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

An intracellular beta-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 degrees C. The purified beta-xylosidase is fully stable at pH 6.0-8.0 and temperatures up to 50 degrees C and retained over 58% of its activity after 1 h at 60 degrees C. The enzyme hydrolyzes beta-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 K-m and V-max values from p-nitrophenyl beta-D-xylopyranoside are 1.1 mM and 114 mu mol 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 beta-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. (c) 2006 Elsevier Ltd. All rights reserved.