TABLE 4.

Kinetic parameters for β-lactamase RTG-4a

Substratekcat (s−1)Relative Vm (%)bKm (μM)kcat/Km (μM−1 s−1)Relative Vm/Km (%)b
Benzypenicillin20100102100
Amoxicillin30175152120
Ticarcillin1594101.5100
Piperacillin531100.535
Cephalothin0.31.6500.0060.04
Cefuroxime<0.01<0.01NHc
Cefotaxime<0.01<0.01NH
Ceftazidime0.10.6NDd
Cefepime>1>5>1,0000.0010.06
Cefpirome0.150.93000.00050.03
Aztreonam<0.01<0.01NH
Imipenem<0.01<0.01NH
  • a Data are the means of three independent experiments. Standard deviations were within 10% of the means.

  • b Values are relative to those for benzylpenicillin, which were set equal to 100.

  • c NH, no detectable hydrolysis was observed with 1 μM of purified RTG-4 and up to 500 μM of substrate.

  • d ND, not determinable due to a Km value that was too high.