A number of specialized xylanase assays have been developed that make use
of dyed or derivatized substrates. Carboxymethyl xylan will differentiate
between xylanases that react with the xylan backbone and those that remove
side chains (Khowala et al. 1988). Assays based on dyed substrates are often
more sensitive, but the results are also more difficult to interpret from a kinetic
perspective (Schmidt and Kebernik 1988). Dyed substrates are particularly
useful in developing zymograms from electrophoresis gels (Biely et al. 1985a,
1988). As with all unnatural or substituted substrates, care must be taken to
assure that the assay reflects the activity sought. Methods used to assay
xylanase activities in various laboratories around the world were summarized
by Ghose and Bisaria (1987).