Alpha-amylase displaying a robust amylolytic activity toward p-nitrophenyl maltoheptaoside (BPNP-G7), amylopectin and beta-limit dextrin (PubMed:24089528). 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. Redox-insensitive. Optimum pH is 5.5 with p-nitrophenyl maltoheptaoside or amylopectin as substrate. Monomer. Production of alpha-amylase is hormonally regulated. Germinating embryos produce the hormone gibberellic acid, which within 10 hours stimulates the aleurone cells covering the endosperm of the seed to produce alpha-amylase. The enzyme then degrades the starch within the endosperm for use by the developing plant embryo. There are at least 4 types of alpha-amylase in barley. Mutagenesis experiments indicate that His-117 and His-314 participate in transition state stabilization but not directly in catalysis. 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.