This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Biosynthesis → Secondary Metabolites Biosynthesis → Phenylpropanoid Derivatives Biosynthesis → Lignins Biosynthesis|
Expected Taxonomic Range: Spermatophyta
In terms of both frequency and magnitude of plant biomass accumulation, the transfer of the glycosyl moiety is one of the most important biochemical reactions known. Two-thirds of the biosphere`s carbon existing as carbohydrates is due to this kind of reaction. Transfer of the glycosyl moiety from sugar nucleotides to a large number and molecular diversity of acceptors is catalyzed by glycosyltransferases [Sinnott90].
Glucosyltransferases as one subclass of glycosyltransferases are involved in the glucosylation of a broad variety of secondary plant metabolites, amongst them monolignols involved in the metabolic sequence of lignin biosynthesis [Ibrahim77, Foerster99]. Modifying enzymes such as the multigene family of glucosyltransferases contribute to the plasticity of metabolism where corresponding products are either involved in a particular biosynthetic route or may act as gateways into different metabolic pathways [Lim01] [Vogt00].
The presence and significance to lignification of glucosylated cinnamyl alcohols in the cambium of woody plants were emphasized several decades ago by Freudenberg [Freudenberg63] [Freudenberg67]. Although gucosyltransferases in general may cover a broad substrate spectrum it has been demonstrated that certain glucosyltransferases exhibit a rather strict specificity towards their substrates [Sutter73] [Steeves01] [Lim05].
About This Pathway
The most prominent monolignol glucoside accumulating in a variety of plants is the 4-O-β-D-glucopyranoside of trans-coniferyl alcohol, i.e. coniferin (coniferin metabolism). The enzyme catalyzing the formation of coniferin has been purified from different plant sources [Ibrahim76] and appears to be most active in developing xylem of gymnosperms [Schmid82] [Steeves01].
The UDPG:coniferyl alcohol glucosyltransferase (CAGT) also glucosylates sinapyl alcohol with high efficiency in pine cambium [Savidge98] [Foerster00] and cell cultures of Forsythia and Rosa spec. [Ibrahim77] [Ibrahim76]. In addition, coniferyl and sinapyl aldehydes have been converted with comparable catalytic efficiency [Schmid82] [Steeves01] [Ibrahim76]. Recent investigation of the multigene family encoding enzymes conjugating lignin monomers in Arabidopsis thaliana [Lim05] revealed a single gene expressing a CAGT highly specific for coniferyl and sinapyl aldehydes. The recombinant expressed enzyme significantly differs from the other members of this gene family with regard to substrate preference as they specifically encode enzymes for the glucosylation of the monolignol alcohols. These findings confirm the long assumed incorporation of aldehydic components into lignin because the phloroglucinol-HCl lignin specific dye reaction depends on the presence of aldehyde groups [Freudenberg68].
Additionally, it has been demonstrated that dihydroconiferyl alcohol, a monomer isolated from developing xylem of Pinus contorta [Savidge] but usually not regarded as an important component of the lignin biosynthetic pathway had also been converted into the 4-O-β-D-glucopyranoside [Steeves01]. Moreover, the catalytic activity for the formation of dihydroconiferyl alcohol has been found in the microsomal fraction of developing pine xylem [Savidge01]. In addition, this rare monolignol has been determined as a major component in lignin of a mutant loblolly pine accounting for around 30% per unit [Ralph97] emphasizing the metabolic plasticity of monomeric components involved in lignin biosynthesis.
Unification Links: AraCyc:PWY-83
Foerster00: Foerster H, Steeves V, Pommer U, Savidge RA (2000). "UDPG:coniferyl alcohol glucosyltransferase and coniferin biosynthesis - a regulatory link to seasonal cambial growth in conifers." In: Savidge, R.A., Barnett,T.R., Napier,R. (Eds.), Cell and Molecular Biology of Wood Formation. BIOS,Oxford, 189-202.
Foerster99: Foerster H, Pommer U, Savidge RA (1999). "Metabolic activity of uridine 5'-diphosphoglucose: cinnamyl alcohol glucosyltransferase as an intrinsic indicator of cambial growth in conifers." In: Gross, G.G.,Hemingwa y,R.W.,Yoshida, T. (Eds.),Plant Polyphenols 2: Chemistry and Biology. Kluwer/Plenum,New York, pp. 371-392.
Ibrahim76: Ibrahim RK, Grisebach H (1976). "Purification and properties of UDP-glucose: coniferyl alcohol glucosyltransferase from suspension cultures of Paul's scarlet rose." Arch Biochem Biophys 176(2);700-8. PMID: 10853
Lim01: Lim EK, Li Y, Parr A, Jackson R, Ashford DA, Bowles DJ (2001). "Identification of glucosyltransferase genes involved in sinapate metabolism and lignin synthesis in Arabidopsis." J Biol Chem 276(6);4344-9. PMID: 11042211
Lim05: Lim EK, Jackson RG, Bowles DJ (2005). "Identification and characterisation of Arabidopsis glycosyltransferases capable of glucosylating coniferyl aldehyde and sinapyl aldehyde." FEBS Lett 579(13);2802-6. PMID: 15907484
Savidge98: Savidge RA, Foerster H (1998). "Seasonal activity of uridine 5'-diphosphoglucose:coniferyl alcohol glucosyltransferase in relation to cambial growth and dormancy in conifers." Can. J. Bot. 76, 486-493.
Schmid82: Schmid G, Grisebach H (1982). "Enzymic synthesis of lignin precursors. Purification and properties of UDP glucose: coniferyl-alcohol glucosyltransferase from cambial sap of spruce (Picea abies L.)." Eur J Biochem 123(2);363-70. PMID: 6210530
Steeves01: Steeves V, Forster H, Pommer U, Savidge R (2001). "Coniferyl alcohol metabolism in conifers -- I. Glucosidic turnover of cinnamyl aldehydes by UDPG: coniferyl alcohol glucosyltransferase from pine cambium." Phytochemistry 57(7);1085-93. PMID: 11430981
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