Used as a chromogenic substrate in enzymatic assays to measure the activity of proteolytic enzymes, particularly elastase and other serine proteases. Upon enzyme action, the p-nitroaniline moiety is released, producing a yellow-colored product that can be detected spectrophotometrically at around 405 nm. This allows for real-time monitoring of enzyme kinetics and inhibition studies. Commonly employed in biochemical research and drug development to evaluate potential enzyme inhibitors.