PURIFICATION AND CHARACTERIZATION OF AN EXTRACELLULAR BETA-GLUCOSIDASE-II WITH HIGH HYDROLYSIS AND TRANSGLUCOSYLATION ACTIVITIES FROM ASPERGILLUS-NIGER

An extracellular beta-glucosidase II (beta-Glu II) has been purified t o homogeneity by column chromatography from Aspergillus niger CCRC 314 94. Its molecular mass was estimated to be 360 kDa by gel filtration a nd 120 kDa by SDS-PAGE. The enzyme has a pI of 4.0 and has optimum act ivity at pH 4.5 and 60 degrees C. The beta-Glu II was completely inhib ited by 5.0 mM Fe2+. Methanol (20%, v/v) activated the enzyme activity at 1.8-fold. V-max values of 10.2 and 464 units/mg were found for p-n itrophenyl beta-D-glucoside (K-m = 2.2 mM) and for cellobiose (K-m = 1 5.4 mM). The enzyme was strongly inhibited by substrates, p-nitropheny l beta-D-glucopyranoside in excess of 7.5 mM and cellobiose in excess of 50 mM, and was competitively inhibited by glucose with a K-i of 5.7 mM. Transglucosylation products of cellotriose, methyl beta-glucoside and ethyl beta-glucoside, were obtained under neutral conditions and in the presence of methanol and ethanol, respectively.