Biochemical Study on the Nonprotein Trypsin and Chymotrypsin Inhibitors in the Soybean

The chemical properties of nonprotein trypsin inhibitor (NPTI) and nonprotein chymotrypsin inhibitor (NPCTI) in the soybean were studied. NPTI was extracted with 50% methanol and treated with TCA to a final concentration of 16% (W/V). Two dimensional thin‐layer chromatography was used to make a peptide map of the methanol extract; 14 spots were observed. To distinguish the active peptides, the sample was mixed with trypsin or chymotrypsin; some peptides disappeared which formed complexes with the enzyme. The relative rate of inhibition indicated that inhibition was stoichiometric for trypsin and chymotrypsin. Dissociation constants of complexes (enzyme and inhibitor) showed that inhibition of chymotrypsin and trypsin were competitive and uncompetitive, respectively.