Purification and characterization of low molecular weight extreme alkaline xylanase from the thermophilic fungus Myceliophthora thermophila BF1-7

The thermo-alkali-stable xylanase from Myceliophthora thermophila BF1-7 was purified and characterized. The enzyme was purified using a procedure including ammonium sulfate precipitation, gel filtration and ion exchange chromatographies. The xylanase was purified to 77.1-fold apparent homogeneity with a recovery yield of 7.48% and maximum specificity was obtained as 2.31 U mg−1 protein. The purified xylanase appeared as a single protein band on sodium dodecyl sulfate polyacrylamide gel electrophoresis with a molecular mass of approximately 14 kDa. Xylanase was most active at pH 12.0 and retained 55% of the original activity in the pH range of 9.0-12.0 after incubation at 4 °C for 24 h. The optimal temperature of the xylanase was 50 °C and it retained more than 77% and 56% of its original activity after heating at 50 °C for 30 and 60 min, respectively. Xylanase was inhibited by Hg2+ and stimulated by Mg2+, Cu2+, Ag+, Zn2+, ethylenediaminetetraacetic acid (EDTA) and sodium dodecyl sulfate (SDS) at 1 mM. The Km and Vmax values of the purified xylanase were 9.67 mg/mL and 5.38 μmol/min/mg, respectively. The purified xylanase only showed activity on xylan and hydrolyzed beechwood xylan to yield mainly xylotetraose and xylobiose as end products which suggesting that it was an endo-xylanase.