Whilst the rates of carbapenem deacylation differ significantly between carbapenem hydrolyzing and carbapenem inhibited Class A enzymes, crystal structures do not show large differences between enzymes with these different activities . The main structural differences within the class A beta-lactamases (and their carbapenem acyl-enzymes) include the environment of the carbapenem 6α-1R-hydroxyethyl group and its interactions with the deacylating water and Asn132, subtle shifts in the positions of active site residues such as Asn170, Ser130 and Ser70, changes in the distances between components of the oxyanion hole (i.e. the backbone amide groups of Ser70 and Ala/Ser/Thr237) and the presence/absence of a disulfide bridge between Cys69 and Cys238 .