Chalcones chalcone isomerase

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]... 

Flavonoids are the largest class of phenylpropanoids in plants. The basic flavonoid structure is two aromatic rings (one from phenylalanine and the other from the condensation of three malonic acids) linked by three carbons (Fig. 3.6). Chalcone is converted to naringenin by the enzyme chalcone isomerase, which is a key enzyme in flavonoid synthesis. This enzyme, like PAL and chalcone synthase (CHS), is under precise control and is inducible by both internal and external signals. Naringenin is the... 

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.

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).

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.

JEZ, J.M., BOWMAN, M.E., DIXON, R.A., NOEL, J.P., Structure and mechanism of chalcone isomerase an evolutionarily unique enzyme in plants, Nature Struct. Biol., 2000, 7,786-791. 

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. 

CAIN, C.C., SASLOWSKY, D.E., WALKER, R.A., SHIRLEY, B.W., Expression of chalcone synthase and chalcone isomerase proteins in Arabidopsis seedlings, Plant Mol. Biol., 1997, 35,377-381. 

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. 

Koca U (2007) Elevation of the flavonoid content in grapefruit by introducing chalcone isomerase gene via biotechnological methods. Turk J Pharm Sci 4(3) 115-124... 

Bednar RA, Hadcock JR (1988) Purification and characterization of chalcone isomerase from soybeans. J Biol Chem 263(20) 9582-9588... 

Jez JM, Bowman ME, Dixon RA, Noel JP (2000) Structure and mechanism of the evolutionarily unique plant enzyme chalcone isomerase. Nat Struct Biol 7(9) 786-791... 

Fouche SD, Dubery lA (1994) Chalcone isomerase from Citrus sinensis purification and characterization. Phytochemistry 37 127-132... 

HV032 Reuber, S., B. Jende-Strid, V. Wray, and G. Weissenbock. Accumulation of the chalcone isosalipurposide in pri- HV042 mary leaves of barley flavonoid mutants indicates a defective chalcone isomerase. Physiol Plant 1997 101(4) ... 

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. ... 

Gensheimer, M. and Mushegian, A., Chalcone isomerase family and fold no longer unique to plants. Prot. Scl, 13, 540, 2004. 

Shimada, N. et al., A cluster of genes encodes the two types of chalcone isomerase involved in the biosynthesis of general flavonoids and legume-specific 5-deoxy(iso)flavonoids in Lotus japonicus. Plant Physiol, 131, 941, 2003. 

Muir, S.R. et al.. Overexpression of petunia chalcone isomerase in tomato results in fruit containing increased levels of fiavonols. Nat. BiotechnoL, 19, 470, 2001. 

Mehdy, M.C. and Lamb, C.J., Chalcone isomerase cDNA cloning and mRNA induction by elicitor, wounding and infection. EMBO J., 6, 1527, 1987. 

FIGURE 9.3 The hydrogen bond network in the (5 -4, 7-dihydroxyflavanone-chalcone isomerase complex. (Adapted from Jez, J.M., Bowman, M.E., and Noel, J.P., Biochemistry, 41, 5168, 2002. With permission.)... 

Herbicides are the biocides most likely to affect the metabolism of plants, including secondary metabolism [107]. The synthesis of hydroxyphenolics and anthocyanin in plants can be influenced by a variety of environmental and chemical stimuli. Some herbicides were found to raise the levels of these compounds in plants [108] whilst others had the opposite effect [109]. The products of secondary metabolism are controlled by enzymes, including PAL and chalcone isomerase (Cl), and several herbicides appear to intensify the activities of those enzymes involved in the accumulation of hydroxyphenolic compounds and anthocyanin biosynthesis in several plant species [109-111] whereas others depress this activity [112]. For example,... 

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