The anionic protease inhibitor BWI-1 from buckwheat seeds. Kinetic properties and possible biological role

Kinetic characteristics and effects on the growth of filamentous fungi of one of the main anionic protease inhibitors, BWI-1, isolated from buckwheat seeds, have been studied. The inhibition constants of bovine trypsin, chymotrypsin and cathepsin G from human granulocytes with BWI-1 were found to be 1.1, 67 and 200 nM, respectively. Analysis of the amino acid sequence of BWI-1 in the vicinity of the reactive site revealed its homology to the potato proteinase inhibitor I family. It is suggested that the inability of BWI-1 to bind elastase of human granulocytes is due to the basic nature of the amino acid residue (Arg) at the P₁ position in its reactive site. It was demonstrated that BWI-1 was able to suppress the germination of the spores and the growth of the mycelium of two filamentous fungi.