In our experimentes, it has been demonstrated that the N-terminal fragment of the mungbean inhibitor could be isolated by affinity chromatography with immobilized trypsin aftertreating the inhibitor with CNB_r and pepsin. The properties of this active fragment have beenstudied. The C-terminal fragment of the hihibitor, however, will lose its activity during CNB_rcleavage because of the scission of the methionyl peptide bond near the active center. It isdeemed desirable to find out a more suitablo method for the cleavage of these two domains,both retaining inhibitory activity. Ths aim has new been achieved by using peptic digestion only, and the active centers ofthese two domains are identified as Lys and Arg by chemical modification. In alkaline pH,these two active fragments could be easily separated by affinity chromatography with immobi-lized trypsin. This amkes it possible to study and compare these two active fragmentsseparately. It is worth pointing out that such a C-terminal fragment with trypsin inhibitory activityhas not yet been reported among the Bowman-Birk inhibitors. The activities of the mung bean trypsin inhibitor decrease to about 50% during thecourse of modification with maleic anhydride and phenylglyoxal respectively. The two activecenters seem to be Lys nd Arg. The mung bean inhibitor could endure peptic digestionwithout any loss of activyty. On Sephadex gel filtration, two smaller active fragments with asize approximately one half of the original molecule are found. At pH 11.4 these two activefragments could be separated from each other by affinity chromatography with immobilizedtrypsin. The active fragment with Lys as the active center could be completely inhibitedwith maleic anhydride and the activity is completely restored after incubation at pH 3.5.This fragmeut consists of two paptide chains with about 35 amino acil residues. The N-termini are found to be Ser and Phe, and the C-termini to be Leu and Met. The activityof the fragment with Arg as the active center could be inhibited completely by phenylglyoxal.This fragment is a single peptide chain with about 27 amino acid residues. The N- and C-terminis are shown to be Asn and Asp respectively. In our experimentes, it has been demonstrated that the N-terminal fragment of the mungbean inhibitor could be isolated by affinity chromatography with immobilized trypsin aftertreating the inhibitor with CNB_r and pepsin. The properties of this active fragment have been determined. The C-terminal fragment of the hihibitor, however, will lose its activity during CNB_rcleavage because of the scission of the methionyl peptide bond near the active center. It isdeemed desirable to find out a more suitablo method for the cleavage of these two domains, both retaining inhibitory activity. Ths aim has new been achieved by using peptic digestion only, and the active centers of the two proteins are identified as Lys and Arg by chemical modification. In alkaline pH, these two active fractions could be separated by affinity chromatography with immobi-lized trypsin. This amkes it possible to study and compare these two active fragmentsseparately. It is worth pointing out that such a a C-terminal frag ment with trypsin inhibitory activityhas not yet been reported among the Bowman-Birk inhibitors. The activities of the mung bean trypsin inhibitor decrease to about 50% during thecourse of modification with maleic anhydride and phenylglyoxal respectively. The two activecenters seem to be Lys nd Arg. The mung bean inhibitor could endure peptic digestionwithout any loss of activyty. On Sephadex gel filtration, two smaller active fragments with asize approximately one half of the original molecule are found. At pH 11.4 these two activefragments could be separated from each other by affinity chromatography with The active fragment with Lys as the active center could be completely inhibited with maleic anhydride and the activity is completely restored after incubation at pH 3.5. These fragmeut consists of two paptide chains with about 35 amino acil residues. The N-termini are found to be Ser and Phe, and the C-termini to be Leu and Met. The activity of the fragment with Argas the active center could be inhibited completely by phenylglyoxal. This fragment is a single peptide chain with about 27 amino acid residues. The N- and C-terminis are shown to be Asn and Asp respectively.