The enzyme soybean lipoxygenase (SLO) serves as a prototype for hydrogen tunneling reactions because of its unusually large deuterium kinetic isotope effect (KIE) of 80 for the wild-type enzyme and over 500 for a double mutant.  The proton-coupled electron transfer reaction catalyzed by SLO has been studied with a vibronically nonadiabatic theory that includes the quantum mechanical effects of the active electrons and the transferring proton, as well as the proton donor-acceptor and solvent motions.  The calculations reproduced the experimentally observed magnitude and temperature dependence of the KIE for wild-type SLO and a series of single mutants.   Theoretical modeling of the double mutant illustrated that the large KIE arises from a combination of a non-optimal active site conformation corresponding to longer equilibrium donor-acceptor distances and reduced sampling of shorter donor-acceptor distances.  These calculations highlight the critical role of hydrogen tunneling and protein conformational motions in enzyme catalysis.<br/>

Proton-coupled electron transfer in soybean lipoxygenase: Hydrogen tunneling and conformational motions

251st National Meeting (2016)

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