Purification and characterization of alkaline xylanase from Thermoascus aurantiacus var. levisporus KKU-PN-I2-1 cultivated by solid-state fermentation

Abstract

Alkaline xylanase from Thermoascus aurantiacus var. levisporus KKU-PN-I2-1 was purified and characterized. The enzyme was enriched to apparent homogeneity by ammonium sulfate precipitation, Sephadex G-100 gel filtration and DEAE-cellulose ion-exchange column chromatography; it was purified 14.5 fold, with 2.3% recovery of the total activity and a specific activity of 2.56 × 103 mU/mg protein. Xylanase appeared to be monomeric, with a molecular weight of 27 kDa and isoelectric point (pI) of 7.2. Purified xylanase exhibited an optimum pH and temperature of 9.0 and 60 °C, respectively. The enzyme retained more than 70% of its original activity in the pH range of 7.0–9.0. In thermostability tests, xylanase retained more than 70% of its original activity after 90 min incubation at temperatures up to 50 °C. The enzyme had a Km of 40.9 mol/L and Vmax of 6.2 μmol/min/mg. Xylanase was inhibited by Hg2+ and stimulated by Cu2+, EDTA, Mg2+ and Co2+ at 1 mM. The purified xylanase only showed activity on xylan and hydrolyzed beechwood xylan to yield mainly xylotetraose and xylobiose, suggesting that it is an endo-xylanase.