In comparison to other pyruvate lyases in the shikimate pathway, PchB is more similar to chorismate mutases of the AroQ class such as EcCM from E. coli, both structurally and functionally. The apparent origin of PchB is a gene duplication of an AroQ CM requiring a few minor mutations in the active site for efficient isopyruvate lyase activity, influencing a reduction in chorismate mutase activity. Mutation of the positively charged Arg90 to the nonnatural neutral amino acid citrulline in BsCM decreased the catalytic rate significantly with only a modest decrease in KM, suggesting that electrostatic stabilization plays a key role in the CM catalytic activity. In EcCM, Val35Ile and Val35Ala mutations results in an increase in kcat of about 1.5 times and decrease in kcat by about 2 times, respectively, reflecting an Ala35Ile mutation which in EcCM introduces an overall increase in kcat by about 3 times. The lower enzymatic efficiency of PchB compared to BsCM has been suggested to be due to a less restricted effect on the substrate in the former. Thus, an equivalent Ala38Ile mutation in the active site of PchB contributes to a significant increase in kcat, as it results in a better electrostatic stabilization for the transition state. This suggests enzyme efficiency is increased by favoring active sites which contribute to substrate preorganization, thereby reducing the entropic penalty paid. In both AroQ-and AroH-class chorismate mutases, preorganization of the substrate into a compressed conformer appears to be a key component in making the activation entropy less negative and therefore decreasing activation free energy in the enzyme catalysed reaction. Thus, further understanding of the phase space of the substrate conformation is crucial in elucidating the role of enthalpy and entropy in the reaction.