Lysozyme is an enzyme found in tears, nasal secretions and the white of avian eggs which hydrolyzes the polysaccharides found in many bacterial cell walls. As such, it has mild antibacterial action and indeed was one of the first antibiotics studied by Sir Fleming, the discover of penicillin. Hen egg white lysozyme has been studied in great detail. Because the enzyme is a very effective catalyst, it has been impossible to obtain a stable crystal between enzyme and substrate. However, it has been possible to obtain crystals of the enzyme complexed to trisaccharide inihibitors. The structure shown here contains a trisaccharide of N-acetylglucosamine (NAG3) and is from the pdb file 1HEW.