Purification and properties of an extracellular beta-xylosidase from a newly isolated Fusarium proliferatum

An extracellular beta-xylosidase from a newly isolated Fusarium proliferatum (NRRL 26517) capable of utilizing corn fiber xylan as growth substrate was purified to homogeneity from the culture supernatant by DEAE-Sepharose CL-6B batch adsorption chromatography, CM Bio-Gel A column chromatography, Bio-Gel A-0.5 m gel filtration and Bio-Gel HTP Hydroxyapatite column chromatography. The purified beta-xylosidase (specific activity, 53 U/mg protein) had a molecular weight of 91,200 as estimated by SDS-PAGE. The optimum temperature and pH for the action of the enzyme were 60 degrees C and 4.5, respectively. The purified enzyme hydrolyzed xylobiose and higher xylooligosaccharides but was inactive against xylan substrates. It had a Km value of 0.77 mM (p-nitrophenol-beta-D-xyloside, pH 4.5, 50 degrees C) and was competitively inhibited by xylose with a Ki value of 5 mM. The enzyme did not require any metal ion for activity and stability. Comparative properties of this enzyme with other fungal beta-xylosidases are presented.