5-hydroxyconiferyl aldehyde

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. 

Coniferaldehyde (3.76) can undergo several fates, some of which can ultimately lead to the same end product. It can be reduced to coniferyl alcohol (3.79) by the enzyme cinnamyl alcohol dehydrogenase (CAD). Alternatively, the enzyme coniferyl aldehyde/coniferyl alcohol 5-hydroxylase (C5H), also known by its less accurate name ferulic acid 5-hydroxylase (F5H Humphreys et al., 1999) can catalyze the hydroxylation of C5 to result in 5-hydroxyconiferyl aldehyde (3.77). C5H is also able to form 5-hydroxyconiferyl alcohol (3.80) from coniferyl alcohol (3.79). This enzyme was initially identified as F5H, after analysis of the Arabidopsis ferulic acid hydroxylase 1 (fahl) mutant, which was isolated in a mutant screen based on reduced levels of the UV-fluorescent sinapoyl esters (Section 13 Chappie et al., 1992). The FAH1 gene was cloned using a T-DNA tagged mutant allele (Meyer et al., 1996), which revealed that the... 

Figure 29 (a) Ribbon representation of COMT (PDB ID 1KYZ) from alfalfa, (b) Proposed binding of ferulic acid (6) (orange) and SAH (117) (purple) at the active site of COMT. (c) Stereoview of interaction of active site residues with SAH (117) (purple) and 5-hydroxyconiferyl aldehyde (17) (green). H2O molecule is shown as a yellow sphere. 

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