title: Studies on the mechanism of action of imipenem (N-formimidoylthienamycin) in vitro: binding to the penicillin-binding proteins (PBPs) in Escherichia coli and Pseudomonas aeruginosa, and inhibition of enzyme activities due to the PBPs in E. coli.
abstract: The binding affinities of imipenem (N- formimidoylthienamycin ) to penicillin-binding proteins ( PBSs ) of Escherichia coli and Pseudomonas aeruginosa were determined by two different methods in which competition with [14C]benzylpenicillin for the binding sites was measured. By both methods imipenem was shown to have very high binding affinities to PBPs-2 and -4 in E. coli and P. aeruginosa, and appreciable affinities to most of their other major PBPs. But higher concentrations of imipenem were required for binding to the PBPs-3 in these bacteria. More direct information about the antibacterial activity of imipenem was obtained by measuring its inhibition of the peptidoglycan-synthetic enzyme activities of E. coli PBPs. The results of enzyme inhibitions were compatible with those obtained in binding experiments. The antibiotic inhibited the transpeptidase activities of PBPs-1A, -1B and -2, and the D-alanine carboxypeptidase activities of PBPs-4 and -5. The antibiotic also seemed to cause strong inhibition of the transglycosylase activity of PBP-1A by some unknown mechanism. It inhibited the transpeptidase activity of PBP-3 only weakly, which is consistent with the findings that it had low binding affinity to PBP-3 and did not inhibit septum formation by the cells.
mesh_terms: D000217:Acyltransferases / Q000037:antagonists & inhibitors*; D000900:Anti-Bacterial Agents / Q000633:toxicity*; D001426:Bacterial Proteins; D002268:Carboxypeptidases / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D006602:Hexosyltransferases / Q000037:antagonists & inhibitors* / Q000302:isolation & purification; D015378:Imipenem; D007700:Kinetics; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors* / Q000302:isolation & purification; D002267:Muramoylpentapeptide Carboxypeptidase / Q000378:metabolism*; D046915:Penicillin-Binding Proteins; D010406:Penicillins / Q000378:metabolism*; D010458:Peptidyl Transferases / Q000037:antagonists & inhibitors* / Q000302:isolation & purification; D011485:Protein Binding; D011550:Pseudomonas aeruginosa / Q000378:metabolism*; D013845:Thienamycins / Q000633:toxicity*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D002352:Carrier Proteins; D009097:Multienzyme Complexes; D046915:Penicillin-Binding Proteins; D010406:Penicillins; D013845:Thienamycins; D015378:Imipenem; D000217:Acyltransferases; D010458:Peptidyl Transferases; D006602:Hexosyltransferases; D002268:Carboxypeptidases; D002267:Muramoylpentapeptide Carboxypeptidase