TABLE 2.

WT and position 237 variant substrate kinetics

Drug and enzymeKm (μM)kcat (s−1)kcat/Km (μM−1 s−1)
Piperacillin
    WT15 ± 2a51 ± 53.4 ± 0.3
    T237S variant6 ± 142 ± 47.0 ± 0.8
    T237A variant12 ± 142 ± 43.5 ± 0.3
Cephalothin
    WT14 ± 144 ± 43.1 ± 0.3
    T237S variant18 ± 265 ± 63.6 ± 0.4
    T237A variant30 ± 326 ± 20.9 ± 0.1
NCF
    WT6 ± 152 ± 58.7 ± 0.8
    T237S variant5 ± 150 ± 510 ± 1
    T237A variant15 ± 2191 ± 2013 ± 1
Cefotaxime
    WT207 ± 20142 ± 140.7 ± 0.1
    T237S variant168 ± 1743 ± 40.26 ± 0.03
    T237A variantNDb<0.1ND
Imipenem
    WT19 ± 219 ± 21.0 ± 0.1
    T237S variant21 ± 221 ± 21.0 ± 0.1
    T237A variant31 ± 36.8 ± 0.70.22 ± 0.02
  • a The values shown are means and standard errors of the means.

  • b ND, not determined. kcat was not measurable; thus, Km and kcat/Km could not be determined.