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Metabolism and Enzymology

Wheat Inhibitors of Heterologous -Amylases ¹

Characterization of Major Components from the Monomeric Class

Departmento de Bioquímica, E.T.S. Ingenieros Agrónomos, 28040 Madrid, Spain, Departmento de Bioquímica, Facultad de Medicina, Universidad de Oviedo, 33006 Oviedo, Spain

The four major components of the wheat monomeric -amylase inhibitors (WMAI) from wheat, Triticum aestivum, endosperm have been isolated and characterized. Two of them, WMAI-1 and WMAI-2, are highly active against the -amylase from the insect Tenebrio molitor and their N-terminal amino acid sequences indicate that they are closely related to each other (86% identical residues) and to the other members of the family (subunits of dimeric and tetrameric -amylase inhibitors and trypsin inhibitors). WMAI-1, which is identical to the previously described 0.28 inhibitor, is encoded by a gene located in the short arm of chromosome 6D and WMAI-2 by a gene in the short arm of chromosome 6B. Components 3 and 4, which have blocked N-terminal residues, have identical internal amino acid sequences and are a separate class of proteins with respect to WMAI-1 and WMAI-2, although their amino acid composition and apparent molecular weights are quite similar. Their inhibitory activity versus -amylases is either unstable during the purification process or due to contamination with other inhibitors.