Purification and sequence analysis of the atypical maltohexaose-forming alpha-amylase of the B-stearothermophilus US100

The maltohexaose-forming alpha -amylase, of B. stearothermophilus US100, wa s purified to homogeneity by a combination of osmotic shack, starch adsorpt ion and anion exchange chromatography. This enzyme has a relative molecular mass of 59 kDa. The analysis of the nucleotide sequence, of the correspond ing gene, allowed the identification of a single open reading frame encodin g a 549 amino acid protein, exhibiting a large homology to the other B. ste arothermophilus alpha -amylases. This homology reaches a maximum with those of DY-5 and DN1792 strains with respectively 3 and 4 aa different over 549 . The relatively small differences, between Amy US100 and that of DN1792 st rain, take in more importance since we have demonstrated that these enzymes differ essentially by their starch hydrolysis pattern. (C) 2001 Elsevier S cience Inc. All rights reserved.