Purification and characterization of a thermostable intracellular β-xylosidase from the thermophilic fungus Sporotrichum thermophile

An intracellular β-xylosidase from the thermophilic fungus Sporotricum thermophile strain ATCC 34628 was purified to homogeneity by Q-Sepharose and Mono-Q column chromatographies. The protein properties correspond to molecular mass and pI values of 45 kDa and 4.2, respectively. The enzyme is optimally active at pH 7.0 and 50 °C. The purified β-xylosidase is fully stable at pH 6.0–8.0 and temperatures up to 50 °C and retained over 58% of its activity after 1 h at 60 °C. The enzyme hydrolyzes β-1,4-linked xylo-oligosaccharides with chain lengths from 2 to 6, releasing xylose from the non-reducing end, but is inactive against xylan substrates. The apparent Km and Vmax values from p-nitrophenyl β-d-xylopyranoside are 1.1 mM and 114 μmol p-nitrophenol min−1 mg−1, respectively. Alcohols inactivate the enzyme, ethanol at 10% (v/v) yields a 30% decrease of its activity. The enzyme is irreversibly inhibited by 2,3-epoxypropyl β-d-xylobioside while alkyl epoxides derived from d-xylose were not inhibitors of the enzyme. The enzyme catalyses the condensation reaction using high donor concentration, up to 60% (w/v) xylose.