Abstract
An alpha-amylase gene of Bacillus subtilis (natto) IAM1212 was cloned in a lambda EMBL3 bacteriophage vector, and the nucleotide sequence was determined. An open reading frame encoding the alpha-amylase (AMY1212) consists of 1,431 base pairs and contains 477 amino acid residues, which is the same in size as the alpha-amylase (AMY2633) of B. subtilis 2633, an alpha-amylase-hyperproducing strain, and smaller than that of B. subtilis 168, Marburg strain. The amino acid sequence of AMY1212 is different from that of AMY2633 at five residues. Enzymatic properties of these two alpha-amylases were examined by introducing the cloned genes into an alpha-amylase-deficient strain, B. subtilis M15. It was revealed that products of soluble starch hydrolyzed by AMY1212 are maltose and maltotriose, while those of AMY2633 are glucose and maltose. From the detailed analyses with oligosaccharides as substrates, it was concluded that the difference in hydrolysis products of the two similar alpha-amylases should be ascribed to the different activity hydrolyzing low-molecular-weight substrates, especially maltotriose; AMY1212 slowly hydrolyzes maltotetraose and cannot hydrolyze maltotriose, while AMY2633 efficiently hydrolyzes maltotetraose and maltotriose. Further analyses with chimeric alpha-amylase molecules constructed from the cloned genes revealed that only one amino acid substitution is responsible for the differences in hydrolysis products.