Xylan‐Degrading Enzymes of the Yeast Cryptococcus albidus

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.

Cell Wall Reactive Proteins in the Coat and Wall of Maize Pollen

“…Activities of the various enzyme preparations on 0.15 mg of p-nitrophenyl ␤-D-glucopyranoside (4-NPG; Sigma) were assayed in 0.3 ml of 0.05 M sodium acetate, pH 5.2, at 30°C. The reaction was terminated by the addition of 0.6 ml of 4% (w/v) Na 2 CO 3 (16), and the absorbance of the reaction mixture was read at 410 nm with a spectrophotometer.…”

Spencermartinsiella silvicola sp. nov., a yeast species isolated from rotting wood

“…The xylanases were assayed according to Biely et al (1980) with a few modifications, as suggested by Lara et al (2014). The reducing sugars released were determined using the dinitrosalicylic acid method, i.e.…”

Synthesis and Hydrolysis of 1,3‐β‐Xylosidic Linkages by Endo‐1,4‐β‐xylanase of Cryptococcus albidus

“…It will certainly be of interest to examine isomeric xylooligosaccharides for ability to induce the xylan-degrading enzyme system of the studied yeast because they undergo much slower enzymic degradation than the best natural inducers, 1,4-P-xylobiose and 1,4-P-xyIotriose [31]. There are several examples in the literature of effective induction of glycanases by positional isomers of natural oligosaccharide substrates and products [32-371. …”

“…The specificity could result from the fact that the binding sites of these enzymes consist of several subsites displaced on both sides from the catalytic groups [lo, 131. We expected that this was also true for endo-I ,4-p-xylanase of Cryptococcus albidus catalyzing transfer reactions at high concentrations of 1,4-8-xylooligosaccharides or aryl p-xylosides [14,15]. However, during chromatographic isolation of the main transfer products of phenyl [h-xylopyranoside degradation, identified as 1,4-~-xylooligosaccharides, we observed that the reaction mixture also contained small amount of xylooligosaccharides different from the 1,4-fi-linked products [16].…”