Showing papers on "Chitin published in 1970"

Mechanism of Action of the Antifugal Agent Polyoxin D

Abstract: The antibiotic polyoxin D was shown to inhibit the incorporation of (14)C-glucosamine into cell wall chitin in Neurospora crassa at levels which were comparable with those required for inhibition of fungal growth. At the same time, the antibiotic increased the accumulation of a nucleotide, which was identified as uridine diphosphate (UDP)-N-acetylglucosamine, indicating inhibition of chitin synthesis. Chitin synthetase (UDP-N-acetylglucosamine: chitin N-acetylglucosaminyl transferase, EC 2.4.1.16) of N. crassa was found to be strongly inhibited by polyoxin D, as determined by the transfer of (14)C-N-acetylglucosamine from (14)C-UDP-N-acetylglucosamine to the particulate fraction. The inhibition was competitive with respect to UDP-N-acetylglucosamine and specific for chitin synthetase. The K(i) for polyoxin D in the reaction was 1.40 x 10(-6)m, and the K(m) for UDP-N-acetylglucosamine was 1.43 x 10(-3)m. The formation of osmotically sensitive, protoplast-like structures, when the fungus Cochliobolus miyabeanus was grown in the presence of polyoxin D, also suggested that the primary site of action of polyoxin D was in the formation of cell wall structures.

Chemical Composition of Wild-type and Mutant Aspergillus nidulans Cell Walls. The Nature of Polysaccharide and Melanin Constituents

Abstract: SUMMARY Chitin and a β-linked glucan were the major chemical components of Aspergillus nidulans cell walls. Other monomeric residues identified in enzymic and acid hydrolyses of whole cell walls and cell-wall fractions included galactose, mannose, glucuronic acid and galactosamine. The β-glucan contained (1 → 3) and (1 → 6) linkages and was two-thirds digested by an exo-β-D-1,3 glucanase prepared from a cell-wall lysing Streptomyces species. An α-glucan was identified as a cell-wall component and it also contained (1 → 3) linkages. This latter polysaccharide was distinguishable from nigeran (an α-1,3; α-1,4 glucan present in other Aspergillus species) by infrared spectroscopy and by its low susceptibility to hydrolysis by an endo-α-1,3; α-1,4 glucan glucanohydrolase. Both glucans were alkali-soluble, but the β-glucan was completely solubilized only after acid extraction of the wall. The N-acetylglucosamine to galactosamine ratio in the A. nidulans cell wall was 1.32 and the two hexosamines were shown to be constituents of distinct polymers. The remaining cell wall was accounted for by protein, lipids, readily extractable and bound, and, in the wild-type, melanin. The melanin was distributed throughout the cell wall but was associated particularly with the chitin fraction. The pigment has been partially characterized chemically and contains indolic residues; this result does not substantiate earlier views that indolic melanins are peculiar to the animal kingdom. Melanin appears to be a finite heteropolymer both in terms of its molecular size and its chemistry.

Chemical morphology of glucan and chitin in the cell wall of the yeast phase of Paracoccidioides brasiliensis.

Abstract: Short and thick fibers were observed on the outer surface of the yeast phase of Paracoccidioides brasiliensis, and long and thin fibers were seen on the inner surface The long fibers disappear with chitinase treatment and are composed of chitin The short fibers disappear under alkali treatment and are composed of α-glucan Comparisons with α-(1 → 3)-glucan isolated from Aspergillus niger and Polyporus betulinus and with chitin from fungal origin support our point of view

Chitin and cellulose in the cell walls of the oomycete, Apodachlya sp.

Abstract: Hyphal walls of Apodachlya sp. (Leptomitales) gave a positive reaction when tested cytochemically for chitin. The color reaction indicative of the presence of chitin developed uniformly throughout the walls, but did not appear in the numerous cellulin granules found in this fungus. Chitin and cellulose fractions were prepared from chemically isolated walls and identified by X-ray diffraction.

Structure and Composition of Walls of the Yeast Form of Verticillium albo-atrum

Abstract: SUMMARY: Walls of the yeast form of Verticillium albo-atrum showed a granular appearance on the outer surface. The granular components could be extracted by alkali, revealing a fibrillar wall fabric. A region of circularly oriented microfibrils with a minute central ‘orifice’ was commonly found at one of the cell poles and probably represented a bud scar. The material dissolved by alkali was a heteropolysaccharide-protein complex containing mannose, galactose, glucose, glucuronic acid, glucosamine and the common range of amino acids. The alkali-insoluble microfibrillar network was made of a β-linked glucan and chitin. The glucan was digested by endo-β-glucanases yielding glucose, β-1,3-linked glucose oligomers and cellobiose, but no evidence for cellulose was found. Most of the glucan was also soluble in hot acid. The acid-insoluble glucan (hydroglucan) contained β-1,6-links. Acid treatment produced coarse microfibrils resembling those in Saccharomyces cerevisiae walls treated similarly. The hydroglucan was soluble in alkali leaving an insoluble microfibrillar network composed mainly of chitin. A small amount of lipid (2.7 to 3.4%), mostly of the bound type, and traces of phosphate were also found.

The structure, synthesis and functions of the yeast cell wall—a review

Abstract: Glucan, mannan, chitin, protein, phosphate and lipid are found in the walls of all brewing yeasts so far examined although the contents and composition of each varies, as does the content of wall in the cell. Both glucan and mannan have branched structures and are linked to protein. Chitin is probably also bound to protein and phosphate to mannan. Some of the enzymic activities present in the wall are associated with the mannan-protein fraction. This fraction is located on the outer surface of the wall and appears to play a part in the appearance of flocculence in brewing yeast during fermentation.

Studies on the Mode of Action of Polyoxin D:Part II. Effect of Polyoxin D on the Synthesis of Fungal Cell Wall Chitin

Abstract: In the previous papers we reported that the antibiotic Polyoxin D induced the characteristic swelling of the mycelia of fungi,1,2) and strongly inhibited the incorporation of 14C-glucosamine into the fungal cell wall chitin.3) The present work has been conducted to further investigate the influence of this antibiotic on the fungal cell wall biosynthesis.Polyoxin D did not inhibit the incorporation of 14C-glucose, 14C-amino acids and 14C-sodium acetate into the cell wall. In addition, UDP-N-acetylglucosamine, a precurcor of chitin biosynthesis of cell wall, was accumulated in the Polyoxin D-treated mycelia of Cochliobolus miyabeanus more than 150 to 160% of that accumulated in the untreated one.Chitin synthetase prepared from Piricularia oryzae which is not treated with Polyoxin D was completely inhibited by the addition of 0.1 ppm of Polyoxin D. The fungitoxicity of Polyoxins A to G was positively related to their inhibition of 14C-glucosamine incorporation into the cell wall chitin of C. miyabeanus. From...

Blood sugars in relation to chitin synthesis during cuticle formation in Emerita asiatica

Abstract: Blood sugars of the crustacean Emerita asiatica were studied during the moult cycle to examine their possible role in the synthesis of chitin, which takes place at the time of moulting. Blood sugars occur both in free state as well as bound with proteins, and show quantitative fluctuations in different phases of the moult cycle. The values of sugars were estimated in relation to total blood volume, to obviate the effects o absorption of water and consequent dilution of blood taking place during moulting. The data obtained suggest that the presence of glucosamine only during premoult stage may be due to resorption of chitin preparatory to the shedding of the cuticle. The fluctuations in the protein-bound blood sugars appear significant in the context of the synthesis of chitin, in view of the correlation seen between these and the chitin content. The above suggestion is supported by the observation that they are not involved in the nutritive metabolism of the crustacean. The protein-bound sugars do not appear to undergo further changes in the blood, as may be inferred by the absence of uridine diphosphate, and uridine diphosphate acetylglucosamine compounds, which have been suggested to be the more immediate precursors of chitin during the moult cycle of insects. It is suggested that protein-bound sugars may be transported, as such, to the epidermis, which may be the site of the final steps in chitin synthesis.

The cytochemical localization of lysozyme activity in leucocytes.

Abstract: A method for the cytochemical localization of lysozyme activity has been developed, using chitin as substrate. A homogenous film of substrate is prepared on a microscope slide by precipitation of chitin from a lithium iodide solution. Hydrolysis of the chitin substrate by lysozyme results in breakdown products which stain with Alcian Blue at pH 4. The method permits the cellular localization of lysozyme activity and has been applied to the neutrophils of peripheral blood which are known to be rich in lysozyme.

Studies on the Cell Wall of Piricularia oryzae†: Part II. The Chemical Constituents of the Cell Wall

Abstract: The chemical constituents of the cell wall of Piricularia oryzae, the pathogenic fungus of rice blast disease, were studied with the aids of chemical analysis, X-ray diffraction, infra-red absorption and enzymatic degradation. The sugar constituents were identified by chromatography as glucose (62%), mannose (4%), galactose (0.5%), and hexosamine (13%). The acidic amino acid rich protein was comprised 4.6% in the cell wall. The cell wall consists of at least three different polysaccharide complexes: a) α-Heteropolysaccharide protein complex containing mannose, glucose and galactose, b) β-1,3-Glucan containing β-1, 6-linked branch, c) Chitin like substance.

Chitin and egg-shell prepns for cicatrising wounds

Abstract: Compositions for facilitating the healing of wound: (i) Finely divided chitin, partially depolymerized chitin, a deriv. of chitin, or a mixture of these. (ii) Finely divided egg-shells free of membrane, or a mixture of finely divided egg-shells and finely divided egg-shell membranes. Chitin has cicatrising properties as good as those of cartilage, but is more easily obtainable and of more standardized properties. Egg-shells are also efficacious for cicatrising; egg-shell membranes alone, previously used, are difficult to obtain free of shell.