Hydroxycinnamic acids metabolism

Lactic acid bacteria, including the typical "wine lactic acid bacteria" Leuconostoc oenos (85, 90), can produce ethyl and vinyl derivatives by hydroxycinnamic acid metabolism (91) although, the minimal concentration produced in red wines by Leuconostoc oenos is insignificant compared to the odor threshold (85, 87). 

The metabolism of ferulic acid (3-methoxy-4-hydroxycinnamic acid) by Ent. cloacae to a nnmber of products including phenylpropionate and benzoate (Fignre 2.8) (Grbic-Galic 1986). 

Gasson Ml, Y Kitamura, WR McLaughlan, A Narbad, AJ Parr, ELH Parsons, J Payne, MJC Rhodes, NK Walton (1998) Metabolism of ferulic acid to vanillin. A bacterial gene of the enoyl-SCoA hydratase/ isomerase superfamily encodes an enzyme for the hydration and cleavage of a hydroxycinnamic acid SCoA thioester. J Biol Chem 273 4163-4170. 

The key reaction that links primary and secondary metabolism is provided by the enzyme phenylalanine ammonia lyase (PAL) which catalyzes the deamination of l-phenylalanine to form iran.v-cinnamic acid with the release of NH3 (see Fig. 3.3). Tyrosine is similarly deaminated by tyrosine ammonia lyase (TAL) to produce 4-hydroxycinnamic acid and NH3. The released NH3 is probably fixed by the glutamine synthetase reaction. These deaminations initiate the main phenylpropanoid pathway. 

Studies have shown that phenylpropanoid metabolism can be stimulated by ozone. The activity of PAL increased in soybean [91], Scots pine (Pinus sylvestris L.) [92], and parsley (Petroselinum crispum L.) [93] soon after treatment with 150-200 nmol O3 mol 1. Rapid increases in transcript levels for PAL in response to ozone have been observed in parsley [93], Arabidopsis thaliana L. Heynhold [94] and tobacco (Nicoticma tabacum L.) [95]. Transcript levels for 4-coumarate CoA ligase (4CL), the last enzyme in the general phenylpropanoid pathway, increased commensurately with PAL transcripts in ozone-treated parsley seedlings [93]. Phenolic compunds reported to accumulate in leaf tissue in response to ozone include hydroxycinnamic acids, salicylic acid, stilbenes, flavonoids, furanocoumarins, acetophenones, and proanthocyanidins [85, 92, 93, 96, 97]. 

Heresztyn, T. (1986). Metabolism of phenolic compounds from hydroxycinnamic acids by Bret-tanomyces yeasts. Arch. Microbiol., 146, 96-98. 

As early as 1964 it was recognized that 4-ethyl phenol and 4-ethyl guaiacol were produced by yeast and bacteria during fermentation by the decarboxylation of the hydroxyciimamic acids p-coumaric and fendic acid (88). Later it was reported that among yeast only Brettanomyces species possess the metabolic ability to enzymatically decarboxylate hydroxycinnamic acids to produce ethyl derivatives (29, 89). Heresztyn was the first to identify 4-ethyl phenol and 4t-ethyl guaiacol as the major volatile phenolic compounds formed by Brettanomyces yeast (84). ... 

Keywords phenylpropanoid metabolism hydroxycinnamic acid conjugates lignans coumarins furanocoumarins gallotannins eUagitarmins metabolic channelling... 

Davin, F.B. and Fewis, N.G. (2003) An historical perspective on lignan biosynthesis monolignol, allylphenol and hydroxycinnamic acid coupling and downstream metabolism. Phytochemistry Rev., 2, 257-88. 

Strack, D. and Mock, H.P. (1993) Hydroxycinnamic acids and lignins, in Methods in Plant Biochemistry, Vol. 9, Enzymes of Secondary Metabolism (eds P.M. Dey and J.B. Harborne). Academic Press, London, pp. 45-97. 

It would be instructive to compare the metabolic cost of synthesizing and allocating specific flavonoids, salicylic and hydroxycinnamic acids and their efficacy in filtering biologically active UV radiation. This information could explain their ecological roles in the adaptation or acclimation process. 

Facchini PJ, Hagel J, Zulak KG (2002) Hydroxycinnamic acid amide metabolism physiology and biochemistry. Can J Bot 80 577-589... 

Biochemically, 4-ethyl guaiacol and 4-ethyl phenol originate from ferufic acid and /vcoumaric acid, respectively. The reaction is a two-step process with an initial decarboxylation of the hydroxycinnamic acids catalyzed by cinnamate decarboxylase and the reduction of the vinyl phenol intermediates by vinyl phenol reductase (Fig. 11.1). Although the specific coenzyme involved remains unknown, one possible metabolic benefit of the second reaction to Brettanomyces could be reoxidation of NADH. Under low oxygen conditions such as those found in wines, the availability of NAD can be limited so that carbohydrate metabolism is inhibited (Section 1.5.1). Reduction of the vinyl phenols to the ethyl phenols would allow the cell to increase the availability of NAD and thus maintain metabolic functions. 

The metabolic fate of sinapic acid in humans as well as its derivatives, which represent the naturally occurring form of sinapic acid, has not been studied yet and remains uncertain. But in a study on the metabolic fate of polyphenols from a polyphenol-rich diet, small amounts of sinapic acid were detected in urine post 3-glucuronidase treatment during a 5-day feeding period [37]. This presence of sinapic acid (as glucuronide) in urine implies its bioavailability from the diet in humans and a metabolic fate of dietary sinapic acid derivatives similar to that of other hydroxycinnamic acid derivatives such as chlorogenic acid. 

The colon seems to be the essential site for the release of free hydroxycinnamic acids and ftieir absorption. In a study of the uptake of Relabeled hydroxycinnamates bound to spinach cell walls in rats, the foregut was localized as the site of absorption after the release of the labeled hydroxycinnamic acids form flie cell wall by colonic microorganisms, when 25% of flie ingested dose of label was found to be associated with body tissue after only 2 h [32]. On flie basis of flie results on absorption, metabolism, degradation, and elimination of chlorogenic acid in humans presented, its metabolic fate in... 

In quantitative terms, colonic metabolism and the formed colonic metabolites are more important than the absorption and conjugation of the hydroxycinnamic acids. Whether these colonic metabolites express potential protective or preventive bioactivities in vivo remains to be studied. This also applies to the effect of the dietary hydroxycinnamates and their metabolites on the composition of the colonic microflora. 

Phenylpropanoids are biologically synthesized from phenylalanine as described above. Among them, cinnamic acid is synthesized directly from phenylalanine by phenylalanine ammonia-liase (PAL), and p-hydroxycinnamic acid p-coumaric acid) is synthesized from cinnamic acid by cinnamic acid 4-hydroxylase (C4H, an enzyme in the cytochrome P-450 family).The phenylpropanoid metabolic pathway is important for plants to synthesize lignin, and some phenylpropanoids are seen at junctions of cell wall polysaccharides such as hemicellulose and pectin. 

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