It has been suggested that the stronger stabilization effect of the oxyanion hole in carbapenemases relates to the Cys69-Cys238 disulfide bridge located just behind the oxyanion hole . Indeed, the SME-1 Cys69Ala mutant shows a lack of imipenemase activity . In our simulations, the SFC-1 Cys69Gly mutant has a higher barrier (14.1 kcal/mol), associated with weaker TI interactions with the oxyanion hole, and a stronger destabilizing effect of Asn170 on the TI than was found for wild type SFC-1. This highlights the importance of the Cys69-Cys238 disulfide bridge to carbapenemase activity, as disruption of this places SFC-1 Cys69Gly outside of the ~13 kcal mol -1 activation energy barrier discriminator for carbapenemase activity .