Table 3.

Kinetic parameters of SME β-lactamases

Enzymeakcat(s−1) for:Relativekcatfor:Km (μM) for:kcat/Km for:
SME-1SME-2SME-1SME-2SME-1SME-2SME-1SME-2
Substrate
 LOR980 ± 181081 ± 5100100770 ± 30859 ± 451.271.26
 PEN19.3 ± 1.121.3 ± 0.42.01.916.7 ± 617.7 ± 0.41.161.20
 IPM104 ± 4.2136 ± 211113202 ± 38313 ± 570.520.44
 MEM8.9 ± 0.67.3 ± 4.90.90.713.4 ± 3.29.6 ± 8.90.660.76
 AMP181 ± 13204 ± 181819488 ± 47609 ± 1240.370.34
 ATM108 ± 21140 ± 51113259 ± 23277 ± 8.50.420.51
 FOX<0.15<0.17<0.02<0.02 NDb NDNDND
 CTX<0.98<1.0<0.10<0.09NDNDNDND
 CAZ<0.07<0.09<0.01<0.01NDNDNDND
Inhibitor
 CLA NAc NANANA0.19d 0.18d NANA
 TZBNANANANA0.11d 0.12d NANA
  • a LOR, cephaloridine; PEN, penicillin; IPM, imipenem; MEM, meropenem; AMP, ampicillin; ATM, aztreonam; FOX, cefoxitin; CTX, cefotaxime; CAZ, ceftazidime; CLA, clavulanic acid; TZB, tazobactam.

  • b ND, not determined; hydrolysis was too slow.

  • c NA, not available.

  • d Ki . IC50s for SME-1 and SME-2, respectively: CLA, 0.28 and 0.25 μM; TZB, 0.16 and 0.17 μM.