This inhibitor acts against trypsin, and chymotrypsin and plasmin to a lesser extent. It will also inhibit proteases with mechanisms similar to trypsin, plasma kallikrein and coagulation Factor X. The trypsin inhibitor will not act against metalloproteases, tissue-baseed kallikrein, acid proteases, or thio proteases. This inhibitor acts by forming a 1:1 stoichiometric complex with the protease active site, and then cleaving a single arginine-isoleucine bond on the inhibitor. The inhibition is both reversible and pH dependent.

The soybean trypsin inhibitor is a monomeric protein containing 181 amino acid residues in a single polypeptide chain crosslinked by two disulfide bridges.

One trypsin unit = A₂₅₃ of 0.001 per minute with N-alpha-benzoyl-L-arginine ethyl ester (BAEE) as substrate at pH 7.6 at 25 °C.

The trypsin inhibitor is soluble in water and phosphate buffers at 10 mg/mL. It is soluble in balanced salt solutions at 1 mg/mL and in serum-free media. Concentrated solutions greater than 10 mg/mL may be hazy and have a yellow to amber color. After trypsinizing cells, resuspend in 1 mL trypsin inhibitor solution at 1 mg/mL for every mL of trypsin solution used for dissociation. The cell suspension should then be centrifuged at 1000 rpm, forming a cell pellet.

Solutions can retain activity when stored short-term at 2-8° C. Solutions are stable in frozen aliquots at -20°C.