Characterization and mode of action of xylanases ␁and some accessory enzymes

Three endo-(l,4)-β-D-xylanases; (Endo I, Endo II, and Endo III), a (1,4)-β-xylosidase and an (1,4)-β-D-arabinoxylan arabinofuranohydrolase (AXH) were purified from a culture filtrate produced by Aspergillus awamori CMI 142717. In addition to these enzymes, an acetyl xylan esterase (AE) was purified from a culture filtrate produced by Aspergillus niger DS 16813.The enzymes were characterized by determining specific activities, molecular weight, isoelectric point, kinetic parameters (K m ,V max ), optimum pH and optimum temperature.Arabinoxylan oligosaccharides were derived from alkali-extracted wheat arabinoxylans by complete digestion with Endo I and III. The structures of unknown oligosaccharides were elucidated by 1H-n.m.r. spectroscopy. From these structures a model was proposed for the mode of action of Endo I and Endo III towards arabinoxylans. The same oligosaccharides were also used to specify the action of (1,4)-β-xylosidase, AXH and two α-L-arabinofuranosidases towards these arabinofuranosylated arabinoxylan oligosaccharides.The interaction between the purified enzymes was studied by degradation of xylans from rice bran, oat spelt, wheat-flour, larchwood, and birchwood by single and combined actions of these enzymes on these substrates. The cooperativity was monitored by the amount of reducing sugars and by the types of products released