IV-Acetylglucosamine residues

Related enzymes are N-acetylglucosaminidases, EC 3.2.1.30, some of which can act to hydrolyse the terminal, non-reducing iV-acetylglucosamine residue of chitin and lysozymes, EC 3.2.1.17, some of which can act slowly as endohydrolases. 

With cellular extracts of Staph, aureus and Micrococcus lysodeikticus, novobiocin inhibits the formation of the alternating JV-acetylmuramic acid-pentapeptide and iV-acetylglucosamine residues... 

Ogawa, R. and Tokura, S. 1992. Preparation of bacterial eeUulose containing iV-acetylglucosamine residues. Carbohydrate Polymers 19(3) 171-178. 

Amino acid sequence leu-ser-gly-his Reactive residues ser, his Carbohydrates mannose4, iV-acetylglucosamines... 

Fig. 6. Principle of the poly-iV-acetyllactosamine labelling method. In the first step, cells are treated with endo-fl-galacto-sidase, which cleaves only poly-iV-acetyllactosamine glycans. In the second step, the terminal W-acetylglucosamine residues are labelled by the transfer of radiolabelled galactose from UDP-galactose with the aid of galactosyltransferase [40,41],...

The saccharide sequence of Asn-(GlcNAc)2PMan(aMan)2, in complex stractures is tenned the core and the residues of N-acetylglucosamine within it are internal . Those in outer chains are external . If a residue of GlcNAc is attached to the mannosyl residue it is called a bisecting iV-acetylglucosamine. The use of the word core in high-mannose and intermediate structures is rather less precise. 

The carbohydrate chains of the peptidoglycan consist of up to twelve alternating iV-acetylglucosamine and iV-acetylmuramic acid units (D 1.1) linked to each other through 8-1,4-bonds. The muramic acid residues are either wholly or partly substituted by peptide chains which may consist of L-alanine, D-glutamic acid. 

Variations also occur in the muramic acid itself. In S. aureus approximately half of the muramic acid residues bear an acetyl group on the 6 position. This modification renders the peptidoglycan insensitive to degradation by lysozyme. Similar modifications have been reported in some strains of Proteus, Neisseria and Pseudomonas. Loss of some of the iV-acetyl residues from the V-acetylglucosamine of some Bacillus cereus strains also has the effect of rendering the peptidoglycan resistant to lysozyme. 

The first elucidation of a three-dimensional structure for an enzyme was that for lysozyme, which was soon followed by that of its complex with polymers of iV-acetylglucosamine (see Blake et al., I%7). In subsequent years this enzyme-substrate interaction was the subject of kinetic investigations in a number of laboratories and the results present several interesting general features. Fluorescence changes of two tryptophan residues, as well as pAT changes of two carboxylic add groups at the active site, provided a monitor for a variety of local events at the active site. 

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