TABLE 3.

Substrate and inhibitor profiles of purified CTX-M-5 β-lactamase

Substrate or inhibitor	kcat (s−1)	Relative kcat	Km (μM)	kcat/Km (mM−1s−1)	IC50 (nM)
Substrates
Benzylpenicillin	230	100	50	4,600
Cephaloridine	1,500	680	350	4,400
Cefotaxime	210	95	77	2,800
Ceftazidime	7.4	3.3	440	17
Aztreonam	21	9.3	730	29
Cefoxitin	0.41	0.18	NCa	NC
Imipenem	0.0027	0.0012	NC	NC
Inhibitors
Clavulanic Acid					19
Sulbactam					100
Tazobactam					3.3

^aNC, not calculated (rates were too low to obtain reliable values).