title: Single-turnover and steady-state kinetics of hydrolysis of cephalosporins by beta-lactamase I from Bacillus cereus.
abstract: The kinetics of the hydrolysis of two cephalosporins by beta-lactamase I from Bacillus cereus 569/H/9 has been studied by single-turnover and steady-state methods. Single-turnover kinetics could be measured over the time scale of minutes when cephalosporin C was the substrate. The other substrate, 7-(2',4'-dinitrophenylamino)deacetoxycephalosporanic acid, was hydrolysed even more slowly, and has potential for use in crystallographic studies of beta-lactamases. Comparison of single-turnover and steady-state kinetics showed that, for both substrates, opening the beta-lactam ring (i.e. acylation of the enzyme) was the rate-determining step. Thus the non-covalent enzyme-substrate complex is expected to be the intermediate observed crystallographically.
mesh_terms: D000645:Ammonium Sulfate / Q000494:pharmacology; D001409:Bacillus cereus / Q000201:enzymology*; D002511:Cephalosporins / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D010405:Penicillinase / Q000378:metabolism*; D013053:Spectrophotometry
chemical_list: D002511:Cephalosporins; D010405:Penicillinase; D000645:Ammonium Sulfate