Important for breakdown of endosperm starch during germination. Endohydrolysis of (1->4)-alpha-D-glucosidic linkages in polysaccharides containing three or more (1->4)-alpha-linked D-glucose units. Binds 3 Ca(2+) ions per subunit. Monomer. More abundant in germinating seeds, than in callus, young roots and leaves. Expressed at a high level during germination in the aleurones cells under the control of the plant hormone gibberellic acid and in the developing grains at a low level. Only cereal amylase known to be glycosylated. Binds starch not only at the active site, but also via accessory binding sites on the protein surface that are important for efficient binding to starch granules and thereby increase enzyme activity. Belongs to the glycosyl hydrolase 13 family.