Chemical modification of lysine residues in Bacillus alpha-amylases: effect on activity and stability

Chemical modification of lysine residues in two bacterial a-amylases, a mes ophilic enzyme from Bacillus amyloliquefaciens (BAA) and a thermophilic enz yme from Bacillus licheniformis (BLA) was carried out using citraconic anhy dride. 13 +/- 1 residues in BAA and 10 +/- 1 residues in BLA were found mod ified under defined experimental conditions. Modification brought about dra matic enhancement of thermal stability of BAA and catalytic activity of BLA . Such alterations were found dependent on the temperature and pH. Results obtained on Tm, the extent of deamidation, changes in the circular dichrois m (CD) spectra and kinetic parameters before and after modification are dis cussed in terms of their contributions to the mechanism of irreversible the rmoinactivation and activity enhancement. (C) 2001 Elsevier Science Inc. Al l rights reserved.