TABLE 2.
Steady-state kinetic parameters of GES-2a
| Substrate | GES-2
|
GES-1
|
||||
|---|---|---|---|---|---|---|
| kcat (s−1) | Km (μM) | kcat/Km (mM−1 · s−1) | kcat(s−1) | Km (μM) | kcat/Km (mM−1 · s−1) | |
| Benzylpenicillin | 0.4 | 4 | 96 | 2.8 | 40 | 70 |
| Amoxicillin | 0.7 | 25.8 | 26 | 13 | 200 | 65 |
| Ticarcillin | 0.06 | 13.3 | 4.5 | 0.3 | 400 | 0.7 |
| Piperacillin | 0.3 | 22.8 | 23 | 8 | 900 | 13 |
| Cephalothin | 0.3 | 3 | 112 | 179 | 3,400 | 52 |
| Cephaloridine | 0.5 | 7.7 | 65 | 53 | 2,000 | 26 |
| Cefoxitin | —b | — | — | 0.9 | 30 | 33 |
| Ceftazidime | NDc | >3,000 | ND | 380 | 2,000 | 188 |
| Cefepime | 1.1 | 1,900 | 0.6 | 2.8 | 1,800 | 1.6 |
| Cefotaxime | 2.2 | 890 | 2.5 | 68 | 4,600 | 15 |
| Imipenem | 0.004 | 0.45 | 9 | 0.003 | 45 | 0.07 |
| Meropenem | — | — | — | — | — | — |
| Aztreonam | — | — | — | — | — | — |
a
Parameters of GES-2 are compared to those of GES-1 β-lactamase, as previously published (28). Values are expressed as the mean of three independent measures (standard deviations of the values were within 15%).
b
—, not hydrolyzed (the initial rate of hydrolysis was lower than 0.001 μM−1 · s−1).
c
ND, not determinable due to very high Km values.