TABLE 2.
Kinetic parameters of purified β-lactamases KPC-2 and KPC-74.
| β-Lactam(s) | KPC-2 |
KPC-74 |
||||||
| Km (μM) | kcat (s−1) | kcat/Km (μM−1.s−1) | Km (μM) | kcat (s−1) | kcat/Km (μM−1.s−1) | |||
| Nitrocefin | 10 | 51 | 5.1 | 6.1 | 4.2 | 0.7 | ||
| Ceftazidime | 254 | 1.7 | 0.007 | 29 | 0.4 | 0.014 | ||
| Meropenem | 12 | 3.8 | 0.32 | ND | ND | ND | ||
|
| ||||||||
| Inhibitor | ||||||||
|
IC50(μM)
|
||||||||
| KPC-2 | KPC-74 | |||||||
|
| ||||||||
| Avibactam | 0.027 | 0.454 | ||||||
| Tazobactam | 1.63 | 0.034 | ||||||
| Clavulanic acid | 0.764 | 0.043 | ||||||
Inhibitory concentration 50% (IC50) of β-lactamase inhibitors against KPC-74 and KPC-2 (bottom). ND: Not determinatable due to a low initial rate of hydrolysis. kcat, turnover; Km, Michaelis constant (Affinity); kcat/Km = specificity constant (Hydrolysis). IC50 represents the concentration of a drug that is required for 50% inhibition of the enzymatic activity.