Arabidopsis peroxidase-catalyzed copolymerization of coniferyl and sinapyl alcohols: Kinetics of an endwise process |
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Authors: | Nathalie Demont-Caulet Catherine Lapierre Lise Jouanin Stéphanie Baumberger Valérie Méchin |
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Institution: | 1. Institut Jean-Pierre Bourgin, UMR 1318 INRA/AgroParisTech, Pôle Systèmes Cellulaires, Morphogénèse et Signalisation, 78850 Thiverval-Grignon, Cedex, France;2. UFR des Sciences du Vivant, Université Diderot-Paris 7, 75205 Paris, Cedex 13, France |
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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 H2O2. 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 24 h 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. |
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