Aprotinin is a single chain polypeptide (58 amino-acids) crosslinked by three disulfide bridges, showing competitive and reversible inhibiton of proteolytic and esterolytic activity. Aprotinin forms stable complexes with, and blocks the active sites of serine protease enzymes. It 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.

Aprotinin is used as a proteolytic inhibitor in radioimmunoassays of polypeptide hormones.

• pH: 5.0 - 7.0 (1% aq soln)
• Soluble in water (10 mg/mL - completely soluble) and in aqueous buffers of low ionic strengths.
• Unit Definition:One Kallikrein Inactivating Unit is the quantity of protease inhibitor that has the ability to inhibit 2 Kallikrein units by 50% under optimal conditions.
• Typical Working Concentration: Effective Concentration is Equimolar with protease (1-2 µg/mL).
• Sterilization of Solutions: Sterilization of solutions can be done by filtration through a 0.2 µm filter.

Storage temperature: Store at +4 °C.