Endohydrolysis of (1->4)-alpha-D-glucosidic linkages in polysaccharides containing three or more (1->4)-alpha-linked D-glucose units. Binds 1 Ca(2+) ion per subunit. Binds 1 Cl(-) ion per subunit. Monomer. At least 6 electrophoretic isozymes are known: Amy1, Amy2, Amy3, Amy4, Amy5 and Amy6. Strains J87 and KO123 express Amy2; KO140 and 1420#1 express Amy4; L16 expresses Amy5. Belongs to the glycosyl hydrolase 13 family.