Purification and characterization of an acid-stable and organic solvent-tolerant xylanase from Aspergillus awamori VTCC-F312

Abstract

An acid-stable and organic solvent-tolerant extracellular xylanase was isolated and purified from Aspergillus awamori VTCC-F312 and its properties were investigated. The xylanase was purified by Sephadex G-100 gel filtration chromatography and DEAE-Sephadex A-50 ion exchange chromatography to homogeneity. The enzyme had a molecular mass of 32 kDa and a specific activity of 217 U/mg protein, with optimum temperature of 50-55 °C and optimum pH of 5. This enzyme was stable at up to 45 °C and no loss of enzyme activity was observed after incubation for 6 h at 40 °C. The xylanase was stable within the pH range of 4-8 with no loss of enzyme activity after incubation at 30 °C for 1-4 h, even the enzyme activity was found to increase by 60% after incubation at pH 4 for 4 h. The Km and Vmax values were 12.6 mg oat spelt xylan per ml and 1000 U/mg protein, respectively. Dithiothreitol, -mercaptoethanol, and EDTA were found to increase the xylanase activity by 19%, 46%, and 138%, respectively. Except for Fe 3+ , the presence of 5 mM tested metal ions increased the enzyme activity by 18-52%. The enzyme showed high resistance to organic solvents and retained 63-86% and 44-61% of its activity in the presence of tested organic solvents at 30% and 80% (v/v), respectively. Triton X-100 and Tween 80 activated the xylanase to 128% and 116% of its activity, whereas SDS at the concentration of 5% completely inhibited the enzyme. These results suggested that the xylanase from A. awamori VTCC-F312 could potentially be used as a feed additive for monogastric animals.