TABLE 2.

Kinetic parameters of GES variants for β-lactam substratesa

β-LactamGES-1 (E104, G170)GES-7 (K104, G170)GES-2 (E104, N170)GES-5 (E104, S170)GES-6 (K104, S170)GES-13 (K104, N170)
kcat (s−1)Km (μM)kcat/Km (μM−1·s−1)kcat (s−1)Km (μM)kcat/Km (μM−1·s−1)kcat (s−1)Km (μM)kcat/Km (μM−1·s−1)kcat (s−1)Km (μM)kcat/Km (μM−1·s−1)kcat (s−1)Km (μM)kcat/ Km (μM−1·s−1)kcat (s−1)Km (μM)kcat/ Km (μM−1·s−1)
Penicillin G30.51200.2614.239.00.365.7587.60.0728.688.90.3227.264.20.4213.51390.10
Cephalothin21887.82.4831323.713.22.9453.90.0516761.12.7326054.04.8110.11060.10
CefoxitinNDNDNDNDNDNDNDNDND7.502210.0312.182.30.15NDNDND
Ceftazidime10.51370.07713269.21.900.2198.20.0020.241350.0029.301490.06330.42290.13
AztreonamNDNDND45.52410.19NDNDNDNDNDNDNDNDND35.64050.09
Cefotaxime56.81520.3731.481.60.3837.22610.143.551330.035.1095.60.0569.063.41.09
Imipenem0.0061.20.005NDNDND0.0160.870.020.3321.270.260.1663.920.0420.0093.100.003
  • a Values for kcat and Km are means for three independent measurements not differing by more than 10%, except in cases of very low hydrolysis rates (GES-1, -2, and -13 against imipenem), where differences ranged from 20 to 30%. ND, not determinable. Hydrolysis was either not detectable or too low to be measured reliably.