Purification and characterization of endoxylanase Xln-2 from Aspergillus niger B03

An extracellular multiple form of endoxylanase was isolated from the xylanolytic complex of Aspergillus niger B03. The enzyme was purified to a homogenous form using ultrafiltration, anion exchange chromatography, and gel filtration. It was a nonglycosylated protein with a molecular weight of 20,000 Da as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and 21,000 Da as determined by gel filtration. The optimal pH for the enzyme action was 5.0 and the optimal temperature was 55 °C. Endoxylanase stability was significantly improved in the presence of glycerol and sorbitol. The enzyme activity was activated by Mn^2+ and Co^2+, and it was inhibited by Ag^+, Cu^2+, Fe^3+, Fe^2+, and Pb^2+. The substrate specificity and the product profile of the enzyme suggested that it was an endoxylanase. The enzyme showed a synergism with another endoxylanase from Aspergillus niger B03 in xylan hydrolysis.