The enthalpically driven nature of catalysis by the chorismate mutase enzymes BsCM and PchB can be attributed to highly charged active sites which serve to stabilize the transition state, as seen in Figure . It is notable that in comparison to PchB, the active site of BsCM has a greater degree of hydrogen and ionic bonding between the substrate and active site residues, which contribute to the lower enthalpy seen in BsCM. In particular, there are three key residues in each enzyme which contribute to this effect: Glu78, Arg90, and Tyr108 in BsCM, and Pro48, Lys41, and Arg110 in PchB. Additionally, the second carboxylate of the substrate is stabilized by Arg63 in BsCM and Arg30 in PchB.