Although b-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 b-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 b-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 a-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 b-lactamases and DD-peptidases showed that it might be as difficult for a DD-peptidase to open the b-lactam ring as it is for the b-lactamases to hydrolyse the peptides, an observation which can be explained by geometric and stereoelectronic considerations.
Peptidase activity of b-lactamases
Rhazi, Noureddine, Page, Michael I. and Frere, Jean-Marie
(1999)
Peptidase activity of b-lactamases.
Biochemical Journal, 341 (2).
pp. 409-413.
ISSN 0264-6021
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