TABLE 2.

Kinetic parameters of β-lactamases AmpC HD and AmpC S3

β-LactamaAmpC HDAmpC S3
kcat (s−1)Km (μM)kcat/Km (mM−1 · s−1)kcat (s−1)Km (μM)kcat/Km (mM−1 · s−1)
Benzylpenicillin50105,0003594,000
Amoxicillin0.011100.010.340
Ticarcillin<0.00120.0020.0550
Piperacillin0.10.52000.010.1110
Cephalothin95248,0001,2001259,600
Cefoxitin0.01320.00212
Cefuroxime4.551,0002.57350
Ceftriaxone245000.95180
Cefotaxime522,30067800
Ceftazidime2702013,0005>1,000<5
Cefepime5068,40080>1,000<80
Cefpirome2701002,800120>1,000<120
Aztreonam<0.001<0.001
Imipenem<0.001<0.001
  • a For those compounds with Km values less than 5 μM, Ki values were determined instead of Km, with cephalothin as the substrate. The values are the means of results from at least three independent experiments.