Assay of xylanase and xylosidase activities in bacterial and fungal cultures

The factors causing variation in the determination of xylanase (1,4-β- D-xylan xylanohydrolase, EC 3.2.1.8) and xylosidase (β- D-xyloside xylohydrolase, EC 3.2.1.37) have been studied. The results showed that the reported activities in international units (U) varied by a factor of 3 to 107, depending on the dilution of enzyme made prior to assay. Determination of xylanase was also affected by the type of substrate used, and it varied from 1.5 to 104 U ml −1 among three different xylan preparations from larchwood. The measured units of enzymatic activity appear to vary with the availability of easily degradable xylooligosaccharides in the substrate. The defining of composition and the use of a standard method for the preparation of xylan would help in minimizing variation due to substrate. The use of enzyme dilution to give 0.9 to 1.0 mg of reducing sugars for the calculation of xylanase units and an absorbance between 0.8 and 1.2 for the calculation of xylosidase units would help in minimizing the variation in the results obtained by different laboratories using the same substrate.