Chitin lysozyme hydrolysis

As shown in Table 2, the xerogels prepared by these methods were hydrolyzed at almost the same rate by hen egg-white lysozyme, and the rate was about 6 times higher than that of crab shell chitin. The hydrolysis rate by lysozyme was slightly inhibited by the presence of 0-acetyl group in chitin xerogel, probably because of the steric hindrance of the 0-acetyl group at Ce for forming an enzyme substrate complex. The increase in the rate of enzymic hydrolysis also proves the formation of the same chitin gel by three independent methods. 

Because 0-acyl chitins appear to be scarcely susceptible to lysozyme, the susceptibility of DBG to Upases has been studied to obtain insight into its biodegradability in vivo. The changes in infrared and X-ray diffraction spectra of the fibers support the slow degradation of DBG by Upases [125,126]. The chemical hydrolysis of DBG to chitin is the most recent way to produce regenerated chitin. 

In one case, a small peptide with enzyme-like capability has been claimed. On the basis of model building and conformation studies, the peptide Glu-Phe-Ala-Ala-Glu-Glu-Phe-Ala-Ser-Phe was synthesized in the hope that the carboxyl groups in the center of the model would act like the carboxyl groups in lysozyme 17). The kinetic data in this article come from assays of cell wall lysis of M. lysodeikticus, chitin hydrolysis, and dextran hydrolysis. All of these assays are turbidimetric. Although details of the assay procedures were not given, the final equilibrium positions are apparently different for the reaction catalyzed by lysozyme and the reaction catalyzed by the decapeptide. Similar peptide models for proteases were made on the basis of empirical rules for predicting polypeptide conformations. These materials had no amidase activity and esterase activity only slightly better than that of histidine 59, 60). 

This enzyme [EC 3.2.1.14] (also referred to as chitodex-trinase, l,4-j8-poly-A-acetylglucosaminidase, and poly-j8-glucosaminidase) catalyzes the hydrolysis of the l,4-j8-linkages of A-acetyl-D-glucosamine polymers of chitin. It should be noted that some chitinases will also display the activity observed with lysozyme [EC 3.2.1.17]. 

It is evident that any detailed mechanism of the catalytic action of lysozyme in the hydrolysis of glycosides would involve the role for proton donors and/or acceptors. The most plausible residues near the cleavage site are Asp-52 and Glu-35. The Asp residue lies in a polar environment, where it is a hydrogen bond acceptor in a complex network of hydrogen bonds. Because of its location, it has virtually a normal pK of 3.5 0.2. At pH 5.0, which is near the optimum pH value of hydrolysis of chitin by lysozyme, Asp-52 is in the ionized form. The Glu residue lies in a nonpolar region, has an increased pK, of 6.3 0.2, and would be largely un-ionized at pH 5.0. 

The enzymatic hydrolysis of chitin and chitosan might occur because of the action of chitinases, chitosanases, lysozymes, and cellulases (Shahidi et al., 1999). The products of chitin hydrolysis are of high degree of polymerization... 

Rupley, J.A. 1964. The hydrolysis of chitin by concentrated hydrochloric acid, and the preparation of low-molecular substrate for lysozyme. Biochem. Biophys. Acta 83, 245-255. 

The biodegradability of chitin and chitosan is mainly due to their susceptibility to enzymatic hydrolysis by lysozyme, a non-specific proteolytic enzyme present in all tissues of the human body. Lipase, an enzyme present in the saliva and in human gastric and pancreatic fluids, can also degrade chitosan [142]. The products of the enzymatic degradation of chitosan are non-toxic. The degree of acetylation, the molecular weight, the pH and even the method of preparation of chitosan affect biodegradation. 

Molecular mass determination by MS is also useful for analysis of substrate specificities and cleavage patterns of enzymes, including chitinases, chitosanases, lysozymes, and chitin deacety-lases, as summarized with a few representative examples in Table 11.4. Continuous infusion of reaction mixtures into an ESI mass spectrometer (so called real time monitoring) was nsed to analyze the hydrolysis of D (z = 4 - 6) by several chitosanases and some mutants (Dennhart et al. 2008). ESl-MS is also snitable for simnltaneous measurement of individual kinetic constants of enzymes in mixtures of substrates, as reported for a bacterial sulfotransferase with A (z = 2 - 5) (Pi and Leary 2004). 

Maeda, R., Matsumoto, M., Kondo, K. 1997. Enzymatic hydrolysis reaction of water-soluble chitin derivatives with egg white lysozyme. Journal of Fermentation and Bioengineering 84 478 79. 

The action of lysozyme on the hydrolysis of chitin and chito-oligosaccharides which contain 2-amino-2-deoxy-D-glucosyl residues has been reported. ... 

The effect of A-unsubstitution in chitin and chitin oligosaccharides on the hydrolysis of these carbohydrates by hen egg-white lysozyme has been studied. A series of oligosaccharide substrates was derived from partially deacetylated chitin by the action of the enzyme. The results of digestion of the isolated oligosaccharides with lysozyme, together with the structural features... 

The concept of TSAS was further proven to be vahd by the following experiments. Chi-oxa monomer was subjected to polymerization by enzymatic catalysis. The hydrolysis enzymes used were chitinase (family 18) involving an oxazohnium intermediate and lysozyme involving an oxocarbenium ion intermediate (Fig. 13). With the former enzyme, synthetic chitin was quantitatively obtained after 50 h at pH 10.6, whereas with the latter no chitin was produced after 165 h of reaction [69]. This imphes that the oxazoline monomer could not be a substrate for the lysozyme enzyme. 

Fig. 13 An oxocarbenium ion intermediate involved in the hydrolysis of chitin by lysozyme or chitinase (Family 19)...

The opaque chitosan gel was treated with acetic anhydride in an aqueous methanol solution at room temperature overnight, and a transparent gel was obtained. The gel was indistinguishable from chitin gel prepared from chitosan by N-acetylation in aqueous acetic methanol on the basis of its IR and CP/MAS-NMR spectra, on the hydrolysis rate by lysozyme... 

The bacterial cell wall peptidomurein is hydrolyzed by hen egg-white lysozyme [53] to give di-, tetra-, and octasaccharides by the specific hydrolysis of the glycosidic bond of A -acetyl-D-muramic acid [53]. Lysozyme will also hydrolyze the P-1 4 GlcNAc bond of chitin, but at a much lower rate. There are specific chitinases that will also hydrolyze chitin to give chitobiose and chitodex-trins. 

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