Studies on Soybean Proteinase Inhibitors

Part I. Purification and some properties of acetone insoluble inhibitor

Abstract

Six trypsin inhibitors (F₁, F₂, F₃-I, F₃-II, F₄ and F₅) and three α-chymotrypsin inhibitors (F₃-II, F₄ and F₅) were fractionated from crude soybean acetone insoluble inhibitor by gel filtration with Sephadex G-100 and DEAE-Sephadex A-25 chromatography.
The F₄ inhibitor was found to be homogeneous by electrophoretic and ultracentrifugic analyses, and strongly inhibited both trypsin and α-chymotrypsin, and had separate binding sites for trypsin and α-chymotrypsin, and was stable at temperature in an acidic pH. Molecular weight and sedimentation constant of the F₄ inhibitor were determined to be 8000 and 1.85, respectively. NH₂- and COOH-terminal amino acids of the F₄ inhibitor were aspartic acid and glutamic acid-asparagine, respectively. The reaction between trypsin and the F₄ inhibitor consisted in formation of a dissociable complex.
The chemical and physicochemical properties of the F₄ inhibitor were in good agreement with those of Bowman-Birk inhibitor and 1.95 inhibitor.