabolism of triglyceride rich lipoprotein||11q23|
|ApoB-100||LDL, VLDL||IDL, Lp(a)||50–150||LDLr binding||512||2q23–24|
|ApoC-I||Chylomicrons, HDL||IDL, VLDL||5–6||LCAT activation||6.63||19q13.2|
|ApoC-II||Chylomicrons, VLDL||HDL, IDL||3–5||LPL activation||8.84||19q13.2|
|ApoC-III||Chylomicrons, VLDL||HDL, IDL, LDL||10–14||LPL inhibition||8.76||11q23|
|ApoD||HDL||4–7||CETP (CE transfer protein) activation||33||3q26.2|
|ApoE||Chylomicron remnants, IDL||HDL, LDL,VLDL||2-8||LDLr binding||34||19q13.2|
|ApoH||Chylomicron, VLDL, LDL, HDL||B2 glycoprotein||17q23|
|Apo(a)||Lp(a)||0–200||Plasminogen activation inhibition||250–800||6q27|
- ApoB-48 is exclusively found in chylomicrons. It is derived from the apoB-100 gene and is reduced to 48% of the N-terminal component of B-100 by RNA editing, with no LDL receptor (LDLr) binding domain.
- ApoE is found broadly in HDL, IDL, LDL, VLDL, and chylomicrons and binds to LDLr with varying affinity dependent on the inherited apoE allele. Three different apoE isoforms exist in humans: apoE2 with lower affinity to LDLr, apoE3 with intermediate binding affinity, and apoE4 with higher affinity.
- Apo(a) is a distinguishing structural protein of lipoprotein(a). It is covalently bound to apoB-100 and inhibits plasminogen activation.
Apolipoprotein synthesis in the intestine is regulated principally by the fat content of the diet.
Apolipoprotein synthesis in the liver is controlled by a host of factors, including dietary composition, hormones (insulin, glucagon, thyroxin, estrogens, androgens), alcohol intake, and various drugs (statins, niacin,and fibric acids).