Trypsin is a serine protease that hydrolyses proteins in the digestive system of various vertebrates. Pancreas produces trypsin as inactive proenzyme trypsinogen. Active trypsin cleaves peptide chains predominantly at the carboxyl side of the amino acids (lysine or arginine).  In the Trypsin Activity Colorimetric Assay, trypsin cleaves a substrate to produce p-nitroaniline (p-NA) that is detectable at λ = 405 nm. Trypsin activity can be measured as the color intensity is proportional to p-NA content. The kit detection limit is 10-100 mU (p-NA unit) trypsin in different samples.