Purification and Characterization of a Xylanase from Rhizopus oligosporus

Xylanases are promising eco-friendly candidate for many biotechnological and industrial fields including food, feed processing, biorefining and bio-intermediates production, biofuel, textile industries and paper and pulp industry as a biobleaching agent. An extracellular xylanase secreted by Rhizopus oligosporus produced under solid sate fermentation using wheat bran was purified and characterized. The freeze-dried crude filtrate was subjected to two-step purification using ion exchange chromatography by DEAE-Sepharose and gel filtration chromatography over Sephacryl S-200. The enzyme was purified to homogeneity and showed a monomeric single protein band over SDS-PAGE of a molecular mass of about 23 kDa. The purified xylanase revealed maximum activity at 40 degrees C and at pH 6.0 while remained active over a wide range of pH (4.5-8.0) and temperature ( 40-60 degrees C). The purified enzyme showed a significant activity towards birchwood, beechwood and oat spelt xylan with Km values of 8.0, 4.7 and 3.2 mg ml(-1), respectively. The xylanolytic activity was stimulated by Ni2+ and Na+ ions, while it is completely inhibited by Hg2+.