Purification and characterization of β-xylosidase from Thermoascus sp.

A β-xylosidase was purified from the culture filtrate of the thermophilic fungus Thermoascus sp. by ultrafiltration, ethanol precipitation, and chromatography with DEAE-Toyopearl 650M, Mono Q $\text{HR5}\text{5}$, and Phenyl Superose $\text{HR5}\text{5}$. The purified β-xylosidase was found to be homogeneous on sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Its molecular weight was estimated to be 107 kDA by gel filtration chromatography (Superdex 200 HR) and 100 kDa by SDS-PAGE. The optimum activity of the enzyme was observed at pH 4.5 and 55°C. The enzyme was stable up to 60°C at pH 4.5 for 1 h. The enzyme exhibited hydrolytic activity on phenyl β-d-xyloside and xylan (birch wood). Fifteen of the amino acid residues in the amino terminal region of the Thermoascus sp. β-xylosidase were homologous with residues in the equivalent region of the maturation protein β-glucosidase from Aspergillus aculeatus.