Structural and morphological diversity of (1-->3)-beta-D-glucans synthesized in vitro by enzymes from Saprolegnia monoïca. Comparison with a corresponding in vitro product from blackberry (Rubus fruticosus).

Detergent extracts of microsomal fractions from Saprolegnia monoïca and blackberry (Rubus fruticosus) cells were incubated with UDP-glucose to yield in vitro (1-->3)-beta-d-glucans. The insoluble products were analyzed by conventional and cryo transmission electron microscopy, X-ray diffraction, and (13)C CP/MAS NMR, and their molecular weights were determined by light scattering experiments. All the products were microfibrillar, but for the detergent extracts from S.

Crab shell chitin whisker reinforced natural rubber nanocomposites. 2. Mechanical behavior.

In a previous work (part 1), nanocomposite materials were obtained using a latex of either unvulcanized or prevulcanized natural rubber as the matrix and a colloidal suspension of crab chitin whiskers as the reinforcing phase. The mechanical behavior of the resulting nanocomposite films was analyzed in both the linear and the nonlinear range in the present study. The effects of the filler and processing technique were evaluated, and the results are discussed based on the knowledge of the structural morphology and swelling behavior reported in our previous work.

Crab shell chitin whisker reinforced natural rubber nanocomposites. 1. Processing and swelling behavior.

Nanocomposite materials were obtained from a colloidal suspension of chitin whiskers as the reinforcing phase and latex of both unvulcanized and prevulcanized natural rubber as the matrix. The chitin whiskers, prepared by acid hydrolysis of chitin from crab shell, consisted of slender parallelepiped rods with an aspect ratio close to 16. After the two aqueous suspensions were mixed and strirred, solid composite films were obtained either by freeze-drying and hot-pressing or by casting and evaporating the preparations.

Chemoenzymatic syntheses of linear and branched hemithiomaltodextrins as potential inhibitors for starch-debranching enzymes.

Oligosaccharides embodying the S-maltosyl-6-thiomaltosyl structure have been readily synthesised by using convergent chemoenzymatic approaches. The key steps for the preparation of these molecules involved: 1) transglycosylation reactions of maltosyl fluorides onto suitable acceptors catalysed by the bacterial transglycosylase, cyclodextrin glycosyltransferase (CGTase), and 2) the SN2-type displacement of a 6-halide from acetylated acceptors by activated 1-thioglycoses. The target molecules, which were obtained in good overall yields, proved to be useful for investigating substrate binding in the active sites of several enzymes that act upon the alpha-1,6-linkage of pullulan and/or amylopectin.

In vitro versus in vivo cellulose microfibrils from plant primary wall synthases: structural differences.

Detergent extracts of microsomal fractions from suspension cultured cells of Rubus fruticosus (blackberry) were tested for their ability to synthesize in vitro sizable quantities of cellulose from UDP-glucose. Both Brij 58 and taurocholate were effective and yielded a substantial percentage of cellulose microfibrils together with (1-->3)-beta-d-glucan (callose). The taurocholate extracts, which did not require the addition of Mg(2+), were the most efficient, yielding roughly 20% of cellulose.

Morphological investigation of nanocomposites from sorbitol plasticized starch and tunicin whiskers.

Nanocomposites were prepared from waxy maize starch plasticized with sorbitol as the matrix and a stable aqueous suspension of tunicin whiskers-an animal cellulose-as the reinforcing phase. The composites were conditioned at different relative humidity levels. The conditioned films were characterized using scanning electron microscopy, differential scanning calorimetry, water uptake experiments, and wide-angle X-ray scattering studies.

Mixed-linkage cellooligosaccharides: a new class of glycoside hydrolase inhibitors.

A new class of inhibitors for beta-D-glycoside hydrolases, in which a single alpha-(1-->4)-glycosidic bond is incorporated into an otherwise all-beta-(1-->4)-linked oligosaccharide, is described. Such mixed beta/alpha-linkage cellooligosaccharides are not transition-state mimics, but instead are capable of utilising binding energy from numerous subsites, spanning either side of the catalytic centre, without the need for substrate distortion. This binding is significant; a mixed alpha/beta-D-tetrasaccharide acts competitively on a number of cellulases, displaying inhibition constants in the range of 40-300 microM.

Thiooligosaccharides as tools for structural biology.

Oligosaccharides in which at least one glycosidic oxygen atom is replaced with a sulfur atom can be routinely synthesized and act as competitive inhibitors of various glycoside hydrolases. Recent studies using both X-ray crystallography and other biophysical techniques provide structural insight into binding, recognition, and the catalytic mechanism of action of these enzymes.

A fucoidan fraction from Ascophyllum nodosum.

A fucoidan fraction was purified from the brown alga Ascophyllum nodosum. The polysaccharide contained L-fucose and sulfate as the only constituents. Combination of methylation analysis, Smith degradation, FTIR and NMR spectroscopy on the native and the de-sulfated polymers demonstrated that the fucoidan consisted of a highly branched core region with primarily alpha-(1-->3)-linked fucosyl residues and a few alpha-(1-->4) linkages.

Dynamic Light Scattering Evidence for a Ligand-Induced Motion between the Two Domains of Glucoamylase G1 of Aspergillus niger with Heterobivalent Substrate Analogues.

Heterobifunctional ligands that bind at the same time to the catalytic domain and to the starch-binding domain of glucoamylase induce a conformational change of the protein, as shown by dynamic light scattering. The ligands consist of acarbose and β-cyclodextrin linked together by oligoethylene glycols of variable length (see the schematic diagram).

Conformational properties of a cycle oligosaccharide: cyclotrikis-(1-->6)-[alphaD-glucopyranosyl-(1-->4)-beta-D-glucopyranosy l].

The title compound is a cyclic oligosaccharide having six glucopyranose residues linked alternatively by alpha-(1-->4) and beta-(1-->6) glycosidic linkages. Like cyclodextrin analogues it is expected to exhibit an internal cavity and to form inclusion complexes with other species. In order to investigate its conformational preferences, an extensive conformational search was carried out using a combination of Metropolis Monte-Carlo (MMC) procedure in the glycosidic torsion angle space and molecular mechanics procedures.

High level production of a cellulase-free xylanase in glucose-limited fed batch cultures of a thermophilic Bacillus strain.

Bacillus sp. strain XE and its mutant derivative strain D3 produce a thermostable xylanase which is suitable for enzymatic bleaching of kraft pulp. Xylanase synthesis was shown to be induced by the soluble products of xylan hydrolysis (xylooligosaccharide) and equally, catabolically-repressed when these oligosaccharides accumulate in the medium.

Gram-scale synthesis of recombinant chitooligosaccharides in Escherichia coli.

Cultivation of Escherichia coli harbouring heterologous genes of oligosaccharide synthesis is presented as a new method for preparing large quantities of high-value oligosaccharides. To test the feasibility of this method, we successfully produced in high yield (up to 2.5 g/L) penta-N-acetyl-chitopentaose (1) and its deacetylated derivative tetra-N-acetyl-chitopentaose (2) by cultivating at high density cells of E.

Design and chemoenzymatic synthesis of thiooligosaccharide inhibitors of 1,3:1,4-beta-D-glucanases.

A successful chemoenzymatic synthesis of oligosaccharides with an interglucosidic sulfur atom as inhibitors of 1,3:1,4-D-glucanases is described. The key compound 3a was synthesized from acetylated 1-thio-beta-laminaribiose 4 and the methyl 4'-O-triflyl-lactoside 5. After de-O-acylation, the tetrasaccharide 3b was used as an acceptor and glucose-1-P as a donor in a phosphorolytic elongation catalysed by cellodextrin phosphorylase from Clostridium thermocellum.

Conformations and flexibility of native and re-natured xanthan in aqueous solutions.

The conformation and flexibility of sonicated 'native' and 're-natured' xanthan have been investigated by size exclusion chromatography (SEC) with coupled multi-angle light scattering and viscosity detectors. 'Native' xanthan (NX) refers to xanthan dissolved in moderate ionic strength aqueous solution, which has not been exposed either to high temperature or very low ionic strength, and 're-natured' xanthan (RX) here refers to xanthan which has been heated above the conformational melting temperature and then recooled. The mass distributions of the NX and RX are virtually identical, implying that the RX does not involve aggregates of, or disassociated fragments of, NX.

Steam explosion of woody hemp chènevotte.

This paper concerns the morphology of hemp woody core cells, investigated by optical and scanning electron microscopy, and the chemical analysis of the hemp cells. Steam explosion was investigated as a pre-treatment step for woody hemp 'chènevotte', with the aim of optimizing the separation and delignification of woody fibres. In this study, we report the results of five experiments performed on 'chènevotte' samples impregnated in acid solution (0.

Changes in wall-bound polysaccharidase activities during the culture cycle of a Rubus fruticosus cell suspension.

Several hydrolytic enzyme activities were detected in the wall of developing cells of Rubus fruticosus in suspension culture. The corresponding substrates of the enzymes are mostly polysaccharide wall constituents, except for chitinase activity. The activities measured when the enzymes were in the free state or wall-bound showed the positive influence of the cell wall micro-environment.

Chemoenzymatic synthesis of 6 omega-S-alpha-D-glucopyranosyl-6 omega-thiomaltooligosaccharides: their binding to Aspergillus niger glucoamylase G1 and its starch-binding domain.

A coupling reaction of cyclodextrin glucosyltransferase (CGTase) with glucose and 6-deoxy-6-iodo-cyclomaltoheptaose (1), in the presence of glucoamylase, followed by acetylation, led to a convenient synthesis of acetylated 6III-deoxy-6III-iodo-maltotriose (2) and 6IV-deoxy-6IV-iodomaltotraose (3). Nucleophilic displacement of the iodine atom of these protected maltotriose and maltotetraose analogs by the activated form of 2,3,4,6-tetra-O-acetyl-1-S- acetyl-1-thio-alpha-D-glucose (4) afforded peracetylated 6III-S-alpha-D-glucopyranosyl-6III-thiomaltotriose (5) and 6IV-S-alpha-D-glucopyranosyl-6IV-thiomaltotetraose (6) in high yield. The interaction of OH-free tetra- and penta-saccharides (7 and 8) with both glucoamylase G1 from Aspergillus niger as well as its isolated starch-binding domain fragment were studied by UV difference spectroscopy.

Conformational analysis of carbohydrates inferred from NMR spectroscopy and molecular modeling. Applications to the behavior of oligo-galactomannan chains.

In both the biological functions and industrial applications of carbohydrates, their conformational behavior along with the dynamic fluctuations that their structures experience are of great significance. The elucidation of the three-dimensional characteristics of carbohydrates and carbohydrate-containing molecules is in general performed by a combination of high-resolution nuclear magnetic resonance (NMR) spectroscopy and molecular modeling. Heteronuclear couplings and nuclear Overhauser effect (NOE) data are major tools for structural determination.

Sucrose analogues modified at position 3: chemoenzymatic synthesis and inhibition studies of dextransucrases.

Conditions for the large-scale (molar) oxidation of sucrose by Agrobacterium tumefaciens were improved, thus leading to homogeneous solutions of 3-ketosucrose in 40% yield. Treatment of this solution with hydroxylamine or methoxylamine afforded the corresponding oximes 3a and 3b (isolated as acetates) in excellent yield. Dissolving-metal reduction of these oximes gave mixtures of amino disaccharides in which the gluco epimer (3-amino-3-deoxysucrose) was predominant.

Rheological study on mixtures of different molecular weight hyaluronates.

The shear flow of hyaluronate solutions prepared from mixtures of hyaluronates with different molecular weights has been studied. This paper shows that prediction of the rheological behaviour of polymer mixtures at a given polymer concentration is possible knowing the intrinsic viscosity of the different mixed samples and the general variation of the specific viscosity versus the overlap parameter C[eta]. These characteristics depend on the total ionic strength in solution and have been determined for three conditions: in 0.

Structural features and biological activity of xyloglucans from suspension-cultured plant cells.

Different xyloglucan (XG) fractions were isolated from Rubus fruticosus cells cultured in suspension. Sequential extraction showed that two distinct xyloglucans existed in the primary walls. The first could be easily extracted in alkali and the second was tightly associated to cellulose.