Peptides hydroxyl radical

The results of this study strongly suggest that purified peptides can prevent oxidative damage to DNA when the DNA is exposed to OH generated by the Fenton reaction. With the purified peptide of protective activity against DNA oxidation, a clear dose-dependent effect was observed. In this result, the effect of purified peptide was to protect hydroxyl radical-induced DNA damage. 

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... 

Other proteins play important roles in controlling free metal concentrations in the cytosol. Of particular importance are ferritin and metallothionein. Ferritin is the major iron storage protein in the cell. It is critical that cytosolic iron is kept at low levels, because iron can catalize the Fenton reaction, which generates the most toxic of the ROS—the hydroxyl radical. Copper and superoxide can also participate in the fenton reaction. Metallothioneins are another important family of proteins that helps control cytosolic concentrations of metals such as Cu and Cd. Glutathione is another peptide that controls free Hg and Cd levels in the cell (Figure 21.7). 

U3. Uchida, K., Kato, Y., and Kawakishi, S., A novel mechanism for oxidative cleavage of prolyl peptides induced by the hydroxyl radical. Biochem. Biophys. Res. Commun. 169,265—271 (1990). 

Partial sequence data for pea seed ferritin (J. F. Briat, personal communication) show regions of similarity to those of animals, but pea seed ferritin also has an N-terminal extension, unlike the N-termini of other ferritins (84). On SDS-PAGE, phytoferritin gives two bands, the smaller of which (Mr 26,500) is thought to have arisen from the larger (Mr 28,000), as a result of cleavage of an N-terminal peptide by hydroxyl radicals produced by iron-catalyzed Fenton reactions (84). 

Aminyl radicals have also been detected indirectly during the reaction of hydroxyl radicals (HO ) or their conjugated base ( 0 ) with the free amino group of amino acids (Reactions (3.9) and (3.10)) [40-43], and identified by time-resolved EPR experiments [44]. Similar reactions may be expected for peptides. While Reactions (3.9) and (3.10) show a net hydrogen transfer, they likely proceed via a stepwise electron-transfer and proton-transfer (Reaction (3.11)), a reaction commonly referred to as proton-coupled electron transfer (PCET). Proton transfer from the ami-nium radical cation to the base (OH ) will likely occur within the solvent cage. 

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