Oxidative coupling of tyrosine and ferulic acid residues: Intra- and extra-protoplasmic occurrence, predominance of trimers and larger products, and possible role in inter-polymeric cross-linking

Stephen C. Fry*

*Corresponding author for this work

Research output: Contribution to journalReview articlepeer-review

Abstract

I discuss the range of oxidative phenolic coupling products formed from the tyrosine residues of cell wall glycoproteins and from the feruloyl residues of wall polysaccharides possibly by the action of peroxidases and/or laccases. In the cases of both tyrosine- and ferulate-coupling, the coupling products are not confined to dimers but include trimers and probably higher oligomers, which are sometimes predominant. Thus, some previous assays, in which specifically dimers were monitored, will have underestimated the extent of phenolic coupling. The possibility is discussed that some of the phenolic coupling products, in both glycoproteins and polysaccharides, are inter-polymeric and that they may therefore act as cross-links in the cell wall. The limitations in the evidence for this hypothesis are stressed. The sub-cellular site of oxidative phenolic coupling is discussed. In-vivo radiolabelling of cultured maize cells with [14C]cinnamate has shown that, especially in young, rapidly growing cultures, much oxidative coupling of feruloyl-arabinoxylans occurs within the endomembrane system, before secretion of the polysaccharides into the cell wall. Appreciable feruloyl coupling within the cell wall depended on the supply of H2O2 and on culture age. The situation with tyrosine coupling in glycoproteins is also debated. Although peroxidase activity has long been known to occur in the endomembrane system, the recent finding of intraprotoplasmic feruloyl coupling provided the first evidence that peroxidases (and/or laccases) may act in this sub-cellular location in vivo. I draw attention to the distinction between peroxidase action (in vivo) and activity (assayed in vitro), and to the unknown origin of H2O2 within the endomembrane system.

Original languageEnglish
Pages (from-to)97-111
Number of pages15
JournalPhytochemistry Reviews
Volume3
Issue number1-2
DOIs
Publication statusPublished - 1 Jan 2004

Keywords

  • cell walls
  • cross-linking
  • extensin
  • ferulic acid
  • hydrogen peroxide
  • p-coumaric acid
  • peroxidase
  • polysaccharides
  • tyrosine

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