Proton and electron tunneling effects in enzymes

Accumulating evidence supports the quantum mechanical treatment of both electron and proton transfer associated with homolytic C-H bond cleavage reactions catalyzed by natural enzymes. These reactions are quantified and characterized by inflated kinetic isotope effects corresponding to the primary bond cleaved and the corresponding differential enthalpic barrier for the transfer of hydrogen and its heavy isotopes. Herein, select examples will be presented that demonstrate the quantum behavior in enzyme catalysis and highlight how these kinetic tools can be applied to resolve the origins of enzyme reactions.