One deletion mutant was constructed from the structural gene of a truncated Bacillus sp. strain TS-23 alpha-amylase (BAC Delta NC) by site-directed mutagenesis. BAC Delta NC and BAC Delta NC/Delta R210-S211 were overexpressed in recombinant Escherichia coli M15 cells and purified to nearly homologous by nickel-chelate chromatography. BAC Delta NC and BAC Delta NC/Delta R210-S211 were very similar with respect to specific activity, kinetic parameters, pH-activity profile, and temperature-activity curve. An increased half-life at 70 degrees C was observed for BAC Delta NC/Delta R210-S211, suggesting that Arg210-Ser211 deletion leads to a conformational change of the enzyme. Tryptophan emission fluorescence and circular dichroism spectra were nearly identical for the wild-type enzyme and BAC Delta NC/Delta R210-S211, but they showed a different sensitivity towards temperature-induced denaturation. These results indicated that the rigidity of the enzyme has been altered by Arg210-Ser211 deletion. (C) 2008 Elsevier Ltd. All rights reserved.