Since only maltooligosaccharides up to a chain length of 6 glucose units are actively transported through the cytoplasmic membrane via the membrane-bound complex of three proteins, MalF, MalG, and MalK, longer maltooligosaccharides must first be degraded by the periplasmic alpha-amylase, the MalS protein. 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. Monomer. Under the regulatory control of the MalT protein. Belongs to the glycosyl hydrolase 13 family.