Extra binding energy

Figure 12.2 Where to utilize some extra binding energy AGR when [S] > KM The Gibbs energy changes are for the reaction under the experimental condition of saturating [S], so that v — ca,[E]0. On stabilization of only ES, the activation energy is lowered by AGr, whereas stabilization of only ES leads to an increase of activation energy by that amount. Stabilization of ES and ES equally has a neutral effect.

Although the overall catalytic activity of an enzyme catalyzed reaction can be accounted for both by the affinity of the substrate to the enzyme (K,n or more accurately l/K ) and the substrate reactivity (kcat), the latter value seems to be more important in reflecting the extra binding energy in the ES complex. This binding energy, as mentioned before, will decrease the energy of activation for the reactivity process (kcat). 

Reactions of practical interest involve the breaking or formation of chemical bonds, which require extra energy. The theory of Saveant and its subsequent developments are an ingenious extension of the Marcus-Hush type of theory to the breaking of a simple bond. The binding energy enters into the energy of activation, but the interaction with the metal electrode is still assumed to be weak, i.e., the reactants are not adsorbed. In this sense, the reaction is not catalyzed by the electronic interaction with the metal. 

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