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 → Flavonoids Biosynthesis → Flavanones Biosynthesis|
Some taxa known to possess this pathway include : Glycine max
Expected Taxonomic Range: Fabales
Ponciretin, the 4'-O-methyl derivate of naringenin occurs in plants where its antifungal activity may be involved in the defense against pathogenic attacks. The modification of compounds via O-methylation occurs frequently in nature and is thought to increase their lipophilicity being associated with potentially higher antimicrobial activities [Middleton94]. In contrast to the likewise frequent glycosylation that also modifies compounds O-methylation appears to be far more specific in plants [Ibrahim98].
Besides antimicrobial properties, ponciretin has also been reported to possess anti-allergenic capacities [Park05] and efficiently inhibits growth and activity of the gastritis and peptic ulcer disease causing bacteria Helicobacter pylori in humans [Bae99] [Kim99].
About This Pathway
The enzyme has been characterized in vitro to be regiospecific for naringenin to form ponciretin. However, other substrates such as the isoflavones daidzein and genistein as well as quercetin (dihydroflavone) and apigenin (flavone) were also converted to their 4'-O-methyl derivatives with varying but rather high turnover rates. The fact that ponciretin has not been found in soybean indicates that more likely daidzein represents the in vivo substrate in this plant [Kim05].
In contrast to that the enzyme involved in the 4'-O-methylation of daidzein to form formononetin (formononetin biosynthesis) and genistein to produce biochanin-A (isoflavonoid biosynthesis II) does not accept naringenin [Wengenmayer74] [He00] indicating that the enzymes involved are different. Another 4'-O-methyltransferase purified from Glycyrrhiza echinata involved in the formation of formonoetin is even more specific and does not convert daidzein or flavanone but only 2,7,4'-trihydroxyisoflavanone [Akashi03]. Yet another 4'-O-methyltransferase isolated recently from Catharanthus roseus very specifically methylated homoeriodictyol (3'-O-methyl-eriodictyol) in vitro and was discussed with regard to the substrate substitution pattern preferred for the subsequent enzymes involved in the flavonoid biosynthetic route [Schroder04a].
The 4'-O-methyltransferase forming ponciretin (this pathway) seems to be very similar to the one involved in the biosynthesis of acacetin, the 4'-O-methyl derivate of apigenin (acacetin biosynthesis). However, this enzyme expresses a pronounced specificity towards apigenin and converted naringenin with only half the efficiency compared to apigenin [Kuroki81]. The current lack of relevant data requires the further investigation of those enzymes to determine their in vivo relationship across different species.
Akashi03: Akashi T, Sawada Y, Shimada N, Sakurai N, Aoki T, Ayabe S (2003). "cDNA cloning and biochemical characterization of S-adenosyl-L-methionine: 2,7,4'-trihydroxyisoflavanone 4'-O-methyltransferase, a critical enzyme of the legume isoflavonoid phytoalexin pathway." Plant Cell Physiol 44(2);103-12. PMID: 12610212
He00: He XZ, Dixon RA (2000). "Genetic manipulation of isoflavone 7-O-methyltransferase enhances biosynthesis of 4'-O-methylated isoflavonoid phytoalexins and disease resistance in alfalfa." Plant Cell 12(9);1689-702. PMID: 11006341
Kim05: Kim DH, Kim BG, Lee Y, Ryu JY, Lim Y, Hur HG, Ahn JH (2005). "Regiospecific methylation of naringenin to ponciretin by soybean O-methyltransferase expressed in Escherichia coli." J Biotechnol 119(2);155-62. PMID: 15961179
Kim99: Kim DH, Bae EA, Han MJ (1999). "Anti-Helicobacter pylori activity of the metabolites of poncirin from Poncirus trifoliata by human intestinal bacteria." Biol Pharm Bull 22(4);422-4. PMID: 10328566
Middleton94: Middleton Jr E, Kandaswami C (1994). "The impact of plant flavonoids on mammalian biology: implications for immunity, inflammation and cancer." In: Harborne JB (ed.). The Flavonoids: Advances in Research since 1986. Chapman & Hall, London, 619-652.
Schroder04a: Schroder G, Wehinger E, Lukacin R, Wellmann F, Seefelder W, Schwab W, Schroder J (2004). "Flavonoid methylation: a novel 4'-O-methyltransferase from Catharanthus roseus, and evidence that partially methylated flavanones are substrates of four different flavonoid dioxygenases." Phytochemistry 65(8);1085-94. PMID: 15110688
Wengenmayer74: Wengenmayer H, Ebel J, Grisebach H (1974). "Purification and properties of a S-adenosylmethionine: isoflavone 4'-O-methyltransferase from cell suspension cultures of Cicer arietinum L." Eur J Biochem 50(1);135-43. PMID: 4452353
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