TABLE 2.
Kinetic constants of CTX-M-64, CTX-M-64(S130T), and CTX-M-199 and their IC50s and Kis on β-lactamase inhibitors
| CTX-M enzyme | Kinetic constant | Antibiotic substratea |
Inh | IC50 (nM) | Ki (nM) | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| AMP | PIP | NCF | CEP | CFX | CRO | CTX | |||||
| CTX-M-64 | Km (μM) | 22.04 ± 1.10 | 20.75 ± 2.90 | 20.3 ± 1.80 | 14.57 ± 1.6 | 15.31 ± 0.81 | 1.672 ± 0.15 | 23.89 ± 2.90 | CLA | 2.28 | 7.48 × 10−1 |
| kcat (s−1) | 1,417.93 | 487.65 | 474.31 | 58.17 | 525.6 | 62.28 | 40.18 | TAZ | 7.52 × 10−1 | 2.29 × 10−2 | |
| kcat/Km (μM−1s−1) | 64.33 | 23.50 | 23.37 | 3.99 | 34.33 | 37.25 | 1.68 | SUL | 3.65 × 10−1 | 1.48 | |
| AVI | 2.51 × 105 | 6.64 × 101 | |||||||||
| CTX-M-64 (S130T) | Km (μM) | 20.17 ± 0.60 | 14.64 ± 1.40 | 3.07 ± 0.19 | 11.05 ± 1.00 | 11.59 ± 1.30 | 3.84 ± 0.47 | 6.34 ± 0.86 | CLA | 4.29 × 101 | 7.76 × 10−1 |
| kcat (s−1) | 1,000.77 | 344.73 | 30.83 | 78.07 | 428.66 | 74.51 | 10.21 | TAZ | 8.47 × 105 | 3.22 × 104 | |
| kcat/Km (μM−1s−1) | 49.62 | 23.55 | 10.04 | 7.07 | 36.99 | 19.40 | 1.61 | SUL | 2.21 × 106 | 1.16 × 105 | |
| AVI | 4.50 × 105 | 4.86 × 102 | |||||||||
| CTX-M-199 | Km (μM) | 19.37 ± 0.70 | 13.43 ± 1.20 | 2.98 ± 0.13 | 10.95 ± 1.20 | 12.04 ± 1.10 | 3.95 ± 0.42 | 6.11 ± 0.46 | CLA | 4.30 × 101 | 7.65 × 10−1 |
| kcat (s−1) | 1,150.89 | 356.47 | 29.89 | 86.32 | 465.87 | 80.26 | 12.64 | TAZ | 8.52 × 105 | 3.20 × 104 | |
| kcat/Km (μM−1s−1) | 59.41 | 26.54 | 10.03 | 7.88 | 38.69 | 20.31 | 2.07 | SUL | 2.20 × 106 | 1.18 × 105 | |
| AVI | 4.84 × 105 | 4.43 × 102 | |||||||||
a
Each value is the average of the three independent experiments. AMP, ampicillin; PIP, piperacillin; NCF, nitrocefin; CEP, cephalothin; CFX, cefuroxime; CRO, ceftriaxone; CTX, cefotaxime; CLA, clavulanic acid; TAZ, tazobactam; SUL, sulbactam; AVI, avibactam; Inh, inhibitor.