Xylans oligosaccharides

Xyloisosaccharinic acid [2,4-dihydroxy-2-(hydroxymethyl)butanoic acid] is one of the major, alkaline-degradation products of wood xylan, in particular, that of birch. The disaccharide, 2-O-D-xylopyranosyl-L-arabinose, which was isolated as a hydrolysis product of corn-cob hemicellulose, is readily degraded at 100° in 15 mM Ca(OH)2 to acidic products, primarily saccharinic acids. Xylan oligosaccharides from corn-cob hemicellulose produced 2,4-dihydroxy-2-(hydroxymethyl)buta-noic acid when exposed to 0.02 M Ca(OH)2 at 25°. However, it was noted that the xylan, itself, was stable at 100° in Af NaOH. The major acidic component of the hemicellulose fraction of slash pine Pinus el-liotti) after acid hydrolysis was identified as 4-O-methyl-D-glucuronic... 

Pentosan polysulfate (1 —> 4)-/3-linked xylan oligosaccharide that is branched in the center with a single /3-(l — 2)-4-O-methyl-ct-D-glucuronate residue... 

Enzyme preparation Origin of enzyme Source of xylan Oligosaccharide structure M (degrees) References... 

Many isolated catalytic domains are less stable than the holoenzyme from which they are derived, and indeed CBM 22 was first identified as a thermo-stabilizing domain, rather than by its true function of enthalpy-driven binding of xylan and xylan oligosaccharides." ... 

Wheat bran extract containing arabino-xylan-oligosaccharides FISH 0, 2.2 or 4.8 g/day for 21 days Double-blind, controlled, crossover Bifidobacteria at highest dose AXOS Maki et al. ... 

Maki KC, Gibson GR, Dickmann RS, et al. Digestive and physiologic effects of a wheat bran extract, arabino-xylan-oligosaccharide, in breakfast cereal. Nutrition. 2012 28 1115—1121. 

Xylan oligosaccharides coupled to BSA gave rise to antisera with higher affinity for both isolated antigens (in ELISA) and polymeric hemicellulosics on fibres. This is exemplified in Figures 4a and 4c for anti-MeGlcAXyla and anti-xylan antibody in the labelling of xylan on birch fibres. 

Xylans as true homopolymers occur in seaweeds of the Palmariales and Nemaliales, however, their backbone consists of Xylp residues linked by -(1 3) (Type X3, Fig. la) or mixed -(1 3, 1 -> 4)-glycosidic linkages (Type Xmy Fig. lb). They are assumed mainly to have a structural function in the cell-wall architecture, but a reserve function cannot be ruled out [4]. From the microfibrils of green algae (Siphonales) such as Caulerpa and Bryop-sis sp., X3 was isolated and the structure confirmed by methylation analysis, C-NMR spectroscopy [7], as well as by mass spectrometry of enzymically released linear oligosaccharides up to a degree of polymerization (DP) of... 

The heteroxylans (CHX) present in cereals, seeds, gum exudates, and mucilages are structurally more complex [6]. They have a (1 4)-)0-d-xylopyranose backbone decorated, except of the single uronic acid and arabinosyl residues with various mono- and oligoglycosyl side chains. Reinvestigations of CHX isolated from corn bran [52] have confirmed that the xylan backbone is heavily substituted (at both positions 2 and 3) with y0-D-Xylp, y0-L-Ara/, of-D-GlcpA residues and oligosaccharide side chains (1), (3) and (4). 

Xylo-oligosaccharides. Samples of X4 through X7 of 98% purity or better and of X3 and X9 of 90% or better were prepared by acidic hydrolysis of larchwood xylan and preparative chromatography, as previously described (i). 

Xylanases from A. niger with unusual hydrolysis specificities were recently reported (54), and five xylanases were isolated and purified. Xylanase 1 attacked soluble larchwood arabinoglucuronoxylan and xylose oligosaccharides of DP > 3, to mainly Xyl2 and xylose, but was inactive towards an insoluble xylan fraction (larchwood) prepared by dissolving the aforementioned xylan in water and separating the undissolved fraction... 

The specificity of a xylanase preparation may be determined from the isolation and characterization of oligosaccharides formed from xylan hydrolysis. While the oligosaccharides released were mainly dependent on the specificity of the xylanase, the complex structure of the heteroxylan also determines the extent of hydrolysis and the site of cleavage. Two types of xylooligosaccharides are usually produced acidic (from glucuronoxylans) and neutral (from arabino- and arabinoglucurono-xylans). The specificity of the action of several purified xylanases on various heteroxylans is shown below ... 

The xylanolytic enzyme system of Trichoderma reesei, a well-known producer of cellulolytic enzymes, is versatile and well suited for the total hydrolysis of different xylans. It consists of two major, specific and several non-specific xylanases, at least one / -xylosidase, a-arabinosidase and a-glucuronidase and at least two acetyl esterases. The hydrolysis of polymeric xylans starts by the action of endoxylanases. The side-groupcleaving enzymes have their highest activities towards soluble, short xylo-oligosaccharides, and make the substituted oligosaccharides again accessible for xylanases and / -xylosidase. 

Table IV. Enzymatic Hydrolysis of the High-Molecular Fraction of Steamed Birchwood Xylan. The substrate was fractionated by ultrafiltration prior to hydrolysis to remove impurities and the 1-5 DP oligosaccharides. Substrate concentration 10 gl— 1, initial pH 5, temperature 45°C, hydrolysis time 24 h...

Before discussing the various derivatives that have been used, it should be remembered that oligosaccharides are often obtained by chromatography on paper or on cellulose columns, and this may cause them to become contaminated by xylan this may be eliminated by extraction of the crude fractions with hot ethanol.474 For similar reasons, glucose that is really extraneous may be detected in fractions separated by electrophoresis on cellulose acetate.475 Gas-liquid chromatography was used to show the presence in pituitary glyco-... 

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