title: Arabidopsis peroxidase-catalyzed copolymerization of coniferyl and sinapyl alcohols: kinetics of an endwise process.
abstract: In order to determine the mechanism of the earlier copolymerization steps of two main lignin precursors, sinapyl (S) alcohol and coniferyl (G) alcohol, microscale in vitro oxidations were carried out with a PRX34 Arabidopsis thaliana peroxidase in the presence of H(2)O(2). This plant peroxidase was found to have an in vitro polymerization activity similar to the commonly used horseradish peroxidase. The selected polymerization conditions lead to a bulk polymerization mechanism when G alcohol was the only phenolic substrate available. In the same conditions, the presence of S alcohol at a 50/50 S/G molar ratio turned this bulk mechanism into an endwise one. A kinetics monitoring (size-exclusion chromatography and liquid chromatography-mass spectrometry) of the different species formed during the first 24h oxidation of the S/G mixture allowed sequencing the bondings responsible for oligomerization. Whereas G homodimers and GS heterodimers exhibit low reactivity, the SS pinoresinol structure act as a nucleating site of the polymerization through an endwise process. This study is particularly relevant to understand the impact of S units on lignin structure in plants and to identify the key step at which this structure is programmed.
authors.affiliation: Institut Jean-Pierre Bourgin, UMR 1318 INRA/AgroParisTech, Pôle Systèmes Cellulaires, Morphogénèse et Signalisation, Thiverval-Grignon, France.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Demont-Caulet
authors.forename: Catherine
authors.initials: C
authors.lastname: Lapierre
authors.forename: Lise
authors.initials: L
authors.lastname: Jouanin
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Baumberger
authors.forename: Valérie
authors.initials: V
authors.lastname: Méchin
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D008031:Lignin / Q000737:chemistry / Q000378:metabolism*; D010544:Peroxidases / Q000378:metabolism*; D010636:Phenols / Q000032:analysis* / Q000378:metabolism; D010666:Phenylpropionates / Q000032:analysis* / Q000378:metabolism; D058105:Polymerization
chemical_list: D010636:Phenols; D010666:Phenylpropionates; C496130:sinapyl alcohol; D008031:Lignin; C010559:coniferyl alcohol; D010544:Peroxidases