Lysozyme is an enzyme found in egg white, tears, and other secretions. It is responsible for breaking down the polysaccharide walls of many kinds of bacteria and thus it provides some protection against infection. Lysozyme is a enzyme that can provide protection against a broad spectrum of Gram positive bacteria. It is used as a preservative in many food products including wine, tofu, cheese and sake. The use of lysozyme in beer has only recently garnered attention and the applications in brewing, especially to the homebrewer, are numerous.
Lysozyme is odorless, slightly sweet white crystalline powder. It contains 129 amino acid with a molecular weight of 14000. The isoelectric point is 10.7. It is soluble in salt solution, insoluble in acetone or ethanol solution. The function of lysozyme is to hydrolyze the ß(1-4) glycosidic bond between residues of N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG) in certain polysaccharides.
Lysozyme (also called Muramidase) from hen's egg white is a polypeptide of 129 amino acid residues with molecular weight of 14,400 dalton. It is a basic protein (positively charged) with isoelectric point of 10.7~11.0. In the hen's egg white lysozyme accounts for 3.5% of the total egg white protein. Lysozyme is an enzyme which has the ability to lyse certain Gram-positive bacteria by hydrolyzing the b-linkage between N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG) of the peptidoglycan layer in the bacterial cell wall. Lysozyme molecule is ovoid and consists of two domains or lobes, linked by a long a-helix, between which lies the active site of the enzyme. The lower N-terminal lobe (residues 40~88) consists of some helices and is mostly antiparallel b-sheet. The second lobe is made up of residues 1~39 and 89~129 and its secondary structure is largely a-helical. The molecule conforms to the principle of hydrophobic in, hydrophilic out of a protein. All its polar groups are on the surface and the majority of nonpolar (hydrophobic) groups are buried in the interior. Conformational transition in lysozyme involves the relative movement of its two lobes to each other in a cooperative manner, thus allows significant movement of structural regions within the folding unit of the molecule. The relative movement of the domains of lysozyme molecule can cause large global conformational changes which may permit access of substrate and generate an appropriate environment for catalysis.
Lysozyme has been used in pharmaceutical and food applications for many years, due to its lytic activity on the cell wall of gram-positive micro-organisms. These organisms are responsible for many infections of the human body as well as the spoilage of various foods.
Lysozyme is used in "over-the-counter" drugs in order to increase the natural defenses of the body against bacterial infections. The pharmaceutical use of lysozyme encompasses applications such as oto-rhino-laryngology (lozenges for the treatment of sore throats and of canker sores), and in ophthalmology (eye drops and solutions for the decontamination of contact lenses). Lysozyme is also added to infant formulae in order to make them more closely resemble human milk (cow's milk contains very low levels of a lysozyme enzyme).