Before getting into the reaction mechanism of lysozyme it important to review the structure of the ligand that lysozyme cleaves. Like pac man eating little white dots, lysozyme likes to much (catalyze) the reaction that breaks a specific polysaccharide apart. A polysaccharide is nothing more than the linking together of sugar residues to form a chain. The polysaccharide of lysozyme reaction is made up of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). NAM and NAG are joined together by glycosidic linkage. This linkage comes in two forms. Either as an alpha configuration where the linking oxygen comes from an OH group below the plane of the sugar ring (Fig 1) or a beta configuration where the oxygen comes from an OH group above the plane of the sugar ring (Fig 2) In figures 1 and 2, the linking oxygen between NAM and NAG comes from an OH- group on NAG. The type of bond that lysozyme cleaves is called a beta (1-4) NAM-NAG glycosidic bond. More accurately it is the glycosidic bond between the C-1 of NAM and the oxygen attached to the C-4 of NAG. [Stryer, 1981] The portion of the polysaccharide ligand that lysozyme binds to contains six alternating NAM and NAG rings labeled A through F. |
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.![]() Figure 3 Reaction mechanism of glycosidic bond cleavage by lysozyme. [Stryer, 1981] |
![]() Figure 4 Removal of the carbonium ion on NAG and reprotonating Glu 35. [Stryer, 1981] |
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