Photooxidative damage

Fig. 9 Long-range oxidative damage in DNA is regulated by the structure of the DNA n-stack. Photoexcited [Rh(phi)2(bpy )]3+ intercalated within B-DNA oxidizes guanine doublets positioned 17 A and 40 A away with approximately equal efficiency. When a bulge is introduced in the DNA oxidation at the distal guanine doublet is inhibited. As shown by the NMR structure, bulges introduce local distortions in the DNA r-stack, although the kinking of the helical actually positions the distal guanine closer to the Rh(III) photooxidant...

Xanthophylls can further inhibit the peroxidation of membrane phospholipids (Lim et al. 1992) and reduce photooxidation of lipofuscin fluorophores (Kim et al. 2006), which are implicated in the pathogenesis of AMD (Sparrow and Boulton 2005). Furthermore, it was shown that light-induced damage to photoreceptors was reduced in quails fed zeaxanthin, with the number of apoptotic photoreceptor cells being inversely related to the concentration of zeaxanthin in the retina (Thomson et al. 2002). 

Polle, A., Defense against photooxidative damage in plants, in Oxidative Stress and the Molecular Biology of Antioxidant Defenses, Scandalios, J.G., Ed., Cold Spring Harbor Laboratory Press, New York, 1997, 623. 

Ultraviolet light damages proteins as well as DNA. Residues of Trp, Tyr, His, Cys, and Met are especially susceptible to photolysis, or photooxidation by 02, or by singlet oxygen. Also damaged are unsaturated lipids, porphyrins, flavins, etc. Kynurenic acid (Fig. 25-11) and urocanic acid (Eq. 14-44), an important ultraviolet filter in skin,196 are also decomposed by light. 

Do you predict that plant cells lacking carotenoids are more or less susceptible to damage by photooxidation Explain. 

Adam W, Marquard S, Kemmer D, Saha-Moller CR, Schreier P (2002) 2 -Deoxyguanosine (dG) oxidation and strand break formation in DNA by the radicals released in the photolysis of N-tert-bu-toxy-2-pyridone. Are tert-butoxyl or methyl radicals responsible for the photooxidative damage in aqueous media Org Lett 4 225-228... 

Photooxidation and y-radiolysis agree in their products reasonably well as long as the base is damaged. The reason for this may be that in the photooxidation a dCyd radical cation / menadione radical anion pair is the first intermediate. The reaction of the dCyd radical cation with water could give rise to OH-adducts (as in radiolysis). The most important product, however, is dUrd, that is, deaminated dCyd (Table 10.16) which is not, and cannot be, formed upon radiolysis. The mechanism of its formation is not discussed in the original paper, but it is not unlikely that it results from an unstable intermediate (adduct ) formed in the reaction of the dCyd radical cation / menadione radical anion pair in the solvent cage. 

Adam W, Arnold MA, Saha-Moller CR (2001) Photooxidative damage of guanine in DG and DNA by the radicals derived from the a cleavage of the electronically excited carbonyl products generated in the thermolysis of alkoxymethyl-substituted dioxetanes and the photolysis of alkoxyac-etones. J Org Chem 66 597-604... 

---