Arabino- xylans structure

Fig. 3 Primary structure of (L-arabino)-4-0-methyl-D-glucurono-D-xylan (AGX)...

Fig. 5 Primary structure of water-soluble L-arabino-D-xylan (AX)...

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 ... 

Unlike starch or cellulose, BSG hemicellulose has a complex structure, which is still present, in part, on its autohydrolysis products. Oligosaccharides from BSG hydrolysis consist mainly of branched arabino-xylo-glucurono oligosaccharides that are not highly acetylated when compared to other xylans, such as from Eucalyptus wood (31). The action of several enzymatic activities including endo-l,4-P-xylanase P-xylosidase and accessory activities such as acetyl xylanesterase, a-glucuronidase, and a-arabino-furanosidase is therefore required for the complete hydrolysis of OCL to monosaccharides. 

Kg. 24. Partial chemical structure of some hemicelluloses A — 0-acetyl-(4-0-methyl-glucurono)xylan from hardwood B = arabino-(4-0-methylglucurono)xylan from softwood C = 0-acetyl-galactoglucomannan D = arabinogalactan from larch wood (138). 

The gibberellic acid-induced biosynthesis and release of cell-wall degrading e/jrfo-D-xylanase by isolated aleurone layers of barley have been studied. Studies on the D-xylanase system of Streptomyces species have included a study of the action of the enzyme on various o-xylans and D-xylo-oligosaccharides. The isolation and structural identification of arabino-D-xylo-oligosaccharides arising from action of the enzyme on corn cob arabino-D-xylan were reported. Mutant strains of Trichoderma viride not producing D-xylanase have been induced and isolated with the aid of nystatin selection. ... 

The precise location of the 0-acetyl substituents within the (arabino-)xylo-oligosaccharides has not been established yet. To our knowledge only few publications reported the presence of O-acetyl substituents in xylans from grasses (38,39) and is it for the first time that O-acetyl substituents are presented to occur in xylan-fragments obtained from cereals. A reason to explain the fact that the O-acetyl substituents are overseen in general can be that studies regarding the structural features of xylans normally include alkali-extractions to... 

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