Flavanone biosynthesis

Turnbull JJ, Nakajima J, Welford RW, Yamazaki M, Saito K and Schofield CJ. 2004. Mechanistic studies on three 2-oxoglutarate-dependent oxygenases of flavonoid biosynthesis anthocyanidin synthase, flavonol synthase, and flavanone 33-hydroxylase. J Biol Chem 279 1206-1216. 

Figure 6.1 Major branch pathways of flavonoid biosynthesis in Arabidopsis. Branch pathways, enzymes, and end products present in other plants but not Arabidopsis are shown in light gray. Abbreviations cinnamate-4-hydroxylase (C4H), chalcone isomerase (CHI), chalcone synthase (CHS), 4-coumarate CoA-ligase (4CL), dihydroflavonol 4-reductase (DFR), flavanone 3-hydroxylase (F3H), flavonoid 3 or 3 5 hydroxylase (F3 H, F3 5 H), leucoanthocyanidin dioxygenase (LDOX), leucoanthocyanidin reductase (LCR), O-methyltransferase (OMT), phenylalanine ammonia-lyase (PAL), rhamnosyl transferase (RT), and UDP flavonoid glucosyl transferase (UFGT).

Lewinsohn E, Britsch L, Mazur Y, Gressel J (1989) Flavanone glycoside biosynthesis in Citrus chalcone synthase, UDP-glucose flavanone-7-0-glucosy-transferase and -rhamnosyltransferase activities in cell-free extracts. Plant Physiol 91 1321-1328... 

Flavanones are converted stereospecifically to the respective (2i ,3i )-dihydroflavonols (DHFs) by flavanone 3(3-hydroxylase. Stereospecificity for (2S)-flavanones has been confirmed by analysis of the recombinant protein. Flavanone 3(3-hydroxylase is commonly abbreviated to F3H, which is what has been used in this chapter, but FHT is also used in the literature, which agrees with the nomenclature for phenylpropanoid biosynthesis proposed in Heller and Forkmann. ... 

Some species contain a closely related enzyme activity to DFR that can act on tlavanones, termed the flavanone 4-reductase (FNR), which may represent a variant DFR form. This is discussed in more detail in Section 3.4.7. 5-Deoxyleucoanthocyanidin compounds are known to occur in legumes, and analysis of two recombinant DFR proteins (MtDFRl and MtDFR2) from Medicago truncatula (barrel medic) has found activity on the 5-deoxyDHF substrates fustin and dihydrorobinetin. Indeed, fustin was the preferred substrate of both recombinant enzymes. MtDFRl and MtDFR2 showed distinct enzyme characteristics, and overexpression of MtDFRl but not MtDFR2 promoted anthocyanin biosynthesis in flowers of N. tabacum. 

Hashim, M.F. et al.. Reaction mechanism of oxidative rearrangement of flavanone in isofiavone biosynthesis. FEBS Lett., 271, 219, 1990. 

Akashi, T. et al.. New scheme of the biosynthesis of formononetin involving 2,7,4 -trihydroxyiso-flavanone but not daidzein as the methyl acceptor. Biosci. BiotechnoL Biochem., 64, 2276, 2000. 

Biogenetically, chalcones are the immediate precursors of flavanones, and some flavanones isomerize by ring opening into chalcones during isolation from plants or after chemical treatment with alkali. In turn, flavanones are intermediates in the biosynthesis of most other flavonoid groups, including flavones, flavonols, and isoflavonoids. For more information on the biosynthesis of flavonoids and flavanones in particular, the reader is referred to Chapter 3 and reviews by Heller and Forkmann. ... 

Flavonoids can be classified according to their biosynthetic origins. Some flavonoids are both intermediates in biosynthesis and end-products, e.g. chalcones, flavanones, flavanon-3-ols and flavan-3,4-diols. Other classes are only known as the end-products of biosynthesis, e.g. anthocyanins, flavones and flavonols. Two further classes of flavonoids are those in which the 2-phenyl side-chain of flavonoid isomerizes to the 3-position (giving rise to isoflavones and related isoflavonoids) and then to the 4-position (giving rise to the neoflavonoids). The major classes of flavonoids, with specific examples, are summarized helow. 

Similarly to L. densiflora, L. heteromorpha is unusual for its biosynthesis of methoxylated flavonoids glycosides (with the methoxyl groups at C-4 of ring B and C-7 of ring A). The production of such flavonoids could be a response to local environmental factors. In comparison to the other Licania species, L. heteromorpha predominantly yields flavonol glycosides instead of flavones or flavanones. 

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),...

Yan Y, Kohli A, Koffas MAG. 2005. Biosynthesis of natural flavanones in Sacchar-omyces cerevisisae. Appl Environ Microbiol 71 5610-5613. 

The results from our investigation of D. mannii indicated that this plant is a rich source of diprenylated flavanones. It is possible to speculate the biosynthesis of most of the dorsmanins 94, 86-96 from 6, 8-diprenyleriodictyol (83) which is in fact present in the plant in rather significant amount. Fig.(8) shows various epoxide intermediates arising from 83, which undergo subsequent opening by phenolic hydroxyls to yield the various diprenylated dorsmanins. 

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.

Cytochrome P450 monooxygenases play two important roles in flavonoid biosynthesis. One involves the modification of ring C of flavanones, where they attack nonphenolic carbon atoms, thus resulting in the creation of new flavonoid classes such as flavones, flavonols, and isoflavonoids. The other involves the introduction of new hydroxyl groups on phenolic rings A and B, thus increasing the... 

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