title: The acyl-enzyme mechanism of beta-lactamase action. The evidence for class C Beta-lactamases.
abstract: Methanol or ethanol can replace water in the action of certain chromosomal beta-lactamases on benzylpenicillin: the products are alpha-methyl or alpha-ethyl benzylpenicilloate. The beta-lactamases were from a mutant of Pseudomonas aeruginosa 18S that produces the enzyme constitutively [Flett, Curtis & Richmond (1976) J. Bacteriol. 127, 1585-1586; Berks, Redhead & Abraham (1982) J. Gen. Microbiol. 128, 155-159] and from Escherichia coli K12 (the ampC beta-lactamase) [Lindström, Boman & Steele (1970) J. Bacteriol. 101, 218-231]. The variation of the rates of alcoholysis and hydrolysis with concentration of alcohol show that the rate-determining step is breakdown of an intermediate. This intermediate is likely to be the acyl-enzyme. The esters, alpha-methyl or alpha-ethyl benzylpenicilloate, are themselves substrates for the Pseudomonas beta-lactamase, benzylpenicilloic acid being formed. Thus this beta-lactamase can be an esterase. The kinetics for the hydrolysis of cloxacillin by the Pseudomonas beta-lactamase are consistent with the acyl-enzyme, formed by acylation of serine-80, being an intermediate in the overall hydrolysis.
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D004926:Escherichia coli / Q000201:enzymology; D000431:Ethanol; D007527:Isoenzymes / Q000145:classification / Q000378:metabolism*; D007700:Kinetics; D000432:Methanol; D010400:Penicillin G / Q000378:metabolism; D011550:Pseudomonas aeruginosa / Q000201:enzymology; D001618:beta-Lactamases / Q000145:classification / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D007527:Isoenzymes; D000431:Ethanol; D001618:beta-Lactamases; D010400:Penicillin G; D000432:Methanol