Purification and Biochemical Characterization of Two Xylanases from Aspergillus sydowii SBS 45

Abstract

Two xylanases were isolated and purified from crude culture filtrate of Aspergillus sydowii SBS 45 after 9 days of growth on wheat bran containing 0.5% (w/v) birch wood xylan as the carbon source under solid-state fermentation. After a three-step purification scheme involving ammonium sulfate precipitation, gel filtration chromatography (Sephadex G-200), and anion exchange chromatography (DEAE-Sephadex A-50), xylanase I was purified 93.41 times, and xylanase II was purified 77.40 times with yields of 4.49 and 10.46, respectively. Molecular weights of xylanase I and II were 20.1 and 43 kDa, respectively, in sodium dodecyl sulfate–polyacrylamide gel electrophoresis. Optimum temperature was 50 °C, and optimum pH was 10.0 for both xylanase I and II. The K _m value of xylanase I for birch wood xylan was 3.18 mg ml⁻¹ and for oat spelt xylan 6.45 mg ml⁻¹, while the K _m value of xylanase II for birch wood xylan was 6.51 mg ml⁻¹ and for oat spelt xylan 7.69 mg ml⁻¹. Metal ions like Al³⁺, Ba²⁺, Ca²⁺, Na⁺, and Zn²⁺ enhanced the activity of xylanase I and II at 10 mM concentration. Among the additives, l-tryptophan enhanced the activity of xylanase I and II at 10-, 20-, and 30-mM concentrations. Both xylanases appeared to be glycoproteins.