Characteristics of two forms of alpha-amylases and structural implication

Complete (Ba-L) and truncated (Ba-S) forms of alpha-amylases from Bacillus subtilis X-23 were purified, and the amino- and carboxyl-terminal amino aci d sequences of Ba-L and Ba-S were determined. The amino acid sequence deduc ed from the nucleotide sequence of the alpha-amylase gene indicated that Ba -S was produced from Ba-L by truncation of the 186 amino acid residues at t he carboxyl-terminal region. The results of genomic Southern analysis and W estern analysis suggested that the two enzymes originated from the same alp ha-amylase gene and that truncation of Ba-L to Ba-S occurred during the cul tivation of B. subtilis X-23 cells. Although the primary structure of Ba-S was approximately 28% shorter than that of Ba-L, the two enzyme forms had t he same enzymatic characteristics (molar catalytic activity, amylolytic pat tern, transglycosylation ability, effect of pH on stability and activity, o ptimum temperature, and raw starch-binding ability), except that the therma l stability of Ba-S was higher than that of Ba-L. An analysis of the second ary structure as well as the predicted three-dimensional structure of Ba-S showed that Ba-S retained all of the necessary domains (domains A, B, and C ) which were mast likely to be required for functionality as alpha-amylase.