Inhibitor of serine proteases. Can inhibit trypsin but is ineffective against chymotrypsin, papain and elastase. Strongly inhibits the trypsin-like protease activity isolated from the third instar larva of P.truncatus, and also inhibits more weakly the trypsin-like protease activity isolated from the third instar larva of M.sexta. Protects the plant by inhibiting proteases of invading organisms. Detected in seeds (at protein level).