Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The present paper describes the purification, characterization and determination of the partial primary structure of the first trypsin inhibitor isolated from the family Sapindaceae. A highly stable, potent trypsin inhibitor (SSTI) was purified to homogeneity. SDS-PAGE analysis revealed that the protein consists of a two-polypeptide chain with molecular masses of approximately 15 and 3 kDa. The purified inhibitor inhibited bovine trypsin at a 1:1 M ratio. Kinetic analysis revealed that the protein is a competitive inhibitor with an equilibrium dissociation constant of 10(-9) M for trypsin. The partial NH(2)- terminal sequence of 36 amino acids in SSTI indicates homology with other members of the trypsin-inhibitor family from different sources. This inhibitor is highly stable in the presence of denaturing agents. SSTI showed significant inhibitory activity against trypsin-like proteases present in the larval midgut on Anagasta kuehniella, Corcyra cephalonica, Diatreae saccharalis and Anticarsia gemmatalis.301919FUNDECT(Fundacao de Apoio ao Desenvolvimento do Ensino, Ciencia e Tecnologia do Estado de Mato Grosso do Sul)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)PROPP/UFMS (Pro-Reitoria de Pesquisa e Pos-graduacao da Universidade Federal de Mato Grosso do Sul)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)