Enzyme Explorer


Physical Properties

While aprotinin and bovine pancreatic trypsin inhibitor (BPTI) are the same protein sequence, the term aprotinin is typically used when describing the protein derived from bovine lung.

Aprotinin is a single peptide chain with three disulfide bonds. Molecular Weight: ~ 65111
E1%280 nm=8.3(water)
pI = 10.56

Inhibitor Activity

Aprotinin is a competitive serine protease inhibitor which forms stable complexes with and blocks the active sites of enzymes. The binding is reversible, and most aprotinin-protease complexes dissociate at pH >10 or <3.2.

Enzyme Inhibition
Acrosin Weak inhibition6
Chymotrypsin Ki = 9 nM9
Chymotrypsinogen (bovine), pH 8.0 Ki = 9 nM4
CMP-Sialic Acid: Lactosylceramide -(2,3)-Sialyltransferase 74% Inhibition at 300 nM9
Elastase (human leukocytes), pH 8.0 Ki = 3.5 µM4
Kallikrein (pancreatic), pH 8.0 Ki = 1.0 nM4
Kallikrein (plasma) Ki = 30 nM; 100 nM9
Kallikrein (tissue) Ki = 1 nM9
Kallikrein (urine) Ki = 1.7 nM9
Plasmin (porcine), pH 7.8 Ki = 4.0 nM4
Plasminogen activator Ki = 8 µM; 27 µM9
Trypsin (bovine), pH 8.0 Ki = 0.06 pM4
Trypsinogen (bovine), pH 8.0 Ki = 1.8 µM4
Tryptase TL-2 16% Inhibition at 10 µM9
Urokinase (human), pH 8.8 Ki = 8.0 µM4

Unit Definition
One Trypsin Inhibitor Unit (TIU) will decrease the activity of 2 trypsin units by 50%, where 1 trypsin unit will hydrolyze 1.0 µmole of N-α-benzoyl-DL-arginine p-nitroanilide (BAPNA) per minute at pH 7.8 and 25 °C.

Another commonly used unit of activity is the KIU (Kallikrein Inhibitor Unit).

From our data, a conversion factor for Aprotinin is: 1 TIU equals ~1,300 KIU. A published ratio is: 1 TIU equals ~1,025 KIU.10

Solubility and Stability

Aprotinin is freely soluble in water (>10 mg/mL) and in aqueous buffers of low ionic strengths. Dilute solutions are generally less stable than concentrated ones. Solution stability also depends on pH; values of 1-12 can be tolerated. Repeated freeze-thaw cycles should be avoided. The Cys14-Cys38 disulfide bridge is readily split by reducing agents like 2-mercaptoethanol. Due to its compact tertiary structure, aprotinin is relatively stable against denaturation due to high temperature, acids, alkalies, organic solvents or proteolytic degradation (only thermolysin has been found capable of effectively degrading aprotinin after heating to 60-80 °C). The high basicity of aprotinin causes it to adhere to commonly used dialysis tubing and even gel filtration matrices, but the use of acetylated materials and concentrated salt solutions (e.g., 0.1 M NaCl in buffer)3 minimizes the problem. Sterilization may be achieved by filtration through a 0.2 µm filter.

Solvent Concentration Storage Temp. % Loss/TIme
Sterile water with 0.9% NaCl and 0.9% benzyl alcohol, pH 5.7-6.2 10 mg/mL 0-5°C <4.3%/year5
2.5% Trichloroacetic acid N/A 80°C No loss2
pH <12.6 N/A N/A No loss observed after 24 hrs.7
pH >12 N/A N/A Irreversibly denatured8
pH 7-8 0.065-1.95 µg/mL 4°C About 1 week6
pH 7-8 0.065-1.95 µg/mL -20°C >6 months6

Related Products

Product No. Description
A6106 Aprotinin from bovine lung, BioUltra, ≥4 TIU/mg solid, ≥98%
A6103 Aprotinin from bovine lung, BioUltra, recombinant, expressed in Nicotiana, ≥5 TIU/mg protein, ≥98%
A6279 Aprotinin from bovine lung, Saline solution, 3-7 TIU/mg protein
A1153 Aprotinin from bovine lung, lyophilized powder, 3-8 TIU/mg solid
A4529 Aprotinin from bovine lung, lyophilized powder, 3-7 TIU/mg solid
A3428 Aprotinin from bovine lung, lyophilized powder, 3-8 TIU/mg solid, cell culture tested
A5421 Aprotinin, immobilized on Eupergit® C
A2268 Aprotinin-Agaros
AP5 Aprotinin-Agarose prepacked column 2.5 mL
P1860 Protease Inhibitor Cocktail for tissue culture media
P2714 Protease Inhibitor Cocktail for general Use
S8830 SIGMAFAST™ Protease Inhibitor Cocktail Tablets, EDTA-Free
S8820 SIGMAFAST Protease Inhibitor Cocktail Tablets for general Use


  1. Merck Index, 12th Ed., S. Budavari, Ed., # 796, p. 128 (1996).
  2. J. Gen. Physiol., 19, 991 (1936).
  3. Hoppe-Seyler's Z. Physiol. Chem., 192, 1 (1930).
  4. Drug Res., 33(1), No. 4, 479 (1983).
  5. Our internal data.
  6. Biochemica Information, 1st Ed., J. Keesey, Ed., Boehringer Mannheim Biochemicals, p. 111, Indianapolis (1987).
  7. Biochemistry, 7, 3634 (1968).
  8. Life Sci., 28, 1861 (1981).
  9. Handbook of Enzyme Inhibitors, 2nd Ed., Part B, H. Zollner, Ed., p. 572, VCH Verlagesgesellschaft, Weinheim (1993).
  10. Biotechnology, p. 565 (June 1990).