Assay for enzyme activity by following the absorbance change of pH-indicators.

Based on the absorbance change of indicators with the concentration of hydrogen ion released from an enzyme-catalyzed reaction, a convenient colorimetric method was established for the assay of acidic phospholipase A2 and glycogen phosphorylase b. Brilliant yellow and bromothymol blue were chosen as indicators for assays of acidic phospholipase A2 and glycogen phosphorylase b by following the absorbance changes at 495 and 615 nm, respectively. The method is simple, sample-saving, sensitive and valid for a wide range of enzyme concentrations. It can be extended for assaying other enzymes catalyzing reactions with hydrogen ion concentration changes.