Chemical Replacement of P1' Arginine Residue at the First Reactive Site of Peanut Protease Inhibitor B-III

Abstract

The contribution of the P₁′ residue at the first reactive site of peanut protease inhibitor B–III to the inhibition was analyzed by replacement of the P₁′ Arg(11) with other amino acids (Arg, Ser, Ala, Leu, Phe, Asp) after selective modification of the second reactive site. The Arg derivative had the same trypsin inhibitory activity as the native inhibitor (K₁ = 2 × 10⁻⁹ M). The Ser derivative inhibited more weakly (K₁ = 2 × 10⁻⁷M). The Ala and Leu derivatives inhibited trypsin very weakly (K₁ = 2 × 10₋₇ M and 4 × 10⁻⁷ M, respectively), and the Phe and Asp derivatives not at all. These results suggest that the P₁′ arginine residue is best for inhibitory activity at the first reactive site of B.-III, although it has been suggested that a P₁′ serine residue at the reactive site is best for inhibitory activity of Bowman-Birk type inhibitors.