N-Acetyl glucoseamine

Hen egg-white lysozyme catalyzes the hydrolysis of various oligosaccharides, especially those of bacterial cell walls. The elucidation of the X-ray structure of this enzyme by David Phillips and co-workers (Ref. 1) provided the first glimpse of the structure of an enzyme-active site. The determination of the structure of this enzyme with trisaccharide competitive inhibitors and biochemical studies led to a detailed model for lysozyme and its hexa N-acetyl glucoseamine (hexa-NAG) substrate (Fig. 6.1). These studies identified the C-O bond between the D and E residues of the substrate as the bond which is being specifically cleaved by the enzyme and located the residues Glu 37 and Asp 52 as the major catalytic residues. The initial structural studies led to various proposals of how catalysis might take place. Here we consider these proposals and show how to examine their validity by computer modeling approaches. 

The saccharide blocks are obtained by enzymatic (pronase) degradation of ovomucoid extracted from hen egg white followed by column chromatography fractionation and purification Thus two glycoamino acids Oq and Op are obtained. For instance, the (3 fraction (Op) has a molecular weight 3 200 and contains 16 saccharide residues 1 residue of galactose in terminal position, 5 of mannose and 10 of N-acetyl glucoseamine (Fig. 39). 

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