Kunitz STI Protease Inhibitor - Action and Consequences of Trypsin Inhibitors

Action and Consequences of Trypsin Inhibitors

Trypsin inhibitors require a specific three-dimensional structure in order to follow through with inactivation of trypsin in the body. They bind strongly to trypsin, blocking its active site and instantly forming an irreversible compound and halting digestion of certain proteins. Trypsin, a serine protease, is responsible for cleaving peptide bonds containing carbonyl groups from arginine or lysine. After a meal, trypsin is stimulated by cholecystokinin and undergoes specific proteolysis for activation. Free trypsin is then able to activate other serine proteases, such as chymotrypsin, elastase, and more trypsin (by autocatalysis), or continue breaking down proteins. However, if trypsin inhibitors (specifically KTI) are present, the majority of trypsin in the cycle of digestion is inactivated and ingested proteins remain whole. Effects of this occurrence include gastric distress, and pancreatic hyperplasia (proliferation of cells) or hypertrophy (enlargement of cells). The amount of soy inhibitors is directly related to the amount of trypsin it will inhibit, therefore a product with high concentration of soy is suspect to produce large values of inhibition. In a rat model, animals were fed either soy protein concentrate or direct concentrate of the Kunitz trypsin inhibitor. In both instances, after a week the rats showed a dose-related increase in pancreas weight due to both hyperplasia and hypertrophy. This indicates that long-term consumption of a diet high in soy with strong trypsin inhibitor activity may produce unwanted effects in humans as well.