Phenol metabolization

Parke D, F Rynne, A Glenn (1991) Regulation of phenolic metabolism in Rhizobium leguminosarum biovar trifolii. J Bacteriol 173 5546-5550. 

Schiihle K, G Fuchs (2004) Phenylphosphate carboxylase a new C-C lyase involved in anaerobic phenol metabolism in Thauera aromatica. J Bacterial 186 4556-4567. 

Thus, modeling the kinetics of benzene and phenol metabolism involves considering an array of compounds which may themselves be responsible for any observed toxic effects. 

This model incorporates observations made in an earlier kinetic study that investigated benzene and phenol metabolism in vitro in mouse and rat liver microsomes (Schlosser et al. 1993). In that study, the following reaction sequences were postulated benzene phenol catechol trihydroxybenzene and phenol hydroquinone trihydroxybenzene. 

It has been suggested that phenol exposure results in cardiac effects because it blocks the cardiac sodium channel subtype, with little effect on sodium channels in skeletal muscle (Zamponi et al. 1994). Phenol does not appear to be carcinogenic following oral exposure (NCI 1980), although the chemical combinations that result from benzene and phenol metabolism may contain compounds that do initiate or promote cancer. Metabolites such as hydroquinone and catechol have been demonstrated to be genotoxic and clastogenic. 

Davies MI, Lunte CE. 1996. Simultaneous microdialysis sampling from multiple sites in the liver for the study of phenol metabolism. Life Sci 59 1001-1013. 

Schlosser PM, Bond JA, Medinsky MA. 1993. Benzene and phenol metabolism by mouse and rat liver microsomes. Carcinogenesis 14 2477-2486. 

Fukumoto, L. R., Toivonen, P. M., and Delaquis, P. J. (2002). Effect of wash water temperature and chlorination on phenolic metabolism and browning of stored iceberg lettuce photosynthetic and vascular tissues. ]. Agric. Food Chem. 50,4503 4511. 

When soybean leaves and pine needles were exposed to ozone, there was an initial decrease in the levels of soluble sugars followed by a subsequent increase. Ozone exposure also caused a decrease in the activity of the glycolytic pathway and the decrease in the activity was reflected in a lowered rate of nitrate reduction. Amino acids and protein also accumulated in soybean leaves following exposure. Ozone increased the activities of enzymes involved in phenol metabolism (phenylalanine ammonia lyase and polyphenoloxidase). There was also an increase in the levels of total phenols. Leachates from fescue leaves exposed to ozone inhibited nodulation. 

Gitz, D.C., Liu, L., and McClure, J.W., Phenolic metabolism, growth, and LTV-B tolerance in phenylalanine ammonia-lyase-inhibited red cabbage seedlings. Phytochemistry, 49, 377, 1998. 

Phillips, D.A., Flavonoids plant signals to soil microbes, in Phenolic Metabolism in Plants, Stafford, H.A. and Ibrahim, R.K., Eds., Plenum Press, New York, 1992, 201. 

The sulfation of phenol and the glucuronidation of its hydroquinone metabolite were measured in human liver cytosols and microsomes, respectively. The rate of phenol sulfation varied between 0.31 and 0.92 nmol/mg protein/min this is slightly higher than the rate for mice (0.46) and lower than that for rats (1.20). The rate of hydroquinone glucuronidation was between 0.10 and 0.28 mnol/mg protein/min, slightly higher than that for rats (0.08) and lower than that for mice (0.22). These enzyme-kinetic data were subsequently used to simulate phenol metabolism in mice, rats and humans in vivo, using a com-partmental pharmacokinetic model with benzene as phenol precursor (Seaton et al., 1995). 

From a physiological standpoint, molecular and biochemical studies have suggested that ozone stimulates phenolic metabolism and the biosynthesis of lignin or other substances partly derived from coniferyl alcohol [89]. Lignification of mesophyll cell walls might confer some protection against oxidation, and thus be a defence response against ozone [90]. 

As indicated above, although less data is available that for herbicides, fungicides also have been implicated in the appearance of variations in phenolic metabolism. Molina et al. [116] have demostrated that the systemic acquired resistance signal transduction pathway, a salicylic acid-dependent plant-defence mechanism, mediates fungicide action in the plant. 

Different works show that the nutritional status of certain nutrients, such as boron (B), calcium (Ca), nitrogen (N), phosphorus (P) and iron (Fe) can trigger changes in phenolic metabolism. Of these nutrients, B is attributed with a clear and significant effect on the metabolism of these secondary compounds. As we shall discuss below, the relationship between B metabolism and phenolics is complex and depends largely on the sensitivity of the plant to B deficiency or toxicity. 

As commented above, most works that relate B to phenol metabolism centre on the effect of B deficiency. Nevertheless, other works show the effect of growing dosages of the micronutrient on the metabolism of these secondary compounds. For example, Fawzia et al. [120] found that as the B dosage increased to 500 ppm, the phenolic concentration declined, as did the PAL and PPO activity, while the contrary effect was evident in POD activity. The high POD activity, together with the low PAL activity perhaps decreased the phenolic content. These same authors found... 

As opposed to the case of B, very few works investigate the direct effect of Ca on phenolic metabolism. Castaneda and Perez [131], working with lemon trees, observed that the application of 10 pM of CaCh increased PAL activity one hour earlier than control only if the trees were treated with cell walls isolated from the fungus Alternaria alternater, or... 

Another of the nutrients which has been related to the bioactivity of phenolics has been N. In present-day agriculture, the main types of stress commonly generated as a consequence of the heavy use of inorganic fertilizers are related to the nutritional status of certain nutrients, primarily N, given its extensive use. In general, although only scant literature is available on the relationship between N and phenol metabolism, it appears... 

Finally, several works have also implicated the nutrients P and Fe as possible inductors of changes in phenolic metabolism. However, studies of these relationships have been scarce. With regard to the former nutrient, P deficiency has been observed to raise the level of anthocyanins, but the reason for this rise remains unclear [4]. Meanwhile, low levels of Fe can increase the release of phenolic acids, presumably to help solubilize metals and thereby facilitate their uptake [135]. 

The accumulation or oxidation of phenolic compounds principally in stored agricultural products normally gives rise to the physiological disorders that result in a major loss of commercial value of the products. Among the most common of these disorders in which phenol metabolism is involved is fruit browning and the russet spotting (RS) in harvested lettuce. 

With regard to the first point, most of the final enzymes of phenolic metabolism, that is, those that give rise to the formation of lignin, have not been characterized nor are their biochemical properties known, and therefore in the future it would be useful to elucidate these stages of phenylpropanoid metabolism. 

Ranocha P., Chabannes, M., Chamayou, S., Danoun, S., Jauneau, A., Boudet, A.-M., and Goffner, D., 2002, Laccase down-regulation causes alterations in phenolic metabolism and cell wall structure in poplar, Plant Physiol. 129 145-155. 

Comprehensive information on the network of pathways responsible for the synthesis of numerous secondary metabolites can be found in Chapter 21. In addition, information on this aspect is also available in articles by Shimada et al. [2003], Toshiaki [2003], Tanner et al. [2003], Boatright et al. [2004], Hoffmann et al. [2004], Dixon et al. [2005], Niemetz and Gross [2005], Xie and Dixon [2005], and Ferrer et al. [2008], Nonetheless, the complete dissection of phenolic metabolic pathway is far from being complete. For example, recent reports underline that important questions still remain to be answered in the field of protoanthocyanidins and tannins [Xie and Dixon, 2005], and that the exact nature of the biosynthetic pathway(s) leading to lignin monomers has not been fully elucidated [Boudet, 2007]. 

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