Complete amino acid sequence of an alpha-amylase inhibitor in wheat kernel

We recently purified a new alpha-amylase inhibitor (called 0.53-inhibitor according to its mobility on polyacrylamide gel electrophoresis, at pH 8.5, relative to Bromophenol blue (taken as 1), under the conditions described by O'Donnell, M.D. and McGeeney, K.F. (1976) Biochim. Biophys. Acta 422, 159-169)) from wheat kernel, which has 500-times greater inhibitory activity towards human salivary amylase than towards human pancreatic amylase (Maeda, K., Takemori, Y. and Oka, O. (1982) Agric. Biol. Chem. 41, 2873-2875). Elucidation of the primary structure and structural comparison with other amylase inhibitors are essential to understand the mechanism of the selective inhibitory behavior of 0.53-inhibitor. The complete amino acid sequence of 0.53-inhibitor has been determined after cleaving the protein with CNBr and trypsin separately. 0.53-Inhibitor is composed of two identical subunits with 124 amino acid residues and contains nine cysteine residues in each subunit. Comparison of the sequence of 0.53- and 0.28-inhibitor, which is a major alpha-amylase inhibitor in wheat, with Mr 12 000, of monomeric form, shows high sequence homologies of nine cysteine regions, but significant differences are evident.