Enzymatic chitin

The enzymatic chitin synthesis together with the TSAS concept provided with a new way for the synthesis of mucopolysaccharides having N-acetyl group at the 2-position of the sugar unit, which are widely found polysaccharides in nature. Scheme 35 explains that the MeOZO moiety in the monomer... 

Smucker, R. A. 1986. Interpretative model for enzymatic chitin hydrolysis pp. 254-258 in R.A.A. Muzzarelli, C. Jeuniaux and G. W. Gooday, eds. Chitin in Nature and Technology. Plenum Press, New York, London. 

Fungal chitin synthases are found as integral proteins of the plasma membrane and in chitosomes a divalent cation, Mg(II), is necessary for enzyme activity but neither primers nor a hpid intermediate are required. The substrate and free GlcNAc activate the allosteric enzyme. UDP, the byproduct of the enzymatic activity, is strongly inhibitory to chitin synthase however, it may be metabohzed readily to UMP by a diphosphatase. 

In addition, such an increase in enzymatic activity could result from changes in the conformation of the enzymatic molecules due to the high electrostatic activity of chitin (Dunand et al., 2002 Ozeretskovskaya et al., 2002). ft can be proposed that the PO sorption on chitin could not be considered to be a classic ion exchange process because both the anionic and cationic isoforms of the plant POs interact with chitin. Additionally, it contains 3 high anionic POs (3.5, 3.7, 4.0) but only 2 of them (3.5 and 3.7) adsorbed on chitin alongside with some cationic isoforms (Fig. 2). 

Recently, an enzymatic method was reported to recover the three main components of industrial shrimp waste (protein, chitin, and astaxanthin) using treatments with alcalase and pancreatin. The first enzyme was more efficient in increasing the recovery of protein from 57.5 to 64.6% and of astaxanthin from 4.7 to 5.7 mg/lOO g of dry waste. 

The polymerization of 1 mentioned above should be compared with the enzymatic synthesis of chitin reported by Kobayashi and coworkers, in which an oxazoline derivative of A, A -diacetylchitobiose, the repeating unit of chitin was polymerized in the presence of chitinase enzyme via ring-opening addition process to give an artihcial chitin (Scheme 6) [5]. The method using an enzyme, however, may not enable synthesis of nonnatural-type aminopolysaccharide because the reaction catalyzed by chitinase enzyme is limited to the formation of (1 4)-P-glycosidic linkage. 

Waste-treatment processes commonly result in the production of solid wastes that must be disposed of safely. Enzymatic treatment is no exception. For example, although enzymatic treatment may not produce as large a quantity of solid products as does biological treatment, some solid residues may be formed, e.g., the polymer precipitates formed during the treatment of phenols with peroxidases, spent adsorbents such as talc, chitin, or activated carbon that are used to eliminate the soluble products of enzymatic reactions, or residues of plant materials such as raw soybean hulls when they are used in place of purified enzymes during treatment. Perhaps, the polymers and adsorbents could be incinerated to recover some energy if the emission of dangerous combustion by-products can be controlled or prevented. The residues of plant materials could potentially be composted and used as soil conditioners, provided that pollutants do not leach from them at substantial rates. To date, none of these disposal problems have been addressed adequately. 

Muzzarelli RAA (1997) Human enzymatic activities related to the therapeutic administration of chitin derivatives. Cell Mol Life Sci 53 131-140 Muzzarelli RAA, Xia W, Tomasetti M and Ilari P (1995) Depolymerization of chitosan and substituted chitosans with the aid of a wheat germ lipase preparation. Enz Microbial Tech 17 541-545... 

The most important derivative of chitin is chitosan obtained by partial deacetylation of chitin in the solid state under alkaline conditions or by enzymatic hydrolysis in the presence of a chitin deacetylase. The ratio of 2-acetamido-2-deoxy-D-glucopyranose to 2-amino-2-deoxy-D-glucopyra-nose moieties determines the identity of the product, that is, chitin or chitosan [9]. The published methods used for the production of chitosan from chitin are summarized in Table 2.3. 

Enzymatic hydrolysis is a useful method for the preparation of monomers from chitin and chitosan because the yield of monomers is greater by enzymatic hydrolysis than by acid hydrolysis. The enzyme chitin deacetylase hydrolyzes the acetamido group in the N-acetylglucosamine units of chitin and chitosan, thus generating glucosamine imits and acetic acid (Fig. 2.5). 

FIGURE 2.5 Enzymatic hydrolysis of chitin and chitosan into their monomers. 

Chitin is a stable compoimd, incompatible with oxidizing agents [59]. In the solid state imder alkaline condition (e.g., NaOH, KOH, heat at about 120 °C) or by enzymatic hydrolysis in the presence of a chitin deacetylase, it hydrolyses to form the deacetylated degradation product chitosan [6,7,10,11]. It was found that the presence of urea in basic media and at low temperature (—20 °C) had little effect on chitin structure and that urea is of benefit to the stability of chitin solution [38]. 

Chitin was prepared by the catalysis of chitinase. Incubation of a chitobiose oxazoline monomer with chitinase form bacillus sp. in phosphate buffer afforded chitin in quantitative yield (122). Using regiospecific 3-0- and/ or 3 -0-methylated derivatives of a chitobiose oxazoline as new substrate monomers, 3-0-methylated chitin oligomers were produced by enzymatic oligomerization using chitinase (123). 

Sakamoto J, Kobayashi S. Enzymatic synthesis of 3-0-Methylated chitin oligomers from new derivatives of a chitobiose oxazoline. Chem. Lett. 2004 33 698-699. 

Chitin is the most abundant biomacromolecule in the animal field, which is found normally in invertebrates as a structural component. This important polysaccharide was synthesized for the first time by the enzymatic polymerization using chitinase and a chitobiose oxazoline derivative (Scheme 14).131 The latter activated monomer has a distorted structure with an a configuration at Cl, which resembles a transition-state structure of substrate chitin at the active site during a hydrolysis process (Scheme 15).3b 131132 The ring-opening polyaddition of the chitobiose oxazoline derivative was exclusively promoted by chitinase at pH 10.6, where the hydrolytic activity of chitinase was very much lowered. 

Upon enzymatic polymerization to produce the artificial chitin, spherulites of 20—50 fim in diameter were also obtained (Figure 3).133 Platelike single crystals were gradually shaped into ribbons, followed by formation of bundlelike assemblies to grow into spherulites in the polymerization solution. 

Tan, E. W. Y. and Lee, V. R. (2002). Enzymatic Hydrolysis of Prawn Shell Waste for the Purification of Chitin. Final report R D project supervised by Hall GM, Department of chemical Engineering, Loughborough University, UK. 

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