Hydrolysis of 3-substituted cephalosporins catalysed by ?-lactamases I and II from Bacillus cereus and by hydroxide ion

Buckwell, Stephen C., Page, Michael I., Longridge, Jethro L. and Waley, Stephen G. (1988) Hydrolysis of 3-substituted cephalosporins catalysed by ?-lactamases I and II from Bacillus cereus and by hydroxide ion. Journal of the Chemical Society, Perkin Transactions 2 (10). pp. 1823-1827. ISSN 1472-779X

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 -lactam ring is opened and the expulsion of the leaving group does not enhance the rate of -lactam C–N bond fission. The zinc enzyme -lactamase II is about a 100-fold better catalyst than the serine enzyme -lactamase I for the hydrolysis of the same cephalosporin. The second-order rate constant kcat/Km for both -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 -lactamase I-catalysed hydrolysis may be complicated by the formation of intermediates.

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