In order to modify the catalytic properties of trypsin, lysine-188 (S1) of the substrate binding pocket was substituted by an aromatic amino acid residue (Phe, Tyr, Trp) or by a histidyl residue. Two other mutants were obtained by displacement or elimination of the negative charge of aspartic acid-189 (K188D/D189K and G187W/K188F/D189Y, respectively). The high affinity inhibitors, like PSTI II and BPTI, behaved as specific substrates of the trypsin and its mutants. Their inhibiting effect toward modified trypsins was studied. The bovine inhibitor had a higher affinity for all tested enzymes than pea inhibitor. The inhibition constants differed according to the mutations on the protease.
Pouvreau, L., Chobert, J. M., Briand, L., Quillien, L., Tran, V., Guéguen, J., & Haertlé, T. (1998). Effect of pea and bovine trypsin inhibitors on wild-type and modified trypsins. FEBS Letters, 423(2), 167–172. https://doi.org/10.1016/S0014-5793(98)00062-3