Hydrolysis of (1----3)- and (1----2)-beta-D-xylosidic linkages by an endo-(1----4)-beta-D-xylanase of Cryptococcus albidus

The substrate specificity of an endo-(1----4)-beta-D-xylanase of the yeast Cryptococcus albidus was investigated using a series of methyl beta-D-xylotriosides. In addition to (1----4) linkages, the enzyme could cleave (1----3) and (1----2) linkages adjacent to a (1----4) linkage and further from the non-reducing end of the substrate. The enzyme could hydrolyse a (1----3) linkage that attached a terminal xylopyranosyl group to a (1----4)-linked xylobiosyl moiety. The enzyme did not attack alpha-D-xylosidic linkages. The rate of cleavage of (1----4) linkages was much higher than those of other linkages at 0.5mM substrate, but the rates were comparable at 20mM substrate when transglycosylation reactions also occurred that facilitated degradation of the substrates.