Tocopherols, in plants

Selected applications of coupled SEE-SEC consider the analysis of tocopherols in plants and oil by-products (65) or the analysis of lipid-soluble vitamins (66) by using a dynamic on-line SEE-SEC coupling, integrated in the SE chromatograph, based on the use of micropacked columns. 

Gruszka, J. Kruk, J. 2007. RP-LC for determination of plastochromanol, tocotrienols and tocopherols in plant oils. Chromatographia 66 909-913. 

We end this section on enzyme inhibition with a case study about 4-hydroxyphenyl-pyruvate dioxygenase (HPPD) and disorders in tyrosine catabolism. After transamination of tyrosine, 4-hydroxyphenylpyruvate (148) is formed which is then decarboxylated, isomerized and oxygenated by HPPD to yield homogentisate (149) or by hydroxyman-delate synthase (HMS) to yield p-hydroxymandelate (150). 149 serves as the precursor for plastoquinones and tocopherols in plants . Thus, inhibitors of HPPD have been designed... 

Figure 12.1 Structure of the eight natural tocopherols. In plant tissues, four tocopherols and four tocotrienols are synthesized, all with a side-chain in the natural RRR configuration (here referred to as a-, p-, y, 6-tocopherol/tocotrienol). The relative concentration of the tocopherols and tocotrienols depends on the plant species and on the plant tissue.

Munne-Bosch, S. and Falk, J., New insights into the function of tocopherols in plants, Planta 218 (3), 323-326, 2004. 

Moxon AL, Rhian M (1943) Selenium poisoning. Physiol Rev 23 305-337 Munne-Bosch S (2005) The role of a-tocopherol in plant stress tolerance. 1 Plant Physiol 162 743-748... 

Figure 5. Proteolysis and loss of tocopherol in plant subcellular membranes in response to xanthine oxidase. Adapted from Ref. 11.

Price, A. Hendry, G. (1987). The significance of the tocopherols in stress survival in plants. In Free Radicals, Oxidant Stress and Drug Action, ed. C. Rice Evans, pp. 443-50. London Richelieu Press. 

DellaPenna, D. and Pogson, B.J., Vitamin synthesis in plants tocopherols and carotenoids, Annu. Rev. Plant Biol. 57, 711, 2006. 

Richelle, M. et al. (2004). Both free and esterified plant sterols reduce cholesterol absorption and the bioavailability of beta-carotene and alpha-tocopherol in normocholesterolemic humans. Am. J. Clin. Nutr. 80(1) 171-177. 

Paran I, Van Der Knaap E (2007) Genetic and molecular regulation of fruit and plant domestication traits in tomato and pepper. J Exp Bot 58 3841-3852 Wang D, Bosland P (2006) The genes of Capsicum. HortScience 41 1169-1187 DellaPenna D, Pogson BJ (2006) Vitamin synthesis in plants tocopherols and carotenoids. Annu Rev Plant Biol 57 711-738... 

Vitamin E (tocopherol) and related compounds only occur in plants (e.g., wheat germ). They contain what is known as a chro-man ring. In the lipid phase, vitamin E is mainly located in biological membranes, where as an antioxidant it protects unsaturated lipids against ROS (see p. 284) and other radicals. 

Vitamin E, a natural antioxidant, is essential for growth, disease prevention, tissue integrity and reproduction in all fauna. Natural vitamin E, as it occurs in plants, consists mainly of a-tocopherol (III, R = H) with minor amounts of y-tocopherol (IV), although this ratio can vary as for example in the vegetable oil composition shown in Fig. 5a. In animal husbandry, such as dairy farms or cattle feed lots, the stock diets are commonly supplemented with vitamin E, because processed grain-based cereal fodder, hay, and silage are deficient in vitamin This results in higher levels of a-tocopherol... 

Munne-Bosch, S., Weiler, E. W., Alegre, L., Muller, M., Duchting, R, Falk, J. (2006). alpha-Tocopherol may influence cellular signaling by modulating jasmonic acid levels in plants. Planta. ... 

A closely related and important family of chro-manols are the tocopherols or vitamins E (Fig. 15-24, Box 15-G). Tocopherols are plant products found primarily in plant oils and are essential to proper nutrition of humans and other animals. a-Tocopherol is the most abundant form of the vitamin E family smaller amounts of the P, 8, and y forms occur, as do a series of tocotrienols which contain unsaturated isoprenoid units.495 The configuration of a-tocopherol is 2R,4 R,8 R as indicated in Fig. 15-24. When a-toco-pherol is oxidized, e.g., with ferric chloride, the ring can be opened by hydrolysis to give tocopherolquinones (Fig. 15-24), which can in turn be reduced to tocopherol-hydroquinones. Large amounts of the tocopherolquinones have been found in chloroplasts. 

Aromatic compounds arise in several ways. The major mute utilized by autotrophic organisms for synthesis of the aromatic amino acids, quinones, and tocopherols is the shikimate pathway. As outlined here, it starts with the glycolysis intermediate phosphoenolpyruvate (PEP) and erythrose 4-phosphate, a metabolite from the pentose phosphate pathway. Phenylalanine, tyrosine, and tryptophan are not only used for protein synthesis but are converted into a broad range of hormones, chromophores, alkaloids, and structural materials. In plants phenylalanine is deaminated to cinnamate which yields hundreds of secondary products. In another pathway ribose 5-phosphate is converted to pyrimidine and purine nucleotides and also to flavins, folates, molybdopterin, and many other pterin derivatives. 

Labeling experiments have shown that the plasto-quinones of chloroplasts as well as the tocopherols each bear one methyl group (marked with an asterisk in Fig. 25-4) that originates from chorismate. The dihydroxy compound homogentisate is probably an intermediate.80 83 It is a normal catabolite of tyrosine in the animal body (Fig. 25-5, Eq. 18-49). Both pren-ylation and methylation by AdoMet are required to complete the synthesis of the plastoquinones and tocopherols. Possible biosynthetic intermediates with one or more double bonds in the polyprenyl side chain have been found in plants and also in fish oils.83a... 

The biological function of the tocopherols is still a matter of discussion (83MI22400). They behave as antioxidants (68MI22401), protecting the lipids in plants from excessive oxidation,... 

Structures ot vitamins K and K2. K is found in plants, K2 in Structure of vitamin E (a-tocopherol). 

Vitamin E is required for normal growth and reproduction. The most important natural source is a-tocopherol found in plant oils and seeds. The ester form (e.g. vitamin E acetate) can be synthesized and is used for feed supplementation. One international unit is defined as being equivalent to the activity of 1 mg DL-a-tocopherol acetate. The nutritional role of vitamin E is closely interrelated with that of selenium and is involved mainly in the protection of lipid membranes such as cell walls from oxidative damage. Although these signs are similar to those of selenium deficiency, it is not possible to substitute selenium completely for vitamin E. Both nutrients are required in the diet. 

The use of a modified starch, corn starch sodium octenyl succinate derivative, for encapsulation of sea buckthorn kernel oil (containing polyunsaturated fatty acids, tocopherols, tocotrienols, plant sterols and carotenoids) by spray-drying was found to improve oil stability. Better protection was afforded when the starch encapsulant was stored in its glassy state (Partanen et al. 2002). Methylcellulose and hydroxymethy-oellulose in combination with soy lecithin enabled the production of 40% (W/W) fish oil powders with improved stability (Kolanowski et al. 2004). 

Barua, A.B. Olson, J.A. 1998. Reversed-phase gradient high-performance liquid chromatographic procedure for simultaneous analysis of very polar to nonpolar retinoids, carotenoids and tocopherols in animal and plant samples. J. Chromatogr. B 707 69-79. 

Munne-Bosch, S. Alegre, L. 2002. The function of tocopherols and tocotrienols in plants. Grit. Rev. Plant Sci. 21 31-57. 

The non-mevalonate route to terpenoids appears to be localized in the plas-tids. In plant cells, terpenoids are manufactured both in the plastids and the cytosol (Gray, 1987 Kleinig, 1989). As a general rule, the plastids produce monoterpenes, diterpenes, phytol, carotenoids and the side chains of plas-toquinone and a-tocopherol, while the cytosol/ER compartment produces sesquiterpenes, sterols and dolichols. In the studies discussed above, nearly all of the terpenoids labelled by deox30cylulose (Sagner et al, 1998b Eisenreich et al, 2001) and 2-G-methyl erythritol feeding (Duvold et al, 1997) or... 

Ascorbic acid and tocopherols are the most important commercial natural antioxidants. In addition, many naturally occurring phenolic antioxidants have been identified in plant sources and vegetable extracts that may lend themselves for use in a variety of food applications (53). Recent research has focused on isolation and identification of effective antioxidants of natural origin (11). 

Tocopherols and tocotrienols, collectively known as tocols, are monophenolic and lipophilic compounds that are widely distributed in plant tissues (7). The main commercial source of natural tocopherols is the soybean oil. Tocotrienols, less common than tocopherols, are present in palm oil, rice bran oil, as well as cereals and legumes (11). Tocopherols and tocotrienols are classified into a-, (3-, y-, and 5-, depending on their chemical structures (Figure 7). In general, tocotrienols have a stronger antioxidant effect on lipid oxidation than tocopherols. The antioxidant activity of tocopherols is dependent on temperature and is in the order of 5- > y->P-> oc-tocopherol (7). Tocopherols (mixed natural concentrate) are a golden... 

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