Peroxidation of polyunsaturated

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... 

Detection of Products Arising from the Badical-mediated Peroxidation of Polyunsaturated Patty Acids... 

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. 

Hydroxyl radicals are probably the most toxic for microorganisms [30], They promote peroxidation of polyunsaturated phospholipid components of the lipid membrane and induce disorder in the cell membrane [31]. The damage of the outer membrane increases the permeability to ROSs. This process is possible thanks to a sufficient lifetime of ROSs generated at the Ti02 surface. ROS diffusion was studied by Fujishima et al. Their experiments demonstrated the bactericidal effect of irradiated Ti02 film on E. coli even at the distance of 50pm from the film [21], Furthermore, oxidative perforation of the cellular membrane allows the photocatalyst nanoparticles to penetrate the interior of the cell, causing severe, efficient oxidation of the cell content [27,32], ROSs are responsible for oxidation of amino acids, peptides [33], enzymes [34], and nucleic acids [32, 35-37]. Destruction of... 

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... 

Peroxidation of polyunsaturated lipids is thought to be an important pathological event involved in the development of tissue damage and dysfimction. In recent studies, Rubbo and colleagues [113] demonstrated that NO inhibits lipid peroxidation and therefore may be important in the modulation of the inflammatory response by inhibiting the formation of proinflammatory lipids. 

The major function of vitamin E is to act as a natural cmtioxidant by scavenging free radicals and molecular oxygen. In particular vitamin E is important for preventing peroxidation of polyunsaturated membrane fatty acids. 

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

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