Effect of N‐Acyl Substitution at Glucosamine Residues on Lysozyme‐Catalyzed Hydrolysis of Cell‐Wall Peptidoglycan and its Oligosaccharides

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Abstract
The effect of N‐substitution with various acyl groups at glucosamine residues on lysozyme‐catalyzed hydrolysis of cell wall peptidoglycan and its oligosaccharides was studied.The lysozyme‐resistant cell wall peptidoglycan from Bacillus cereus, N‐unsubstituted at most of its glucosamine residues, was N‐acylated and used as substrate for lysozyme. The N‐acetylated, N‐formylated, N‐propionylated and N‐butyrylated preparations of the peptidoglycan were hydrolyzed by lysozyme with relative maximum rates of 1.00, 0.05, 0.38 and 0.10 respectively, and with apparent Km values, expressed in disaccharide unit concentration, of 0.1, 0.6, 2.4 and 10 mM respectively, whereas the N‐succinylated preparation was unsusceptible to this enzyme.Peptidoglycan oligosaccharides, GlcN‐MurAc‐GlcNAc‐MurAc, GlcNAc‐MurAc‐GlcN‐MurAc‐GlcNAc‐MurAc and GlcN‐MurAc‐GlcN‐MurAc‐GlcNAc‐MurAc, were also N‐acylated to be examined as substrates for lysozyme. The N‐acetylated, N‐formylated, N‐propionylated and N‐butyrylated preparations from the tetrasaccharide were hydrolyzed at 0.5 mM with relative rates of 1.00, 0.04, 0.1 and 0.01 respectively, but the N‐succinylated tetrasaccharide was unaffected by lysozyme. The N‐formylated, N‐propionylated, N‐butyrylated and N‐succinylated preparations from the former hexasaccharide were hydrolyzed with relative rates of 1.5, 22, 1.6 and 0.8 respectively, as compared to the value of about 2000 for the N‐acetylated hexasaccharide. The N‐acylated preparations from the latter hexasaccharide, except the N‐succinylated one, were hydrolyzed at rates similar to those of hydrolysis of the corresponding preparations from the former hexasaccharide.The above results seem to be accounted for by the predominant importance of the alkyl moieties of the N‐acyl substituents on the glucosamine residues located in subsite C in the enzyme‐substrate complexes.

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