TABLE 2.

Steady-state kinetic parameters of purified CMY-2 and CMY-33 plasmid-mediated AmpC β-lactamases^a

β-Lactamb	Km or Ki app (μM)c		kcat or kinact for inhibitors (s−1)		kcat /Km or kinact/Ki app for inhibitors (μM−1 s−1)
	CMY-2	CMY-33	CMY-2	CMY-33	CMY-2	CMY-33
NCF	11.2	3.4	534.8	3.1	47.6	0.9
CEF	7.8	1.7	140.0	0.8	17.9	0.5
FOX	17.9	22.9	6.8	4.7	0.4	0.2
CAZc	NMd	20.0	NM	3.2	NM	0.2
CTXc	1.8	3.9	NM	3.2	NM	0.8
FEPc	108.1	18.3	NM	3.0	NM	0.2
ATMc	0.12	1.5	NM	4.2	NM	2.8
SUL	101.3	35.0	0.025	0.025	0.0002	0.0007
TAZ	50.0	16.6	0.045	0.028	0.0009	0.0018

^aExperimental error was ±10%.

^bNCF, nitrocefin; CEF, cephalothin; FOX, cefoxitin; CAZ, ceftazidime; CTX, cefotaxime; FEP, cefepime; ATM, aztreonam; SUL, sulbactam; TAZ, tazobactam.

^cK_{i app} measured in the presence of NCF. The data regarding CMY-2 are from Endimiani et al. (25).

^dNM, not measurable.