Description General description Aprotinin is a 58 amino acid-long protein, with a calculated molecular weight of 6512 Da, that acts as a serine protease inhibitor. Known also as bovine pancreatic trypsin inhibitor (BPTI), aprotinin inhibits serine proteases such as chymotrypsin, kallikrein, plasmin and trypsin. Application Aprotinin is largely used as an inhibitor of trypsin. Biochem/physiol Actions Aprotinin is a competitive serine protease inhibitor that forms stable complexes with and blocks the active sites of enzyme. This binding is reversible, and most aprotinin-protease complexes will dissociate at extreme pH levels >10 or <3. Structurally, Aprotinin is a monomeric globular protein derived from bovine lung that consists of 58 amino acids, arranged in a single polypeptide chain with three crosslinking disulfide bridges. Caution Aprotinin products should be stored at 2-8°C. Unit Definition One Trypsin Inhibitor Unit (TIU) will decrease the activity of two trypsin units by 50%, where one trypsin unit will hydrolyze 1.0 μmole of N-alpha-benzoyl-DL-arginine p-nitroanilide per minute at pH 7.8 and 25°C. Another commonly used unit is the KIU, with 1 TIU = 1,300 KIU. Preparation Note This product is an aseptically filled solution in 0.9% NaCl and 0.9% benzyl alcohol. It has an activity of 3-7 TIU/mg protein and 3-21 TIU/mL solution.