Chitin

Chitin is a linear biopolymer formed by N-acetyl-D-glucosamine units linked by glycosidic β (1,4) bonds.

From: Journal of Bioresources and Bioproducts, 2022

Chitin

Nidal H. Daraghmeh, ... Adnan A. Badwan, in Profiles of Drug Substances, Excipients and Related Methodology, 2011

3.3.1 Chitin polymorphs and their sources [19,20]

Chitin is isolated from the exoskeletons of crustaceans (e.g., crabs, lobsters, crayfish, shrimp, krill, barnacles), molluscs or invertebrate animals (e.g., squid, octopus, cuttlefish, nautilus, chitons, clams, oysters, scallops, geoducks, mussels, fossils, snails), insects (e.g. ants, scorpions, cockroaches, beetles, spiders, brachiopods), and certain fungi. Commercially, crab and shrimp shells are the major sources of α-chitin, whereas squid is the source of β-chitin. There are three polymorphic forms of chitin: α, β, and γ. They differ in the arrangement of chains in the crystalline phase. The most abundant and stable form is α-chitin, which displays orthorhombic crystals. The crystallographic parameters of α- and β-chitins are shown in Table 2.7. The neighboring sheets in α- and β-chitin are connected by hydrogen bonds via C=O and N–H groups. In addition, each chain has intramolecular hydrogen bonds between the neighboring sugar rings (C=O and OH groups on C-6 and a second hydrogen bond between the OH– group on C-3 and the ring oxygen) (Fig. 2.7). The differences among chitin polymorphs are due to the arrangement of the chains in the crystalline regions. α-Chitin has a structure of antiparallel chains, β-chitin has intra-sheet hydrogen bonding resulting in parallel chains, and γ-chitin, being a combination of α- and β-chitin, has both parallel and antiparallel structures. Because of these differences, each chitin polymorph differs in specific properties. The poor solubility of chitin is a result of the close packing of chains and its strong inter- and intramolecular bonds between the hydroxyl and acetamide groups. However, β-chitin lacks these interchain hydrogen bonds; therefore, it swells readily in water, and it is more prone to N-deacetylation than α-chitin.

Table 2.7. Crystallographic parameters of α- and β-chitins

Compound a (nm) b (nm) c (nm) γ (°) Space group
α-Chitin 0.474 1.886 1.032 90.0 P212121
β-Chitin 0.485 0.926 1.038 97.5 P21

Figure 2.7. Modes of hydrogen bonding in (A) α-chitin: (a) intrachain C(3′) OH⋯OC(5) bond, (b) intrachain C(6′1)OH⋯O=C(71) bond, (c) interchain C(6′1)O⋯HOC(62) bond, and (d) interchain C(21)NH⋯O=C(73); (B) β-chitin: (a) intrachain C(3′)OH⋯OC(5) bond, (b) interchain C(21)NH⋯O=C(73) bond, and C(6′1)OH⋯O=C(73) bond (ac plane projection); (c) interchain C(21)NH⋯O=C(73) bond (ab plane projection).

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CHITIN

ROY L. WHISTLER, in Industrial Gums (Third Edition), 1993

SOURCE

Chitin was first found as a component of mushrooms, and a potential commercial source is the mycelia and spores of fungi such as Chytridiaceae, Blastocladiaceae, and Ascomydes. Mycelia of some species of Penicillium may contain up to 20% chitin. Aspergillus niger, also, represents a sizeable source of chitin.

Chitin sometimes functions in a manner similar to that of collagen in chordates. It forms the tough, fibrous exoskeletons of insects, crustaceans and other athropods,1 and, in addition to its presence in some fungi, it occurs in at least one alga.2,3 It is estimated that over 100 gigatons of chitin are synthesized in the biosphere per annum.

However, the present source of chitin is the shells, or skeletal mantels, of invertebrates, particularly shrimp, crab, and lobster. The name chitin stems from the Greek work for tunic or envelope. Chitin is the most abundant organic constituent in the skeletal material of arthropods, annelids, and mollusks, where it provides skeletal support and body armor.

Modern freezing and canning operations with lobster, crab, and shrimp result in the availability of substantial quantities of crustacean waste materials. These wastes consist mainly of shells and heads that can be processed to yield chitin. Approximately 200,000 tons of shrimps, 35,000 tons of lobsters, and 90,000 tons of crabs are processed in the United States. Some of the catch is shipped alive and other portions are partially cleaned at sea, but most is processed in land installations. Other large sources of shell are available at processing centers in many parts of the world.

The world market for chitin is currently estimated at 1000 to 2000 tons. Japan, with an estimated production of 1.5 million lb (6.8 × 105 kg) per year, is by far the largest user. Europe may use 500,000 lb, whereas the United States appears to use about 150,000 to 200,000 lb (70–90 103 kg), but this estimate may be too high. Prices quoted range from $3.50 to $4.50 per pound for chitin and are $6.50 to $100 per pound for chitosan.

Hard crustacean shells contain 15–20% chitin and as much as 75% calcium carbonate, along with skeletal protein. Softer shelled crustaceans, such as shrimp, contain 15–30% chitin and 13–40% calcium carbonate, plus skeletal protein. Lobster shells contain less calcium carbonate than do hard-shelled crabs, but more than do the shells of shrimp.

Chitin is found throughout the exoskeletons of most insects, where it may be present in amounts ranging up to 60% in special parts such as the flexible portions. The average chitin content in the cuticle of a number of different species is reported to be 33%. The cuticle consists of alternate layers of protein and chitin impregnated with calcium carbonate and pigments and interspersed with polyphenols.

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Chitin

Ephraim Cohen, in Encyclopedia of Insects (Second Edition), 2009

Chitin Degradation

Degradation of chitin is physiologically crucial for normal growth and development of insects. Chitin is degraded by the joint action of chitinase, which yields oligomeric fragments, and exochitinase, or β-N-acetylglucosaminidase, which hydrolyzes terminal polymers or dimers. These hydrolytic enzymes are widespread in plants, vertebrates, invertebrates, and microorganisms. During the complex molting process in arthropods, the chitin in the cuticular region (the endocuticle), which is close to the epidermal cells, is degraded. Since chitin microfibrils are tightly associated with various cuticular proteins, proteolytic activity accompanies and facilitates chitin hydrolysis. Hydrolysis of chitin does not occur in the exocuticle, where sclerotization of the cuticular protein takes place. Formation and secretion of chitinases by epidermal cells, processes that are under hormonal control, are vital for the molting process. The mono- and disaccharide degradation products are absorbed by the epithelial cells and may be recycled to serve for biosynthesis of the new chitin.

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Analysis of Glycans; Polysaccharide Functional Properties

S. Tokura, H. Tamura, in Comprehensive Glycoscience, 2007

2.14.4 Crystalline Structures of Chitin and Chitosan

Chitin, one of the naturally abundant polysaccharides, is thought to be the most prominent natural polymer due to its multifunctions, such as biodegradability, low toxicity in animal body, and enabling accelerated skin recovery. However, some application has been reported owing to its sparingly soluble property in general solvents. Chitosan, on the other hand, has been studied in various practical applications due to additive functions over chitin such as biodegradability, low toxicity and acceleration of fibroblast formation in animal body, acceleration blood clotting, antimicrobial activity, and high solubility against water following the formation of salts with various organic acids and hydrochloric acid. According to the predominant properties of chitosan, a number of reports have been published, including chemical modifications and biomedical applications.

Although chitin, a muco-polysaccharide of natural abundance, is hardly found in plant supporting systems, it is popular in animal support or the tissue of lower evolutions such as crustacean, insects, and mushrooms. The yield of chitin in nature is said to be second to that of cellulose. Chitin is also known to be biodegradable in nature and in animal body due to the close chemical structure of sialic acid which is a component of cell wall supporting materials. Since chitinases are contained in animal self-defense systems against bacterial infections by breaking down the cell wall, chitin is hydrolyzed easily in animal body. N-Acetylglucosamine (GlcNAc), the main product in the hydrolysate, joins the nutrient pathway by Salvage route to recycle GlcNAc for chitin biosynthesis.31 The main function of chitin is acceleration of skin recovery with only a little immunological response.31 The main target of recent research on chitin has been the regeneration under mild conditions for applications to biomedical materials by employing these important functions, although it is tough to find good solvents for chitin.

On the other hand, chitosan, the deacetylated derivative of chitin, exists in small quantities in several mushrooms and is mainly supplied as the chemical product of chitin. The predominant functions of chitosan seem to be the antimicrobial activity and inhibitory function toward chitinases in addition to the acceleration of fibroblast formation in animal body. These functions have been applied for biomedical purposes, in addition to their use in food preservation, due to the high solubility of chitosan into aqueous organic acid solutions and hydrochloric acid aqueous solution, which is a limited solvent for chitosan, among other mineral acid aqueous solutions.

The identification of chitin was studied for more than a century to become clear. The general recognition of the chitin chemical structure and crystalline structure was achieved first in the 1960s. Although the first report of chitin was made by Odier in 1823, when he extracted a residue from insects whose structure was similar to that of plants (‘cellulose’),2 there is a long history of practical applications of chitin and chitosan in biomedical and food technology areas. It took almost 150 years until chitin was considered as one of the naturally abundant polysaccharides. According to the description by Muzzarelli,117 there were many proposals to prove a chemical structure of chitin different from that of cellulose. Lassaigne4 isolated the chitinous exoskeleton of the silkworm, Bombyx mori, by warm potassium hydroxide and demonstrated the presence of nitrogen in chitinous exoskeleton to form potassium cyanide following the treatment of the exoskeleton with potassium hydroxide and potassium hypochloride. Finally, Ledderhose118 found chitin composed of glucosamine and acetic acid which was later confirmed by Gilson.119 The reviews of chitin were established by Von Wieseligh,120 Wester,121 von Westein9, Leven and Lopez-Suarez,122 and Von Franciis123 in the first stage of chitin research, in which they tried to confirm the natural occurrence of chitin in living organisms, the biological degradations, the chemical structure, and somewhat the technology of practical applications. The presence of chitin in fungi or crustacea was identified by Rammelberg12 through its biological hydrolyzates.The presence of chitin susceptible bacteria was reported in various marine sediments and animals by Zobell.13 In 1956, Parchase and Brawn concluded that chitin was a polysaccharide consisting mainly of glucosamine residues following several hydrolytic reactions.14

After the first discovery of chitosan by Rouget,22 its dissolution was studied by Von Furth and Russo24 following the formation of salts with organic acids and precipitation of chitosan by removing acids from alkaline reagents. Lowy124 found that the most insoluble acid salt of chitosan was the sulfate salt in spite of soluble salt with hydrochloric acid.

The chitin molecules were found to be packed tightly by binary hydrogen bonds between the acetamide group at the C-2 position of the GlcNAc residue and the C-6 primary hydroxyl group, and between the acetamide group and the C-3 secondary hydroxyl group. These hydrogen bonds are formed intra- and inter-residually to fix chitin molecules rigidly.

The conformation of chitin was first analyzed to be composed of N-acetylglucosamine (GlcNAc) residues and of the glycosidic linkage between GlcNAc residues (chitobiose). The crystalline form of chitobiose was investigated by X-ray diffraction analysis, because chitobiose was supposed to be the elemental unit to form the chitin crystalline structure.

The crystalline structure of α-chitin prepared from arthropods was reported by Gonell;126 these studies were followed by several investigations.127–130 Polymorphic forms of chitin were proposed to be α-, β-, and γ-chitins. α-Chitin is the most abundant polymorph, except for arthropods in deep seas, because β- and γ-chitins were reported to become α-chitin by physical and chemical treatments.131–133 β-Chitin is extracted from squid pen and reported from arthropods in deep sea. β-Chitin exists in a crystalline hydrate of lower stability than the α-chitin polymorph, since small molecules (e.g., water molecules) penetrate between chains of lattice to induce the hydration of chitin molecules.134 γ-Chitin is found in the cocoons of the beetles Ptinus tectus and Rhynchaenus fangi and has a form in which there are two chains ‘up’ for every one ‘down’.133

The detailed analysis of the α-chitin crystalline structure was achieved by Minke and Blackwell as shown in Figure 12. The unit cell of the chitin crystalline structure is orthorhombic with a = 0.47, b = 1.886, and c (fiber axis) = 1.032 nm with a space group of P212121. The cell contains disaccharide (chitobiose) sections of two chains passing through the center and corner of the ab projection of the unit cell where each chitin chain takes an extended two fold helical conformation (zigzag structure). As shown in Figure 12, the space group chitin molecules are arranged in an antiparallel fashion due to the space group of P212121. The direction of the center and corner chains of the unit cell is opposite along the c-axis.135

Figure 12. Proposed crystalline structures of α-chitin (left-hand side) and of β-chitin (right-hand side). From Gardner and Blackwell.138

On the analysis of the β-chitin crystal structure, found in squid pen, pogonophore tubes and spines of several diatoms were investigated by Lotmar136 and followed by Dweltz.137 In 1975, Gardner and Blackwell proposed the results of the X-ray diffraction analysis of the β-chitin crystalline structure as shown in Figure 12.138 According to the report, the unit cell is monoclinic with a = 0.845, b = 0.926, c (fiber axis) = 1.038, and γ = 97.5o. The conformation of the chitin chain is an extended twofold helix similar to that of α-chitin. However, the chitin molecules with β-form are packed in a parallel fashion, with a unit cell packed with only one chitin chain. The chains form hydrogen-bonded sheets along the a-axis with no hydrogen bonds between sheets along the b-axis, quite a different structure from that of α-chitin. The swelling of β-chitin has been reported to form hydrogel by mechanical agitation of β-chitin in water and the slurry was composed of β-form. But the nonwoven fabrics from β-chitin hydrogel were shown to be of α-form.139

The natural occurrence of chitosan is limited to several organisms including Mycelia and sporangiophore of Phycomyces blakesleeanus.129 There have also been only a few investigations of the chitosan crystalline structure. The first report on chitosan hydrated crystalline structure was made by Clark and Smith (1936).128 Okuyama et al. (1971)140 reported that four chitosan chains and eight water molecules were packed in an orthorhombic unit cell with the following dimensions: a = 0.894, b = 1.697, c (fiber axis) = 1.034 nm, and a space group P212121. However, the crystalline structure of chitosan is likely to analyze the specific function of chitin, because various conformations are expected due to the distribution of an acetamide group among amino groups of glucosamine residue, such as random and block distributions with various degrees of deacetylation.

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Biochemistry of Glycoconjugate Glycans; Carbohydrate-Mediated Interactions

A.B. Boraston, ... D.W. Abbott, in Comprehensive Glycoscience, 2007

3.29.4.2.1 Chitin structure

Chitin is the second most abundant organic polymer in nature. It consists of repeating subunits of N-acetylglucosamine (GlcNAc) linked through β1-4 glycosidic bonds (Figure 6). Chitin is primarily found in fungal cell walls and the exoskeletons of arthropods, and is notably absent from plants and vertebrates. The tensile strength of this insoluble polysaccharide results from intermolecular hydrogen bonding between chains of GlcNAc orientated in either a parallel or antiparallel fashion. Chitinases, enzymes invovled in chitin degradation, are found in diverse organisms such as viruses, bacteria, plants, and humans. The structure–function relationship of CBMs in this process will be described below.

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Carbohydrate Bioengineering

H. Schrempf, in Progress in Biotechnology, 1995

1 INTRODUCTION

Chitin, a polymer of N-acetyl-D-glucosamine, is highly abundant in nature, since it is present in the exoskeleton of insects, in mollusca, coelenterata, nematodes, protozoa and the cell walls of certain fungi. Naturally occurring chitins vary in the length of their chains which are stabilized by hydrogen bridges to a highly ordered crystalline structure. Chitin is frequently associated with proteins and may be stabilized by additional inorganic compounds. The natural annual production is judged to amount to 108 tons. Thus, apart from cellulose, it constitutes the second most abundant polysaccharide in nature [14]. Chitin can be hydrolyzed by enzymes produced by plants, fungi, and bacteria.

Gram-positive streptomycetes are highly abundant in soil and known as important antibiotic producers. Though nearly all Streptomyces species have been shown to be chitinolytic, and chitin has been successfully used to enrich predominantly streptomycetes from soil [11], relatively few studies on chitinolytic enzymes have been performed. Streptomyces olivaceoviridis was identified as the most efficient degrader of crystalline chitin [1]. Recently, five chitinases (20.5 kDa, 30 kDa, 47 kDa, 70 kDa and 92 kDa) from S. olivaceoviridis have been purified to homogeneity [17].

Many extracellular hydrolases produced by bacteria consist of two or more domains. Most details are known about the catalytic and the binding domains of cellulases (CBDs). Proteins predicted from different bacterial chitinase genes showed in various cases an architecture of several domains, and comparisons of the deduced aminoacids allowed the identification of the individual catalytic domains [23, 2]. With the help of biochemical and genetic data, chitin-binding domains could be identified within chitinases from Bacillus circulans [24].

We succeeded in analysing the catalytic and binding characteristics of an overproduced exochitinase and a novel lectin-like chitin-binding protein from S. olivaceoviridis as well as their corresponding chitin-inducible genes.

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Role of psychrotrophic bacteria and cold-active enzymes in composting methods adopted in cold regions

Vivek Manyapu, ... Rakshak Kumar, in Advances in Applied Microbiology, 2022

4.5 Chitin degradation by chitinases

Chitin is a very significant structural part of the fungal cell wall, which also makes up the exoskeletons of insects and crustaceans (Javed et al., 2013). Chitin and cellulose have many similarities chemically. N-acetylglucosamine is the monomer of chitin, whereas glucose is the monomer of cellulose. There are two allomorphic types of chitin: α-chitin and β-chitin. The packing and polarity of neighboring chains in the following sheets differ between these two types of chitin (Bussink, Speijer, Aerts, & Boot, 2007). Exoenzymes break down chitin to N-acetylglucosamine, which is then reabsorbed, converted to fructose-6-P, and therefore included in the metabolism of carbohydrates. Chitin is broken down into N-acetylglucosamine and monosaccharides in two separate processes chitinases and chitobiases. Chitin is first broken down into chitin oligosaccharides by chitinases (Suginta, Robertson, Austin, Fry, & Fothergill-Gilmore, 2000). Endochitinases and exo-chitinases are the two primary categories of chitinases. Sahai and Manocha (1993) defined that the endo-chitinases cleave chitin internally, which results in the formation of soluble and low molecular mass GlcNAc multimers such as chitotetraose and chitotriose as well as the dimer di-cetylchitobiose. The exo-chitinases, N-aceyl-β-1,4-glucosaminidases (EC 3.2.1.30), which create monomers of GlcNAc and Chitobiosidases (E.C. 3.2.1.29) by cleaving the oligomeric byproducts of endochitinases and chitobiosidases (Agrawal & Kotasthane, 2012) are included in the progressive release of di-acetylchitobiose from the non-reducing end of the chitin fibers (Sahai & Manocha, 1993). Chitinase enzyme is also the most crucial enzyme in composting process.

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Enzyme-aimed extraction of bioactive compounds from crustaceans by-products

Luis A. Cabanillas-Bojórquez, ... J. Basilio Heredia, in Value-Addition in Food Products and Processing Through Enzyme Technology, 2022

2.1 Chitin

Chitin is the second natural polysaccharide most abundant globally; the chemical structure of chitin is β-(1  4)-N-acetyl-d-glucosamine (Schmitz et al., 2019). Chitin is found in different sources such as insects and crustaceans (shrimps, crabs) by-products; in this sense, diverse extraction methods for chitin have been studied (Marzieh et al., 2019). In crustaceans, chitin is linked with proteins and reinforced with salts; thus, several steps must be carried out to obtain high purity (Pachapur et al., 2016). The conventional method for chitin is a chemical treatment with high concentrations of acid and basic solutions, which results in environmental problems; therefore, alternative methods for chitin extraction have been studied (Marzieh et al., 2019). Enzyme-assisted extraction has been reported to be a promising technique for obtaining chitin from crustacean by-products because the enzymatic process separates chitin from proteins and minerals efficiently and protects the molecule from phytochemical changes; additionally, this process is an eco-friendly method (Doan et al., 2019; Guo et al., 2019; Marzieh et al., 2019; Arnold et al., 2020).

Shrimp by-products such as head, cephalothorax, and shells are a rich source of chitin. Several reports show different chitin extraction methods, like the widely used enzymatic processes (Pachapur et al., 2016; Paul et al., 2015; Valdez-Peña et al., 2010). Different enzymes have been studied to extract chitin (Tables 24.1). Synowiecki and Al-Khateeb (2000) demonstrated that alcalase effectively extracts chitin from Shrimp (Crangon crangon) shells with less degradation than conventional extraction. Also, Manni et al. (2010) reported that enzymatic process with microorganism protease such as Bacillus cereus SV1 (crude protease) produces chitin with an acetylation degree similar to commercial chitin from shrimp (Metapenaeus monoceros) shells. On the other hand, Valdez-Peña et al. (2010) studied the chitin extraction from shrimp heads by different enzymes, and they found that the treatment with alcalase was the most effective for chitin extraction. Likewise, optimized enzyme chitin extraction from shrimp shells (M. monoceros) as well as tiger shrimp (P. monodon) shells was studied by Younes et al. (2012) and Paul et al. (2015), respectively. They found that an enzyme (Bacillus mojavensis A21 crude protease)/substrate ratio of 7.75 U/mg, incubated for 6 h at 60°C and pH 8.82, followed by agitation 100.98 rpm at 50.05°C were the best conditions to obtain a chitin yield of 18.5%–20% from shrimp shells, and a chitin yield of 62.06%–77.23% as well as acetylation degree of 80.34%–82.25% from tiger shrimp shells.

Table 24.1. Chitin and chitosan extracted by enzymes from crustaceans' by-products.

Crustacean by-product Enzymatic extraction process Chitin acetylation degree (DA), chitosan deacetylation degree (DDA), and yield Identification technique References
Shrimp (Crangon crangon) shells Alcalase DA = 88.9% FTIR Synowiecki and Al-Khateeb (2000)
Shrimp (Metapenaeus monoceros) shells Bacillus cereus SV1 crude protease DA = 89.6% and yield = 16.55 ± 1.5% NMR Manni et al. (2010)
Shrimp (Litopenaeus vannamei) heads Alcalase, papain, trypsin Yield = 22% FTIR Valdez-Peña et al. (2010)
Shrimp (M. monoceros) shells Bacillus mojavensis A21 crude protease DDA = 96% and yield = 18.5–20.0%, NMR Younes et al. (2012)
Shrimp (Penaeus longirostris) cephalothorax Barbel (Barbus callensis) viscera crude protease DA = 85%, DDA = 85%, and yield = 17.24 ± 0.87 NMR Sila et al. (2014a)
Shrimp (M. monoceros) shells Bacillus mojavensis A21 and gray triggerfish (Balistes capriscus) crude protease DA = 91% and DDA = 80% NMR Younes et al. (2014)
Tiger shrimp (Penaeus monodon) shells Crude and commercial protease Yield = 62.06–77.23% and DA = 80.34–82.25% FTIR Paul et al. (2015)
Shrimp (L. vannamei) shells Streptomyces griseus protease DA = 90.83–92.67% NMR Hongkulsup et al. (2016)
Crab, shrimp, prawn, krill, and lobster shells Bacillus licheniformis NRS-1264 and Bacillus subtilis B-59994 proteases DDA = 71–81% FTIR Pachapur et al. (2016)
Shrimp (Penaeus merguiensis) shells Pseudomonas aeruginosa, Serratia marcescens, and Bacillus pumilus crude proteases DDA = 86% FTIR Sedaghat et al. (2016)
Shrimp (L. vannamei) shells Trichoderma harzianum and Mucor circinelloides proteases Yield = 88.9% FTIR Deng et al. (2020)

FTIR, Fourier transform infrared; NMR, Nuclear magnetic resonance.

On the other hand, Younes et al. (2014) found that a mixture of microorganisms and viscera proteases improves the quality of the extracted chitin until an acetylation degree (91%) similar to chitin obtained by alkaline treatment (84%). Similarly, Sila et al. (2014a) found that crude protease from barbel (Barbus callensis) viscera was studied on shrimp (Penaeus longirostris) cephalothorax producing chitin with high yield and degree of acetylation. Also, Hongkulsup et al. (2016) reported that the use of commercial protease (Streptomyces griseus) treatment from shrimp (Litopenaeus vannamei) shells produced chitin with high quality (acetylation degree of 90.83%–92.67%) than chitin obtained by chemical treatment (acetylation degree of 81.47 ± 0.70%).

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Biochemistry and Molecular Biology

K.J. Kramer, S. Muthukrishnan, in Comprehensive Molecular Insect Science, 2005

4.3.4.9 Other Possible Enzymes of Chitin Metabolism

Chitin deacetylases and chitosanases are two other enzymes that play major roles in chitin catabolism in other types of organisms. Chitin deacetylase catalyzes the removal of acetyl groups from chitin. This enzyme is widely distributed in microorganisms and may have a role in cell wall biosynthesis and in counteracting plant defenses (Tsigos et al., 2000). There is one report of an insect chitin deacetylase in physogastric queens of the termite Macrotermetes estherae (Sundara Rajulu et al., 1982). However, there have been no follow-up studies about this enzyme in other insect species. To our knowledge, there are no reports of chitosanases present in insects.

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Cuticle

J.F.V. Vincent, in Encyclopedia of Materials: Science and Technology, 2001

9 Pesticides

Since chitin is almost diagnostic of arthropods (otherwise it occurs only in fungi) it makes an easy target for pesticides. In the late 1960s a Dutch firm, Duphar, stumbled upon a chemical (later named Dimilin) effectively made from two herbicide molecules which totally inhibited the polymerization of chitin. It has been followed by other pesticides with similar action (Binnington and Retnakaran 1991). Fed to developing insects it stops the proper development of the cuticle, so that the newly emerging insect bursts as it swallows air to expand itself to its new size for the next stage in its life.

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