Flavanone-chalcone isomerase

Moustafa E, Wong E (1967) Purification and properties of chalcone-flavanone isomerase from soya bean seed. Phytochemistry 6 625-632... 

Van Tunen, A.J., Hartman, S.A., and Mur, L.A., Regulation of chalcone flavanone isomerase (CHI) gene expression in Petunia hybrida the use of alternative promoters in corolla, anthers and pollen, Plant Mol Biol, 12, 539, 1989. 

Fig. 1. Simplified diagram of the phenylpropanoid and flavonoid biosynthetic pathways. Enzymes that catalyze the reactions are placed on the left-hand side, and transcription factors on the right-hand side of the arrows. Both transcription factors for which their control over the enzymatic steps has been genetically proven, as well as transcription factors that have been shown to interact with promoters of the structural genes, are shown. PAL Phenylalanine ammonia lyase C4H cinnamate 4-hydroxylase 4CL 4-coumaroyl-coenzyme A ligase CHS chalcone synthase CHI chalcone-flavanone isomerase F3H flavanone 3(3-hydroxylase DFR dihydroflavonol 4-reductase AS anthocyanin synthase UFGT UDP glucose-flavonol glucosyl transferase RT anthocyanin rhamnosyl transferase...

It shlklmate dehydrogenase, 2t phenylalanine ammonia-lyase, 3> cinnamic acid 4-hydroxylase, 4 SAMI caffeate 3-0-methyltransferase, 5t hy-droxyclnnamatet CoA llgase, 6t "flavanone synthase", 7t chalcone-flavanone isomerase, 8t SAMt 3, 4 -dihydroxyflavonoid 3 0-methyltrans-[Pg.236]

Fig. (1). Schematic view of some branches of phenylpropanoid metabolism. Solid arrows indicate enzymatic reactions with the respective enzyme indicated on the right. PAL, phenylalanine ammonia-lyase C4H, cinnamate 4-hydroxylase 4CL, 4-coumarate CoA ligase CHS, chalcone synthase CF1, chalcone flavavone isomerase F3H, flavanone 3-hydroxylase DFR, dihydroflavonol reductase CHR, chalcone reductase. Broken arrows indicate metabolic branches towards several classes of phenylpropanoids, or several subsequent enzymatic steps. In some cases the enzymes indicated are also involved in other reactions, not shown.

Flavonoids are a large class of plant natural products of low molecular weight. Over 3,000 different flavonoids have been chemically characterised and novel ones are still being reported. Flavonoids are aromatic molecules synthesised from the amino acid phenylalanine and an acetate-derived precursor as malonyl-coenzyme A (Fig. 11.1) (Winkel-Shirley 2001). This reaction is carried out by the enzyme chalcone synthase (CHS) to produce chalcone. The chalcone can subsequently be isomerised by the enzyme chalcone flavone isomerase (CHI) to yield a flavanone. From these intermediates the pathway diverges into several side branches yielding different subclasses of flavonoids, as summarised in Fig. 

The immediate product of flavanone synthase (naringenin) in parsley was converted to the isomeric chalcone (XX) by a separate enzyme whose properties were examined by Kreuzaler and Hahlbrock (1975a). A different chal-cone-flavanone isomerase has also been highly purified from soybean seeds (Boland and Wong, 1975). 

Flax Petunia hybrid/ overexpression CaMV35S/CHS + CHI + DFR Chalcone synthase, chalcone isomerase, and dihydroflavonol 4-reductase Chalcones, flavanones, chlorogenic acid Higher in flavonoids (kaempferol), phenolic acids (coumaric, ferulic, synaptic acids) in seedcake extracts [65]... 

Fig. 5 Scheme of the flavonoid pathway leading to synthesis of proanthocyanidins. The enzymes involved in the pathway are shown as follows CHS = chalcone synthase CHI = chalcone isomerase F3H = flavanone-3B-hydroxylase DFR = dihydroflavonol-4-reductase LDOX = leucoanthocynidin dioxygenase LAR = leucoanthocyanidin reductase ANR = anthocyanidin reductase adapted from [27] and [28]... 

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).

PELLETIER, M.K., SHIRLEY, B.W., Analysis of flavanone 3-hydroxylase in Arabidopsis seedlings Coordinate regulation with chalcone synthase and chalcone isomerase, Plant Physiol., 1996, 111, 339-345. 

CL, 4-coumarate CoA ligase CHS, chalcone synthase CHI, chalcone isomerase F3H, flavanone 3-hydroxylase DFR, dihydroflavonol 4-reductase ANS, anthocyanidin synthase FGT, flavonoid 3-O-glucosyltransferase. 

The stereospecific cyclization of chalcones to (2S)-flavanones is a prerequisite for the synthesis of the majority of fiavonoid subclasses derived from this branch point metabolite. This reaction is catalyzed by chalcone isomerase (CHI, CFI EC 5.5.1.6). CHI exists in two forms, one that accepts only 6 -hydroxychalcones and another that accepts both 6 -hydroxy-(naringenin chalcone) and 6 -deoxychalcones (isoliquirgentin), the latter generally found in legumes. Although 6 -hydroxychalcones will spontaneously convert to a racemic flavanone mixture, the CHI-catalyzed reaction proceeds at a rate 36 million-fold faster and is highly stereoselective for the formation of (25)-flavanones [60]. Spontaneous isomerization of 6 -deoxychalcones does not substantially occur without enzyme catalysis. 

In a reaction that establishes the flavonoid heterocyclic C-ring, chalcone isomerase (CHI) catalyzes the stereospecific isomerization of chalcones to their corresponding (2S)-flavanones, via an acid base catalysis mechanism. Almost 40 years ago, the first flavonoid enzyme to be described was CHI (in the adopted hometown of the authors of this chapter). Since then CHI has been analyzed in great detail, and surprisingly, it shows little similarity to other known protein sequences, although CHI-like sequences have recently been reported from plants and other organisms. ... 

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.

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.

Chalcone synthase (CHS) and chalcone reductase (CHR) convert 4-coumaro-yl-CoA (15) and 3 mol malonyl-CoA (16) to trihydroxychalcone (a chalcone) (17) via tetrahydroxychalcone (a chalcone) (18). Chalcone isomerase (CHI) converts trihydroxychalcone (a chalcone) (17) into liquiritigenin (7,4/-dihydroxyllavanone, a flavanone) (19). Isoflavone synthase (IFS) converted flavanone (19) to isoflavones (20) such as daidzein (21) and genis-tein (22). Isoflavone 2/-hydroxylase (I2 H) hydroxylated isoflavones (20) to 4/-methoxyisoflavones (23). Isoflavone 2 -hydroxylase (I2 H) hydroxylated 4/-methoxyisoflavones (23) into 2/-hydroxy-4/-methoxyisoflavones (24). Isoflavone reductase (IFR) reduced 2/-hydroxy-4/-methoxyisoflavones (24) to 2/-hydroxy-4/-methoxyisoflavonones (25). Finally, vestitone reductase (VR) and 4/-methoxyisoflavanol dehydrogenase (DMID) cyclized 2/-hydroxy-4/-methoxyisoflavonones (25) to form isoflavonoids (26) such as medicarpin (27) (Fig. 4) [23,24]. 

Fig. 11.1 Simplified diagram of the flavonoid biosynthetic pathway, starting with the general phenylpropanoid metabolism and leading to the main types of flavonoids. Only a few examples are illustrated of the large variety of flavonoids that arise through modification at different positions (not indicated or shown as R). Enzymes catalysing some key reactions are indicated by the following abbreviations PAL, phenylalanine ammonia-lyase CHS, chalcone synthase CHI, chalcone isomerase DFR, dihydroflavonol reductase F3H, flavanone 3-hydroxylase F3 5 H, flavonoid 3 5 -...

Fig, 5.2. Biosynthesis of flavonoids and proanthocyanidins (condensed tannins). Enzymes in bold have been cloned from P. tremuloides and show induction by herbivory (Peters and Constabel, 2002 R. Mellway and C. P. Constabel, unpublished data). Abbreviations are as follows Phe, phenylalanine PAL, phenylalanine ammonia lyase 4CL, 4-coumarate CoA Ligase CHS, chalcone synthase CHI, chalcone isomerase F3H, flavanone 3-hydroxylase FLS, flavonol synthase DFR,... 

Mutants that lack chalcone isomerase, the next enzyme in the sequence, accumulate chalcones, not flavanones, and establish that the initial product of the reaction is a chalcone (Grisebach, 1985). Recessive genotypes of certain flowers that lack chalcone synthase accumulate cinnamic acid gluco-sides (Grisebach, 1985). 

As described above, chalcones and flavanones are easily interconverted under mild conditions and the original isomerization in plants may have been nonenzymatic (Stafford, 1991). However, because most hydrolyases utilize the (2S)-isomer, enzymatic control would be more efficient. An enzyme capable of catalyzing this interconversion, chalcone isomerase, has now been demonstrated to be present in a number of plants. The enzyme has no cofactor requirements. A proton is introduced specifically into the axial position at C-3. The effect of illumination suggests that the enzyme is related to and probably essential for the biosynthesis of flavonoids. 

Flavonoids are a diverse family of plant polyphenols and of special interest due to their potential in the treatment of various human diseases. The first attempts to produce flavonoid precursors were accomplished by cloning of the flavanone pathway consisting of cinnamate-4-hydroxylase (CYP73A5) from A. thalima together with 4-coumaroyl CoA ligase (4CL), chalcone synthase (CHS), and chalcone isomerase (CHI) in S. cerevisiae [410], The generated strain was able to convert cinnamic acid to 200 pg naringenin... 

Fig. 8.17 Schematic representation of pathways for the production of flavonoids. 4CL 4-coumaroyl CoA ligase, CHS chalcone synthase, CHI chalcone isomerase, FHT flavanone 3p-hydroxylase, FLS flavonol synthase...

The mutual interconversion of flavanones and chalcones is catalyzed by chalcone isomerase, an enzyme forming 2(S)-flavanones. 

Fig. 314. Formation of the most important groups of flavonoids 1 Chalcone synthase 2 chalcone isomerase 3 flavanone oxidase...

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