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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.

Single-turnover and steady-state kinetics of hydrolysis of cephalosporins by β-lactamase I from Bacillus cereus