The purified acidic alpha-amylase of Bacillus acidicola is a monomer of 66.0 kDa, optimally active at pH 4.0 and 60 A degrees C. The enzyme is Ca2+ independent with T (1/2) for 18 min at 80 A degrees C. The K (m), V (max), and catalytic efficiency (k (cat)/K (m)) of the enzyme are 1.6 mg mL(-1), 23.8 mu mol mg(-1) min(-1), and 981 mu mol s(-1), respectively. Among detergents, Tween 20, 40, and 80 stimulated enzyme activity, whereas sodium dodecyl sulfate and Triton X-100 inhibited even at low concentration. EGTA has not affected the activity, whereas EDTA beta-mercaptoethanol, iodoacetic acid, and Dithiothreitol exhibited a slight inhibitory action. Phenylmethanesulfonyl fluoride, N-bromosuccinimide, and Hg2+ strongly inhibited enzyme activity. The experimental activation energy and temperature quotient are 50.12 kJ mol(-1) and 1.37. When thermodynamic parameters (Delta H and Delta S) of the enzyme have been determined at different temperatures, Delta G is positive suggesting that the enzyme is thermostable. The enzyme hydrolyzes raw starches, and therefore, the enzyme finds application in raw starch saccharification at sub-gelatinization temperatures that saves energy needed for gelatinization of raw starch at 105 A degrees C.