Trypsin (EC 3.4.21.4) is a serine protease found in the digestive system of many vertebrates, where it hydrolyses proteins. Trypsin is produced in the pancreas as the inactive proenzyme trypsinogen. Active trypsin predominantly cleaves peptide chains at the carboxyl side of the amino acids lysine or arginine, except when either is followed by proline. It is used for numerous biotechnological processes. In the assay, trypsin cleaves a substrate to generate p-nitroaniline (p-NA) which is detected at λ=405 nm. Since the color intensity is proportional to p-NA content, trypsin activity can be accurately measured. The kit detects 10-100 mU (p-NA unit) trypsin in various samples.