Complete amino acid sequence of an alpha-amylase inhibitor in wheat kernel (0.19-inhibitor).

Amino acid composition of the 0.19-inhibitor from wheat kernel is very similar to that of the 0.53-inhibitor, but a marked difference in inhibitory activity towards human salivary and pancreatic alpha-amylases was detected between the two inhibitors. Elucidation of the primary structure of the 0.19-inhibitor and structural comparison with the 0.53-inhibitor is essential to understand not only the mechanism of the selective inhibitory behaviors but also evolutional relationship of these inhibitors. The complete amino acid sequence of the 0.19-inhibitor was determined after cleaving the protein with cyanogen bromide and trypsin. As in the case for the 0.53-inhibitor, the 0.19-inhibitor is composed of two identical subunits with 124 amino acid residues. Comparison of the sequence of the 0.53- and 0.19-inhibitor shows very high sequence homology with amino acid substitutions at seven positions.