Aprotinin

Aprotinin is largely used as an inhibitor of trypsin.

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.

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.

Aprotinin, also known as pancreatic trypsin inhibitor and trypsin-kallikrein inhibitor, is a monomeric polypeptide of 58 amino acids found in a number of organs, including lungs, spleen, liver, and pancreas. It is also detectable in a free form in calf serum. It is a competitive inhibitor that forms a loose complex with serine proteases and blocks their active centers. The complex exhibits many interactions between protease and inhibitor. The trypsin-aprotinin complex, for example, does not dissociate at a concentration of 8 M uric acid or 6 M guanidine hydrochloride. Aprotinin is only cleaved slowly by most proteases, with the exception of thermolysin at temperatures >+60°C. Its unique structure is responsible for the molecule’s high stability and remarkable resistance to elevated temperatures, acids, and proteases.