This family consists of several mammalian apolipoprotein CIII (Apo-CIII) sequences. Apolipoprotein C-III is a 79-residue glycoprotein. It is synthesized in the intestine and liver as part of the very low density lipoprotein (VLDL) and the high density lipoprotein (HDL) particles. Owing to its positive correlation with plasma triglyceride (Tg) levels, Apo-CIII is suggested to play a role in Tg metabolism and is therefore of interest regarding atherosclerosis. However, unlike other apolipoproteins such as Apo-AI, Apo E or CII for which many naturally occurring mutations are known, the structure-function relationships of apo C-III remains a subject of debate. One possibility is that apo C-III inhibits lipoprotein lipase (LPL) activity, as shown by in vitro experiments. Another suggestion, is that elevated levels of Apo-CIII displace other apolipoproteins at the lipoprotein surface, modifying their clearance from plasma.