Consecutive Marcus Electron and Proton Transfer in Heme Peroxidase Compound II-Catalysed Oxidation Revealed by Arrhenius Plots

Abstract

Electron and proton transfer reactions in enzymes are enigmatic and have attracted a great deal of theoretical, experimental, and practical attention. The oxidoreductases provide model systems for testing theoretical predictions, applying experimental techniques to gain insight into catalytic mechanisms, and creating industrially important bio(electro)conversion processes. Most previous and ongoing research on enzymatic electron transfer has exploited a theoretically and practically sound but limited approach that uses a series of structurally similar (“homologous”) substrates, measures reaction rate constants and Gibbs free energies of reactions, and analyses trends predicted by electron transfer theory. This approach, proposed half a century ago, is based on a hitherto unproved hypothesis that pre-exponential factors of rate constants are similar for homologous substrates. Here, we propose a novel approach to investigating electron and proton transfer catalysed by oxidoreductases. We demonstrate the validity of this new approach for elucidating the kinetics of oxidation of “non-homologous” substrates catalysed by compound II of Coprinopsis cinerea and Armoracia rusticana peroxidases. This study – using the Marcus theory – demonstrates that reactions are not only limited by electron transfer, but a proton is transferred after the electron transfer event and thus both events control the reaction rate of peroxidase-catalysed oxidation of substrates.

Highly stable and tunable peptoid/hemin enzymatic mimetics with natural peroxidase-like activities

“…ABTS oxidation results showed that these Pep-9/hemin nanotubes exhibited a significant decrease in catalytic activity. Compared with Pep-1 , we reasoned that Pep-9 with six Noe groups is unable to facilitate the proton transfer and thus leads to reduced efficiency in oxidation reaction 11 , 42 .…”

Efficient Bi-enzymatic synthesis of aldonic acids

“…Specifically, we selected horseradish peroxidase (HRP), for which comprehensive data on the reactivity of the enzyme with hydrogen peroxide ( k cat / K M ∼ 10 7 M −1 s −1 ), leucothionine (4.8 × 10 8 M −1 s −1 ), and other substrates are available. 37 In contrast to laccase-based mediator regeneration schemes, the proposed method uses hydrogen peroxide as a terminal electron acceptor instead of oxygen. H 2 O 2 is regarded as a “green” oxidizer in various biocatalytic processes.…”

Contribution Factors of the First Kind Calculated for the Marcus Electron-Transfer Rate and Their Applications

“…For instance, ET rates are estimated for ET from PSII to PSI through chains comprising plastoquinone (PQ), cytochrome b 6 f (Cyt b 6 f ), and plastocyanin (PC). − Additionally, Moser et al rigorously investigated tunneling dynamics in PSII . Recently, the Marcus theory has been widely used, e.g., in molecular design for organic semiconductors, proton-coupled ET, − and extracellular ET. − …”