Used as a chromogenic substrate in enzymatic assays, particularly for measuring the activity of proteolytic enzymes such as chymotrypsin and other serine proteases. Upon cleavage by the enzyme, it releases p-nitroaniline, which produces a yellow color that can be measured spectrophotometrically at around 405 nm. This allows for real-time monitoring of enzyme activity and kinetics in research and diagnostic applications. Commonly employed in studies related to enzyme inhibition, substrate specificity, and mechanistic analysis of proteases.