Purification and characterization of extracellular xylanase from Streptomyces cyaneus SN32

Streptomyces cyaneus SN32 was used in this study to produce extracellular xylanase, an important industrial enzyme used in pulp and paper industry. The enzyme was purified to homogeneity by ammonium sulfate precipitation followed by anion exchange chromatography using DEAE–Sepharose column, with 43.0% yield. The enzyme was found to be a monomer of 20.5 kDa as determined by SDS gel electrophoresis and has a pI of 8.5. The optimum pH and temperature for purified xylanase activity was 6.0 and 60–65 °C, respectively. The half-lives of xylanase at 50 and 65 °C were approximately 200 and 50 min, respectively. The xylanase exhibited Km and Vmax values of 11.1 mg/ml and 45.45 μmol/min/mg. The 15 residue N-terminal sequence of the enzyme was found to be 87% identical up to that of endoxylanases from Steptomyces sp. Based on the zymogram analysis, sequence similarity and other characteristics, it is proposed that the purified enzyme from S. cyaneus SN32 is an endoxylanase and belongs to Group1 xylanases (low molecular weight – basic proteins). The purified enzyme was stable for more than 20 week at 4 °C. Easy purification from the fermentation broth and its high stability will be highly useful for industrial application of this endoxylanase.