The Modes of Action of Three Xylanases from Mesophilic Fungus Strain Y-94 on Xylooligosaccharides

Abstract

The modes of action of three thermostable endo-xylanases (Xn-A, Xn-B, and Xn-C) from the mesophilic fungus strain Y-94 on Xylooligosaccharides and their alditols (DP 2-8) were studied. Non of the enzymes could hydrolyse xylobiose. Oligosaccharides upwards from xylotetraose were immediately hydrolysed by the endo-xylanases, but xylotriose was slowly hydrolysed. Xn-A hydrolysed xylotriose more slowly than the other two. From the dependency of the molecular activity (ko) on the chain length of the substrates, it was suggested that the three xylanases had the same subsite size (5 xylose units). Analysis of the frequency distribution of bond cleavage of oligosaccharide-alditols showed that no enzymes could attack the first bond from the non-reducing end of oligosaccharides. The other bonds were hydrolysed by these enzymes by endo-type action. The action pattern for xylopentaitol suggested that the catalytic site was located between the second and third subsite from the non-reducing end, since the substrate was mainly hydrolysed to xylobiose and xylotriitol.