Purification and characterization of an extracellular beta-xylosidase from a newly isolated Fusarium verticillioides.

An extracellular beta-xylosidase from a newly isolated Fusarium verticillioides (NRRL 26518) was purified to homogeneity from the culture supernatant by concentration by ultrafiltration using a 10,000 cut-off membrane, ammonium sulfate precipitation, DEAE Bio-Gel A agarose column chromatography and SP-Sephadex C-50 column chromatography. The purified beta-xylosidase (specific activity, 57 U/mg protein) had a molecular weight (mol. wt.) of 94,500 and an isoelectric point at pH 7.8. The optimum temperature and pH for action of the enzyme were 65 degrees C and 4.5, respectively. It hydrolyzes xylobiose and higher xylooligosaccharides but is inactive against xylan. The purified beta-xylosidase had a K(m) value of 0.85 mM (p-nitrophenol-beta-D-xyloside, pH 4.5, 50 degrees C) and was competitively inhibited by xylose with a K(i) value of 6 mM. It did not require any metal ion for activity and stability.