The final traces of free label may be visualized by alkalizing aliquots of the filtrate with NaOH and viewing the fluorescence. Dehydrate the FX and dry in vacuo as above. Fluorescent xylan made by this procedure has a degree of substitution of about 0.02. Xylanase Assays . These assays directly measure the depolymerization of the high molecular weight substrate and are thus relatively insensitive to the presence of exoxylanases and xylosidases.
Reagent blanks consisting of sample and assay buffer are essential.
Other buffers and condition may be used. These assays are quite sensitive to the ionic strength of the assay buffer since the alcohol solubility of the BX and FX fragments varies with buffer concentration. The absorbance of RBB is relatively unaffected by pH, but the fluorescence of DTAF should be measure above pH 7. Localizing Xylanase in gels . BX may also be used to localize xylanase activities in non-denaturing PAGE slab gels.