The Action of Lysozyme on Partially Deacetylated Chitin

Abstract

The effect of N ‐unsubstitution of chitin and chitin oligosaccharides on their hydrolysis by lysozyme was studied. Lysozyme digests of chitin deacetylated at about 70% of its glucosamine residues were fractionated by gel chromatography, paper chromatography and paper electrophoresis, giving six oligosaccharides with N ‐unsubstituted glucosamine residues, C1–C6, together with the monomer to tetramer of N ‐acetylglucosamine. Oligosaccharides C1, C2 and C3, which accounted individually for about 4–7% of the total glucosamine residues in the isolated saccharides, were identified as GlcNAc‐GlcNAc‐GlcNAc‐GlcN, GlcNAc‐GlcN‐GlcNAc‐GlcNAc and GlcNAc‐GlcN‐GlcNAc‐GlcN, respectively. Oligosaccharide C4, present in a smaller amount, and oligosaccharide C5, present in a very small amount, were identified as GlcNAc‐GlcNAc‐GlcN and GlcN‐GlcNAc‐GlcNAc, respectively. Oligosaccharide C6, accounting for about 7% of the glucosamine residues recovered, was identified as GlcNAc‐GlcN. On further digestion with excess lysozyme, tetrasaccharide C1 yielded small amounts of N ‐acetylglucosamine and GlcNAc‐GlcNAc‐GlcN in addition to major products, (GlcNAc) 2 and GlcNAc‐GlcN. Tetrasaccharide C2 was hydrolyzed by lysozyme into GlcNAc‐GlcN and (GlcNAc) 2 ; tetrasaccharide C3 into GlcNAc‐GlcN alone; trisaccharide C4 into N ‐acetylglucosamine and GlcNAc‐GlcN. In contrast, trisaccharide C5 was shown to be completely resistant to lysozyme. The results of digestion of the isolated oligosaccharides with lysozyme, together with the structural feature of these saccharides, were accounted for by the importance of the N ‐acetyl groups of the N ‐acetylglucosamine residues located on subsites C and E in the enzyme · substrate complexes.