Carboxy groups as essential residues in beta-lactamases.
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ABSTRACT:
SUBMITTER: Little C
PROVIDER: S-EPMC1147395 | biostudies-other | 1986 Nov
REPOSITORIES: biostudies-other
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Project description:Although beta-lactamases have generally been considered as being devoid of peptidase activity, a low but significant hydrolysis of various N-acylated dipeptides was observed with representatives of each class of beta-lactamases. The kcat/Km values were below 0.1 M(-1). s(-1), but the enzyme rate enhancement factors were in the range 5000-20000 for the best substrates. Not unexpectedly, the best 'peptidase' was the class C beta-lactamase of Enterobacter cloacae P99, but, more surprisingly, the activity was always higher with the phenylacetyl- and benzoyl-d-Ala-d-Ala dipeptides than with the diacetyl- and alpha-acetyl-l-Lys-d-Ala-d-Ala tripeptides, which are the preferred substrates of the low-molecular-mass, soluble dd-peptidases. A comparison between the beta-lactamases and dd-peptidases showed that it might be as difficult for a dd-peptidase to open the beta-lactam ring as it is for the beta-lactamases to hydrolyse the peptides, an observation which can be explained by geometric and stereoelectronic considerations.
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Project description:An acyl-enzyme was isolated from certain chromosomal beta-lactamases and a penicillin. 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 from the mutant of Pseudomonas aeruginosa 18 S that produces the beta-lactamase constitutively [Flett, Curtis & Richmond (1976) J. Bacteriol. 127, 1585-1586; Berks, Redhead & Abraham (1982) J. Gen. Microbiol., in the press] and from Escherichia coli K-12 (the ampC beta-lactamase) [Boman, Nordström & Normak (1974) Ann. N.Y. Acad. Sci. 235, 569-586]. The acyl-enzymes have been degraded to determine the residue labelled, and the sequence around it. The residue labelled is serine. The sequences around the labelled serine in these two beta-lactamases are exceedingly similar. However, the sequences are quite different from those around the active site serine in the beta-lactamases previously studied. There is thus more than one class of serine beta-lactamases.
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