Abstract:
Selection of alkaliphilic Bacillus sp. from 27 isolates which produce raw-starch bindingalkaline amylase based on the maximum activity of amylase to hydrolyse both raw starch andsoluble starch was conducted. The effect of detergents on enzyme efficiency was alsoinvestigated. Bacillus sp. SS-8 was the best strain among all the isolates. Maximum amylaseactivity was achieved in a medium containing 1.5% (w/v) raw cassava starch as the carbon sourcewith the initial pH of 11, at 37OC. No contamination occurred although the medium was notsterilized. The optimum pH and temperature for starch hydrolysis were pH 10 and 60OC and thecrude enzyme was stable in the broad pH range of 7-10 and 30-60OC for 1 hour.The enzyme was purified to homogeneity by 40-60% saturated ammonium sulfateprecipitation and affinity chromatography by adsorption-desorption on cassava starch. Themolecular mass of the purified enzyme was estimated to be 91 kDa by SDS-PAGE. The purifiedenzyme showed maximum activity at pH 8 and 60OC. It had good stability at pH range of 8-11and 30-60OC for 1 hour. The enzyme was strongly inhibited by 10 mM EDTA. The enzymerequired metal ion Ca2+ and Mg2+ for its enzyme activity. In additions the enzyme wasreactivated by Ca2+ and Mg2+ at 110.51% and 123.66%, respectively. However, the enzyme wasnot reactivated by Co2+, Cu2+, Fe2+, Mn2+, Zn2+. However, thermostability was not increased in thepresence of Ca2+ or Mg2+. The raw starch-binding amylase from Bacillus sp. SS-8 preferentiallyhydrolysed ?-1,4 glycosidic bond in soluble starch, amylose, amylopectin and glycogen togenerate glucose, maltose and oligosaccharides. But could not hydrolyse dextran which contains?-1,3 and ?-1,6 glycosidic bonds. This evidence suggested that the enzyme was an endo-actingamylase and it could digest raw-starch granules from wheat higher than rice, corn, cassava, cannaand sago, respectively.