Characterization of the active-site residues asparagine 167 and lysine 161of the IMP-1 metallo beta-lactamase

The roles of lysine at position 161 and asparagine at position 167 in IMP-1 metallo beta -lactamase were studied buy site-directed mutagenesis. These residues are highly conserved in metallo beta -lactamases and are thought t o be present in the active-site cavity. Mutant enzymes with alanine or aspa rtic acid at position 161 showed almost the same properties as the wild-typ e enzyme. Kinetic parameters for the mutant enzymes different at position 1 61 indicated that the positive charge of lysine 161 is required for electro static interaction with the carboxyl moiety of the substrate, i.e. C-3 of p enicillins or C-4 of cephalosporins. (C) 2001 Published by Elsevier Science B.V. on behalf of the Federation of European Microbiological Societies.