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FEMS Microbiol Lett. 1998 Dec 15;169(2):289-93.

Effect of substitution of Asn for Arg-276 in the cefotaxime-hydrolyzing class A beta-lactamase CTX-M-4.

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Department of Microbiology, Medical School, University of Athens, Greece.


The effect of substitution of asparagine for arginine at position 276 (Ambler's numbering) on the properties of the extended-spectrum beta-lactamase CTX-M-4 was studied. Compared with CTX-M-4, the mutant beta-lactamase CTX-M-4(R276N) conferred lower levels of resistance to cefotaxime, ceftriaxone and aztreonam while the levels of resistance to penicillins and penicillin-inhibitor combinations were similar. Arg-276-->Asn substitution rendered CTX-M-4 slightly less susceptible to inhibition by clavulanate and tazobactam. It also caused a three-fold reduction in the relative rate of hydrolysis of cefotaxime. These results indicate that Arg-276 in CTX-M-type beta-lactamases may be implicated in hydrolysis of oxyimino-beta-lactams; they do not, however, support the hypothesis that Arg-276 is the functional equivalent of Arg-244 found in other class A beta-lactamases.

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