RESUMEN
a-amylase (1,4-a-D-glucan glucanohydrolase, EC 3.2.1.1) production by thermophilic Bacillus sp strain SMIA-2 cultivated in liquid media containing soluble starch reached a maximum at 48h, with levels of 57U/mL. Studies on the a-amylase characterization revealed that the optimum temperature for activity was 70§C. The enzyme was stable for 2h at 50§C, while at 60§C, 70§C and 90§C, (4 per cent), 13(per cent) and 38(per cent) of the original activities were lost, respectively. The optimum pH of the enzyme was 7.5. After incubation of crude enzyme solution for 24h at pH 7.5, a decrease of about 5(per cent) of its original activity was observed. The enzyme was strongly inhibited by Co2+, Cu2+ and Ba2+, but less affected by Ca2+, Mg2+, Ni2+, Sr2+ and Mn2+. The enzyme in 1M and 5M NaCl solutions the enzyme retained 70(per cent) and 47(per cent) of the original activity after 24h of incubation at 4§C, respectively.