Apolipoprotein B consists of a single polypeptide chain with a molecular weight of 549 kDa and is mostly synthesised in the liver. It is a major apolipoprotein of very low density, intermediate density and low density lipoproteins (LDL) as well as being a major component of lipoprotein (a). Apolipoprotein B is a ligand for the LDL receptor and elevated levels are associated with premature atherosclerosis. Normal plasma apolipoprotein B levels are around 800 mg/L.