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 → Flavones Biosynthesis|
Expected Taxonomic Range: Viridiplantae
Flavonoids represent a highly diverse class of plant secondary metabolites. The basic chemical structure of flavonoids is a C15 skeleton which consists of two aromatic rings linked by a C3 chain. About 9000 compounds have been identified so far [Martens05]. They are involved in a wide range of biological processes in higher plants such as UV protection, flower coloration, and antimicrobial activity [Harborne00]. They also have demonstrated antioxidant and anticancer properties [Le02b] [Long08].
Flavones are a class of flavonoids synthesized directly from flavanones. Flavone formation in various tissues of a wide range of higher and lower plant species is catalyzed by a flavone synthase which belongs to the plant cytochrome P450 superfamily [Long08]. The flavones can be classified into several subgroups based on (i) hydroxylation, (ii) O-methylation, (iii) C-methylation, (iv) isoprenylation, or (v) methylenedioxy substitutions.
Most of the flavonoids, including flavones such as apigenin occur as glycosides. Glycosylation increases the chemical stability, bioavailability and bioactivity [Vogt00] of flavonoids and potentially improves their intrinsic pharmacological properties for human health [Ross02]. The formation of apigenin-7-O-gentiobioside is catalyzed by a flavonoid 1,6-glucosyltransferase characterized from Catharanthus roseus which adds β-D-glucose to the β-D-glucose attached to the A-ring 7-O-position of apigenin 7-O-β-D-glucoside yielding the corresponding gentiobioside, hence contributing yet another structural variety of apigenin glycosides as displayed in the pathway [Masada09].
BarPeled91: Bar-Peled M, Lewinsohn E, Fluhr R, Gressel J (1991). "UDP-rhamnose:flavanone-7-O-glucoside-2''-O-rhamnosyltransferase. Purification and characterization of an enzyme catalyzing the production of bitter compounds in citrus." J Biol Chem 266(31);20953-9. PMID: 1939145
Long08: Long X, Fan M, Bigsby RM, Nephew KP (2008). "Apigenin inhibits antiestrogen-resistant breast cancer cell growth through estrogen receptor-alpha-dependent and estrogen receptor-alpha-independent mechanisms." Mol Cancer Ther 7(7);2096-108. PMID: 18645020
Masada09: Masada S, Terasaka K, Oguchi Y, Okazaki S, Mizushima T, Mizukami H (2009). "Functional and structural characterization of a flavonoid glucoside 1,6-glucosyltransferase from Catharanthus roseus." Plant Cell Physiol 50(8);1401-15. PMID: 19561332
Sutter72: Sutter A, Ortmann R, Grisebach H (1972). "Purification and properties of an enzyme from cell suspension cultures of parsley catalyzing the transfer of D-glucose from UDP-D-glucose to flavonoids." Biochim Biophys Acta 258(1);71-87. PMID: 5058406
Koester84: Koester J, Bussmann R, Barz W (1984). "Malonyl-coenzyme A:isoflavone 7-O-glucoside-6"-O-malonyltransferase from roots of chick pea (Cicer arietinum L.)." Arch Biochem Biophys 234(2);513-21. PMID: 6497385
Matern83: Matern U, Feser C, Hammer D (1983). "Further characterization and regulation of malonyl-coenzyme A: flavonoid glucoside malonyltransferases from parsley cell suspension cultures." Arch Biochem Biophys 226(1);206-17. PMID: 6639051
Ortmann72: Ortmann R, Sutter A, Grisebach H (1972). "Purification and properties of udpapiose: 7-O-( -D-glucosyl)-flavone apiosyltransferase from cell suspension cultures of parsley." Biochim Biophys Acta 289(2);293-302. PMID: 4650134
Rubio06: Rubio S, Larson TR, Gonzalez-Guzman M, Alejandro S, Graham IA, Serrano R, Rodriguez PL (2006). "An Arabidopsis mutant impaired in coenzyme A biosynthesis is sugar dependent for seedling establishment." Plant Physiol 140(3);830-43. PMID: 16415216
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