title: Inactivation of Bacillus cereus beta-lactamase I by 6 beta-bromopenicillanic acid: kinetics.
abstract: The kinetics of the inactivation of Bacillus cereus beta-lactamase I by 6 beta-bromopenicillanic acid are described. Loss of beta-lactamase activity is accompanied by a decrease in protein fluorescence, by the appearance of a protein-bound chromophore at 326 nm, and by loss of tritium from 6 alpha-[3H]-6 beta-bromopenicillanic acid. It is shown that all of the above changes probably have the same rate-determining step. The inactivation reaction is competitively inhibited by cephalosporin C, a competitive inhibitor of this enzyme, and by covalently bound clavulanic acid, suggesting that 6 beta-bromopenicillanic acid reacts directly with the beta-lactamase active site. It is proposed that this inhibitor reacts initially as a normal substrate and that the rate-determining step of the inactivation is acylation of the enzyme. A rapid irreversible inactivation reaction rather than normal hydrolysis of the acyl-enzyme then follows acylation; 6 beta-bromopenicillanic acid is thus a suicide substrate.
mesh_terms: D001409:Bacillus cereus / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010397:Penicillanic Acid / Q000494:pharmacology* / Q000031:analogs & derivatives; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D014316:Tritium; D065093:beta-Lactamase Inhibitors
chemical_list: D065093:beta-Lactamase Inhibitors; D014316:Tritium; C018008:brobactam; D010397:Penicillanic Acid