Soyabean trypsin inhibitor consists of a single polypeptide chain cross-linked by two disulfide bridges. It is widely used in serum-free cell culture practices to terminate tissue disaggregation and to inhibit protease activity of trypsin. It forms 1:1 stable stoichiometric complex with protease active site on trypsin molecule, thereby inhibiting trypsin activity. It also inhibits chymotrypsin and plasmin to some extent. Inhibition is reversible as well as pH dependent. Optimum binding of trypsin inhibitor to trypsin occurs at pH 8.0. Trypsin Inhibitor is soyabean trypsin inhibitor solution formulated to contain 1mg per ml trypsin inhibitor in Dulbecco's Phosphate Buffered Saline.