TABLE 2.
Kinetic parameters of wild-type and mutant IMP-18 β-lactamases for penicillins and carbapenems
| β-Lactamase and parameter | Value for antibiotic |
|||
|---|---|---|---|---|
| Ampicillin | Penicillin G | Imipenem | Meropenem | |
| Wild type | ||||
| kcat (s−1) | 33.5 ± 3.4 | 49.3 ± 1.1 | 22.9 ± 1.3 | 0.0984 ± 0.0041 |
| Km (μM) | 70.8 ± 7.3 | 48.6 ± 4.5 | 9.43 ± 0.42 | 13.1 ± 1.2 |
| kcat/Km (s−1 μM−1) | 0.474 ± 0.038 | 1.02 ± 0.09 | 2.44 ± 0.17 | 0.00759 ± 0.00076 |
| K44N mutant | ||||
| kcat (s−1) | 48.2 ± 4.1 | 70.3 ± 5.3 | 30.0 ± 1.6 | 0.114 ± 0.005 |
| Km (μM) | 71.2 ± 6.8 | 44.1 ± 3.0 | 9.13 ± 1.2 | 14.8 ± 1.6 |
| kcat/Km (s−1 μM−1) | 0.677 ± 0.018 | 1.60 ± 0.17 | 3.34 ± 0.46 | 0.00779 ± 0.00079 |
| T50P mutant | ||||
| kcat (s−1) | 45.4 ± 5.4 | 63.1 ± 6.3 | 62.1 ± 7.3 | 1.28 ± 0.14 |
| Km (μM) | 212 ± 36 | 184 ± 27 | 24.1 ± 2.2 | 6.4 ± 2.7 |
| kcat/Km (s−1 μM−1) | 0.217 ± 0.017 | 0.345 ± 0.024 | 2.58 ± 0.23 | 0.230 ± 0.081 |
| K44N/T50P mutant | ||||
| kcat (s−1) | 92.6 ± 8.8 | 126 ± 12 | 115 ± 10 | 1.99 ± 0.20 |
| Km (μM) | 204 ± 21 | 242 ± 23 | 20.4 ± 3.0 | 6.29 ± 1.09 |
| kcat/Km (s−1 μM−1) | 0.458 ± 0.058 | 0.524 ± 0.058 | 5.76 ± 0.92 | 0.325 ± 0.067 |
| I69F mutant | ||||
| kcat (s−1) | 16.4 ± 1.7 | 99.7 ± 5.3 | 19.8 ± 1.4 | 0.0972 ± 0.0051 |
| Km (μM) | 7.60 ± 0.61 | 14.5 ± 1.2 | 6.17 ± 0.43 | 8.66 ± 0.47 |
| kcat/Km (s−1 μM−1) | 2.18 ± 0.32 | 6.92 ± 0.60 | 3.22 ± 0.23 | 0.0112 ± 0.0005 |