Alpha-amylase that cleaves starch into oligosaccharides, the first step in starch degradation (By similarity). Endo-acting enzyme which prefers a linear polysaccharide to branched polysaccharides hydrolyzing alpha-1,4 glucosidic bonds efficiently. Has also transglycosylation activity, but does not act on alpha-1,6 bonds. Higher activities of 100%, 79% and 67.8% against amylose, soluble starch and amylopectin, respectively. Lower activity of 22% against glycogen and faint or no activity against alpha-, beta- and gamma-cyclodextrin. Endohydrolysis of (1->4)-alpha-D-glucosidic linkages in polysaccharides containing three or more (1->4)-alpha-linked D-glucose units. Stable and active over a broad range of NaCl concentrations (0.5 to 4.2 M NaCl), with maximal activity at 2.6 M NaCl. 83% and 94% of the maximum activity at 0.6 and 4.2 M NaCl, respectively. Active and stable also in KCl. Optimum pH is 6.5 in 2.0 M NaCl. Stable over a range of pH 5.7-9.2. Optimum temperature is 45 degrees Celsius in 2.0 M NaCl and at pH 6.5. Relatively stable up to 55 degrees Celsius. Glycan degradation; starch degradation. Belongs to the glycosyl hydrolase 13 family.