Journal
JOURNAL OF BIOCHEMISTRY
Volume 131, Issue 4, Pages 587-591Publisher
JAPANESE BIOCHEMICAL SOC
DOI: 10.1093/oxfordjournals.jbchem.a003138
Keywords
beta-amylase; azide; catalytic mechanism; chemical rescue; site-directed mutant
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The hydrolytic activity of beta-amylase from Bacillus cereus var. mycoides was lost on replacement of either of the catalytic residues (Glu172 or Glu367) with an alanyl residue. When maltopentaose and 2 M azide existed together mutant, E367A cleaved the glucosidic linkage of maltopentaose and produced maltose at pH 7.0 and 25degreesC, but the other mutants (E172A and double mutant E172A/E367A) did not. This indicates that azide acts as a general base instead of E367 and Glu172 acting as general acids, and that the hydroxide ion generated from a water molecule activated by azide attacks a reactive pyranose nucleophilically so that beta-maltose is produced.
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