Purification and properties of a xylanase produced by Bacillus circulans BL53 on solid-state cultivation

Xylanase from Amazon isolate Bacillus circulans BL53 grown on solid-state cultivation was purified to apparent homogeneity by ammonium sulphate fractioning, cation-exchange and gel filtration chromatography. A purification factor of 428-fold was achieved, with the purified enzyme presenting a specific activity of about 37 U mg−1 protein. The xylanase molecular weight was calculated as 38 kDa by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and its isoeletric point was determined as 8.8. Determination of pH and temperature for the maximum activity was obtained using a 22 factorial design over an extensive range of pH (5.0–8.0) and temperatures (40–80 °C). The enzyme follows Michaelis–Menten kinetics with KM and Vmax values of 9.9 mg xylan mL−1 and 25.25 μmol min−1, respectively. The purified enzyme hydrolyzes soybean hull, soybean fiber, rice straw, grape skin and sugar cane bagasse. Its activity was stimulated by Co2+, Mn2+ and protein disulphide reducing reagents, but strongly inhibited by Hg2+ ions and SDS.