Hydrolysis of 3-substituted cephalosporins catalysed by β-lactamases I and II from Bacillus cereus and by hydroxide ion
- 1 January 1988
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 10,p. 1823-1827
- https://doi.org/10.1039/p29880001823
Abstract
Second-order rate constants for the alkaline hydrolysis of 3-thiol substituted cephalosporins are independent of the pKa of the thiol over a pKa range of 9. If there is a leaving group at C-3′ it is expelled after the β-lactam ring is opened and the expulsion of the leaving group does not enhance the rate of β-lactam C–N bond fission. The zinc enzyme β-lactamase II is about a 100-fold better catalyst than the serine enzyme β-lactamase I for the hydrolysis of the same cephalosporin. The second-order rate constant kcat/Km for both β-lactamase enzymes shows no dependence on the nature of the substituent at C-3′ which is not explicable by the different chemical reactivity of the cephalosporins. There is no evidence for a significant recognition site in either enzyme for the C-3′ substituent. The kinetic parameters kcat and Km for the β-lactamase I-catalysed hydrolysis may be complicated by the formation of intermediates.Keywords
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