Assay for protease inhibitors: qualitative measurement and detection in polyacrylamide gel electrophoretograms.

A simple and fast method for qualitative measurement of protease inhibitors has been developed. The high sensitivity of the assay is based on a casein-precipitating reaction at pH 5.5. Cellulose paper strips, moistened with protease inhibitor-containing solutions, are applied to the surface of an agar-skim milk gel previously coated with a protease solution. After incubation for 2 h at 37 degrees C, inhibitory activity is indicated by a translucent zone (absence of casein degradation) on a white background of precipitated small casein fragments. In addition to being useful for rapid screening of a large number of complex samples, the method allows the localization of protease inhibitor activity in sodium dodecyl sulfate-polyacrylamide gel electrophoretograms.