title: An investigation of the pH-activity relationships of Cex, a family 10 xylanase from Cellulomonas fimi: xylan inhibition and the influence of nitro-substituted aryl-beta-D-xylobiosides on xylanase activity.
abstract: The kinetic parameters of Cex, a family 10 xylanase from Cellulomonas fimi, were determined at various pH levels using soluble birchwood xylan (BWX) as a natural polymeric substrate along with three other synthetic aryl-beta-D-xylobioside substrates. Using BWX, a high level of substrate inhibition was observed which increased with decreasing pH. In contrast, typical Michaelis-Menten-type profiles were obtained using the three aryl-beta-D-xylobiosides as substrates. The k(cat) values determined using o-nitrophenyl-beta-D-xylobioside did not change as the pH increased, whereas the k(cat) values obtained with BWX, phenyl-beta-D-xylobioside and p-nitrophenyl-beta-D-xylobioside decreased, suggesting that the presence of an ortho nitro group affects the activity displayed by Cex. These differences were not observed with XynB from Clostridium stercorarium F9, a member of the same family of xylanases as Cex. These results indicate that a careful evaluation is required when employing substituted aryl-beta-D-xylobiosides in the characterization of xylanases.
authors.affiliation: Enzyme Laboratory, National Food Research Institute, Kannondai, Ibaraki 305-8642, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Honda
authors.forename: Motomitsu
authors.initials: M
authors.lastname: Kitaoka
authors.forename: Kazuo
authors.initials: K
authors.lastname: Sakka
authors.forename: Kunio
authors.initials: K
authors.lastname: Ohmiya
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Hayashi