Redox Biochemistry and Chemistry最新文献

Boronates react directly and stoichiometrically with peroxynitrite and hydrogen peroxide. For this reason, boronates have been widely used as peroxynitrite- and hydrogen peroxide-sensitive moieties in various donors of bioactive compounds. So far, numerous boronate-based prodrugs and theranostics have been developed, characterized, and used in biological research. Here, the kinetic aspects of their activation are discussed, and the potential benefits of modifying their original structure with a boronic or boronobenzyl moiety are described.

Three decades of research on the biochemistry of peroxynitrite (ONOOH/ONOO⁻) have established that this stealthy oxidant is formed in biological systems, and that its main targets are carbon dioxide (CO₂), metalloproteins and thiols (RSH). Peroxynitrous acid reacts directly with thiols (precisely, with thiolates, RS⁻), forming sulfenic acids (RSOH). In addition, the free radicals derived from peroxynitrite, mainly carbonate radical anion (${{\mathrm{CO}}_3}^{•-}$) and nitrogen dioxide (${{\mathrm{NO}}_2}^{•}$) formed from the reaction of peroxynitrite anion with CO₂, oxidize thiols to thiyl radicals (RS^•). These two pathways are under kinetic competition. The primary products of thiol oxidation can follow different decay routes; sulfenic acids usually react with other thiols forming disulfides, while thiyl radicals can react with oxygen, with other thiols and with other reductants such as ascorbic acid. Peroxynitrite is also able to oxidize hydrogen sulfide (H₂S/HS⁻) and persulfides (RSSH/RSS⁻). Among the different biological thiols, peroxiredoxins stand out as main peroxynitrite reductases due to their very high rate constants of reaction with peroxynitrite together with their abundance. Rooted in kinetic concepts, evidence is emerging for the role of peroxiredoxins in peroxynitrite detoxification, with potential implications in diseases in which peroxynitrite is involved.

The published syntheses of peroxynitrite from azide, nitrite, amylnitrite, hydroxylamine, nitrogen monoxide, and ammonia are discussed. With one exception, all of these syntheses yield peroxynitrite contaminated with nitrate and nitrite as well as reactants. The rate constant for the reaction of nitrogen monoxide with superoxide has been determined by pulse radiolysis and flash photolysis. In pulse radiolysis studies, the formation of the reactants may be rate-limiting and could lead to underestimation of the second-order rate constant. The conditions of flash photolysis experiments can be chosen to minimize conflict between reactant formation and the reaction half-life, thus the rate constant of 1.6 × 10¹⁰ M⁻¹ s⁻¹ determined by flash photolysis is preferred. The toxicity of peroxynitrite can be attributed mainly to its rapid reaction with carbon dioxide to yield the oxidizing trioxidocarbonate(•1−) and nitrogen dioxide radicals.

Since the incorporation of mitochondria in early eukaryotes cells struggle to keep the deleterious effects of reactive oxygen species (ROS), mainly originating from the respiratory chain, at bay. Evolutionary adaptation to ROS burden went so far that by acting as messenger and effector molecules, ROS became important in maintaining homeostasis. The evolutionary success of this phenomenon is underscored by the arising of professional ROS-generating enzymes, namely the family of NADPH oxidases (NOXes). NOXes, by shaping ROS levels at different subcellular locations and in extracellular space, are involved in such fundamental functions as proliferation, differentiation, apoptosis, host defense, fertilization, and hormone biosynthesis. NOX5, being a calcium-regulated professional ROS source exerts its function at the crossroad of these two fundamental but potentially deleterious intracellular signaling pathways (i.e. Ca²⁺ and ROS). The expression of NOX5 in the adult human body under unchallenged conditions is restricted to very few sites, among which the two major tissue groups are genital organs (mainly testis) and immune tissues (mainly spleen). In cases of increased cellular proliferation and protein synthesis (e.g., diverse tumors, cultured primary cells, or sites of tissue damage) the expression and activity of NOX5 is often upregulated in various tissues. This and the evolutionary conserved nature of NOX5 would imply a very fundamental role for this enzyme, but intriguingly the genomes of rodents essentially lack the NOX5 gene. The latter fact had been a major obstacle in determining the physiological roles of NOX5 in normal tissues until the very recent generation of a NOX5-deficient rabbit model.

Peroxynitrite is a very reactive species implicated in a variety of pathophysiological cellular processes. Particularly, peroxynitrite-mediated oxidation of cellular thiol-containing compounds such as cysteine residues is a key process which has been extensively studied. Cysteine plays roles in many redox biochemistry pathways. In contrast, selenocysteine, the 21st amino acid, is only present in 25 human proteins. Investigating the molecular basis of selenocysteine's reactivity may provide insights into its unique role in these selenocysteine-containing proteins. The two-electron oxidation of thiols or selenols by peroxynitrite is a process that is carried out by the thiolate/selenate forms and peroxynitrous acid.

In this work, we shed light on the molecular basis of the differential reactivity of both species towards peroxynitrite by means of state-of-the-art computer simulations. We performed electronic structure calculations of the reaction in the methanethiolate and methaneselenolate model systems with peroxynitrous acid at different levels of theory using an implicit solvent scheme. In addition, we employed a multi-scale quantum mechanics/molecular mechanics approach for obtaining free energy profiles of these chemical reactions in aqueous solution, which enabled the comparison between the simulations and the available experimental data. Our results suggest that the larger reactivity observed in the selenocysteine case at physiological pH is mainly due to the lower pKa, which affords a larger fraction of the reactive anionic species in these conditions, and in a second place to a slightly enhanced intrinsic reactivity of the selenate form due to its larger nucleophilicity.

Through multiple pathways, nitrogen dioxide (•NO₂) is the main species involved in endogenous nitration reactions. Early studies in the field primarily explored tyrosine nitration, a dominant reaction in the field. It was later shown that lipids are also nitration targets and generate an array of reaction products. Conjugated fatty acids are the preferential substrates of lipid nitration in vivo, generating electrophilic nitro-fatty acids (NO₂–FAs), which serve as pleiotropic signaling modulators. In contrast, exposure of bisallylic fatty acids, including linoleic, linolenic and arachidonic acid, to •NO₂ does not lead, under biological conditions, to the formation of nitrated species. This review focuses on the reaction mechanisms and products of lipid nitration and substrate specificity, focusing on the differential reactivity of conjugated dienes and bisallylic alkenes.