Submitted to: Bioresource Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/21/2003
Publication Date: 5/1/2003
Citation: SAHA, B.C. PURIFICATION AND PROPERTIES OF AN EXTRACELLULAR BETA-XYLOSIDASE FROM A NEWLY ISOLATED FUSARIUM PROLIFERATUM. BIORESOURCE TECHNOLOGY. 2003. V. 90. P. 33-38. 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. It has great potential to be used for conversion of corn fiber xylan to xylose. This research will benefit fuel alcohol producers who are trying to develop an environmentally friendly bio-based process for converting corn fiber, corn cob, corn stover, rice straw, wheat straw, or other unutilized agricultural residues to fuel ethanol and/or other value-added fermentation products such as xylitol (a sugar alcohol).
Technical Abstract: 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-0.5m 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 deg 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 deg 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.