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
2002
Honda, Y. (National Food Research Inst., Tsukuba, Ibaraki (Japan)) | Kitaoka, M. | Sakka, K. | Ohmiya, K. | Hayashi, K.
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 Kcat values determined using 0- nitrophenyl-beta-D-xylobioside did not change as the pH increased, whereas the Kcat 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 evaluationis required when employing substituted aryl-beta-D-xylobiosides in the characterization of xylanases.
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