In the determination of b-Glucosidase activity we used different substrates: the natural substrate cellobiose and a sintetic substrate pNGP (p-nitrohpenyl B-D glucopyranoside). In the method with cellobiose we calculate the amount of glucose liberated from cellobiose B-Glucosidase by HPLC. On the pNGP assay we calculated the liberation of p-nitrophenol by UV/vis Spectrometry at 412 nm. We have different results in both assays. It should be the same result or closely related? Does the nature of the substrate affect the enzymatic activity?