Amino acid sequence of the protease inhibitor BWI-4a from buckwheat seeds

The complete amino acid sequence of protease inhibitor BWI-4a from buckwheat (Fagopyrum esculentum Moench) seeds, consisting of 67 amino acid residues with a single disulfide bond, has been established by Edman degradation in combination with matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Its N terminus is blocked by a pyroglutamic acid residue. Mass spectrometric analysis revealed that inhibitor BWI-4a is present in buckwheat seeds in two isoforms with a single amino acid substitution of Ala40 for Gly40. The reactive site of the inhibitor contains an Arg43-Asp44 bond. Analysis of the amino acid sequence suggests that the buckwheat seed protease inhibitor is a member of the potato proteinase inhibitor I family.