Properties of the exo-1,4-beta-xylosidase of Aspergillus niger 15

Properties of exo-1,4-beta-xylosidase from the fungus Aspergillus niger 15 were investigated. The enzyme was homogeneous during gel filtration, electrophoresis in polyacrylamide gel in the presence and absence of Na dodecyl sulfate, ultracentrifugation and isoelectric focusing. The enzyme had a temperature optimum at 70 degrees, pH optimum 3.8-4.0 for p-nitrophenyl-beta-D-xylopyranoside (p-NPX), was stable at pH 3-8, retained its 100% activity for 1 hour at 50 degrees and 42% activity at 60 degrees. Km was 0.23 mM for p-NPX and 0.67 mM for xylobiose. Xylose was a competitive inhibitor of exo-1,4-beta-xylodidase with Ki = 2.9 mM. The enzyme showed a transglycosilase activity. The aminoacid analysis of exo-1,4-beta-xylosidase showed that the enzyme molecule contained predominantly dicarboxylic and hydrophobic amino acids as well as serine. The enzyme contained no carbohydrates. Its activity was inhibited by p-chloromercury benzoate.