Oxidative cleavage of non-phenolic β-O-4 lignin model dimers by an extracellular aromatic peroxygenase

Abstract

The extracellular aromatic peroxygenase of the agaric fungus Agrocybe aegerita catalyzed the H₂O₂-dependent cleavage of non-phenolic arylgiycerol-ß-aryl ethers (ß-O-4 ethers). For instance 1-(3,4-dimethoxyphenyl)-2-(2-methoxy-phenoxy)propane-1,3-diol, a recalcitrant dimeric lignin model compound that represents the major non-phenolic substructure in lignin, was selectively O-demethylated at the para-methoxy group to give formaldehyde and 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)propane-1,3-diol. The phenol moiety of the latter compound was then enzymatically oxidized into phenoxy radicals and a quinoid cation, which initiated the autocatalytic cleavage of the dimer and the formation of monomers such as 2-methoxy-1,4-benzoquinone and phenoxyl-substituted propionic acid. The introduction of ¹⁸O from H₂¹⁸O₂ and H₂¹⁸O₂ at different positions into the products provided information about the routes of ether cleavage. Studies with a ¹⁴C-labeled lignin model dimer showed that more than 70% of the intermediates formed were further coupled to form polymers with molecular masses above 10 kDa. The results indicate that fungal aromatic peroxygenases may be involved in the bioconversion of methoxylated plant ingredients originating from lignin or other sources.

Citation

Kinne, Matthias; Poraj-Kobielska, Marzena; Ullrich, Rene; Nousiainen, Paula; Sipilä, Jussi; Scheibner, Katrin; Hammel, Kenneth E.; Hofrichter, Martin. 2011. Oxidative cleavage of non-phenolic β-O-4 lignin model dimers by an extracellular aromatic peroxygenase. Holzforschung. Vol. 65, no. 5 (Aug. 2011): p. 673-679.