Comparison of physicochemical properties of recombinant buckwheat trypsin inhibitor (rBTI) and soybean trypsin inhibitor (SBTI)

The inhibitory activities of buckwheat trypsin inhibitor (rBTI) towards trypsin were compared with soybean trypsin inhibitor (SBTI) in terms of their sensitivities to temperature, pH, salt ions and organic solvents. Both rBTI and SBTI were stable over a broad pH range of 2.0–12.0. rBTI exhibited higher thermal stability than SBTI. The inhibitory activity of rBTI was decreased by Zinc ions (Zn²⁺), KSCN, vitamin C and urea, while that of SBTI remained unchanged. However, H₂O₂, Mg²⁺ and Cu²⁺ ions had no significant effects on the inhibitory activities of rBTI and SBTI. Acetonitrile enhanced the inhibitory activity of rBTI, but had no effect on SBTI, while dimethylacetamide (DMAC) increased the inhibitory effect of both rBTI and SBTI. On the contrary, the inhibitory activities of rBTI and SBTI were reduced by isopropyl alcohol and methanol. The inhibition constants K_i of rBTI and SBTI were calculated to be 7.41 × 10⁻⁹ M and 6.52 × 10⁻⁹ M, respectively.