Abstract: The activities of three serine proteases in thc midgut of Helicoverpaarmigera larvae were partially characterized. The enzymes were an active alkalinetrypsin-like enzyme with maximal hydrolysis of benzoyl arginine p-nitroanilideat pH 10.50 or higher, a weak alkaline trypsin-like enzyme with maximalhydrolysis of tosyl-L-arginine methyl ester at pH 8.50～9.00, and achymotrypsin-like enzyme with maximal hydrolysis of benzoyl- L- tyrosine ethylester at pH 8.50～9.00.Total proteolysis, measured by using azocasein, hadamaximal activity at pH 10.50 or higher. Ca2+had no activation effect on larval proteases, but Mg2+activated the weak alkaline trypsin-like enzyme. The inhibition with phenyl methyl sulfonyl fluoride and tosyl- L- lysine chloromethyl ketoneto the weak alkaline trypsin-like enzyme activity was greater than that to the active alkaline trypsin- like enzyme activity. The tosyl- L - phenylalininechloromethyl ketone was not only the inhibitor of the chymotrypsin-like enzyme,but also the activator of the weak alkaline trypsin-like enzyme. Comparison between the insect protease and bovine counterpart protease revealed difference in inhibitor sensitivity. Ovomucoid trypsin inhibitor that inhibited bovine trypsin had no effect on insect trypsin-like enzymes. Soybean trypsin inhibitor had great inhibition on both insect and bovine proteases.

Key words: Helicoverpa arrnigera, protease, activator, inhibitor