Purification and characterisation of a malto-oligosaccharide-forming amylase active at high pH from Bacillus clausii BT-21

Bacillus clausii BT-21 produced an extracellular malto-oligosaccharide-forming amylase active at high pH when grown on starch substrates. The enzyme was purified to homogeneity by affinity and anion-exchange chromatography. The molecular weight of the enzyme estimated by sodium dodecyl sulfate polyacrylamide electrophoresis was 101 kDa. The enzyme showed an optimum of activity at pH 9.5 and 55 °C. Maltohexaose was detected as the main initially formed starch hydrolysis product. Maltotetraose and maltose were the main products obtained after hydrolysis of starch by the enzyme for an extended period of time and were not further degraded. The enzyme readily hydrolysed soluble starch, amylopectin and amylose, while cyclodextrins, pullulan or dextran were not degraded. The mode of action during hydrolysis of starch indicated an exo-acting type of amylolytic enzyme mainly producing maltohexaose and maltotetraose. Amino acid sequencing of the enzyme revealed high homology with the maltohexaose-forming amylase from Bacillus sp. H-167.