Table 2. Kinetic constants and IC50 values of SHV-99 and SHV-1 β-lactamases.
Values for kinetic enzyme parameters are means±sd. nd, Not determinable because the hydrolysis rate was too low.
| Antibiotic | SHV-1* | SHV-99 | ||||||
| Km (µM) | kcat (s−1) | kcat/Km (µM−1 s−1) | IC50 (µM) | Km (µM) | kcat (s−1) | kcat/Km (µM−1 s−1) | IC50 (µM) | |
| Clavulanic acid | 0.17 | 0.02 | ||||||
| Tazobactam | 0.11 | 0.03 | ||||||
| Penicillin G | 23±0.42 | 1937±82 | 84.2±2.0 | 12±0.11 | 778±61 | 62.3±4.4 | ||
| Amoxicillin | 31±1.29 | 1044±10 | 33.7±1.1 | 11±0.26 | 563±8 | 49.6±1.8 | ||
| Ticarcillin | 11±3.40 | 220±49 | 20.0±1.7 | 5±0.93 | 58±2 | 13.0±2.4 | ||
| Piperacillin | 24±0.53 | 1490±96 | 62.1±2.7 | 13±1.43 | 563±13 | 43.5±6.5 | ||
| Cefalotin | 40±1.46 | 128±33 | 3.2±0.8 | 102±11.38 | 37±2 | 0.37±0.04 | ||
| Ceftazidime | 142±3.18 | <0.1 | <0.001 | 136±4.09 | <0.1 | <0.001 | ||
| Cefotaxime | 257±20.65 | <0.1 | <0.001 | 183±0.72 | <0.1 | <0.001 | ||
| Aztreonam | nd | <0.1 | <0.001 | 196±0.60 | 0.5±0.001 | 0.003 | ||
*
The kinetic constants for SHV-1 are from Mendonça et al. (2008).