Second-order rate constants for the hydroxide ion-catalysed hydrolysis of 6-alkyl penicillins are independent of the length of the alkyl side-chain and replacement of the amido by an amino group decreases the susceptibility to nuclephilic attack on 6-aminopenicillanic acid only three-fold. B. cereus-lactamase I catalyses the hydrolysis of 6-alkyl penicillins with values of Kcat/Km which are at least 50-fold greater than that shown by 6-aminopenicillanic acid. For the enzyme-catalysed reaction Kcat/Km increases with increasing chain length, reaching a maximum with hexylpenicillin, and then decreases. The binding energy of the alkyl group is weak, only 1.45 kJ mol–1 per methylene residue. Although there appears to be a recognition site for the amido group there is no specific pocket in -lactamase I for the recognition of hydrophobic residues in the 6-acylamido side-chain of penicillins.
Hydrolysis of 6-alkyl penicillins catalysed by ?-lactamase I from Bacillus cereus and by hydroxide ion
Buckwell, Stephen C., Page, Michael I. and Longridge, Jethro L.
(1988)
Hydrolysis of 6-alkyl penicillins catalysed by ?-lactamase I from Bacillus cereus and by hydroxide ion.
Journal of the Chemical Society, Perkin Transactions 2 (10).
pp. 1809-1813.
ISSN 1472-779X
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