Reaction pathways of substrate degradation by an acidic endo-1,4-beta-xylanase of Aspergillus niger.
An acidic endo-1,4-beta-xylanase (1,4-beta-D-xylan xylanohydrolase, EC 3.2.1.8) of Aspergillus niger catalyzes degradation of linear 1,4-beta-xylooligosaccharides by multiple reaction pathways analogous to those catalyzed by lysozyme and alpha-amylases. Quantitative product analysis of enzyme-substrate mixtures using 1-3H-reducing end-labeled xylooligosaccharides and [U-14C]xylotriose led to the following conclusions: (1) bond cleavage frequencies of xylotriose, xylotetraose and xylopentaose are strongly dependent on substrate concentration; (2) at relatively low concentration of the oligosaccharides the enzyme catalyzes transglycosylic reactions leading to products larger than the substrates; (3) xylobiose and to a low extent also xylose, are utilized as glycosyl acceptors in the transfer reactions; (4) the enzyme-glycosyl intermediates effective in the transfer reactions are formed only from the non-reducing part of oligosaccharides, since no evidence was obtained for condensation of two molecules of oligosaccharides; (5) the enzyme does not catalyze degradation of xylobiose and aryl beta-xylosides at an appreciable rate.
D001234:Aspergillus niger / Q000201:enzymology; D004187:Disaccharides / Q000378:metabolism; D043364:Endo-1,4-beta Xylanases; D006026:Glycoside Hydrolases / Q000378:metabolism*; D006027:Glycosides / Q000378:metabolism; D007526:Isoelectric Point; D007700:Kinetics; D013379:Substrate Specificity
D004187:Disaccharides; D006027:Glycosides; C010807:xylosides; D006026:Glycoside Hydrolases; D043364:Endo-1,4-beta Xylanases; C004173:xylobiose