A sensitive assay for proteolytic enzymes using bacterial luciferase as a substrate

A general assay for proteolytic enzymes using bacterial luciferase as a substrate is described. This luciferase is rapidly inactivated by unusually small amounts of different proteases having a wide spectrum of specificities. The activity is lost exponentially; the pseudo-first-order rate constant for inactivation is proportional to the amount of protease. Since luciferase activity can be measured by a very simple and rapid assay, it affords an accurate, sensitive, and convenient assay for proteolytic activity. This technique is capable of detecting as little as 20 ng of trypsin, requires no centrifugation, and is not hampered by the presence of contaminating pigments in the protease preparation. It is compared at pH 6, 7, and 8 to the phenol color assay and the azocoll assay using seven different proteases.