TABLE 2.
Kinetic parameters of selected IMP-type MBLs for the hydrolysis of various β-lactam substratesd
| Substrate |
kcat (s−1) |
Km (μM) |
kcat/Km (M−1·s−1) |
|||
|---|---|---|---|---|---|---|
| IMP-1 | IMP-18 | IMP-1 | IMP-18 | IMP-1 | IMP-18 | |
| Ampicillin | 950 | 65 | 200 | 103 | 4.8 × 106 | 6.3 × 105 |
| Benzylpenicillin | 320 | 54 | 520 | 90 | 6.2 × 105 | 6.2 × 105 |
| Piperacillina | >10 | >200 | 7.2 × 105 | 5.1 × 104 | ||
| Ticarcillin | 1.1 | 30 | 740 | 180 | 1.5 × 103 | 1.5 × 105 |
| Temocillin | >0.75 | >2,000 | >1,000 | <102 | 7.5 × 102b | |
| Cephalothin | 48 | 0.4 | 21 | 0.1 | 2.4 × 106 | 4.0 × 106 |
| Cefoxitin | 16 | 2 | 8 | 11 | 2.0 × 106 | 1.8 × 105 |
| Cefuroxime | 8 | 0.9 | 37 | 7 | 2.2 × 105 | 1.3 × 105 |
| Cefotaxime | 1.3 | 0.7 | 4 | 3 | 3.5 × 105 | 2.3 × 105 |
| Ceftazidime | 8 | 1 | 44 | 1.3 | 1.8 × 105 | 7.7 × 105 |
| Cefepime | 7 | 0.35 | 11 | 0.8 | 6.6 × 105 | 4.4 × 105 |
| Nitrocefin | 63 | 55 | 27 | 9 | 2.3 × 106 | 6.1 × 106 |
| Imipenem | 46 | 17 | 39 | 7 | 1.2 × 106 | 2.4 × 106 |
| Meropenem | 5 | 0.05 | 10 | 8.4 | 5.0 × 105 | 6.0 × 103 |
| Ertapenem | 16 | 0.03 | 21 | 2.6 | 7.6 × 105 | 1.2 × 104 |
| Aztreonam | <0.01 | <0.01c | >1,000 | >1,000 | ||
a
First-order kinetics were observed with this substrate.
b
With temocillin, the standard deviation on kinetic parameters was 20%.
c
No hydrolysis was detected by using an enzyme concentration of 1.8 μM in the reaction mixture.
d
Data for IMP-1 (except ertapenem [this study]) are from reference 14. Individual kinetic parameters are the means of three measurements, and standard deviations were always <10%, unless otherwise specified.