Direct spectrophotometric determination of α-amylase activity in saliva, with p-nitrophenyl α-maltoside as substrate

The assay makes use of a well-defined substrate, p-nitrophenyl α-maltoside, which is hydrolyzed by α-amylase to a chromogenic product, p-nitrophenol. Activity is determined by directly monitoring the increase in absorbance of the reaction mixture. Amylase activity can be defined in international (IUB) units of micromoles of product/min per liter of saliva. For 22 healthy subjects, the mean ± SD of amylase activity in mixed saliva was 2.77±1.12 U/liter. Activity and instrumental response were linearly related over the entire range tested (0.224 to 11.90 U/liter). The within-run precision (CV) over this range was better than 3% for all but the lowest activities. Values obtained with this assay correlate well with those obtained with a modified Nelson-Somogyi saccharogenic method (r=0.979). The precision and simplicity of this assay suggest that it is the method of choice for determining amylase activity in human saliva.