Deoxychalcone synthase

The KR is monomeric and co-acts with CHS in 1 2 molar ratio at the optimal pH of 6.0. The enzyme has a high affinity for NADPH (K ,= 17 pmol/1) and replacement of NADPH by NADH in the enzyme assay decreased the yield of 20 

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The peptide sequences obtained for codeinone reductase aligned well with the amino acid sequences for 6 -deoxychalcone synthase (chalcone reductase) from alfalfa, Glycerrhiza, and soybean. Knowledge of the relative positions of the peptides allowed for a quick RT-PCR based isolation of cDNAs encoding codeinone reductase from P. somniferum. The codeinone reductase isoforms are 53 % identical to chalcone reductase from soybean.25 By sequence comparison, both codeinone reductase and chalcone reductase belong to the aldo/keto reductase family, a group of structurally and functionally related NADPH-dependent oxidoreductases, and thereby possibly arise from primary metabolism. Six alleles encoding codeinone... 

Alternatively, chalcone reductase (CHR also known as deoxychalcone synthase) together with chalcone synthase and NADPH as a cofactor act in the formation of isoliquiritigenin, which is then isomerized, again by the enzyme chalcone isomerase, to form liquiritigenin, the precursor to daidzein, and the pterocarpan phytoalexins. A type II chalcone isomerase that seems to be found exclusively in the legumes catalyzes this isomerization reaction. Glycitein synthesis is not yet clearly defined, but is likely derived from liquiritigenin via flavonoid 6-hydroxylase, and an unidentified methyltransferase. 

Ayabe, S., A. Udagawa, and T. Furuya Studies on Plant Tissue Cultures. 54. NAD(P)H-Dependent 6 -Deoxychalcone Synthase Activity in Glycyrrhiza echinata Cells Induced by Yeast Extract. Arch. Biochem. Biophys., 261, 458 (1988). 

Recently, a new polyketide biosynthetic pathway in bacteria that parallels the well studied plant PKSs has been discovered that can assemble small aromatic metabolites.8,9 These type III PKSs10 are members of the chalcone synthase (CHS) and stilbene synthase (STS) family of PKSs previously thought to be restricted to plants.11 The best studied type III PKS is CHS. Physiologically, CHS catalyzes the biosynthesis of 4,2, 4, 6 -tetrahydroxychalcone (chalcone). Moreover, in some organisms CHS works in concert with chalcone reductase (CHR) to produce 4,2 ,4 -trihydroxychalcone (deoxychalcone) (Fig. 12.1). Both natural products constitute plant secondary metabolites that are used as precursors for the biosynthesis of anthocyanin pigments, anti-microbial phytoalexins, and chemical inducers of Rhizobium nodulation genes.12... 

This enzyme [EC 2.3.1.74] (also known as narmgenm-chalcone synthase, flavonone synthase, and 6 -deoxy-chalcone synthase) catalyzes the reaction of three malonyl-CoA with 4-coumaroyl-CoA to produce four coenzyme A, three carbon dioxide, and naringeninchal-cone. If both NADH and a particular reductase is also present, the final product is 6 -deoxychalcone. 

Tropf, S. et al., Reaction mechanisms of homodimeric plant polyketide synthases (stilbenes and chalcone synthase) a single active site for the condensing reaction is sufficient for synthesis of stilbenes, chalcones, and 6 -deoxychalcones. J. Biol. Chem., 270, 7922, 1995. 

FIGURE 16.3 Overview of the biosynthesis of (I) chalcones and (II) 6 -deoxychalcones. The sequential condensation of three molecules of malonyl-CoA (acetate pathway) and p-coumaroyl-CoA (shikimate pathway) is catalyzed by the enzyme chalcone synthase.The production of 6 -deoxychalcones is thought to involve an additional reduction step at the tri- or tetraketide level, catalyzed by polyketide reductase.The origin of the A-ring carbons derived from the acetate pathway is indicated in bold. CoA, coenzyme A. 

The main flavonoid skeleton derives from the stepwise condensation of three molecules of malonyl CoA with one molecule of 4-coumaroyl CoA, a reaction catalyzed by chalcone synthase (CHS) to form naringenin (2, 4,4 ,6,-tetrahydroxy) chalcone, the common intermediate in the formation of all flavonoids with 5,7-dihydroxy (flavone numbering) A-ring substitution. In some plants, however, an NADP-dependent chalcone-ketide reductase coacts with CHS to form 6 -deoxychalcone, the precursor of 5-deoxyflavonoids. The resulting chalcones undergoe a stereospecific cyclization to the corresponding (2S) flavanones, the... 

Fig. 10A-D. Pathways for plant polyketide synthase catalyzed biosynthesis of A chalcone and stilbene B 6 -deoxychalcone C methylchalcone D 2-pyrone...

Tomato (Petunia) (alfalfa)/ oveiexpiession CaMV35S/ CHSl + CHR Chalcone synthase + chalcone reductase Chalcones -I- deoxychalcones Higher butein, isoliquiritigenin, naringenin, chalcone, and rutin [63]... 

Fig. 2.5 Biosynthetic routes to flavonoids and 5-deoxyflavonoids in the Leguminosae. CHS, chalcone synthase CHR, chalcone reductase CHI, chalcone isomerase IFS, isoflavone synthase. The acetate-derived A-ring carbon atoms of chalcones and 6 -deoxychalcones are indicated in bold.

Welle, R. and Grisebach, H. (1988) Isolation of a novel NADPH-dependent reductase which coacts with chalcone synthase in the biosynthesis of 6 -deoxychalcone. FEBS Lett., 236, 221-225. 

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