Hydroxycinnamoyl-CoA

How the aliphatic monomers are incorporated into the suberin polymer is not known. Presumably, activated co-hydroxy acids and dicarboxylic acids are ester-ified to the hydroxyl groups as found in cutin biosynthesis. The long chain fatty alcohols might be incorporated into suberin via esterification with phenylpro-panoic acids such as ferulic acid, followed by peroxidase-catalyzed polymerization of the phenolic derivative. This suggestion is based on the finding that ferulic acid esters of very long chain fatty alcohols are frequently found in sub-erin-associated waxes. The recently cloned hydroxycinnamoyl-CoA tyramine N-(hydroxycinnamoyl) transferase [77] may produce a tyramide derivative of the phenolic compound that may then be incorporated into the polymer by a peroxidase. The glycerol triester composed of a fatty acid, caffeic acid and a>-hydroxy acid found in the suberin associated wax [40] may also be incorporated into the polymer by a peroxidase. 

Hydroxycinnamoyl- CoAs Sugar acids (glucuronate, glucarate, galactarate) Monoesters exact position of the O-ester group unclear 25... 

The general phenylpropanoid pathway links the shikimate pathway to the lignin branch pathway. The latter pathway leads to the formation of a series of hydroxycinnamic acids and hydroxycinnamoyl-CoA esters varying in their degrees of hydroxylation and methylation [5]. 

The substitution of the phenyl ring necessary for the biosynthesis of coniferyl alcohol (3.79) and sinapyl alcohol (3.81) begins with the hydroxylation of C3. This is a conversion that requires the formation of the ester of /5-coumaroyl-CoA with D-quinate (3.73) or shikimate (3.74) catalyzed by the enzyme hydroxycinnamoyl-CoA shikimate/quinate hydroxy-cinnamoyl transferase (HCT Hoffmann et al., 2003). The hydroxylation of this ester intermediate is catalyzed by the enzyme /i-coumarovl-Co A 3 -hydroxylase (C3 H Schoch et al., 2001 Franke et al., 2002a,b). The resulting shikimate or quinate ester (3.75 3.76) is subsequently hydrolyzed by the same HCT, resulting in caffeoyl-CoA (3.36). 

Figure 3-9. Biosynthesis of monolignols. The enzymes involved in this pathway are ( ) hydroxycinnamoyl-CoA shikimate/quinate hydroxy-cinnamoyl transferase, (b) p-coumaroyl-CoA 3 -hydroxylase (E.C. 1.14.14.1), (c) caffeoyl-CoA O-methy 1 Iranslerasc (E.C. 2.1.1.104), (d) cinnamoyl-CoA reductase (E.C. 1.2.1.44) (e) cinnamyl alcohol dehydrogenase (E.C. 1.1.1.195), (f) coniferyl aldehyde/coniferyl alcohol 5-hydroxylase (E.C. 1.14.13), (g) coniferaldehyde/coniferyl alcohol O-methyltransferase (E.C. 2.1.1.68).

The irreversible condensation reaction between a starter hydroxycinnamoyl-CoA molecule and three acetate extender units derived from malonyl-CoA constitute the first committed step of flavonoid and stilbene biosynthesis [Springob et al., 2003] (Fig. 21.2). The reactions catalyzed by two type III... 

Ramirez Ahumada, M. del C., Timmermann, B.N. and Gang, D.R. (2006) Biosynthesis of curcuminoids and gingerols in turmeric (Curcuma longa) and ginger (Zingiber officinale) identification of curcuminoid synthase and hydroxycinnamoyl-CoA thioesterases. Phytochemistry 67(18), 201 7-2029. 

Recently, curcuminoid synthase has been identified as being capable of forming the curcuminoids in turmeric (Maria et al., 2006). This activity required malonyl-CoA and phenylpropanoid pathway-derived hydroxycinnamoyl-CoA esters as substrates, suggesting that the corresponding protein was a polyketide synthase or an enzyme that was closely related. It is postulated that this activity could be the result of a single enzyme, or of multiple enzymes in sequence. 

A new model (Fig. 15.4) for hydroxy-cinnamate chain-shortening and vanillin formation in plants was revealed with the isolation of 4-hydroxycinnamoyl-CoA hydratase/lyase (HCHL) and its gene from a soil bacterium, Pseudomonas fluorescens strain AN103, which had been isolated by growth on ferulic acid as a sole carbon source (Gasson et al., 1998 Narbad and Gasson, 1998 Mitra et al., 1999). 

Mitra, A., Kitamura, Y., Gasson, M.J., Narbad, A., Parr, A.J., Payne, J., Rhodes, M.J.C., Sewter, C. and Walton, N.J. (1999) 4-hydroxycinnamoyl-CoA hydratase/lyase (HCHL) - an enzyme of phenylpropanoid chain cleavage from Pseudomonas. Archives of Biochemistry and Biophysics 365, 10-16. 

The biogenesis of flavonoids in plants is well documented and known to take place by chain extension of 4-hydroxycinnamoyl-CoA (126) with malonyl CoA through the acetate pathway involving enzymes like chalcone S3mthase (86). Here, the initially formed polyketide 127 may undergo a Claisen-type condensation to form a chalcone and subsequently other flavonoids, as shown in Fig. 25. It is pertinent to... 

Negrel, J. and Javelle, F. (1997) Purification, characterization and partial amino acid sequencing of hydroxycinnamoyl-CoA tyramme N-(hydroxycinnamoyl)transferase from tobacco cell-suspension cultures. Eur.. Biochem., 347,1127-135. 

Rhodes, M.J.C., Wooltorton, L.S.C. and Lourenco, E.J. (1979) Purification and properties of hydroxycinnamoyl-CoA quinate hydroxycinnamoyl transferase from potatoes. Phytochemistry, 18,1125-9. 

Ulbrich, B. and Zenk, M.H. (1980) Partial purification and properties of p-hydroxycinnamoyl-CoA shikimate-p-hydroxycinnamoyl transferase from higher plants. Phytochemistry, 19,1625-9. 

HAL and PAL Proposed Tyr loop-in model for breathing motion tor substrate access The molecular basis of PAL and TAL substrate versatility Hydroxycinnamoyl CoA Shikimate/Quinate Hydroxycinnamoyltransferase Cytochrome P-450 Hydroxylation Reactions (Cinnamate 4-Hydroxylase, p-Coumarate 3-Hydroxylase , and Ferulate 5-Hydroxylase ) Comparison to Bacterial/Mammalian P-450s Subcellular localization of C4H, pC3H , and F5H ... 

Figure 4 Current view of the phenylpropanoid pathway to the monolignols 19-23. 4CL, 4-hydroxycinnamate coenzyme Aligases pC3H , p-coumarate 3-hydroxylase C4H, cinnamate 4-hydroxylase CAD, cinnamyl alcohol dehydrogenases CCOMT, hydroxycinnamoyl CoA O-methyltransferases CCR, cinnamoyl-CoA oxidoreductases COMT, caffeic acid O-methyltransferases F5H , ferulate 5-hydroxylase HCT, hydroxycinnamoyl-CoA shikimate hydroxycinnamoyltransferase HOT, hydroxycinnamoyl-CoA quinate hydroxycinnamoyltransferase PAL, phenylalanine ammonia lyase TAL, tyrosine ammonia lyase.

Cloning of a cDNA encoding HCT from tobacco N. tabacum, NtHCT) stems and expression of the recombinant protein in fully functional form in E. coli as a fusion product have also been carried out, with kinetic parameters of the purified protein determined (C. L. Cardenas etal, manuscript in preparation). " The overall catalytic propenies of recombinant NtHCT with various hydroxycinnamoyl CoAs (9-13) using either shikimic (29) or quinic (28) acid as substrate were quite informative (C. L. Cardenas et al, manuscript in preparation). With shikimic acid (29) at a saturating concentration, the observed /feat/Am of recombinant NtHCT established that the dominant HCT activity was with -coumaroyl CoA (9) (114840mor ls ) over that of caffeoyl (10), feruloyl (11), or sinapoyl (13) CoA (48 420, 6880, and 420 moF 1 s , respectively). Recombinant NtHCT was able, however, to less efficiently transfer hydroxycinnamoyl moieties from -coumaroyl CoA (9) and caffeoyl CoA (10) to quinic acid (28). Indeed, /fcat/Am values at saturating concentration of quinic acid (28) were lower by approximately 7.5- and 131-fold for/)-coumaroyl CoA... 

The kinetic studies of the recombinant NtHCT also further provided evidence for the reverse reaction towards formation of the hydroxycinnamoyl CoAs 9 and 10 (C. L. Cardenas etal, manuscript in preparation). In the presence of coenzyme A, NtHCT catalyzed cleavage of the ester bond of the respective hydroxycinnamoyl shikimate esters 25 and 27. The reverse reaction kinetics demonstrated that NtHCT was able to convert -coumaroyl shikimate (25) to -coumaroyl CoA (9) and caffeoyl shikimate (27) to caffeoyl CoA (10), with cat/Am values of 31 000 and 19 llOmoF Is , respectively, at saturating concentrations of CoA. 

Type I and Type II PKSs catalyze multiple rounds of reactions by catalytic modules encoded either by a single polypeptide (PKS I) or on separate polypeptides (PKS II) by analogy to FAS-I and FAS-II. In contrast, PKS Ills are dimers of KASs that catalyze multiple condensation reactions in one active site and include chalcone synthase, stilbene synthase, and 2-pyrone synthase (see Chapters 1.05, 1.07, and 1.04). In the case of chalcone synthase, three consecutive condensation reactions each utilizing malonyl-CoA, followed by a cyclization reaction, lead to the formation of 4, 2, 4, 6 -tetrahydroxychalcone from 4-hydroxycinnamoyl-CoA (Figure 3). Recruitment of a reductase leads to the formation of a product lacking the 6 -hydroxy group, a reaction that requires an intermediate in the synthesis of chalcone to dissociate from the synthase active site. 

Ulbrich, B. and M.H. Zenk Partial purification and properties of hydroxycinnamoyl-CoA Quinate hydroxycin-namoyl transferase from higher plants Phytochemistry 18 (1979) 929-933. 

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