Purification and general properties of xylanase from Aspergillus terreus

Aspergillus terreus THOM produced appreciable yield of xylanase on medium containing acid pretreated rice straw as sole carbon source. The enzyme was purified approximately 25-fold by ammonium sulfate precipitation, gel filtration through Sephadex G-50 and ion-exchange chromatography on DEAE-cellulose with a yield of about 23% and specific activity of 15.38 units/mg protein. Optimum activity against xylan was at 45 degrees C and pH 4.5. Relative stability of the enzyme was recorded at pH range of 4-5.5. Heating the enzyme preparation at 60 degrees C for one hour resulted in a 82.61% loss of activity. After exposing to 90 degrees C for 10 minutes xylanase retained 4.28% of its original activity. The purified enzyme lost 25% of the original activity after keeping at 4 degrees C for 9 months in 0.05 M acetate buffer (pH 4.5). The Km value of the enzyme was found to be 0.83 mM. Zn2+ was the most enhancing agent for xylanase activity. Cu2+ followed by Co2+ and K+ were the more deterrent cations. Xylanolytic activity of A. terreus was strongly inhibited by HgCl2, 2,4-dinitrophenol (DNP), phloridzin and ethylene diamino tetra acetic acid (EDTA).