Table 2.
Kinetic parameters of AmpC-MEV β-lactamase and the wild-type AmpC-A enzyme
| ß-Lactams | AmpC-MEV |
AmpC-A |
||||
|---|---|---|---|---|---|---|
| kcat (s−1) | Km (μM) | kcat/Km (μM−1.s−1) | kcat (s−1) | Km (μM) | kcat/Km (μM−1.s−1) | |
| Cephalothin | 135 ± 15c | 18 ± 2 | 7.5 | 500 ± 20 | 30 ± 2 | 16 |
| Cephaloridine | 160 ± 12 | 38 ± 4 | 4.2 | 230 ± 15 | 650 ± 30 | 0.35 |
| Cefoxitina | 0.056 ± 0.01 | 0.08 ± 0.01 | 0.7 | 0.3 ± 0.02 | 1 ± 0.05 | 0.3 |
| Cefotaximea | 0.25 ± 0.005 | 0.05 ± 0.01 | 5 | 0.2 ± 0.005 | 25 ± 2 | 0.008 |
| Ceftazidimea | 0.78 ± 0.03 | 0.4 ± 0.08 | 1.95 | 0.5 ± 0.03 | 70 ± 3 | 0.007 |
| Cefepime | 1.5 ± 0.2 | 60 ± 4 | 0.025 | NDb | >1,000 | >0.01 |
| Imipenema | 0.01 ± 0.005 | 0.3 ± 0.08 | 0.03 | 0.1 ± 0.005 | 10 ± 0.4 | 0.01 |
a
For those compounds with a Km value of <5 μM, the Ki was determined, instead of the Km, with cephaloridine as the substrate.
b
ND, not determinable.
c
The values shown are the means ± the standard deviations of at least three independent experiments.