Figure 5.

Free energy reaction profiles illustrating how preferential E•S ground state destablization relative to the free E+S ground state and transition state can contribute to catalysis in the E•S → E•S^‡ reaction step. (A) A hypothetical enzyme, E_a, that stabilizes the ground state (E•S) and transition state (E•S^‡) equally, resulting in a reaction barrier, $\mathrm{\Delta }{\text{G}}_{\text{a}}^{‡}$, equal to the uncatalyzed reaction barrier $\mathrm{\Delta }{\text{G}}_{\text{uncatalyzed}}^{‡}$. Thus, this enzyme is not a catalyst. (B) Enzyme E_b is modified from E_a such that additional interactions are added that specifically stabilize the transition state relative to the E+S and E•S states. Thus, $\mathrm{\Delta }{\text{G}}_{\text{b}}^{‡}$ is less than $\mathrm{\Delta }{\text{G}}_{\text{a}}^{‡}$ and the rate constant k_b is larger than k_a (in Part A). This type of effect could arise from addition of a general acid or base catalyst for example. (C) Enzyme E_c destabilizes the ground state relative to the E+S and transition state such that $\mathrm{\Delta }{\text{G}}_{\text{c}}^{‡}$ is less than $\mathrm{\Delta }{\text{G}}_{\text{b}}^{‡}$ and the rate constant k_c is larger than k_b (in Part B).