TABLE 4.

Steady-state kinetic parameters for PenA and AmpC1 with selected β-lactams^a and avibactam^b

Compound	β-Lactamase	Km or Ki app (μM)	kcat (s−1)	kcat/Km (μM−1 s−1)
Cephalothin	PenAc	71 ± 7	221 ± 21	3.1 ± 0.3
	AmpC1	392 ± 88	43 ± 5	0.11 ± 0.02
Nitrocefin	PenAc	142 ± 14	460 ± 46	3.2 ± 0.3
	AmpC1	176 ± 36	251 ± 25	1.4 ± 0.3
Avibactam	PenAd	0.5 ± 0.1	NAe	NA
	AmpC1	>600	NA	NA

^aK_m and k_cat were determined under pseudo-1st-order conditions, and a nonlinear least-square fit of the data to the Henri-Michaelis-Menten equation determined the kinetic parameters. Each experiment was completed in triplicate, and the error values represent the standard errors of the mean.

^bK_{i app} was determined using a direct-competition assay under steady-state conditions. Each experiment was completed in triplicate, and the error values represent the standard errors of the mean.

^cData were previously published (17).

^dData were previously published (20).

^eNA, not applicable.