Table 3.

Substrate profiles of β-lactamases CTX-M-9 and CTX-M-16

SubstrateCTX-M-9CTX-M-16
Kcat (s−1)Km (μM)Kcat/Km (μM−1 · s−1)Kcat (s−1)Km (μM)Kcat/Km (μM−1 · s)
Penicillin G2952.511.865610.8
Amoxicillin90204.540104.0
Ticarcillin60351.710130.8
Piperacillin110205.54585.6
Cephalothin3,00015020.02,8008333.7
Cefuroxime350507.05004511.0
Cefotaxime4501203.71,4001509.3
Cefpirome9508001.28405201.6
Aztreonam102200.043170.2
Ceftazidime2600a 0.003153500.04
  • a Km values were determined as Ki by substrate competition with penicillin G.