TABLE 3.
Kinetic parameters determined with the purified OXA-46 β-lactamasef
| Substratea | kcat (s−1) | Km (μM) | kcat/Km (M−1 · s−1) |
|---|---|---|---|
| Oxacillin | 300 | 320 | 9.4 × 105 |
| Penicillin G | 18 | 48 | 3.8 × 105 |
| Ampicillin | 6 | 20 | 3.0 × 105 |
| Carbenicillin (V0) | 85 | 730 | 1.2 × 105 |
| Carbenicillin (Vss) | 5 | 545 | 9.2 × 103 |
| Azlocillin | 11 | 46 | 2.4 × 105 |
| Mezlocillin | 12 | 30 | 4.0 × 105 |
| Temocillin | NHb | >1,000c | —d |
| Nitrocefin (Vss)e | 20 | 18 | 1.1 × 106 |
| Cephalothin | 8 | 23 | 3.5 × 105 |
| Cefazolin (V0) | 17 | 23 | 7.4 × 105 |
| Cefazolin (Vss) | 7 | 40 | 1.7 × 105 |
| Cefsulodin | NH | >1,000c | — |
| Cefuroxime | NH | >1,000c | — |
| Cefotaxime | NH | >1,000c | — |
| Ceftazidime | NH | >1,000c | — |
| Cefepime | NH | >1,000c | — |
| Aztreonam | NH | >1,000c | — |
a
Biphasic kinetics were observed with this substrate; the volumes of distribution were calculated either under initial-rate conditions (V0) or under steady-state conditions (Vss).
b
NH, no hydrolysis detected at a substrate concentration up to 1 mM and an enzyme concentration up to 850 nM.
c
Measured as an inhibition constant (Ki), as described in Materials and Methods.
d
—, not calculated.
e
Biphasic kinetics were observed with nitrocefin, but only kinetic parameters under steady- state conditions could be measured.
f
Km and kcat values are the means of three different measurements. The standard deviation was always lower than 10%.