Minor apolipoprotein that associates with LDL. Inhibits cholesteryl ester transfer protein (CETP) activity and appears to be an important regulator of cholesterol transport. Also associates to a lesser degree with VLDL, Apo-AI and Apo-AII. Expressed by the liver and secreted in plasma. O-glycosylated with core 1 or possibly core 8 glycans. Belongs to the apolipoprotein F family. It is uncertain whether Met-1 or Met-12 is the initiator.