Abstract
Extracellular xylan-degrading enzymes (xylanase I, xylanase II and β-xylosidase) were purified as electrophoretically and isoelectrophoretically homogeneous proteins from the culture broth of Penicillium expansum O-385-10 concerning the spoilage of apple fruit. The molecular weights of xylanase I, xylanase II and β-xylosidase were 21.0, 40.0 and 91.0 kDa, respectively. The pIs of xylanase I, xylanase II and β-xylosidase were 9.20, 4.30 and 4.20, respectively. Xylanase I produced xylose and several xylooligosaccharides from xylan. On the other hand, xylanase II mainly produced xylose and xylobiose from an early stage of the reaction, and oligosaccharides over xylotriose were almost absent. In the presence of K+ ion, the activity of xylanase I increased almost two-fold, while the activity of xylanase II decreased to about 80%. When xylanase I and II were simultaneously incubated with apple fruit, reducing sugar was hardly liberated from the fruit tissue, but the tissue was significantly affected by adding β-xylosidase to this incubation mixture, and a large amount of the sugar was liberated.
