Xylan-degrading enzymes, including β-xylosidase (EC, were induced when was grown at 50 ° in liquid medium containing 0.2% xylan. The intracellular β-xylosidase activity was concentrated and characterized by fast protein liquid chromatography and gel electrophoresis. A zymogram technique was developed to identify β-xylosidase directly on polyacrylamide gels. A single enzyme (168 kDa; pI 4.37) was identified and purified to homogeneity. The consistent detection of a single band on denaturing SDS gels suggested that the enzyme was composed of identical subunits; since the subunit molecular mass was 56 kDa, a trimeric structure is suggested. High activity against -nitrophenyl β--xylopyranoside (pNPX) occurred in the pH range 5.0-9.0 and temperature range 40-60 °. The enzyme was stable at room temperature at pH 6.0-8.0; it had a half-life of 8 h at 65 °, and of 1.5 h at 70 °. The purified enzyme did not exhibit any detectable activity against arabinoxylan, carboxymethylcellulose or -nitrophenyl β--glucopyranoside. The enzyme had a of 0.89 m (pNPX) and was inhibited by -xylose (K 19 m) but not -glucose. The size of the enzyme is in the range reported for the few other bacterial β-xylosidases described, but the acidic nature of the protein and its affinity for the substrate have more in common with some of the monomeric β-xylosidases described in fungi.


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