CHARACTERIZATION OF A BETA-XYLOSIDASE FROM ASPERGILLUS-TERREUS (IJIRA-6.2)

Aspergillus terreus (IJIRA 6.2), a common soil microorganism, produces an extracellular beta-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 beta-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 degrees C; and in the absence of substrate, the beta-xylosidase was stable up to 50 degrees 0 and between pH 4.5 to 6.5. The purified enzyme hydrolysed p-nitrophenyl-beta-D-xylopyranoside (PNPX) and xylooligosaccharides but not xylan, carboxymethyl cellulose or cellobiose. With PNPX as the substrate, the purified beta-xylosidase exhibited a Km of 1.0 mM and D(+) xylose served as a competitive inhibitor with a K-1 of 10.5 mM.