Abstract
Xylanases are glycoside hydrolases (GH) that degrade β-1,4-xylan, a linear polysaccharide found as hemicellulose in cell wall of plants. Endoxylanase (Endo-1,4-β-xylanase, EC 3.2.1.8) randomly catalyses xylan to produce varying short xylooligosaccharides (XOS). This study aimed to determine the characteristics of a partially purified endoxylanase from Leohumicola incrustata. Enzyme production was carried out using beechwood (BW) xylan, after which the cell-free crude filtrate was concentrated using the ammonium sulphate precipitation method. The hydrolysed products were analysed by thin-layer chromatography (TLC) and zymography. The result showed that the enzyme produced varying smaller-sized linear xylooligosaccharides with Rf values corresponding to those of xylobiose, xylotriose, xylotetraose, xylopentaose, xylohexaose and other higher oligomers. The endoxylanase had a molecular mass of 72 kDa. The enzyme is stable in the presence of K+, Na+, Ca2+, Fe2+, Mg2+, Zn2+, Co2+, pH of 5.0 and temperature of 37oC. However, the activity gradually decreased after 60 min at 50oC and retained over 69% activity after 120 min, while at 60 and 70oC, the enzyme activity sharply decreased (pre-incubation periods). Endoxylanase from L. incrustata is comparable to those of other microorganisms and should be considered an attractive candidate for future industrial applications.
Highlights
Xylan is an essential component of hemicellulosic polysaccharide in cell walls of most plants, making up to 7-12% and 15-30% of the total dry weight in softwood from gymnosperms and hardwood from angiosperms, respectively (Saha, 2003)
Hardwood hemicellulose mainly consists of O-acetyl-L-4-O-methyl-glucuronic acid xylan, e.g., the content of hemicellulose in birchwood is approximately 35% (Chen, 2014; Sakthiselvan et al, 2014)
BW xylan consists of a backbone of p-1,4-linked D-xylopyranose residues, with side chains of 4-O-methylglucuronic acid attached to the C-2 position of xylose and O-acetyl groups at C-2 or C-3 positions (Freixo and De Pinho, 2002)
Summary
Xylan is an essential component of hemicellulosic polysaccharide in cell walls of most plants, making up to 7-12% and 15-30% of the total dry weight in softwood from gymnosperms and hardwood from angiosperms, respectively (Saha, 2003). Endo-1,4-β-xylanase is the most important xylan degrading enzyme, it removes or cleaves the internal glycosidic linkages of the heteroxylan backbone, leading to a decreased degree of polymerisation of the substrate (Corral and Villaseñor-Ortega, 2006). Xylanases belonging to the GH10 family are composed mostly of endo-1,4-β-xylanases with a few endo-1,3-β-xylanases (biose, triose, and tetraose are the primary products, whereas the xylose, pentraose, and other oligosaccharides with more than five xylose units are produced in small quantities). They can hydrolyse cellulose and aryl β-D-cellobiosides. GH11 members are monospecific, as they consist exclusively of an appropriate enzyme that cleaves internal β-1,4-xylosidic linkages only
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