Apolipoprotein A-II (ApoA-II) is the second major apolipoprotein of high density lipoprotein in human plasma. Mature ApoA-II is present as a dimer of two 77-amino acid chains joined by a disulphide bridge. ApoA-II regulates many steps in HDL metabolism, and its role in coronary heart disease is unclear. In bovine serum, the ApoA-II homolog is present in almost free form. Bovine ApoA-II shows antimicrobial activity against Escherichia coli and yeasts in phosphate buffered saline (PBS).