Submitted to: Journal of Industrial Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 6, 2001
Publication Date: N/A
Interpretive Summary: Corn fiber is available in sufficient quantities from the corn wet milling industry to serve as a low-cost feedstock for production of fuel ethanol and other value-added fermentation products. For this, the corn fiber has to be broken down to simple sugars. The structure of xylan in corn fiber is very complex, and commercially available enzyme preparations are not effective to hydrolyze it to simple sugars. Thus, this research was undertaken to isolate an organism that can produce enzymes for conversion of corn fiber xylan to simple sugars. Beta-xylosidase is an important enzyme for breakdown of xylan to xylose (a simple sugar). The enzyme from a newly isolated fungal strain that can utilize corn fiber xylan as growth substrate has been purified and characterized. The purified enzyme is optimally active at 65 deg C and is useful for conversion of xylan to xylose.
Technical Abstract: An extracellular beta-xylosidase from a newly isolated Fusarium verticillioides (NRRL 26518) was purified to apparent 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 of 94,500 and an isoelectric point at pH 7.8. The optimum temperature and pH for the action of the enzyme were 65 deg C and 4.5, respectively. It hydrolyzed xylobiose and higher xylooligosaccharides but was inactive against xylan. The purified beta-xylosidase had a Km value of 0.85 mM (p-nitrophenol-beta-D-xyloside, pH 4.5, 50 deg C) and was competitively inhibited by xylose with a Ki value of 6 mM. It did not require any metal ion for activity and stability.