Redox Biochemistry and Chemistry最新文献

It has been established that hydrogen peroxide (H₂O₂) acts as a signalling messenger by triggering the reversible oxidation of redox-regulated proteins via a redox-relay provided by peroxiredoxins (Prdxs). Exceptionally high reactivity of Prdxs with H₂O₂ exceeding other thiols by orders of magnitude places Prdxs as sensors of H₂O₂ and distributers of oxidizing equivalents to specific thiol targets which can't be oxidized by H₂O₂ directly. By this mechanism the oxidative stress response can be achieved.

Despite its involvement in oxidative stress responses, H₂O₂ is continuously generated as a normal metabolite necessary for regular cell functioning. The challenge lies in understanding how the Prdx-dependent redox relay can differentiate between basal levels of H₂O₂ and excessive amounts that lead to oxidative stress.

Peroxymonocarbonate, an oxidant formed when H₂O₂ reacts with CO₂/HCO₃⁻, emerges as a potent cellular oxidant. The peroxymonocarbonate formation could be catalysed and then consumed at localised sites by certain thiol proteins. This mechanism could prevent H₂O₂ from reacting with Prdx, thereby averting the redox-relayed activation of regulatory thiol proteins and subsequent oxidative stress response below a certain level of H₂O₂.

Melatonin (N-acetyl-5-methoxytryptamine, MLT), an evolutionarily conserved indoleamine, is known to act as an antioxidant. However, the evidence indicating the role of MLT as a powerful chain-breaking antioxidant by scavenging peroxyl radical remains controversial. The radical-scavenging rate of MLT determined in this study in methanol using galvinoxyl radical (GO^•) was much lower than that of an α-tocopherol model compound. The acceleration of the GO^•-scavenging reaction by MLT was observed in the presence of magnesium ion (Mg²⁺), a bio-related redox-inactive metal ion, suggesting that this reaction may proceed via a rate-determining electron transfer followed by proton transfer. The coordination of Mg²⁺ to the carbonyl oxygen in the one-electron reduced species of GO^• (GO^–) may stabilize the product, resulting in the acceleration of the electron-transfer process. We also demonstrated that prophylactically administrated MLT efficiently inhibited the lipid peroxide-derived protein modification, which can be detected by a sensitive marker, N^ε-(hexanoyl)lysine adduct, in the plasma of X-irradiated mice. The relatively weak GO^•-scavenging activity of MLT suggests that the ameliorative effect of MLT against in vivo lipid peroxidation does not result from the direct scavenging of lipid peroxyl radicals by MLT. Therefore, the observed superior protective efficiency of MLT against in vivo lipid peroxidation may partly support the earlier studies, which reported the synergistic antioxidative effect of the metabolites of MLT.

Polyunsaturated fatty acids (PUFA) are particularly susceptible to free radical-induced lipid peroxidation (LPO). Specific deuteration at bis-allylic positions of PUFA (D-PUFA) has been recently proposed as a way to inhibit the LPO. Here, a high mass resolution untargeted lipidomic analysis protocol was applied to examine the changes in the lipidome of keratinocytes supplemented with bis-allylic deuterated linoleic acid (D₂-LA). Incorporation of D₂-LA occurs preferentially in membrane phospholipids such as phosphatidylcholine and phosphatidylethanolamine, followed by triglycerides. However, the relative contribution of D₂-LA among membrane lipids is highest in cardiolipin (60%) followed by its precursor phosphatidylglycerol (50%). Cardiolipins are enriched in PUFA and exclusively located in mitochondrial membranes, thus representing major targets for lipid peroxidation. These findings indicate that D₂-LA supplementation is linked to the preservation of mitochondrial function under oxidative stress. Finally, our study highlights the suitability of high mass resolution lipidomic analysis to investigate lipid metabolism at the level of individual molecular species in stable isotope tracing experiments.

The absorption of ionizing radiation initiates redox reactions, producing chemical species resulting from single electron loss or electron gain. Radiation chemists have developed methods to study individual redox species selectively and to monitor their reactions in real time. This has provided an enormous resource of kinetic, thermodynamic and spectroscopic information concerning the characteristics and reactions of free radicals and their redox reactions, mainly in aqueous solution. While the techniques are specialized and exploiting them is certainly more difficult than initiating redox changes by simple mixing of two chemicals or adding a reagent to a biological target, it is useful to gain an understanding of the basic mechanisms and approaches involved in exploiting radiation chemistry in the wider context of redox reactions in biochemistry, chemistry, and biology. This should enable readers both to appreciate the reliance which can be placed on the kinetic and other information resulting from such studies, as well as identify potential new applications of the technique which might be exploited in their research, by seeking partners who have access to the necessary specialized equipment or just basic irradiation facilities. This review outlines how radiation can be used to initiate selective redox reactions, mainly in water, and helps point readers to resources which should be useful in considering such reactions in a wider context.

Cysteine residues are the most favored targets for oxidation by hypochlorous acid and other reactive halogen species. The end-products of cysteine oxidation are usually considered to be reversibly formed disulfides and the more highly oxidized sulfinic and sulfonic acids. However, reactive halogen species are capable of generating additional products in which cysteine is cross-linked to other amino acids. Here we have treated a range of peptides with hypochlorous acid (HOCl) and hypobromous acid (HOBr), and used mass spectrometry to demonstrate sulfenamide, sulfinamide and sulfonamide formation with lysine residues, as well as –S(O)- and –S(O₂)- linkages with tyrosine, tryptophan and arginine residues. The -(SO₂)- products were more prevalent with HOCl than HOBr, reflecting its higher oxidizing ability. There was also considerable variation between peptides in efficiency of cross-linking compared with other modifications. The –S(O)- and –S(O₂)- forms were much more resistant than the disulfide to reduction by dithiothreitol. Using calprotectin as a representative cysteine-containing protein, we show that a range of products containing each of these cross-links is formed when the protein is treated with HOCl. Two of the identified cysteine-lysine calprotectin cross-links were also detected in bronchoalveolar lavage fluid from children with cystic fibrosis. Our results imply that cross-linked species would be formed when cysteine-containing proteins are exposed to reactive halogen species, with the nature of the specific products depending on structural features around the cysteine residue. Cross-linking could have a modulatory effect on protein function or be detrimental in causing oligomerization and aggregation.