title: A xylose-tolerant beta-xylosidase from Paecilomyces thermophila: characterization and its co-action with the endogenous xylanase.
abstract: An extracellular beta-xylosidase from the thermophilic fungus Paecilomyces thermophila J18 was purified 31.9-fold to homogeneity with a recovery yield of 2.27% from the cell-free culture supernatant. It appeared as a single protein band on SDS-PAGE with a molecular mass of approx 53.5 kDa. The molecular mass of beta-xylosidase was 51.8 kDa determined by Superdex 75 gel filtration. The enzyme was a glycoprotein with a carbohydrate content of 61.5%. It exhibited an optimal activity at 55 degrees C and pH 6.5, respectively. The enzyme was stable in the range of pH 6.0-9.0 and at 55 degrees C. The purified enzyme hydrolyzed xylobiose and higher xylooligosaccharides but was inactive against xylan substrates. It released xylose from xylooligosaccharides with a degree of polymerization ranging between 2 and 5. The rate of xylose released from xylooligosaccharides by the purified enzyme increased with increasing chain length. It had a K(m) of 4.3mM for p-nitrophenol-beta-d-xylopyranoside and was competitively inhibited by xylose with a K(i) value of 139 mM. Release of reducing sugars from xylans by a purified xylanase produced by the same organism increased markedly in the presence of beta-xylosidase. During 24-hour hydrolysis, the amounts of reducing sugar released in the presence of added beta-xylosidase were about 1.5-1.73 times that of the reaction employing the xylanase alone. This is the first report on the purification and characterization of a beta-xylosidase from Paecilomyces thermophila.
authors.affiliation: Bioresource Utilization Laboratory, College of Engineering, China Agricultural University, Beijing 100083, China.
authors.forename: Q J
authors.initials: QJ
authors.lastname: Yan
authors.forename: L
authors.initials: L
authors.lastname: Wang
authors.forename: Z Q
authors.initials: ZQ
authors.lastname: Jiang
authors.forename: S Q
authors.initials: SQ
authors.lastname: Yang
authors.forename: H F
authors.initials: HF
authors.lastname: Zhu
authors.forename: L T
authors.initials: LT
authors.lastname: Li
mesh_terms: D004591:Electrophoresis, Polyacrylamide Gel; D043364:Endo-1,4-beta Xylanases / Q000378:metabolism*; D004795:Enzyme Stability; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008970:Molecular Weight; D010143:Paecilomyces / Q000201:enzymology* / Q000254:growth & development; D013379:Substrate Specificity; D014908:Triticum; D014994:Xylose / Q000378:metabolism*; D014995:Xylosidases / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D014994:Xylose; D014995:Xylosidases; D043364:Endo-1,4-beta Xylanases