Of monolignols

Hypothetical two-electron oxidation of monolignols and coupling reactions of potential quinone methides. (See text for details.)... 

Li, L. Popko, J. L. Umezawa, T. Chiang, V. L. 5-Hydroxyconiferyl aldehyde modulates enzymatic methylation for syringyl monolignol formation, a new view of monolignol biosynthesis in angiosperms. J. Biol. Chem. 2000, 275, 6537-6545. 

Onnerud, H. Zhang, L. Gellerstedt, G. Henriksson, G. Polymerization of monolignols by redox shuttle-mediated enzymatic oxidation a new model in lignin biosynthesis I. Plant Cell 2002, 14, 1953-1962. 

Validation of the role of femloyl-CoA in the synthesis of the vanillin precursor will be detection of the appropriate intermediates and/or enzyme activities in placental extracts that could account for the production of the predicted levels of capsaicinoids. The presence of low levels of monolignol intermediates could be explained by lignin biosynthesis. An alternate route from phenylalanine to vanillin has been considered by some investigators Orlova et al. [68] demonstrated the role of the benzenoid pathway in petunia flowers for the biosynthesis of phenylpropanoid/benzenoid volatiles. 

Boerjan W, Ralph J, Baucher M (2003) Lignin biosynthesis. Annu Rev Plant Biol 54 519-546 Dixon RA, Reddy MSS (2003) Biosynthesis of monolignols. Genomic and reverse genetic approaches. Phytochem Rev 2 289-306... 

Figure 1. Proposed mechanisms of monolignol transport into the cell wall.

H/14C ratio of monolignol —3 H/14C ratio of polymer 3H/14C ratio of monolignol... 

The double-labeling technique is also useful for in vitro studies on the mechanism of dehydrogenative polymerization of monolignols. 

The monolignol utilized varies with type and age of the cell. Indeed, incorporation of monolignols into protolignin occurs in order of in-... 

Cell wall peroxidase/H202 — Formation of phenoxy radicals of monolignols 1. Lignin peroxidase/H202 — Formation of aryl radical cations of nonphenolic units... 

The term lignan typically refers to dimers of monolignols that are linked via an 8-8 (P-P ) bond, whereas the term neolignan refers to dimers and oligomers that contain bonds other than the 8-8 bond. Most lignans are optically active, and typically only one enantiomer is found in a given species. Examples of lignans include (+)-pinoresinol (1.72), (+)-sesamin (1.73), and (-)-plicatic acid (1.74). 

Figure 2-14. Oxidation of monolignols via a manganese oxalate redox shuttle as proposed by Onnerud et al. (2004).

The reduction of />coumaroyl-CoA (3.31) to />coumaryl aldehyde (3.69) is catalyzed by the enzyme cinnamoyl-CoA NADP oxidoreductase (CCR). This enzyme was initially purified from soybean cultures (Wegenmayer et al., 1976), and was later on efficiently isolated from lignifying cambium of eucalyps (Eucalyptus gunnii) (Gofifiier et al., 1994). A CCR cDNA was identified in a cDNA library that was screened with oligonucleotiede derived from the peptide sequence of the CCR protein. CCR is considered the first enzyme committed towards the biosynthesis of monolignols and shows... 

Figure 3-9. Biosynthesis of monolignols. The enzymes involved in this pathway are ( ) hydroxycinnamoyl-CoA shikimate/quinate hydroxy-cinnamoyl transferase, (b) p-coumaroyl-CoA 3 -hydroxylase (E.C. 1.14.14.1), (c) caffeoyl-CoA O-methy 1 Iranslerasc (E.C. 2.1.1.104), (d) cinnamoyl-CoA reductase (E.C. 1.2.1.44) (e) cinnamyl alcohol dehydrogenase (E.C. 1.1.1.195), (f) coniferyl aldehyde/coniferyl alcohol 5-hydroxylase (E.C. 1.14.13), (g) coniferaldehyde/coniferyl alcohol O-methyltransferase (E.C. 2.1.1.68).

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