TABLE 3.
Steady-state kinetic parameters of OXA-20 β-lactamasea
| Substrate | kcat (s−1) | Km (μM) | kcat/Km (μM−1 · s−1) |
|---|---|---|---|
| Oxacillin | 116 ± 5 | 329 ± 34 | 0.35 ± 0.020 |
| Cloxacillin | 70 ± 7 | 788 ± 114 | 0.088 ± 0.005 |
| Penicillin Gb | 26 ± 0.90 | 4.4 ± 1.30 | 5.9 ± 1.70 |
| Ampicillin | 80 ± 1.40 | 33 ± 2.20 | 2.4 ± 0.13 |
| Ticarcillin | 4 ± 0.45 | 147 ± 34 | 0.03 ± 0.004 |
| Cephalothin | 13 ± 0.05 | 5 ± 0.20 | 2.6 ± 0.08 |
| Cephaloridine | 20 ± 0.90 | 69 ± 5.00 | 0.3 ± 0.009 |
| Aztreonam | 6 ± 0.50 | 69 ± 12.00 | 0.09 ± 0.009 |
| Ceftazidime | NDc | ND | ND |
| Cefoxitin | ND | ND | ND |
a
Values are means ± standard errors.
b
The IC50 for penicillin inhibition by clavulanate was 2.2 ± 0.25 μM.
c
ND, not determinable (the initial rate was lower than 0.001 μM−1 · s−1).