Purification and Characterization Including Dextran Hydrolysis of Dextranase from Aspergillus allahabadii X26

Abstract

Dextranase is commonly used for eliminating dextran contamination in sugar factory. This research, dextranase from Aspergillus allahabadii X26, was produced, purified and characterized including on dextran hydrolysis. A. allahabadii X26 was cultured in a medium containing 1% dextran T2000 as a carbon source in 5-l fermenter aerobically at 30 °C and obtain 110 U/ml crude extracellular dextranase activity within 9 days of incubation. Extracellular dextranase could be purified by the 2 steps of ammonium sulfate precipitation and affinity chromatography using Sephacryl S-300 HR. This resulted in 6.5-fold and a 39.1% recovery yield obtaining 3009 U/mg mg protein. The purified enzyme exhibited 66 kDa on SDS-PAGE and was specified as a glycoprotein. The optimum pH and temperature for enzyme activity were 5.8 and 55 °C, respectively. The enzyme exhibited thermostability in the range of 20–50 °C and pH 5–9 over the incubation period of 1.5 h. The dextranase activity was enhanced by Co2+, Mn2+ and Ca2+, whereas most ions and reagents did not inhibit its activity. The enzyme only had specificity to the α(1 → 6) glycosidic bond of dextran. Partial sequences of the enzyme determined by an ESI mass spectrometer showed similarity toward dextranase GH49. This purified dextranase (0.2 U/ml) from A. allahabadii X26 could degrade high molecular weight dextran into fragments of 5–10 kDa and oligodextrans within 5 min. These A. allahabadii X26 dextranase properties indicated high potential for dextran elimination in sugar production process.