Comparison of the electrostatic stabilization by individual residues in SFC-1 Cys238Gly and wild-type SFC-1, and other class A β-lactamases, reveals that the largest differences lie in the contributions of components of the oxyanion hole (Figure ), and of Thr237 in particular (TI stabilization by Thr237 drops from -6.8 kcal/mol to -4.3 kcal/mol between wild type SFC-1 and SFC-1 Cys238Gly). A small decrease was also observed for the Ser70 amide (from -7.0 kcal/mol to -6.4 kcal/mol). Together, these changes make SFC-1 Cys238Gly similar to the carbapeneminhibited enzymes with regard to interactions involving the oxyanion hole. The lack of the disulfide bridge in the Cys238Gly SFC-1 (and in carbapenem-inhibited enzymes) causes a slight relaxation of the structure around the active site, increasing the distance between the Thr237 backbone amide and the carbonyl oxygen.