title: Polymerization of monolignols by redox shuttle-mediated enzymatic oxidation: a new model in lignin biosynthesis I.
abstract: Lignin is one of the most abundant biopolymers, and it has a complex racemic structure. It may be formed by a radical polymerization initiated by redox enzymes, but much remains unknown about the process, such as how molecules as large as enzymes can generate the compact structure of the lignified plant cell wall. We have synthesized lignin oligomers according to a new concept, in which peroxidase is never in direct contact with the lignin monomers coniferaldehyde and coniferyl alcohol. Instead, manganese oxalate worked as a diffusible redox shuttle, first being oxidized from Mn(II) to Mn(III) by a peroxidase and then being reduced to Mn(II) by a simultaneous oxidation of the lignin monomers to radicals that formed covalent linkages of the lignin type. Furthermore, a high molecular mass polymer was generated by oxidation of coniferyl alcohol by Mn(III) acetate in a dioxane and water mixture. This polymer was very similar to natural spruce wood lignin, according to its NMR spectrum. The possible involvement of a redox shuttle/peroxidase system in lignin biosynthesis is discussed.
authors.affiliation: Department of Pulp and Paper Chemistry and Technology, Royal Institute of Technology, KTH SE-100 44 Stockholm, Sweden.
authors.forename: Hans
authors.initials: H
authors.lastname: Onnerud
authors.forename: Liming
authors.initials: L
authors.lastname: Zhang
authors.forename: Göran
authors.initials: G
authors.lastname: Gellerstedt
authors.forename: Gunnar
authors.initials: G
authors.lastname: Henriksson
mesh_terms: D000171:Acrolein / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D001704:Biopolymers / Q000737:chemistry / Q000378:metabolism*; D002384:Catalysis; D002473:Cell Wall / Q000378:metabolism; D002845:Chromatography / Q000379:methods; D004798:Enzymes / Q000378:metabolism*; D008031:Lignin / Q000096:biosynthesis* / Q000138:chemical synthesis; D009682:Magnetic Resonance Spectroscopy; D008345:Manganese / Q000378:metabolism; D017895:Manganese Compounds / Q000378:metabolism; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010544:Peroxidases / Q000378:metabolism; D010636:Phenols / Q000737:chemistry / Q000378:metabolism; D014934:Wood
chemical_list: D001704:Biopolymers; D004798:Enzymes; D017895:Manganese Compounds; D010636:Phenols; C075384:coniferaldehyde; D008345:Manganese; D000171:Acrolein; D008031:Lignin; C010559:coniferyl alcohol; D010544:Peroxidases; C051129:manganese peroxidase; D010100:Oxygen