Apolipoprotien A-I (Apo AI) is one of the major protein components in high density lipoprotein(HDL). The molecular weight is reported to be 28.3 kDa. Apo A-I acts as a cofactor for lecithin cholesterol acyl transferase(LCAT), which is important in removing excess cholesterol from tissues and incorporating it into HDL for reverse transport to the liver. Some of the apolipoproteins act as ligands to tissue receptors, while others activate or inhibit enzymes involved in metabolic steps in the circulation or tissues. Apo A-I plays important roles in atherosclerosis, tangier disease, coronary heart disease.