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apigeninidin 5-O-glucoside biosynthesis

Anthocyanins can be divided in two groups, the common 3-hydroxyanthocyanins which bear a hydroxyl group at the 3-position of the C-ring and the rare 3-deoxyanthocyanidins which are lacking this hydroxyl group. 3-Deoxyanthocyanidins are found mostly in mosses and ferns and have been reported in higher plants especially in the New World angiosperm families |FRAME:TAX-26122| and |FRAME:TAX-24079| |CITS:[Harborne66]| and some members of the |FRAME:TAX-4479| such as maize, sorghum and sugarcane |CITS:[Styles75]|. In the highly developed |FRAME:TAX-26122| species the 3-deoxyanthocyanidins are mostly involved in providing orange-red to scarlet flower colors which have been discussed as attractants for bird pollinators |CITS:[Harborne66]|. In addition, they are known to be induced as phytoalexins in response to pathogenic attacks in apple and sorghum |CITS:[12667486]|. The occurrence of the 3-deoxyanthocyanidins |FRAME:CPD-7096| (this pathway) and |FRAME:CPD-11945| has been reported from petals of |FRAME:TAX-189007| |CITS:[Stich88]| |CITS:[Winefield05]| and silk tissue of maize |CITS:[Halbwirth03]|. Both 3-deoxyanthocyanidins are precursors to the corresponding 5-O-glucosides, i.e. |FRAME:CPD-15272| (this pathway) and |FRAME:CPD-15269| (see |FRAME:PWY-7252|) |CITS:[Swinny00]| and the polymerized phlobaphenes in maize |CITS:[11402179]|. The first committed step of the pathway is the reduction of the respective flavanones forming flavan 4-ols. The structures of the flavan 4-ols have been questioned and a retrodihydrochalcone structure (|FRAME:CPD-15275|) proposed instead |CITS:[Khalil12]|. However, further research is needed to address this question in more detail. |FRAME:Naringenin Naringenin| is the flavanone that starts the |FRAME:PWY-7253|. The flavanone 4-reductase catalyzing this reaction has been purified and characterized from |FRAME:TAX-48789| |CITS:[Stich88]| |CITS:[Winefield05]| and maize |CITS:[Halbwirth03]|. It could be demonstrated that the enzyme had a dual activity as it also accepted dihydroflavonols, hence acted as dihydroflavonol 4-reductase (DFR)/flavanone 4-reductase (FNR). The formation of 3-deoxyanthocyanins is influenced by the activity of the flavonoid 3-hydroxylase (F3H), an enzyme involved in the formation of 3-hydroxyanthocyanins, which also competes for the available flavanones. Is the F3H inhibited, e.g in |FRAME:CPD-15293| treated |FRAME:TAX-3749| |CITS:[12667486]| or naturally absent or suppressed in certain genotypes |CITS:[Halbwirth03]| the flavanone 4-reductase directs the substrate flow towards the 3-deoxyanthocyanin biosynthesis as no flavan-3,4-diols are available for the dihydroflavonol 4-reductase to act on. The specific anthocyanidin synthase activity which converts the flavanones (here |FRAME:CPD-11940|) to the 3-deoxyanthocyanidins, i.e. |FRAME:CPD-7096| has been shown to be expressed in petals of |FRAME:TAX-48789| |CITS:[Winefield05]| but has not yet been purified and characterized. The final step in the pathway is the formation of the 5-O-glucosides which is catalyzed by the 3-deoxyanthocyanin 5-Oglucosyltransferase. This enzyme has been identified and biochemically characterized in petals of |FRAME:TAX-189007| and shown to be very specific for the 3-deoxyanthocyanidins |FRAME:CPD-11945| and |FRAME:CPD-7096| (this pathway) because it did not accept any other flavonoid substrates (flavonols, flavones, flavanones, 3-hydroxyanthocyanidins) |CITS:[20458497]|. It has been classified as an UGT88 enzyme, a phylogenetic clade which involves |FRAME:MONOMER-12113| (see |FRAME:PWY-5160|) |CITS:[15944692]| and |FRAME:MONOMER-12697| (see |FRAME:PWY-1901|) |CITS:[16832053]|.

from BIOCYC source record: META_PWY-7253
Type: pathway
Taxonomic scope
conserved biosystem

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