Peptidase activity of beta-lactamases.
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.
Centre d'Ingénierie des Protéines and Laboratoire d'Enzymologie, Université de Liège, Institut de Chimie B6, Sart Tilman, B-4000 Liège, Belgium.
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N
Rhazi
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Galleni
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Page
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Frère
D001407:Bacillus / Q000201:enzymology; D002268:Carboxypeptidases / Q000737:chemistry / Q000378:metabolism*; D002384:Catalysis; D006868:Hydrolysis; D013379:Substrate Specificity; D001618:beta-Lactamases / Q000737:chemistry / Q000378:metabolism*
D002268:Carboxypeptidases; D001618:beta-Lactamases