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Chitin
About: Chitin is a research topic. Over the lifetime, 6590 publications have been published within this topic receiving 253993 citations.
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131 citations
TL;DR: Both residues were needed for cleavage, and polymers containing equal proportions of acetylated and non-acetylated sugars were optimal for chitosanase activity, which strongly indicated that P. islandicum chitOSanase cleaved chitan between N- acetylglucosamine and glucosamine.
Abstract: Penicillium islandicum produced an inducible extracellular chitosanase when grown on chitosan. Large-scale production of the enzyme was obtained using Rhizopus rhizopodiformis hyphae as substrate. Chitosanase was purified 38-fold to homogeneity by ammonium sulphate fractionation and sequential chromatography on DEAE-Biogel A, Biogel P60 and hydroxyl-apatite. Crude enzyme was unstable at 370C, but was stabilized by 1·0 mm-Ca2+. The pH optimum for activity was broad and dependent on the solubility of the chitosan substrate. Various physical and chemical properties of the purified enzyme were determined.
Penicillium islandicum chitosanase cleaved chitosan in an endo-splitting manner with maximal activity on polymers of 30 to 60% acetylation. No activity was found on chitin (100% acetylated chitosan) or trimers and tetramers of N-acetylglucosamine. The latter two oligomers and all small oligomers of glucosamine inhibited the activity of chitosanase on 30% acetylated chitosan. The pentamer of N-acetylglucosamine and glucosamine oligomers were slowly cleaved by the enzyme. Analysis of the reaction products from 30% acetylated chitosan indicated that the major oligomeric product was a trimer; with 60% acetylated chitosan as substrate a dimer was also found. The new terminal reducing groups produced by chitosanase hydrolysis of 30% acetylated chitosan were reduced by sodium boro[3H]hydride. The new end residues were found to be N-acetylglucosamine. The analyses strongly indicated that P. islandicum chitosanase cleaved chitosan between N-acetylglucosamine and glucosamine. Both residues were needed for cleavage, and polymers containing equal proportions of acetylated and non-acetylated sugars were optimal for chitosanase activity. The products of reaction depended on the degree of acetylation of the polymer.
131 citations
05 Jul 2011
TL;DR: In this paper, the degree of deacetylation of chitin was determined by the proportion of D-glucosamine and N-acetylD-glocosamine units in the polymeric chain.
Abstract: The biopolymer is characterized as either chitin or chitosan according to the degree of deacetylation (DD) which is determined by the proportion of D-glucosamine and N-acetylD-glucosamine. Structurally, chitosan is a straight-chain copolymer composed of D-glucosamine and N-acetyl-D-glucosamine being obtained by the partial deacetylation of chitin. Chitosan is the most abundant basic biopolymer and is structurally similar to cellulose, which is composed of only one monomer of glucose (Fig. 1). Chitosan solubility, biodegradability, reactivity, and adsorption of many substrates depend on the amount of protonated amino groups in the polymeric chain, therefore on the proportion of acetylated and non-acetylated D-glucosamine units. The amino groups (pKa from 6.2 to 7.0) are completely protonated in acids with pKa smaller than 6.2 making chitosan soluble. Chitosan is insoluble in water, organic solvents and aqueous bases and it is soluble after stirring in acids such as acetic, nitric, hydrochloric, perchloric and phosphoric (Guibal, 2004; Kluget al., 1998; Kubota et al., 2000; Kurita, 2006; Anthonsen & Smidsroed, 1995; Rinaudo, 2006; Sankararamakrishnan & Sanghi, 2006).
131 citations
TL;DR: Both the initiation and maintenance of Lectin-mediated adhesion requires continuous protein synthesis; expression of lectin activity is a major priority of these cells and functions under conditions adequate for minimal protein synthesis, but insufficient to support cell growth.
131 citations
TL;DR: LPMOs are copper-dependent enzymes that, with glycoside hydrolases, participate in the degradation of recalcitrant carbohydrate polymers, and their activity and structural underpinnings provide insights into biological mechanisms of polysaccharide degradation.
Abstract: Natural carbohydrate polymers such as starch, cellulose, and chitin provide renewable alternatives to fossil fuels as a source for fuels and materials. As such, there is considerable interest in their conversion for industrial purposes, which is evidenced by the established and emerging markets for products derived from these natural polymers. In many cases, this is achieved via industrial processes that use enzymes to break down carbohydrates to monomer sugars. One of the major challenges facing large-scale industrial applications utilizing natural carbohydrate polymers is rooted in the fact that naturally occurring forms of starch, cellulose, and chitin can have tightly packed organizations of polymer chains with low hydration levels, giving rise to crystalline structures that are highly recalcitrant to enzymatic degradation. The topic of this review is oxidative cleavage of carbohydrate polymers by lytic polysaccharide mono-oxygenases (LPMOs). LPMOs are copper-dependent enzymes (EC 1.14.99.53−56) that,...
131 citations