Xylan-hydrolysing enzymes of the yeast Pichia stipitis

Two xylanolytic enzymes, xylanase and β-xylosidase from the yeast Pichia stipitis were purified to homogeneity and characterized. Both enzymes are secreted into the culture medium upon growth on xylan. The xylanase is a glycoprotein with an approximate molecular mass of 43 kDa. The N-linked carbohydrate content was estimated to be 26% by endoglycosidase H digestion. The β-xylosidase protein has a molecular mass of 37 kDa as determined by sodium dodecyl sulphate gel electrophoresis. Synthesis of xylanase was found to be inducible by xylan and repressible by xylose and glucose. By contrast, β-xylosidase is synthesized constitutively to a considerable degree. The purified β-xylosidase is able to hydrolyse aryl-β-D-glucosides with an even higher rate than β-xylosides. Thus, this enzyme may not be a specific component of the xylan-degrading system of P. stipitis.