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PubMed1993

A study of embolizing materials for chemo-embolization therapy of hepatocellular carcinoma: effects of chitin concentration on cis-diamminedichloroplatinum(II) albumin microsphere properties and antitumor effect in VX2 hepatocellular carcinoma model rabbits.

cis-Diamminedichloroplatinum(II) (CDDP) albumin microspheres were prepared with various chitin concentrations and microsphere CDDP contents, specific surface area, surface structure and other microsphere properties. CDDP release in vitro and the antitumor effect in VX2 tumor model rabbits were investigated. CDDP content was increased as the concentration of chitin increased; at a chitin concentration of 6.0% it was about 2 times that without chitin. Specific surface area also increased with chitin concentration. CDDP release rate from various microspheres in vitro was suppressed as chitin concentration increased. Thus, microsphere properties, especially surface structure, are affected by an increase in chitin concentration. In experiments in vivo, various microspheres were injected into the hepatic artery of VX2 hepatocellular carcinoma model rabbits, and the effects of the chitin concentration on the time course of blood platinum (Pt) level and the antitumor effect were assessed. The blood Pt concentration increased with increase in chitin concentration, with a maximum of 0.45 microgram/ml at a concentration of 6.0%, even 7 d following microsphere administration. Tumor growth was suppressed when the chitin concentration was increased. Tissue Pt concentrations also increased in the presence of chitin. These findings suggest that increasing the chitin concentration might promote microsphere decomposition and hence CDDP release in vivo, thus improving immunopotentiating activity and resulting in enhanced CDDP antitumor effect. The detailed mechanisms of the action, however remains to be studied.

Albumins↗
PubMed2005

Synthase III-dependent chitin is bound to different acceptors depending on location on the cell wall of budding yeast.

In yeast, chitin is laid down at three locations: a ring at the mother-bud neck, the primary septum and, after cytokinesis, the cell wall of the daughter cell. Some of the chitin is free and the remainder attached to beta(1-3)glucan or beta(1-6)glucan. We recently reported that the chitin ring contributes to the prevention of growth at the mother-bud neck and hypothesized that this inhibition is achieved by a preferential binding of chitin to beta(1-3)glucan at that site. Here, we devised a novel strategy for the analysis of chitin cross-links in [14C]glucosamine-labeled cell walls, involving solubilization in water of alkali-treated walls by carboxymethylation. Intact cell walls or their digestion products with beta(1-3)glucanase or beta(1-6)glucanase were carboxymethylated and fractionated on size columns, and the percentage of chitin bound to different polysaccharides was calculated. Chitin dispersed in the wall was labeled in maturing unbudded cells and that of the ring in early budding cells. The former was mostly attached to beta(1-6)glucan and the latter to beta(1-3)glucan. This confirmed our hypothesis and indicated that the cell has mechanisms to attach chitin, a water-insoluble substance, synthesized here through chitin synthase III, to different acceptors, depending on location. In contrast, most of the chitin synthase II-dependent chitin of the primary septum was free, with the remainder linked to beta(1-3)glucan.

Cell Cycle↗
PubMed1997

A septin-based hierarchy of proteins required for localized deposition of chitin in the Saccharomyces cerevisiae cell wall.

Just before bud emergence, a Saccharomyces cerevisiae cell forms a ring of chitin in its cell wall; this ring remains at the base of the bud as the bud grows and ultimately forms part of the bud scar marking the division site on the mother cell. The chitin ring seems to be formed largely or entirely by chitin synthase III, one of the three known chitin synthases in S. cerevisiae. The chitin ring does not form normally in temperature-sensitive mutants defective in any of four septins, a family of proteins that are constituents of the "neck filaments" that lie immediately subjacent to the plasma membrane in the mother-bud neck. In addition, a synthetic-lethal interaction was found between cdc12-5, a temperature-sensitive septin mutation, and a mutant allele of CHS4, which encodes an activator of chitin synthase III. Two-hybrid analysis revealed no direct interaction between the septins and Chs4p but identified a novel gene, BNI4, whose product interacts both with Chs4p and Cdc10p and with one of the septins, Cdc10p; this analysis also revealed an interaction between Chs4p and Chs3p, the catalytic subunit of chitin synthase III. Bni4p has no known homologues; it contains a predicted coiled-coil domain, but no other recognizable motifs. Deletion of BNI4 is not lethal, but causes delocalization of chitin deposition and aberrant cellular morphology. Overexpression of Bni4p also causes delocalization of chitin deposition and produces a cellular morphology similar to that of septin mutants. Immunolocalization experiments show that Bni4p localizes to a ring at the mother-bud neck that lies predominantly on the mother-cell side (corresponding to the predominant site of chitin deposition). This localization depends on the septins but not on Chs4p or Chs3p. A GFP-Chs4p fusion protein also localizes to a ring at the mother-bud neck on the mother-cell side. This localization is dependent on the septins, Bni4p, and Chs3p. Chs3p, whose normal localization is similar to that of Chs4p, does not localize properly in bni4, chs4, or septin mutant strains or in strains that accumulate excess Bni4p. In contrast, localization of the septins is essentially normal in bni4, chs4, and chs3 mutant strains and in strains that accumulate excess Bni4p. Taken together, these results suggest that the normal localization of chitin synthase III activity is achieved by assembly of a complex in which Chs3p is linked to the septins via Chs4p and Bni4p.

Amino Acid Sequence↗
PubMed1984

The co-ordination of chitosan and chitin synthesis in Mucor rouxii.

Chitin synthetase preparations from cell walls and chitosomes of the fungus Mucor rouxii were tested for their ability to synthesize chitosan when incubated with uridine diphosphate N-acetyl-D-glucosamine in the presence of chitin deacetylase. The most effective chitin synthetase preparation was one dissociated from cell walls with digitonin. The rate of chitosan synthesis by the wall-dissociated chitin synthetase was about three times that of an equivalent amount of cell walls. The chitosan-synthesizing ability of chitosomes was relatively low, but was more than tripled by treatment with digitonin. Presumably, digitonin improves chitosan yields of dissociating chitin synthetase. The dissociated enzyme would produce dispersed chitin chains that could be attacked by chitin deacetylase before they have time to crystallize into microfibrils. The regulation of chitin and chitosan syntheses in vivo may be determined by the organization of chitin synthetase molecules at the cell surface. Those molecules that remain organized as a complex, similar if not identical to that found in chitosomes, would produce mainly chitin. Chitosan would be preferentially produced by chitin synthetase molecules which are dispersed upon reaching the cell surface.

Cell Wall↗
PubMed2006

serpentine and vermiform encode matrix proteins with chitin binding and deacetylation domains that limit tracheal tube length in Drosophila.

Many organs contain epithelial tubes that transport gases or liquids . Proper tube size and shape is crucial for organ function, but the mechanisms controlling tube diameter and length are poorly understood. Recent studies of tracheal (respiratory) tube morphogenesis in Drosophila show that chitin synthesis genes produce an expanding chitin cylinder in the apical (luminal) extracellular matrix (ECM) that coordinates the dilation of the surrounding epithelium . Here, we describe two genes involved in chitin modification, serpentine (serp) and vermiform (verm), mutations in which cause excessively long and tortuous tracheal tubes. The genes encode similar proteins with an LDL-receptor ligand binding motif and chitin binding and deacetylation domains. Both proteins are expressed and secreted during tube expansion and localize throughout the lumen in a chitin-dependent manner. Unlike previously characterized chitin pathway genes, serp and verm are not required for chitin synthesis or secretion but rather for its normal fibrillar structure. The mutations also affect structural properties of another chitinous matrix, epidermal cuticle. Our work demonstrates that chitin and the matrix proteins Serp and Verm limit tube elongation, and it suggests that tube length is controlled independently of diameter by modulating physical properties of the chitin ECM, presumably by N-deacetylation of chitin and conversion to chitosan.

Amidohydrolases↗
PubMed2004

Analysis of the chitin recognition mechanism of cuticle proteins from the soft cuticle of the silkworm, Bombyx mori.

Insect cuticle is composed mainly of chitin, a polymer of N-acetylglucosamine, and chitin-binding cuticle proteins. Four major cuticle proteins, BMCP30, 22, 18, and 17, have been previously identified and purified from the larval cuticle of silkworm, B. mori. We analyzed the chitin-binding activity of BMCP30 by use of chitin-affinity chromatography. The pH optimum for the binding of BMCP30 to chitin is 6.4, which corresponds to hemolymph pH. Competition experiments using chitooligosaccharides suggested that BMCP30 recognizes 4-6 mer of N-acetylglucosamine in chitin fiber as a unit for binding. The comparison of the binding properties of BMCP30 with those of BMCP18 showed that their binding activities to chitin are similar in a standard buffer but that BMCP30 binds to chitin more stably than BMCP18 in the presence of urea. BMCPs possess the RR-1 form of the R&R consensus, about 70 amino acids region conserved widely among cuticle proteins mainly from the soft cuticle of many insect and arthropod species. Analysis of the binding activity using deletion mutants of BMCPs revealed that this type of conserved region also functions as the chitin-binding domain, similarly to the RR-2 region previously shown to confer chitin binding. Thus, the extended R&R consensus is the general chitin-binding domain of cuticle proteins in Arthropoda.

Amino Acid Sequence↗
PubMed2004

The extracellular constitutive production of chitin deacetylase in Metarhizium anisopliae: possible edge to entomopathogenic fungi in the biological control of insect pests.

The possible contribution of extracellular constitutively produced chitin deacetylase by Metarhizium anisopliae in the process of insect pathogenesis has been evaluated. Chitin deacetylase converts chitin, a beta-1,4-linked N-acetylglucosamine polymer, into its deacetylated form chitosan, a glucosamine polymer. When grown in a yeast extract-peptone medium, M. anisopliae constitutively produced the enzymes protease, lipase, and two chitin-metabolizing enzymes, viz. chitin deacetylase (CDA) and chitosanase. Chitinase activity was induced in chitin-containing medium. Staining of 7.5% native polyacrylamide gels at pH 8.9 revealed CDA activity in three bands. SDS-PAGE showed that the apparent molecular masses of the three isoforms were 70, 37, and 26 kDa, respectively. Solubilized melanin (10microg) inhibited chitinase activity, whereas CDA was unaffected. Following germination of M. anisopliae conidia on isolated Helicoverpa armigera, cuticle revealed the presence of chitosan by staining with 3-methyl-2-benzothiazoline hydrazone. Blue patches of chitosan were observed on cuticle, indicating conversion of chitin to chitosan. Hydrolysis of chitin with constitutively produced enzymes of M. anisopliae suggested that CDA along with chitosanase contributed significantly to chitin hydrolysis. Thus, chitin deacetylase was important in initiating pathogenesis of M. anisopliae softening the insect cuticle to aid mycelial penetration. Evaluation of CDA and chitinase activities in other isolates of Metarhizium showed that those strains had low chitinase activity but high CDA activity. Chemical assays of M. anisopliae cell wall composition revealed the presence of chitosan. CDA may have a dual role in modifying the insect cuticular chitin for easy penetration as well as for altering its own cell walls for defense from insect chitinase.

Amidohydrolases↗
PubMed2000

Preparation and solubility in acid and water of partially deacetylated chitins.

Partially deacetylated chitins with different degrees of deacetylation (DD) were prepared by alkaline treatment under homogeneous conditions, and the effect of DD on their solubility was discussed in terms of crystal structure and mode of hydrogen bonding. With an increase in the treatment time, the DD of chitin increased proportionally. The chitin became soluble in dilute acetic acid at the DD of ca. 28% or over and soluble in water at the DD of ca. 49%. The solubility of the partially deacetylated chitins had a close relationship with their crystal structure, crystallinity, and crystal imperfection as well as the glucosamine content. The wide-angle X-ray diffractometry (WAXD) revealed that the chitin with ca. 28% DD retained the crystal structure of alpha-chitin with significantly reduced crystallinity and perfection of the crystallites. The water-soluble chitin of ca. 49% DD had a new crystal structure similar to that of beta-chitin rather than either alpha-chitin or chitosan, suggesting that the homogeneous deacetylation transformed the crystal structure of chitin from the alpha to the beta form. Some hydrogen bonds existing in raw alpha-chitin were found to be missing at a DD of ca. 49%.

Acetylation↗
PubMed2000

Enhancement of rat hypoglossal nerve regeneration by chitin sheet plus gangliosides.

The effects of chitin sheet interposition with and without brain gangliosides on the regeneration of hypoglossal nerve fibres was studied in the rat following resection of a 5mm length of the nerve. At 10 weeks after operation, the number of horseradish peroxidase (HRP)-labelled motor neurones, indicative of the axonal repair process, on the side treated with chitin and gangliosides was higher than on the control side (where 5mm of the nerve was simply resected). The ratios of HRP-positive neurones in the right hypoglossal nucleus (treated side)/left hypoglossal nucleus (intact side) was 0 in the 5mm-resected group, 53% in the chitin-grafted group, 88% in the ganglioside (0.2 microg)-injected group, 90% in the ganglioside (2 microg)-injected group, 91% in the chitin with ganglioside (0.2mg)-injected group, 91% in the chitin with ganglioside (2 microg)-injected group and 85% in the autograft group, respectively. There were significant differences between the 5 mm-resected group and chitin-grafted group, ganglioside-injected group, chitin with ganglioside group and autograft group, and between the chitin-grafted group and ganglioside-injected, chitin with ganglioside and autograft groups (P< 0.005, respectively). Our results indicated that the use of chitin and gangliosides stimulated the regeneration of severed motor nerve fibres. These findings suggest that chitin and gangliosides might be therapeutically useful for treatment of neuronal degeneration.

Animals↗
PubMed2003

Production, properties, and some new applications of chitin and its derivatives.

Chitin is a polysaccharide composed from N-acetyl-D-glucosamine units. It is the second most abundant biopolymer on Earth and found mainly in invertebrates, insects, marine diatoms, algae, fungi, and yeasts. Recent investigations confirm the suitability of chitin and its derivatives in chemistry, biotechnology, medicine, veterinary, dentistry, agriculture, food processing, environmental protection, and textile production. The development of technologies based on the utilization of chitin derivatives is caused by their polyelectrolite properties, the presence of reactive functional groups, gel-forming ability, high adsorption capacity, biodegradability and bacteriostatic, and fungistatic and antitumour influence. Resources of chitin for industrial processing are crustacean shells and fungal mycelia. Fungi contain also chitosan, the product of N-deacetylation of chitin. Traditionally, chitin is isolated from crustacean shells by demineralization with diluted acid and deproteinization in a hot base solution. Furthermore, chitin is converted to chitosan by deacetylation in concentrated NaOH solution. It causes changes in molecular weight and a degree of deacetylation of the product and degradation of nutritionally valuable proteins. Thus, enzymatic procedures for deproteinization of the shells or mold mycelia and for chitin deacetylation were investigated. These studies show that chitin is resistant to enzymatic deacetylation. However, chitin deacetylated partially by chemical treatment can be processed further by deacetylase. Efficiency of enzymatic deproteinization depends on the source of crustacean offal and the process conditions. Mild enzymatic treatment removes about 90% of the protein and carotenoids from shrimp-processing waste, and the carotenoprotein produced is useful for feed supplementation. In contrast, deproteinization of shrimp shells by Alcalase led to the isolation of chitin containing about 4.5% of protein impurities and recovery of protein hydrolysate.

Animals↗
PubMed1991

Chitosomes and chitin synthetase in the asexual life cycle of Mucor rouxii: spores, mycelium and yeast cells.

To help understand the subcellular machinery responsible for cell wall formation in a fungus, we determined the abundance and subcellular distribution of chitin synthetase (chitin synthase, EC 2.4.1.16) and chitosomes in the asexual life cycle of Mucor rouxii. Cell-free extracts of ungerminated sporangiospores, hyphae/mycelium in exponential and stationary phase, and yeast cells were fractionated by isopycnic centrifugation in sucrose density gradients. The total amount of chitin synthetase per cell increased exponentially during aerobic germination of spores. In all developmental stages, the profile of chitin synthetase activity encompassed a broad range of sucrose density (d = 1.12-1.22) with two distinct zones: a low-density chitosome zone (d = approx. 1.12-1.16) and a high-density, mixed-membrane zone (d = approx. 1.16-1.22). Chitosomes were a major reservoir of chitin synthetase in all stages of the life cycle, including ungerminated spores. Two kinds of chitin synthetase profiles were recognized and correlated with the growth state. In nongrowing cells (ungerminated sporangiospores and stationary-phase mycelium), the profile was skewed toward lower densities with a sharp chitosome peak at d = 1.12-1.13. In actively growing cultures (aerobic mycelium or anaerobic yeast cells), the entire profile of chitin synthetase was displaced toward higher densities; the average buoyant density of chitosomes was higher (d = 1.14-1.16), and more chitin synthetase was associated with denser (d = 1.16-1.23) membrane fractions. In all life cycle stages, chitosomal chitin synthetase was almost completely zymogenic. In contrast to the enzyme from spores or from growing cells, samples of chitosomal chitin synthetase from stationary-phase mycelium were unstable and contained a high proportion of larger vesicles in addition to the typical microvesicles. The presence of chitosomes in ungerminated spores indicates that these cells are poised to begin synthesizing somatic (= vegetative) cell walls at the onset of germination. The increased buoyant density of chitosomes in actively growing cultures suggests that the composition of these microvesicles changes significantly as they mobilize chitin synthetase to the cell surface.

Aerobiosis↗
PubMed1997

The properties and localization of Saprolegnia monoica chitin synthase differ from those of other fungi.

The presence of non-fibrillar alpha-chitin in cellulosic fungi (class Oomycetes) poses intriguing questions as to its role, subcellular localization and evolutionary significance. Previous studies reported on the similarity of chitin synthase from Saprolegnia monoica with that of other fungi. The present work describes important dissimilarities. There was no evidence that the chitin synthase of S. monoica was present in small low-density vesicles (chitosomes). Chitin synthase sedimented with membranous components of high specific gravity (sp. gr. 1.177) that could be partially but distinctly separated from membranes harbouring most of the 1,3-beta-glucan synthase in the cell (sp. gr. 1.158). In contrast to other fungi, the chitin synthase from S. monoica was greatly stimulated by digitonin: both membrane-bound and dissociated chitin synthase showed little activity in the absence of digitonin. As in other fungi, the chitin synthase from S. monoica was solubilized by digitonin and remained zymogenic after dissociation. However, unlike the enzyme from other fungi, the solubilized chitin synthase of S. monoica had a lower sedimentation coefficient, was not stimulated by phospholipids and was not inhibited by high concentrations of digitonin. Unlike the enzyme from Mucor rouxii, the solubilized chitin synthase from S. monoica did not bind to a cation exchanger. The enzyme was partially purified by four-step scheme that included sucrose density-gradient centrifugation, a single passage through a strong anion exchanger and two consecutive passages through a weak anion exchanger. The final preparation contained five to seven polypeptide bands that cochromatographed with the chitin synthase activity, some of which may be part of a presumed chitin synthase macromolecular complex.

Chitin Synthase↗
PubMed2004

Survival and cytokinesis of Saccharomyces cerevisiae in the absence of chitin.

Most fungal cell walls are constructed with significant amounts of chitin, a linear polysaccharide that contributes mechanical resistance to the structure. In the yeast Saccharomyces cerevisiae, chitin is synthesized by three different isozymes, each of which has a separate cellular function. In this yeast, the most important role of chitin is in cytokinesis, when a thin primary septum is synthesized by chitin synthase II to separate mother and daughter cells. If no primary septum can be formed, an irregular remedial septum is synthesized, a process that relies on chitin synthase III. It was found that, with osmotic stabilization, S. cerevisiae tolerates a loss of all chitin synthase activities. Chitin-deficient mutants display a cytokinesis defect which leads to the formation of cell chains with incompletely separated cytoplasms. In these mutants septa are formed rarely. The few septa found are bulky structures which contain inclusions of cytoplasm. Nuclear division proceeds under these conditions, demonstrating that there is no cell cycle arrest triggered by a failure to form a septum between mother and daughter cell. A genetic suppressor arises quickly in chitin-deficient mutants, giving rise to the synthesis of chitin-free remedial septa. The suppressed chitin-free mutants grow well without osmotic stabilization and display hyper-resistance against the chitin-synthase inhibitor polyoxin D.

Cell Division↗
PubMed2006

Drosophila Knickkopf and Retroactive are needed for epithelial tube growth and cuticle differentiation through their specific requirement for chitin filament organization.

Precise epithelial tube diameters rely on coordinated cell shape changes and apical membrane enlargement during tube growth. Uniform tube expansion in the developing Drosophila trachea requires the assembly of a transient intraluminal chitin matrix, where chitin forms a broad cable that expands in accordance with lumen diameter growth. Like the chitinous procuticle, the tracheal luminal chitin cable displays a filamentous structure that presumably is important for matrix function. Here, we show that knickkopf (knk) and retroactive (rtv) are two new tube expansion mutants that fail to form filamentous chitin structures, both in the tracheal and cuticular chitin matrices. Mutations in knk and rtv are known to disrupt the embryonic cuticle, and our combined genetic analysis and chemical chitin inhibition experiments support the argument that Knk and Rtv specifically assist in chitin function. We show that Knk is an apical GPI-linked protein that acts at the plasma membrane. Subcellular mislocalization of Knk in previously identified tube expansion mutants that disrupt septate junction (SJ) proteins, further suggest that SJs promote chitinous matrix organization and uniform tube expansion by supporting polarized epithelial protein localization. We propose a model in which Knk and the predicted chitin-binding protein Rtv form membrane complexes essential for epithelial tubulogenesis and cuticle formation through their specific role in directing chitin filament assembly.

Animals↗
PubMed1993

Application of polymeric N-acetyl-D-glucosamine (chitin) to veterinary practice.

The sponge-, cotton-, and flake-type remedies made of chitin (chitin-sponge, chitin-cotton, and chitin-flake, respectively), and non-woven fabric of polyester (NWF) composited with chitin (chitin-NWF) were applied to various types of trauma, abscess, surgical tissue defect and herniorrhaphy in 147 clinical cases including 72 dogs, 38 cows, 33 cats, 2 rabbits, one monkey and one horse. Chitin-sponge was applied in 30 cases as filling agent of surgical tissue defect, and in 25 cases of trauma, 31 cases of abscess as wound dressing or tissue defect filling agent. In 77 out of 86 cases (89.5%), good healing developed. When chitin-sponge was buried in surgical tissue defects due to oncotomy in 20 cases, recurrence of the tumor developed in one case on one month post-operatively, but was not recognized for 3-24 months in 19 cases. Chitin-NWF was applied in 2 cases of trauma and 12 cases of abscess as wound dressing or tissue defect filling agent, 6 cases as filling agent of surgical tissue defect, and 12 cases of umbilical hernia as prosthesis of suture site of hernia ring. In 28 out of 32 cases (87.5%), good healing developed. Chitin-cotton was applied in 8 cases of trauma and 12 cases of abscess as wound dressing or tissue defect filling agent. In 18 out of 20 cases (90.0%), good healing developed. Chitin-flake was applied in 9 cases of trauma as wound dressing or tissue defect filling agent. In 8 out of 9 cases (88.9%), good healing developed. In all cases, no side effects were observed.

Abscess↗
PubMed1979

Localized deposition of chitin on the yeast cell surface in response to mating pheromone.

Treatment of a mating-type Saccharomyces cerevisiae cells with the pheromone alpha-factor (secreted by alpha mating-type cells) induces the synthesis of chitin. Small daughter cells, which start with no detectable chitin, make 3 times more chitin when grown in the presence of alpha-factor than do untreated exponentially growing cells. Budding cells accumulate chitin in the nascent division septum [Cabib, E. & Bowers, B. (1975) J. Bacteriol. 124, 1586), as detected by staining with the fluorescent dye primulin. In the absence of a division septum, alpha-factor-treated cells accumulate chitin in the area of pheromone-stimulated growth. Enzymatic lysis of budding and pheromone-treated cells allows the separation of membrane-bound chitin synthase (UDP-2-acetamido-2-deoxy-D-glucose: chitin 4-beta-acetamidodeoxyglucosyltransferase, EC 2.4.1.16) activity from a dense particulate fraction containing chitin. Chitin synthase activity is associated with both the plasma membrane and small intracellular particles. During pheromone treatment, the levels of chitin synthase in the plasma membrane and in intracellular particle fractions increase 11- and 4-fold, respectively. Although chitin synthase is made as zymogen that requires proteolytic activation, the plasma membrane of pheromone-treated cells shows a significant fraction of preactivated enzyme; intracellular membrane-bound synthase is found exclusively in the zymogen form.

Journal Article↗
PubMed1994

Evolution and multi-functionality of the chitin system.

Chitin, that is, the beta-1, 4 linked polysaccharide of N-acetylglucosamine, is best known as a cell wall component of fungi and as skeletal material of invertebrates. In recent years this simple picture has changed dramatically. Three developments have taken place: the discovery of chitinous tissues in vertebrates, the molecular analysis of the chitin-synthase genes, and the discovery that chitin derivatives play a crucial role in the interaction between higher plants and symbiotic bacteria. In this paper the methods for chitin detection and the current data on the evolution of chitin synthesis are reviewed. In addition, data is summarized which suggest that chitin synthesis may serve roles other than the production of skeletal material. In particular, anecdotal evidence suggests that chitin derivatives may play a role as signals in plant as well as animal development. Two major unresolved questions are identified: 1) Is there historical continuity of all the chitin synthesizing systems in protists, animals and, in particular, the deuterostome animals. 2) Are chitin derivatives actually involved in the development of plants and animals?

Animals↗
PubMed1999

Molecular and biochemical aspects of chitin synthesis inhibition.

Chitin, is a beta-1,4-linked aminopolysacharide homopolymer of GlcNAc that occurs as a glycoprotein in the exoskeleton of arthropods, the cell wall of fungi and in various components of diverse invertebrates. It is synthesized in two different ways: in fungi the chitin synthase enzyme occurs as an inactive zymogen in vesicles called chitosomes and requires proteolytic activation; in arthropods this enzyme is membrane-bound and catalyzes the addition of GlcNAc units to a dolichol carrier. Chitin is degraded by three different chitinases, the endochitinase that degrades chitin into oligosaccharides of differing chain lengths, the exochitinase that degrades oligosaccharides into diacetylchitobiose and chitobiase, which degrades diacetylchitobiose into GlcNAc monomers. Inhibition of chitin synthesis as well as degradation can both result in deleterious effects that are often similar. Chitin synthesis can be blocked during the various steps by a variety of antibiotics, metabolic inhibitors, insect growth regulators, alkaloids and hormone analogs. During the molting process in arthropods, genes are sequentially expressed and repressed by developmental hormones. When these hormones or their analogs are administered temporally out of sequence, it can result in the blocking of cuticle formation, including chitin synthesis. With the advent of biotechnology and the availability of both complementary DNA and antibody probes, it is possible to develop high throughput assays for discovering new chemicals that can block chitin formation. Chitin synthesis inhibitors as well as inhibitors of chitin degradation that produce similar effects are promising agents for controlling insect pests, fungal pathogens and helminthic parasites.

Animals↗