TABLE 2.
Kinetic constants of KPC-53 and KPC-3 toward some β-lactams
| Substrate | Parameter | Mean ± SD |
KPC-3/KPC-53 ratio | |
|---|---|---|---|---|
| KPC-3a | KPC-53 | |||
| Benzylpenicillin | Km (μM) | 144 ± 22 | 23 ± 2 | 6.3 |
| kcat (s−1) | 708 ± 15 | 1 ± 0.1 | 708 | |
| kcat/Km (μM−1 s−1) | 4.92 | 0.04 | 123 | |
| Carbenicillin | Km (μM) | 108 ± 10 | 3 ± 0.2 | 36 |
| kcat (s−1) | 18 ± 1 | 0.18 ± 0.014 | 100 | |
| kcat/Km (μM−1 s−1) | 0.17 | 0.06 | 2.8 | |
| Cefazolin | Km (μM) | 189 ± 25 | 383 ± 34 | 0.49 |
| kcat (s−1) | 351 ± 9 | 21 ± 2 | 16.7 | |
| kcat/Km (μM−1 s−1) | 1.86 | 0.05 | 37.2 | |
| Ceftazidime | Km (μM) | 100 ± 15 | 31 ± 2 | 3.2 |
| kcat (s−1) | 1.4 ± 0.1 | 0.35 ± 0.02 | 4 | |
| kcat/Km (μM−1 s−1) | 0.01 | 0.01 | 1 | |
| Imipenem | Km (μM) | 88 ± 6 | 0.3 ± 0.02 | 293 |
| kcat (s−1) | 41 ± 2 | 0.015 ± 0.001 | 2733 | |
| kcat/Km (μM−1 s−1) | 0.46 | 0.05 | 9.2 | |
| Meropenem | Km (μM) | 68 ± 3 | 0.76 ± 0.06 | 89.5 |
| kcat (s−1) | 51 ± 2 | 0.024 ± 0.001 | 2125 | |
| kcat/Km (μM−1 s−1) | 0.75 | 0.03 | 25 | |
| Tazobactamb | Km (μM) | 277 ± 12 | PSc | NDd |
| kcat (s−1) | 6 ± 1 | PS | ND | |
| kcat/Km (μM−1 s−1) | 0.022 | PS | ND | |
| Nitrocefin | Km (μM) | 138 ± 10 | 106 ± 10 | 1.3 |
| kcat (s−1) | 72 ± 5 | 4 ± 0.4 | 18 | |
| kcat/Km (μM−1 s−1) | 0.52 | 0.04 | 13 | |
a
Values are expressed as means ± the standard deviations where applicable.
b
KPC-3 kinetic data were obtained from reference 17. The kinetic constants of KPC-3 against tazobactam were determined in this study.
c
PS, poor substrate.
d
ND, not determined.