Lysozyme catalyzation

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. 

Thus, investigation of the kinetics of lysozyme-catalyzed lysis of bacterial cell walls has shown that the presence of an organic solvent decreased the overall reaction rate reversibly with the rados of the maximum rate constant of lysis in water and in mixed solvent given by... 

Observations carried out on lysozyme in mixed solvents as a function of temperature demonstrate that lysozyme-catalyzed lysis can he performed under such abnormal conditions and that the reaction can be quenched at subzero temperatures and resumed by heating. The problem is now to check whether one can obtain an enzyme-substrate complex (in this case lysozyme-oligosaccharide) stabilized at low temperature. Such a complex can be detected by differential absorption spectroscopy. Difference spectra in the UV region (240-320 nm) were recorded. The reference cell contained a solution of lysozyme (1.39 x 10 M) and the sample cell contained a solution of lysozyme at the same concentration plus substrate, here hexa-NAG (1.66 x lO " M). The buffer used is acetate at pH 5 plus organic solvent. Also, difference spectra have been determined in the presence of the small-chain sac-... 

It is possible to obtain a lysozyme-catalyzed lysis of substrates in mixed solvents. There is a partial and reversible inhibition showing that any organic solvent acts as a modifier of the enzyme specific activity. 

Fig. 14. The effect of ionic strength on the pH-rate profile of the lysozyme-catalyzed hydrolysis ofM. lysodeikticus cell walls. As ionic strength increases, the pH optimum shifts toward acidic pH values.

Let us consider the classical secondary kinetic isotope experiments on lysozyme-catalyzed hydrolysis of glycosides. Earlier X-ray work indicated that the enzyme... 

Lysozyme catalyzes the hydrolysis of the polysaccharide component of plant cell walls and synthetic polymers of j8(l — 4)-linked units of A-acetylglucosamine (NAG) (Chapter 1). It is expected from studies on nonenzymatic reactions that one of the intermediates in the hydrolytic reaction is a oxocarbenium ion in which the conformation of the glucopyranose ring changes from a full-chair to a sofa (half-chair) conformation (Chapter 1). The transition state analogue I, in which the lactone ring mimics the carbonium ion-like transition state n, binds tightly to lysozyme = 8.3 X 10 8M.10... 

Lysozyme catalyzes the hydrolysis of a polysaccharide that is the major constituent of the cell wall of certain bacteria. The polymer is formed from /3( 1 —> 4)-linked alternating units of IV-acetylglucosamine (NAG) and N-acetyl-muramic acid (NAM) (Figure 1.25). The solution of the structure of lysozyme... 

Nakamura, F., et al. 1992. Lysozyme-catalyzed degradation properties of the conjugates between chitosans having some deacetylation degrees and methotrexate. Yakuzaigaku 52 59. 

The data shown in Figure 12 indicate that the rate of glucose oxidase released from the hydrogel is directly proportional to the concentration of the protein in the hydrogel, suggesting that lysozyme catalyzed degradation of the hydrogel occurs predominantly by surface erosion process. 

Fig. 6. Proposed reaction mechanisms by which lysozyme catalyzes the cleavage of a polysaccharide substrate. Scheme I is that proposed by Post and Karplus (1986) and indicates the possibility of cleavage with no prior assumption of distortion of the sugar ring at site D. Scheme II is that originally developed by Blake, Johnson, Phillips, and co-workers and involves ring distortion as a critical step. (Reproduced with permission from Post and Karplus, 1986.)...

Enzymes are biological catalysts. The enzyme lysozyme catalyzes a process that results in the destruction of the cell walls of many harmful bacteria. This helps to prevent disease in organisms. 

Proposed mechanism for the lysozyme-catalyzed hydrolysis of a cell wall. 

Baneq ee, S.K., Kregar, I., Turk, V., Rupley, J.A. Lysozyme-catalyzed reaction of the N-acetylglucosamine hexasaccharide. Dependence of rate on pH. J. Biol. Ghem. 1973, 248,4786-92. 

Akiyama, K., Kawazu, K., and Kobayashi, A. 1995. A novel method for chemo-enzymatic synthesis of elicitor-active chitosan oligomers and partially Af-acetylated chitin ohgomers using M-acetylated chitotrioses as substrate in a lysozyme-catalyzed transglycosylation reaction system. Carbohydr. Res. 279 151-160. 

Eikeren, P.V. and McLaughin, H. 1977. Analysis of the lysozyme-catalyzed hydrolysis and transglycosyla-tion of N-acetyl-D-glucosamine ohgomers by high-pressure liquid chromatography. Anal. Biochem. 11 513-522. 

Fukamizo, T., Minematsu, T., Yanase, Y, Hayashi, K., and Goto S. 1986a. Substrate size dependence of lysozyme-catalyzed reaction. Arch Biochem. Biophys. 250 312-321. 

Kuhara, S., Ezaki, E., Fukamizo, T., and Hayashi, K. 1982. Estimation of the free energy change of substrate binding lysozyme-catalyzed reactions. J. Biochem. 92 121-127. 

Masaki, A., Fukamizo, T., Otakara, A., Torikata, T., Hayashi, K., and Imoto, T. 1981a. Lysozyme-catalyzed reaction of chitooligosaccharides. J. Biochem. 90 527-533. 

K. Hayashi, Mechanism of Lysozyme Catalyzed Hydrolysis, Tampakushitsu Kakusan Koso 13, 121-128 (1968). 

Proteins are drawn in a variety of ways to illnstrate different aspects of their structure. Figure 28.12 illustrates three different representations of the protein lysozyme, an enzyme found in both plants and animals. Lysozyme catalyzes the hydrolysis of bonds in bacterial cell walls, weakening them, often causing the bacteria to burst. 

Redox catalysts can be stabilized by encapsulation during silica sol-gel formation [33-35], in which the conductivity of the silica matrix is achieved by coimmobilization of a conductive material, such as carbon nanotubes (CNTs). The cationic protein lysozyme catalyzes and templates the formation of silica directly onto a conductive carbon paper electrode. Inclusion of CNT and glucose oxidase (GOx) into the reaction mixture results in a catalytic composite that becomes encapsulated as the silica forms [36]. 

For example, in 2008, Ivnitski et al. used the N/C ratio to confirm entrapment of GOx in a silica-CNT composite obtained through lysozyme-catalyzed synthesis of silica on a Toray carbon paper electrode [26]. For samples containing both GOx and lysozyme, the N/C ratio of 0.11 was very close to that of GOx alone, indicating that the majority of enzyme detected by XPS is GOx. By comparison, the ratio in a GOx-free control was much larger (0.24), as would be expected for lysozyme alone. 

Natural catalysts such as ribonuclease A and lysozyme catalyze reactions by using both GA and GB catalysis through transition states TS27 and TS28, respectively, during the course of catalytic reactions. Whether the occurrence of GA and GB catalyses in ribonuclease A-catalyzed reactions is concurrent (TS27) or stepwise is still a topic of debate. But the essence of catalysis, i.e., involvement of both GA and GB catalyses is almost certain. 

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