Chemical and Physicochemical Characterization of the Permanent and Temporary Trypsin Inhibitors from Buckwheat

Abstract

Seven buckwheat trypsin inhibitors (BTI’s) were characterized in terms of their chemical and physicochemical properties. Among them, the four permanent inhibitors, BTI I, Ha, lib, and Ilia had molecular weights of about 6000 to 7600. They were composed of 51 to 67 amino acid residues including two half-cystine residues, and their amino acid compositions were closely related. The amino-terminal residue and the carboxyl-terminal sequence of these inhibitors were leucine and -Ala-Met-Val, respectively. On the other hand, the three temporary inhibitors, BTI He, Illbl, and IIIb2, had molecular weights of approximately 10,000 to 11,500. These inhibitors comprised 85 to 99 amino acid residues including eight half-cystine residues and had very similar amino acid compositions. The inhibitors possessed the identical amino-terminal residue, serine, and the identical carboxyl-terminal sequence, -Asp-Leu-Asn.

These suggest that a high degree of homology exists among the permanent inhibitors or among the temporary inhibitors. Thus, the trypsin inhibitors in buckwheat seeds were found to be composed of at least two different groups, i.e., the permanent isoinhibitors of low molecular weights and the temporary isoinhibitors of comparatively high molecular weights.