Analysis of ground-state and transition-state effects in enzyme catalysis.
"The entire and sole source of catalytic power is the stabilization of the transition state; reactant-state interactions are by nature inhibitory and only waste catalytic power". So reads a literature quote expressing the current view on enzyme catalysis proposed by Pauling over 40 years ago. Its validity is now examined by means of a "split-site" model in which an active site is subdivided into a region of binding and a region of reaction. Analysis of the resulting free energy levels clarifies several points of confusion regarding the nature of enzyme catalysis, including why enzyme/substrate complexes form if, indeed, they only "waste catalytic power". Circumstances are defined in which an evolving enzyme can both lower Km (i.e., enhance substrate binding) and improve the forward catalytic rate while never meddling with the transition structure at the reactive site. It is argued that this process is most advantageously viewed as a substrate destabilization embodying "conserved" interactions at the binding region. Classical transition-state stabilization and an "anti-Pauling" effect are both capable of inducing rate accelerations. In certain circumstances, the latter can predominate as it does with many enzyme-like intramolecular reactions. Behavioral modes discussed herein are applicable to the chemistry of catalytic host/guest and enzyme systems.
Menger
F M
FM
Department of Chemistry, Emory University, Atlanta, Georgia 30322.
D002384:Catalysis; D004798:Enzymes / Q000737:chemistry*; D008962:Models, Theoretical; D013816:Thermodynamics
D004798:Enzymes