A novel trypsin inhibitor was purified from the seeds of Peltophorum dubium (Spreng.). SDS-PAGE under reducing conditions showed that the inhibitor consisted of a single polypeptide chain (ca. 20 kDa). The dissociation constants of 4x10(-10) and 1.6x10(-10) M were obtained with bovine and porcine trypsin, respectively. This constant was lower (2.6x10(-7) M) for chymotrypsin. The inhibitory activity was stable over a wide range of temperature and pH and in the presence of DTT. The N-terminal sequence of the P. dubium inhibitor showed a high degree of homology with other Kunitz-type inhibitors. When fed to the insect Anagasta kuehniella, in an artificial diet (inhibitor concentration 1.6%), the inhibitor produced similar to56% and delayed the development of this lepidopteran. The concentration of inhibitor in the diet necessary to cause a 50% reduction in the weight (ED50) of fourth instar larvae was similar to1%. The action of the P dubium trypsin inhibitor (PDTI) on A. kuehniella may involve inhibition of the trypsin-like activity present in the larval midgut, resistance of the inhibitor to digestion by midgut enzymes and bovine trypsin, and association of the inhibitor with a chitin column and chitinous structures in the peritrophic membrane and/or midgut of the insect. (C) 2003 Elsevier Science B.V. All rights reserved.16212170182