Protease inhibitors in buckwheat seeds: Comparison of anionic and cationic inhibitors

Protease inhibitors in buckwheat seeds are separated into two main groups - anionic and cationic inhibitors, according to their behaviour on ion-exchange chromatography. Three anionic inhibitors (BWI-1a, BWI-2a and BWI-4a) and two cationic (BWI-2c and BWI-4c) were purified to homogeneity and characterized. Molecular masses of anionic inhibitors were in the range 7.7-9.2 kD and of cationic 6.0 kD. Both anionic and cationic inhibitors were highly pH- and thermostable. All anionic and cationic inhibitors inhibited trypsin. In addition to trypsin BWI-1a and BWI-2a inhibited chymotrypsin, however, less effectively. Cationic inhibitor BWI-4c besides trypsin and chymotrypsin inhibited also bacterial subtilisin. Inhibitors BWI-1a, BWI-2a, BWI-4a and BWI-2c contain an Arg residue at the reactive site whereas BWI-4c contains a Lys residue. According ro determined amino acid sequences anionic inhibitors BWI-1a, BWI-2a and BWI-4a belong to the potato proteinase inhibitor I family.