Xylan‐Degrading Enzymes of the Yeast Cryptococcus albidus

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Abstract
During growth on wood β-1,4-xylans the yeast Cryptococcus albidus produced at least two enzymes which convert the polysaccharide to xylose catabolized by the cells. The enzyme almost completely secreted into culture fluid was identified as an endo-1,4-β-xylanase.The function of the extracellular β-xylanase is to hydrolyze xylan to oligosaccharides, mainly to xylobiose and xylotriose, which enter the cell where they are split by the second identified enzyme, a cell-bound β-xylosidase (xylobiase). Aryl β-xylosidase activity detected in the culture fluid was shown to be due to low affinity of β-xylanase for p-nitrophenyl β-D-xylopyranoside. This property of β-xylanase was preserved after purification of the enzyme by chromatography on DEAE-cellulose, CM-Sephadex and Biogel A 1.5 m or Biogel P 100. Purified β-xylanase exhibited certain microheterogeneity after polyacrylamide gel electrophoresis. Both extracellular β-xylanase and intracellular β-xylosidase were produced in much lower amounts by the cells grown on glucose than by the cells grown on xylan. This suggested that they are not produced constitutively. The investigated strain was not able to grow on cellulose and the crude and purified β-xylanase were unable to hydrolyze cellulose or its soluble derivatives.