β-D-Xylanases of Bacillus circulans WL-12

Abstract

Bacillus circulans WL-12 secretes two endo-β-D-xylanases (A and B, respectively) (EC 3.2.1.8.) and one β-D-xylosidase (EC 3.2.1.37) when cultured in liquid media with xylan as the sole carbon source. Xylanases A and B have been partially characterized with respect to their main physicochemical parameters and β-D-xylosidase to a lesser extent on account of its low stability. Both endo-β-D-xylanase A and β-D-xylosidase were adsorbed on DEAE-Biogel A, had similar molecular weights (approximately 85 000), and had optimum pH values of 5.5–7, but exhibited different isoelectric points (4.5 for β-D-xylanase A and 4.7 for β-D-xylosidase) and different mobilities in polyacrylamide gel electrophoresis. The apparent Michaelis constant for β-D-xylanase A was 8 mg∙mL−1 and the hydrolysis products produced were xylose, xylobiose, xylotriose, and xylotetraose.The second endo-β-D-xylanase (β-D-xylanase B) bound to CM-Biogel A and exhibited a molecular weight of approximately 15 000 and an optimum pH value in the range of 5.5–7. The isoelectric point was 9.1 and the apparent Michaelis constant was 4 mg∙mL−1. The hydrolysis products produced by this enzyme were xylobiose, xylotriose, and xylotetraose, but never xylose. In polyacrylamide gel electrophoresis at pH 8 the enzyme moved towards the negative electrode.