Peptidoglycan (or murine, or mucocomplex, or mucopeptide) is a component of the bacterial wall maintaining the shape of cells and providing mechanical protection against osmotic pressure. It forms a thin layer in Gram-negative bacteria and a thick layer in Gram-positive bacteria.
It consists of a carbohydrate moiety (= polysaccharide) and a peptide moiety. The polysaccharide is a glycosaminopeptide polymer wherein N-acetylglucosamine (NAG) and N-acetyl-muramic acid (NAM) are linked by beta (1-4) osidic bonds. This bond can be cut off by lysozyme. NAM is a specific compound of bacterial walls. Two polysaccharides are linked by peptide bridges at the level of the NAM, formed by different amino acids: D-alanine, L-alanine, glutamic acid, L-lysine, diaminopimelic acid (lysine analog). Amino acids D are specific for the bacterial wall, they are never found elsewhere.
