TABLE 2.

Kinetic parameters of the purified IMP-12 enzymea

Substratekcat (s−1)Km (μM)kcat/Km (M−1 · s−1)
IMP-12IMP-1IMP-12IMP-1IMP-12IMP-1
Ampicillin189501,5002001.2 × 1044.8 × 106
PiperacillinNDbNDNDND2.3 × 1047.2 × 105
Carbenicillin3.7ND175ND2.1 × 1042.0 × 104
Ticarcillin6.91.14707401.5 × 1041.5 × 103
Temocillin<0.1cdNIe
Nitrocefin5706372277.9 × 1062.3 × 106
Cephalothin1184816217.4 × 1062.3 × 106
Cefotaxime561.32242.5 × 1063.3 × 105
Cefuroxime6187378.7 × 1062.2 × 105
Ceftazidime6.7815444.5 × 1051.8 × 105
Cefepime15726115.8 × 1056.4 × 105
Imipenem24046920392.6 × 1051.2 × 106
Meropenem9.557.2101.3 × 1065.0 × 105
Aztreonam<0.1c<0.01NI
  • a The corresponding values previously measured for IMP-1 (21) are also shown for comparison. Data are means of three measurements. Standard deviations never exceeded 10%.

  • b ND, not determined (first-order kinetic reaction in the range of the tested concentrations; with IMP-12, a piperacillin concentration up to 1 mM was assayed).

  • c No hydrolysis detected by using an enzyme concentration of 350 nM in the reaction mixture.

  • d —, not calculated.

  • e NI, no interaction with the substrate.