Laboratory of Plant Molecular Biology/Biotechnology, Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins, CO 80523, USA
Corresponding author; phone (970) 491–7224, Fax: (970) 491–0564.
1Present address: Biology Division, Indian Jute Industries Research Association, Calcutta 700 088, India.
Aspergillus terreus (IJIRA 6.2), a common soil microorganism, produces an extracellular β-xylosidase during its growth on wheat bran. The enzyme has been purified 328 fold (with a sp act of 4233 units/mg protein) by chromatography on DEAE-Sephadex A-25, hydroxyapatite, ConA-Sepharose and gel filtration on Sephacryl-S-300. Molecular mass of β-xylosidase by gel filtration was estimated to be about 95,000 and sedimentation coefficient of 5.6S was determined by glycerol density gradient centrifugation. The enzyme displayed maximum activity at pH 5.0 and 40°C; and in the absence of substrate, the β-xylosidase was stable up to 50°C and between pH 4.5 to 6.5. The purified enzyme hydrolysed β-nitrophenyl-β-D-xylopyranoside (PNPX) and xylooligo-saccharides but not xylan, carboxymethyl cellulose or cellobiose. With PNPX as the substrate, the purified β-xylosidase exhibited a Km of 1.0 mM and D(+) xylose served as a competitive inhibitor with a K1, of 10.5 mM.
β-xylosidase, xylan, xylanases, xylose, Aspergillus terreus
