PURIFICATION AND CHARACTERIZATION OF 3 ENDO-(1,4)-BETA-XYLANASES AND ONE BETA-XYLOSIDASE FROM ASPERGILLUS-AWAMORI

Three endo-(1,4)-beta-xylanases (endo-xylanase I, II, and III) and one beta-D-xyloside xylohydrolase (beta-xylosidase) were purified from a crude culture filtrate of Aspergillus awamori CMI 142717, grown on milled oat straw as carbon source. Aspergillus awamori xylanases differ in some characteristics of known xylanases. The optimum pH for the endo-xylanases were between 4.0 and 5.5 and the optimum temperature between 45-degrees-C and 55-degrees-C; beta-xylosidase was optimal around pH 6.5 and 70-degrees-C. All endo-xylanases were able to degrade xylan to xylobiose and xylotriose. Endo-xylanase I also produced small amounts of xylose. The molecular weights of endo-xylanase I, II, and III were, respectively, 39000, 23000, and 26000. The molecular weight of beta-xylosidase was 110000. The specific activities of endo-xylanase I, II, and III towards water-soluble oat spelts arabinoxylan were, respectively, 69.6 U mg-1, 68.6 U mg-1, and 16.3 U mg-1. The specific activity of beta-xylosidase towards p-nitrophenyl-beta-xylopyranoside was 34.1 U mg-1. The activity of these enzymes was significantly inhibited by Hg2+, Pb2+, and Ag+.