Enzyme Explorer



Bovine, Recombinant
Animal-Free Alternative
Expressed in Nicotiana (Tobacco)


Introducing the newest member of the family of recombinant animal-free alternatives. Our recombinant aprotinin avoids the issue of bovine pathogens altogether.

This protein is available
in the BioUltra Grade.

BioUltra Proteins Logo
Learn more here.



3-8 TIU/mg solid


Minimum 98% by SDS-PAGE

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.


White to off-white powder

Cell Culture Test:


3 lots with Certificates of Analysis available.
For Bulk Quantities, please call 1-800-336-9179.

Product Description

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.
Molecular Weight: ~ 6511
E1%(280 nm) = 8.3 (water)


Stability / Storage as Supplied

If stored at 2-8°C Product Code A6103 has a designated shelf-life of two years.


Solubility / Solution 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 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.

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



  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. Internal company data.
  6. Biochemica Information, 1st Ed., J. Keesey, Ed., Boehringer Mannheim Biochemicals, p. 111, Indianapolis (1987).
  7. Biochem., 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).

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