A trypsin inhibitor from Dimorphandra mollis seeds was isolated to apparent homogeneity by a combination of ammonium sulfate precipitation, gel filtration, ion-exchange and affinity chromatographic techniques. SDS-PAGE analysis gave an apparent molecular weight of 20 kDa, and isoelectric focusing analysis demonstrated the presence of three isoforms. The partial N-terminal amino acid sequence of the purified protein showed a high degree of homology with various members of the Kunitz family of inhibitors. This inhibitor, which inhibited trypsin activity with a K-i of 5.3 x 10(-10) M, is formed by a single polypeptide chain with an arginine residue in the reactive site. (C) 2000 Elsevier Science Ltd. All rights reserved.546553558