TABLE 3.

Kinetic parameters of purified β-lactamase ERP-1a

Substratekcat (s−1)Km (μM)kcat/Km (s−1 · mM−1)Relative kcat/Kmb
Benzylpenicillin1712c1,400100
Amoxicillin122845032
Ticarcillin24c50035
Piperacillin1011c90064
Cephalothin47441,10073
Cefuroxime443907
Cefoxitin<0.01NDdNDND
Cefotaxime589604
Ceftazidime<0.1NDNDND
Ceftriaxone115221015
Cefpirome<0.01NDNDND
Cefepime<0.01NDNDND
Aztreonam287231
Imipenem<0.0135<0.001ND
  • a Data are the means of three independent experiments. Standard deviations were within 15%.

  • b kcat/Km values were expressed relative to that of benzylpenicillin, which was set at 100.

  • c In cases with low Km values, Ki values were determined with cephalothin as the substrate.

  • d ND, not determinable.