Xylanase-oligosaccharide interactions studied by a competitive enzyme assay

A competitive enzyme assay has been employed to estimate the relative bindi ng of xylo- and cello-oligosaccharides to the active site of the Family 10 xylanase A from Pseudomonas fluorescens sp. cellulosa. The substrate used i n the assay was pNPC, the hydrolysis of which can be detected colorimetrica lly. Consistently with the endo-xylanase nature of this enzyme, the K-i(app ) for xylo-oligosaccharides decreases with increase in degree of polymeriza tion. Cello-oligosaccharides were poorer inhibitors of pNPC hydrolysis than xylo-oligosaccharides, and the K-i(app) did not decrease as dramatically w ith degree of polymerization. The implications of these results are discuss ed in the context of other studies on xylanase A and other Family 10 xylana ses. (C) 1999 Elsevier Science Inc. All rights reserved.