Active sites of β-lactamases. The chromosomal β-lactamases of Pseudomonas aeruginosa and Escherichia coli

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Abstract
An acyl-enzyme was isolated from certain chromosomal .beta.-lactamases and a pencillin. The penicillin was cloxacillin which, although it is a substrate for these enzymes, has such a low Kcat that it functions as an inhibitor. The enzymes were isolated from a mutant of P. aeruginosa 18 S that produces the .beta.-lactamase constitutively and from E. coli K-12 (the ampC .beta.-lactamase). The acyl-enzymes were degraded to determine the residue labeled and the sequence around it. The residue labeled is serine. The sequences around the labeled serine in these 2 .beta.-lactamases are exceedingly similar. The sequences are quite different from those around the active site serine in the .beta.-lactamases previously studied. There is apparently more than 1 class of serine .beta.-lactamases.