H2O2 generation during the auto‐oxidation of coniferyl alcohol drives the oxidase activity of a highly conserved class III peroxidase involved in lignin biosynthesis

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Abstract
Characterization of lignified Zinnia elegans hypocotyls by both alkaline nitrobenzene oxidation and thioacidolysis reveals that coniferyl alcohol units are mainly found as part of 4‐O‐linked end groups and aryl‐glycerol‐β‐aryl ether (β‐O‐4) structures. Z. elegans hypocotyls also contain a basic peroxidase (EC 1.11.1.7) capable of oxidizing coniferyl alcohol in the absence of H2O2. Results showed that the oxidase activity of the Z. elegans basic peroxidase is stimulated by superoxide dismutase, and inhibited by catalase and anaerobic conditions. Results also showed that the oxidase activity of this peroxidase is due to an evolutionarily gained optimal adaptation of the enzyme to the μM H2O2 concentrations generated during the auto‐oxidation of coniferyl alcohol, the stoichiometry of the chemical reaction (mol coniferyl alcohol auto‐oxidized/mol H2O2 formed) being 0.496. These results therefore suggest that the H2O2 generated during the auto‐oxidation of coniferyl alcohol is the main factor that drives the unusual oxidase activity of this highly conserved lignin‐synthesizing class III peroxidase.