Characterization of Endoxylanase Activity From Thermomonospora Fusca BD25

Thermomonospora fusca BD25 produces relatively high levels of activity of endoxylanases. Only oat spelt xylan, RBB-xylan and birchwood xylan reacted with endoxylanases with the maximum specific activity of 47.65 U mg-1 protein on birchwood xylan. The endoxylanase remained stable up to 70 °C. At 60 °C endoxylanase activity showed stability (92 %) for 16 h, however it showed a half-life of 8 h at 70 °C and 30 min at 80 °C in the absence of substrate at pH 8.0. The relative endoxylanase activity in the pH ranges of 6.5 to 9.5 remained between 68 % and 72 % of the activity at pH 8.0. The apparent Km value for the crude endoxylanase was 6.66 mg of oat spelt xylan ml -1, while the Vmax value was 2.5 μmol reducing sugar min-1 ml-1. Endoxylanase activity was affected by the addition of xylobiose (1 mM) to the reaction mixture of endoxylanase preparation and resulted in approximately 25 % reduction in activity. Also, the addition of supernatant fluids from cultures grown on xylan (reducing sugar concentration of 1 mg ml-1 xylose equivalent) to the reaction mixture resulted in approximately 30 % reduction in activity.