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.