Enhanced Rigidification within a Double Mutant of Soybean Lipoxygenase Provides Experimental Support for Vibronically Nonadiabatic Proton-Coupled Electron Transfer Models.

The latter is often relatively minor in native enzymes due to favorable alignment of the donor and acceptor groups within the active substates 19 , 25 but can become quite significant when the protein is perturbed by, for example, site-specific mutagenesis. 43 , 44 The recent observation of an unusually high room-temperature KIE of ca. 500–700 for an active-site double-mutant L546A/L754A of SLO (DM-SLO) 45 was shown to be fit within a vibronically nonadiabatic PCET theory and to arise from a significant increase in barrier width (i.e., a longer equilibrium DAD), resulting in poor overlap of the reactant and product proton vibrational wave functions.

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