Aprotinin is a protein consisting of 58 amino acids, arranged in a single polypeptide chain that is crosslinked by three disulfide bridges. Aprotinin is found in bovine lymph nodes, lung, parotid gland, spleen, liver, pancreas, seminal vesicles, thyroid gland, kidney, mucous membranes of the trachea and esophagus, ovaries, heart, posterior pituitary and cartilage.
Aprotinin is a competitive serine protease inhibitor that inhibits trypsin, chymotrypsin, kallikrein and plasmin. Aprotinin forms stable complexes with and blocks the active sites of enzymes. Binding is reversible with most aprotinin-protease complexes dissociating at pH >10 or < 3.