Peroxidation of polyunsaturated fatty

The main function of vitamin E is as a chain-breaking, free radical trapping antioxidant in cell membranes and plasma lipoproteins. It reacts with the lipid peroxide radicals formed by peroxidation of polyunsaturated fatty acids before they can establish a chain reaction. The tocopheroxyl free radical product is relatively unreactive and ultimately forms nonradical compounds. Commonly, the tocopheroxyl radical is... 

Chamirlitrat, W. and Mason, KP. (1989). Lipid preroxyl radical intermediates in the peroxidation of polyunsaturated fatty acids by lipoxygenase. J. Biol. Chem. 264, 20968—20973. 

Isoprostanes are a relatively new class of lipids and are produced in vivo principally by a free radical-catalyzed peroxidation of polyunsaturated fatty acids. Isoprostanes... 

Vitamin E (a-tocopherol) (fig. 10.26) was recognized in 1926 as an organic-soluble compound that prevented sterility in rats. The function of this vitamin still has not been clearly established. A favorite theory is that it is an antioxidant that prevents peroxidation of polyunsaturated fatty acids. Tocopherol certainly prevents peroxidation in vitro, and it can be replaced by other antioxidants. However, other antioxidants do not relieve all the symptoms of vitamin E deficiency. 

Figure 18.2. Cholesterol autoxidation initiated by peroxy (LOO ) or alkoxyl (LO ) radicals arising from peroxidation of polyunsaturated fatty acids (LH). Compounds are as follows (1) CHOL (2) 7-CHOL (3) CHOO (4) 7a-OOH (5) 7fLOOH (6) CHO (7) 7a-OH (8) 7(3-OH (9) 7-keto (10) 7-keto-3,5-dien. For abbreviations, see Table 18.1.

Lipoxygenases. Lipoxygenases catalyze the peroxidation of polyunsaturated fatty acids with a cis.cis 1-4-pentadiene moiety to form conjugated diene hydroperoxides (Figure lc). Free fatty acids are formed following wounding from the deacylation of membrane... 

Figure 22.6. Major lipid peroxidation products that can damage DNA. Linoleic acid is a co-6 polyunsaturated fatty acid. It is used as an example to illustrate peroxidation of polyunsaturated fatty acids. Many different products are formed following peroxidation of the polyunsaturated fatty acids. Only four major products are shown that are known to damage DNA. MDA, malondialdehyde.

Most of these effects of vitamin E deficiency can be attributed to membrane damage. In deficiency, there is an accumulation of lysophosphatidylcholine in membranes, which is cytolytic. The accumulation of lysophosphatidylcholine is a result of increased activity of phospholipase A. It is not clear whether a-tocopherol inhibits phospholipase A whether there is increased phospholipase activity because of increased peroxidation of polyunsaturated fatty acids in phospholipids, and hence an attempt at membrane Upid repair or whether the physicochemical effects of a-tocopherol on membrane organization and fluidity prevent the cytolytic actions of lysophosphatidylcholine (Douglas et al., 1986 Erin et al., 1986). 

Radical processes involving membrane phospholipids are mainly referring to the peroxidation of polyunsaturated fatty acids (PUFA). In the previous decade, reactions of PUFA with a variety of RS radicals were studied. Pentadienyl-type radicals (Chart 5, left structure) and radical... 

Figure 2. Mechanism of peroxidation of polyunsaturated fatty acids,...

Xu, L., T. A. Davis, and N. A. Porter. 2009. Rate constants for peroxidation of polyunsaturated fatty acids and sterols in solution and in liposomes. 131-... 

This chapter snmmarized protein lipoxidation, mainly focusing on protein adduction chemistry with reactive aldehydes generated from the peroxidation of polyunsaturated fatty acids. On the basis of a large number of reports concerning the chemical and immunochemical detection of lipoxidation products in vivo, there may be no... 

Lipid peroxidation of polyunsaturated fatty acids yields a group of reactive unsaturated aldehydic compounds (enals) such as 2-alkenals (acrolein [Acr], crotonaldehyde [Cro], 2-hexenal), 4-hydroxy-2-alkenals (4-hydroxy-2-nonenal [HNE], 4-hydroxy-2-hexenal [HHE]), and ketoaldehydes (malondialdehyde [MDA], glyoxal, 4-oxo-2-nonenal [ONE]) (Uchida 2003) (Eigure 18.1). 

The lipids that constitute the cell membrane, especially those lipids containing unsaturated double bonds, are susceptible to free radical attack, leading to the formation of lipid peroxides and aldehydes (Kako 1985). A number of short chain fragments produced from peroxidation of polyunsaturated fatty acids as 4-hydroxyperoxy nonenal and 4-hydroxy 2-alkenals react with sulphydryl groups of various enzymes modifying their activities. 

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