Abstract

An extracellular xylanase from Aspergillus niger C3486 grown on a medium containing D-xylose was purified to homogeneity as indicated by disc acrylamide gel electrophoresis with an apparent molecular mass of about 25 kDa using DEAE-Sephadex A-50 and Sephadex G-100 column chromatography. The xylanase was purified 14.79 fold with 29.88% recovery. Optimal temperature and pH for activity was observed at 55°C and 5.5, respectively. The extracellular purified xylanase had K_m value and V_max of 0.104 mg/ml and 24.8 μmol min^-1 mg^-1, respectively. The metal ions Hg²⁺ and Cu²⁺ showed some inhibition effects, while Mg²⁺ and Cr³⁺ had small stimulating effects on the activity. The xylanase only showed activity on the xylan, and the zymogram analysis indicated that this enzyme was an active xylanase. N-terminal amino acid sequence analysis indicated that the first 18 amino acid residues of N-terminal sequence of the enzyme were PVLVSRSAGINYVQNYNG. Enzyme modification showed that tryptophan was in the active site of the enzyme.

Key words: Aspergillus niger C3486, xylanase, purification, characterization.