Lysozyme is a protein that is found in tears, saliva, and other secretions. It can degrade the cell walls of certain kinds of bacteria and acts as a natural antibiotic. Lysozyme is also found inegg white and is one of the major egg white proteins that contributes to egg allergy.
While most of the body is protected by a covering of skin, the eyes and mucus membranes do not have this protection. Lysozyme is produced in tears and mucus secretions to protect against invasion by bacteria. It is also present in the blood to help keep bacteria from being spread throughout the body. It is part of the immune system and is also found in human milk. It is passed to children through breast-feeding, helping them to establish their immune system.
Eggs from hens have a large quantity of lysozyme in their whites, which are more prone to cause allergies than the yolks. It is one of the top four proteins in the egg white, to which people who have food allergies from eggs have the strongest allergic response. There is no treatment for egg allergy except for scrupulously avoiding egg products. This can be a difficult process. Even the anesthetic propofol contains an egg product, egg lecithin.
Lysozyme is of historical interest, since it was the first antibacterial substance discovered. Sir Alexander Fleming, who went on to discover penicillin, had a cold and put a drop of mucus on a plate of bacteria. He discovered that the mucus killed the bacteria, but the molecule is too large to be practical as a drug. Many years later, lysozyme was the first enzyme to have its three-dimensional structure solved.
The manner in which lysozyme protects against bacterial invasion is through its activity as an enzyme — an agent that speeds up reactions. The bacteria affected have polysaccharides in their cell walls that are chains of sugars with side chains that contain amine, NH2, groups. Lysozyme degrades these polysaccharides by adding a molecule of water to the sugar linkage, causing it to break open. This is known as glycoside hydrolase, or water breakdown of sugar. Once the polysaccharide chain is disrupted, the bacterial cells burst.
There are several types of lysozymes found in a variety of different organisms, forming a family of enzymes. In humans, the gene is known as the LYZ gene. Another term for the enzyme ismuramidase, because it cleaves the bond that connects N-acetylmuramic acid to its adjoining sugar molecule. The technical name for the enzyme is N-acetylmuramide glycanhydrolyase.
