Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Avenida Bandeirantes 3900, Ribeirão Preto, SP 14040-901, Brazil.
World J Microbiol Biotechnol. 2012 Nov;28(11):3179-86. doi: 10.1007/s11274-012-1128-9. Epub 2012 Jul 25.
Aspergillus ochraceus, a thermotolerant fungus isolated in Brazil from decomposing materials, produced an extracellular β-xylosidase that was purified using DEAE-cellulose ion exchange chromatography, Sephadex G-100 and Biogel P-60 gel filtration. β-xylosidase is a glycoprotein (39 % carbohydrate content) and has a molecular mass of 137 kDa by SDS-PAGE, with optimal temperature and pH at 70 °C and 3.0-5.5, respectively. β-xylosidase was stable in acidic pH (3.0-6.0) and 70 °C for 1 h. The enzyme was activated by 5 mM MnCl₂ (28 %) and MgCl₂ (20 %) salts. The β-xylosidase produced by A. ochraceus preferentially hydrolyzed p-nitrophenyl-β-D-xylopyranoside, exhibiting apparent K(m) and V(max) values of 0.66 mM and 39 U (mg protein)⁻¹ respectively, and to a lesser extent p-nitrophenyl-β-D-glucopyranoside. The enzyme was able to hydrolyze xylan from different sources, suggesting a novel β-D-xylosidase that degrades xylan. HPLC analysis revealed xylans of different compositions which allowed explaining the differences in specificity observed by β-xylosidase. TLC confirmed the capacity of the enzyme in hydrolyzing xylan and larger xylo-oligosaccharides, as xylopentaose.
土曲霉，一种在巴西从分解材料中分离出来的耐热真菌，产生了一种细胞外β-木糖苷酶，该酶通过 DEAE-纤维素离子交换层析、Sephadex G-100 和 Biogel P-60 凝胶过滤进行纯化。β-木糖苷酶是一种糖蛋白（39%的碳水化合物含量），SDS-PAGE 显示其分子量为 137 kDa，最适温度和 pH 值分别为 70°C 和 3.0-5.5。β-木糖苷酶在酸性 pH（3.0-6.0）和 70°C 下稳定 1 小时。该酶被 5 mM MnCl₂（28%）和 MgCl₂（20%）盐激活。土曲霉产生的β-木糖苷酶优先水解对硝基苯基-β-D-木吡喃糖苷，表现出明显的 K(m)和 V(max)值分别为 0.66 mM 和 39 U（mg 蛋白）⁻¹，对 p-硝基苯基-β-D-葡萄糖苷的水解作用较小。该酶能够水解来自不同来源的木聚糖，表明存在一种新型的β-D-木糖苷酶，可降解木聚糖。HPLC 分析显示了不同组成的木聚糖，这可以解释β-木糖苷酶观察到的特异性差异。TLC 证实了该酶水解木聚糖和较大的木二糖的能力，如木五糖。
