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Xylan (/ ˈ z aɪ l æ n /; [3] / ˈ z aɪ l ən / [4]) (CAS number: 9014-63-5) is a type of hemicellulose, a polysaccharide consisting mainly of xylose residues. It is found in plants, in the secondary cell walls of dicots and all cell walls of grasses. [5] Xylan is the third most abundant polysaccharide on Earth, after cellulose and chitin ...
Diverse kinds of hemicelluloses are known. Important examples include xylan, glucuronoxylan, arabinoxylan, glucomannan, and xyloglucan. Hemicelluloses are polysaccharides often associated with cellulose, but with distinct compositions and structures.
As with all xylan, the backbone of arabinoxylan chains is composed of a large number of 1,4-linked β-D-xylopyranosyl units. In arabinoxylan many of these xylose units are 3-linked with single α-L-arabinofuranosyl units and some of these arabinose in turn have ester-linked ferulic acid residues.
Xylose is the main building block for the hemicellulose xylan, which comprises about 30% of some plants (birch for example), far less in others (spruce and pine have about 9% xylan). Xylose is otherwise pervasive, being found in the embryos of most edible plants.
Plant cell overview, showing secondary cell wall. The secondary cell wall has different ratios of constituents compared to the primary wall. An example of this is that secondary wall in wood contains polysaccharides called xylan, whereas the primary wall contains the polysaccharide xyloglucan. The cells fraction in secondary walls is also ...
Molecular structure of an hypothetical xylooligosaccharide, where n is a variable number of xylose units such as xylobiose and xylotriose. Xylooligosaccharides (XOS) are polymers of the sugar xylose. [1] They are produced from the xylan fraction in plant fiber.
[1] [2] In many dicotyledonous plants, it is the most abundant hemicellulose in the primary cell wall. [3] Xyloglucan binds to the surface of cellulose microfibrils and may link them together. It is the substrate of xyloglucan endotransglycosylase , which cuts and ligates xyloglucans, as a means of integrating new xyloglucans into the cell wall.
Endo-1,4-β-xylanase (EC 3.2.1.8, systematic name 4-β-D-xylan xylanohydrolase) is any of a class of enzymes that degrade the linear polysaccharide xylan into xylose, [1] thus breaking down hemicellulose, one of the major components of plant cell walls: Endohydrolysis of (1→4)-β-D-xylosidic linkages in xylans