Flavone synthase

Flavone [525-82-6 Flavone dyes Flavone synthase Flavonoids... 

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.

Martens S and Mithofer A. 2005. Flavones and flavone synthases. Phytochem 66 2399-2407. 

Flavone synthase (FNS EC 1.14.11.22) introduces a double bond between C2 and C3 of a flavanone to produce the corresponding flavone. This activity was initially identified in parsley cell suspension cultures and subsequently shown to be encoded by a 2-oxoglutarate-dependent dioxygenase [67, 78, 79], This enzyme, now known as FNS-I, appears to have very limited distribution. To date, it has only been identified in the Apiaceae family (Umbellifers). The more widely occurring FNS-II (CYP93B) was initially identified from snapdragon (Antirrhinum majus) flowers [80] and was subsequently shown to be a P450 enzyme. FNS-I, FNS-II, and the various roles flavones play in plant species have recently been reviewed by Martens and Mithofer [81], Subsequent to this review, Yu et al. [82] demonstrated that the characteristic lack of natural accumulation of flavones in Brassicaceae could not be overcome in A. thaliana even by overexpression of recombinant parsley FNS-I. 

Martens S, Forkmann G, Matern U, Lukacin R (2001) Cloning of parsley flavone synthase I. Phytochemistry 58 43-46... 

Yun CS, Yamamoto T, Nozawa A, Tozawa Y (2008) Expression of parsley flavone synthase I establishes the flavone biosynthetic pathway in Arabidopsis thaliana. Biosci Biotechnol Biochem 72(4) 968-973... 

RIBOFLAVIN KINASE FLAVONE SYNTHASE FLAVONOL SYNTHASE Flicker,... 

Martens, S. and Forkmann, G., Cloning and expression of flavone synthase 11 from Gerbera hybrids. Plant J., 20, 611, 1999. 

Akashi, T. et al.. Molecular cloning and biochemical characterization of a novel cytochrome P450, flavone synthase II, that catalyzes direct conversion of flavanones to flavones. Plant Cell Physiol, 40, 1182, 1999. 

Britsch, L., Purification and characterization of flavone synthase 1, a 2-oxoglutarate-dependent desaturase. Arch. Biochem. Biophys., 282, 152, 1990. 

Akashi, T., Aoki, T., and Ayabe, S., Identification of a cytochrome P450 cDNA encoding (25)-flavanone 2-hydroxylase of licorice Glycyrrhiza echinata L. Fabaceae) which represents licodione synthase and flavone synthase II. FEES Lett., 431, 287, 1998. 

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),...

The biosynthetic pathway leading to maysin starts with flavanone (6.18), which is hydroxylated by flavone 3 hydroxylase to yield di-hydroxyl flavanone (6.19) and is the reduced by flavone synthase to the flavone luteolin (6.20). The next steps were recently investigated in more detail by McMullen et al. (2004) using two salmon silk mutants, sml (Anderson, 1921) and a newly discovered mutant sm2. These mutants have salmon colored silks instead of green silks as a result of pigment accumulation throughout the shaft of the silks, as opposed to only in the silk hairs, but do require a functional PI gene in order for the mutant phenotype to be apparent (see also Chapter 3, Section 9.2). 

Figure 6-2. Biosynthesis of maysin proposed by McMullen et al. (2004) based on the analysis of flavones in the silks of maize salmon silk mutants, a. flavone 3 hydroxylase (encoded by the maize Prl gene), b. flavone synthase, c. C-glucosyltransferase, d. putative rhamnosyl transferase (encoded by the Salmon silk2 gene), e. the step(s) controlled by the Salmon silkl gene.

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.

Leonard E, Chemler J, Lim KH, Koffas MA. 2006a. Expression of a soluble flavone synthase allows the biosynthesis of phytoestrogen derivatives in Escherichia coli. Appl Microbiol Biotechnol 70 85-91. 

Leonard E, Yan Y, Lim KH, Koffas MAG. 2005. Investigation of two distinct flavone synthases for plant-specific flavones biosynthesis in Saccharomyces cerevisiae. Appl Environ Microbiol 71 8241-8248. 

Lukacin R, Matern U, Junghanns KT, Heskamp ML, Britsch L, Forkmann G, Martens S. 2001. Purification and antigenicity of flavones synthase I from irradiated parsley cells. Arch Biochem Biophys 393 177-183. 

Scheme 1.1 Pathway for the biosynthesis of the major classes of flavonoids. 1, Chalcone synthase 2, chalcone isomerase 3, flavone synthase 4, flavanone 3-hydroxylase 5, flavonol synthase 6, dihydroflavonol reductase 7, anthocyanidin synthase 8, anthocyanidin glucosyltransferase 9, chalcone-ketide reductase 10, chalcone isomerase 11, isoflavone synthase 12, isoflavone 2 -hydroxylase 13, isoflavone reductase 14, pterocarpan synthase 15, pterocarpan 6a-hydroxylase 16, prenyltransferase 17, prenylcyclase.

KOCHS, G., GRISEBACH, H., Isolation and characterization of an NADPH-dependent flavone synthase from cell cultures of soybean. Z Naturforsch, 1987, 42c, 343-348. 

MARTENS, S., FORKMANN, G., Genetic control of flavone synthase II activity in flowers of Gerbera hybrids. Phytochemistry, 1998,49,1953-1958. 

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