Similarly, Arg110 and Lys41 serve this function in PchB. The ionic interactions are essential in the chorismate mutase reaction, as they orient the pyruvate fragment with the cyclohexadienyl moiety such that it facilitates the formation of the C1-C9 bond in prephenate. The differences in the active sites between the two enzymes can thus explain the lowering of activation enthalpy seen in BsCM in comparison to PchB. Enhanced hydrogen bonding in the active site of BsCM results in more favorable internal energetics within the reacting atoms and between the reacting atoms and their surroundings.