β-Xylosidase from Streptomyces sp. CH7 was purified by fractionation with 40-70% saturation of ammonium sulfate and consecutive chromatography on DEAE Bio-Gel A and Sephadex G-200, respectively. The purified enzyme was about 9.23 folds in specific activity with 29.99% recovery. This enzyme was inhibited by N-ethylmaleimide and 2-mercaptoethanol could reverse the inhibition. The apparent molecular weight of the purified enzyme was 93,000 daltons estimated by SDS-polyacrylamide gel electrophoresis and 183,000 daltons estimated by gel filtration indicating the native enzyme behaved as a dimer of identical subunits. The optimal temperature and pH for the enzyme activity were 55℃ and 6.5, respectively. The enzyme was stable to temperature up to 50℃ and to a broad pH range of 6.0-9.0. The Km values of the enzyme for p-NPX and O-NPX were 0.56 and 0.94 mM, respectively. It was competitively inhibited by D-xylose with Ki value of 40 mM. Metal ions such as Fe2+, Hg+, Cu2+and Zn2+ strongly inhibited the enzyme activity, whereas Mg2+ acted as an activator. The enzyme barely hydrolyzed p-NPAF and xylan substrates and did not exhibit cellulase and glucose-isomerase activities.
