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.http://www.creative-enzymes.com/product/Native-Bovine-Aprotinin_831.html