An assay for detecting nanogram levels of proteolytic enzymes

A rapid, cheap, and sensitive method has been developed for determining proteolytic activity of different classes of endoproteinases. The method is based on a solid-phase assay employing as substrate biotinylated gelatin adsorbed onto microtiter plates. Enzymatic activity is measured by incubating proteinase with the immobilized biotin-protein. Any remaining, undigested substrate bound to the microtiter plate is assayed with streptavidin-alkaline phosphatase. It was established that papain, pepsin, thermolysin, and trypsin all hydrolyzed the biotinylated substrate to varying degrees. Furthermore, the activity of these proteinases was blocked by their respective inhibitors. The assay presented is quick, highly reproducible, inexpensive, and useful for detecting all classes of endoproteolytic enzymes. By using different biotinylated proteins or peptides as substrates, and employing specific buffers and inhibitors, this assay may be utilized for detecting other and more specific endoproteinases.