Table 2.

Kinetic constants for IRKO-1 enzyme (strain KER) and OXY-2-2 enzyme (strain HB60)

β-LactamKinetic constants for the following β-lactamasesa:
IRKO-1 (pI 6.3)OXY-2-2 (pI 5.7)
Km(μM)Relative Vmax(%)bKm(μM)Relative Vmax(%)b
Benzylpenicillin11010055100
Amoxicillin120759092
Ticarcillin970128519
Piperacillin21842533
Cephalothin7300.517085
Cephaloridine205018480126
Cefoperazone22542.0
Cefotaxime —c<0.15258.4
Aztreonam<0.160012
  • a Standard deviations are less than 10% for Vmax values and less than 20% forKm values.

  • b Values are relative to those for benzylpenicillin (taken as 100%).

  • c —, affinity was poor and no significant values could be determined by competition procedures (highKi).