Human Trypsin 1, encoded by the PRSS1 gene, is also known as cationic trypsinogen. Constituting approximately two-thirds of the total trypsin content in normal pancreatic juice, it is the most abundant trypsin isoform produced by the pancreas. It contains a signal peptide (residues 115), a pro region (residues 1623), and a mature chain (residues 24247). Trypsin 1 is synthesized in the pancreas and secreted into the duodenum lumen, where it is activated by enterokinase. Its major physiologic function is to digest food and to activate other pro-enzyme. Mutations in the PRSS1 gene can cause hereditary pancreatitis. The activity of recombinant human PRSS1 is measured by its ability to cleave a fluorogenic peptide substrate Mca-Arg-Pro-Lys-Pro-Val-Glu-Nval-Trp-Arg-Lys(Dnp)-NH2 in the assay buffer 100 mM Tris, 150 mM NaCl, 10 mM CaCl2, 0.05% (w/v) Brij-35, pH 8.0. The rhPRSS1 is diluted to 200 ug/ml in activation buffer 50 mM Tris, 0.15 M NaCl, 10 mM CaCl2, 0.05% (w/v) Brij-35, pH 7.5, then activated with 1ul Enterokinase at 37 ℃ for 15min. The activated rhPRSS1 is diluted to 3 ug/mL in assay buffer. Loading into a black well plate 50 µL of 3 ug/mL rhPRSS1 and start the reaction by adding 50 µL of 20 µM substrate, with a substrate blank containing 50 µL assay buffer, 50 µL substrate, and no rhPRSS1. Then read at excitiation and emission wavelengths of 320 nm and 405 nm, respectively, in kinetic mode for 5 minutes. The specific activity of recombinant human PRSS1 is > 600 pmol/min/µg.