Flavonoid 6-Hydroxylase

The F6H showed low activity against flavones and little action on the flavonol kaemp-ferol. Nevertheless, it is possible that a similar biosynthetic route through hydroxylation of precursors, perhaps by the same F6H, is involved in the production of other 6-hydroxyfla-vonoids. However, an alternative activity of the 20GD type has been characterized at the biochemical level from C. americanum that catalyzes the 6-hydroxylation of partially methylated flavonoids.  

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Figure 5.4. Abbreviated scheme for biosynthesis of major flavonoid subclasses, showing the primary enzymes and substrates leading to different subclasses. Bold-faced, uppercase abbreviations refer to enzyme names, whereas substrate names are presented in lowercase letters. PAL, phenylalanine ammonia lyase C4H, cinnamate 4-hydroxylase 4CL, 4-coumarate CoA ligase CHS, chalcone synthase CHI, chalcone isomerase CHR, chalcone reductase IPS, isoflavone synthase F3H, flavonone 3-hydroxylase F3 H, flavonoid 3 -hydroxylase F3 5 H, flavonoid 3 5 -hydroxylase FNSI/II, flavone synthase DFR, dihydroflavonol 4-reductase FLS, flavonol synthase ANS, anthocyanidin synthase LAR, leucoanthocyanidin reductase ANR, anthocyanidin reductase UFGT, UDP-glucose flavonoid 3-O-glucosyltransferase. R3 = H or OH. R5 = H or OH. Glc = glucose. Please refer to text for more information.

Table 6.1 Abbreviations BAN, BANYULS bHLH, basic helix-loop-helix CHS, chalcone synthase CHI, chalcone isomerase DFR, dihydroflavonol reductase F3H, flavonol 3-hydroxylase F3 H, flavonoid 3 -hydroxylase FLS, flavonol synthase icx, increased chalcone synthase expression LDOX, leucoanthocyanidin dioxygenase LCR, leucoanthocyanidin reductase MATE, multidrug and toxic compound extrusion NR, not yet reported tt, transparent testa ttg, transparent testa glabrous the WD40 and WRKY transcription factors are named for conserved amino acid sequences within these proteins. PC = personal communication.

SCHOENBOHM, C., MARTENS, S., EDER, C., FORKMANN, G WEISSHAAR, B., Identification of the Arabidopsis thaliana flavonoid 3 -hydroxylase gene and functional expression of the encoded P450 enzyme, Biol. Chem., 2000,381, 749-753. 

The riocus encodes the enzyme flavonoid 3 -hydroxylase (F3 H) [17, 18], and is an important controller of flux in the anthocyanin pathway in soybean seed coats (Fig. 4.1). F3 H diverts metabolic flux away from biosynthesis of orange (pelargoni-din) and blue (delphinidin) anthocyanins toward the red cyanidin-3-(9-glucoside, which is the main anthocyanin in the seed coats of black soybean [7, 8]. T increases the accumulation of delphidin-3-O-glucoside in black seed coats, even though it is not required for its biosynthesis [19]. Possible mechanisms for this include positive feedback, or the stabilization of the putative anthocyanin biosynthetic metabolon [20] by F3 Fl-derived membrane anchoring (Fig. 4.1). 

Toda K, Yang D, Yamanaka N et al (2002) A single-base deletion in soybean flavonoid 3 -hydroxylase gene is associated with gray pubescence color. Plant Mol Biol 50 187-196... 

Zabala G, Vodkin L (2003) Cloning of the pleiotropic T locus in soybean and two recessive alleles that differentially affect structure and expression of the encoded flavonoid 3 hydroxylase. Genetics 163 295-309... 

HagmannML, HeUerW, GrisebachH (1983) Induction and characterization of a microsomal flavonoid 3 -hydroxylase from parsley cell cultures. Eur J Biochem 134(3) 547-554... 

Brugliera F, Barri-ReweU G, Holton TA, Mason JG (1999) Isolation and characterization of a flavonoid 3 -hydroxylase cDNA clone corresponding to the Htl locus of Petunia hybrida. Plant J 19(4) 441 51... 

Ueyama, Y. et al., Molecular and biochemical characterization of torenia flavonoid 3 -hydroxylase and flavone synthase II and modification of flower color by modulating the expression of these... 

Figure 3-7. Flavonoid biosynthesis (this page and next page). The enzymes involved in this pathway are (a) chalcone synthase (E.C. 2.3.1.73), (b) aureusidin synthase (E.C. 1.21.3.6), (c) chalcone isomerase (E.C. 5.5.1.6), (d) flavanone 3-hydroxylase (E.C. 1.14.11.9), (e) flavone synthase (E.C. 1.14.11.22), (f) flavonoid 3 -hydroxylase (E.C. 1.14.13.21),...

Figure 1.36 Schematic diagram of the stilbene and flavonoid biosynthetic pathway. Enzyme abbreviations SS, stilbene synthase CHS, chalcone synthase CHR, chalcone reductase CHI, chalcone isomerase IFS, isoflavone synthase FNS, flavone synthase F3H, flavanone 3-hydroxylase FLS, flavonol synthase F3 H, flavonoid 3 -hydroxylase DFR, dihydroflavonol 4-reductase LAR, leucoanthocyanidin 4-reductase LDOX, leucocyanidin deoxygenase ANR, anthocyanidin reductase EU, extension units TU, terminal unit.

FORKMANN, G., HELLER, W., GRISEBACH, H Anthocyanin biosynthesis in flowers of Matthiola incana flavanone 3-hydroxylase and flavonoid 3 -hydroxylase. Z. Naturforsch, 1980,35c, 691-695. 

Flavanone 3-hydroxylase (F3H) converted naringenin (1) to dihydrokaem-pferol (3-OH-flavanone) (31). Flavonoid 3 -hydroxylase (F3 II) and flavonoid 3 5 -hydroxylasc (r3 5 I I) converted dihydrokaempferol (31) to dihydroflavo-nols (3-OH-flavanones) (32) such as dihydro quercetin (33) and dihydromy-ricetin (34). 

Fig. 11.2 Diagram corresponding to the biosynthetic pathway of anthocyanins from the intermediate naringenin. Enzymes catalysing the reactions are indicated by the following abbreviations F3H, flavanone 3-hydroxylase F3 H, flavonoid 3 -hydroxylase F3 5 H, flavonoid 3 5 -hydroxylase DFR, dihydroflavonol reductase 3GT, 3-O-glucosyl...

Forkmann, G. and G. Stotz, Genetic control of flavanone 3-hydroxylase activity and flavonoid 3 -hydroxylase activity in Antirrhinum majus (snapdragon), Z. Naturforsch., 36c, 411-416 (1981). 

Figure 4. Biosynthetical pathway from L-phenylalanine to anthocyanidins (5... phenylalanine ammonia lyase 6... cinnamate 4-hydoxylase 7, 8... 4-coumarate-CoA ligase, chalcone lyase 9... chalcone isomerase 10, 11... flavonoid-3 hydroxylase, flavonoid-3 , 5 hydroxylase 12, 13... flavanone 3-hydroxylase, dihydroflavonol 4-reductase 14... anthocyanidinhydroxylase.

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