Syringyl lignin units

This level means that the percentage of lignin units only involved in p-O-4 bonds exceeds 50%, a structural trait conventionally correlated to the frequency of S lignin units, since sinapyl alcohol has a pronounced tendency to be involved in P-O-4 bonds [56], In other words, S-rich hardwood lignins have linear domains made of successive P-O-4 linked units [43,56], This correlation between S units and P-O-4 bonds has been confirmed by the isolation of a p-O-4 and syringyl- rich lignin... 

Syringyl Lignin Pathways Two key enzymes (beyond the coniferyl alcohol pathway) are required for the production of sinapyl alcohol, which is the essential monolignol for production of syringyl units in lignins. Ferulate 5-hydroxylase, FH5, now perhaps more appropriately called CAld-5H to reflect coniferaldehyde as the preferred substrate [347,348], effects the 5-hydroxylation. Caffeate 0-methyltransferase,... 

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