Redox Biochemistry and Chemistry最新文献

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.

Peroxynitrite (ONOO⁻/ONOOH) is a short-lived but highly reactive species that is formed in the diffusion-controlled reaction between nitric oxide and the superoxide radical anion. It can oxidize certain biomolecules and has been considered as a key cellular oxidant formed under various pathophysiological conditions. It is crucial to selectively detect and quantify ONOO⁻ to determine its role in biological processes. In this review, we discuss various approaches used to detect ONOO⁻ in cell-free and cellular systems with the major emphasis on small-molecule chemical probes. We review the chemical principles and mechanisms responsible for the formation of the detectable products, and plausible limitations of the probes. We recommend the use of boronate-based chemical probes for ONOO⁻, as they react directly and rapidly with ONOO⁻, they produce minor but ONOO⁻‒specific products, and the reaction kinetics and mechanism have been rigorously characterized. Specific experimental approaches and protocols for the detection of ONOO⁻ in cell-free, cellular, and in vivo systems using boronate-based molecular probes are provided (as shown in Boxes 1-6).

Peroxynitrite is a powerful oxidant formed in vivo in sites where superoxide and nitric oxide coincide. Peroxynitrite is cytotoxic through oxidative modification of target biomolecules that can occur by direct or indirect reactions. Indirect reactions usually involve the generation of peroxynitrite-derived radicals that include nitrogen dioxide, hydroxyl radical, and carbonate radical. All these species have different behaviors in vivo, because of their intrinsic reactivity and how effectively they can be compartmentalized by cellular membranes. In this review, we analyze quantitative information on the estimated half-lives and the corresponding estimated diffusion distances of peroxynitrite, its precursors, and its derived reactive species in vivo. Furthermore, we discuss the permeability of cellular and synthetic lipid membranes to the different species and how effective compartmentalization is achieved for some of them, limiting the biological site of reactions.

HNO (azanone or nitroxyl), formally a product of the one-electron reduction of a nitric oxide, exhibits diverse and unique biological activity. The chemistry, biochemistry, and biological/pharmacological effects of HNO have been studied extensively. Due to rapid dimerization and hence short lifetime in solutions, in chemical and biological studies HNO is typically produced in situ from its thermal donors. To date, a great variety of chemical HNO donors have been synthesized, characterized, and utilized in biological studies. Here, we discuss the chemistry of HNO-releasing compounds, with the emphasis on the complexity of the proposed reaction mechanisms.

Protein tyrosine nitration is a post-translational modification originating from the biological chemistry of nitric oxide. This article highlights key milestones, discusses apparent controversies and perspectives that have emerged in the last 35 years of research on protein tyrosine nitration. Since the execution of nitric oxide signaling is accomplished entirely by protein post translational modifications (PTMs), the prospect that protein tyrosine nitration augments nitric oxide signaling remains an intriguing but incomplete concept deserving further consideration.

Tellurium (Te) is an industrially useful element but its oxyanions, such as tellurite and tellurate, are naturally occurring chemical forms that can become a potential source of toxicity to humans and animals. As a means of mitigating the toxicity of Te oxyanions, the formation of less toxic zero-valent elemental Te (Te⁰) nanostructures has been observed in various species including bacteria, fungi, green algae, and higher plants. In this study, we investigated the formation of Te⁰ nanorods in human hepatoma HepG2 cells. We detected electron-dense Te nanorods in lysosomes after exposure to potassium tellurite. The amount of Te nanorods in the cells gradually increased with the exposure period. Interestingly, the amount of Te in the insoluble fraction of the culture supernatant was approximately 10 times higher than that in HepG2 cells, suggesting that extracellular reducing agents originating from HepG2 cells transformed tetravalent Te (TeO₃²⁻) into Te⁰ in the culture medium. As an extracellular reducing agent, sulfane sulfur species were considered responsible for the reduction of Te(IV). Then, by inhibiting cystathionine γ-lyase with propargylglycine (PPG), we were able to reduce the amount of sulfane sulfur species generated in the cells. In the presence of PPG, the amount of insoluble Te in the culture supernatant, which was possibly composed of Te⁰ nanorods, was significantly decreased. The results suggest that sulfane sulfur species are involved in the formation of Te⁰ nanorods from tellurite in mammalian cells and play a critical role in the amelioration of Te oxyanion toxicity.

Nitration is a well-established post-translational modification of selected free amino acids, as well as proteins, lipids and nucleic acids. Considerable evidence is now available for the formation of long-lived species containing an added –NO₂ function on the aromatic rings of tyrosine (Tyr) and tryptophan (Trp) residues (both free and on proteins), to purine nucleobases (and particularly guanine), and to unsaturated lipids within biological systems. Multiple potential mechanisms that give rise to these nitrated species have been identified including reactions of the potent oxidant and nitrating species peroxynitrous acid/peroxynitrite (ONOOH/ONOO⁻) and via oxidative reactions of heme proteins/enzymes (e.g. peroxidases) with the biologically-relevant anion nitrite (NO₂⁻). ^•NO₂ is likely to be a key intermediate, though involvement of HNO₂, NO₂⁺ and NO₂Cl has also been proposed. The resulting nitrated products have been widely employed as qualitative or quantitative biomarkers of nitration events in vitro and in vivo. Increasing evidence suggests that at least some of these products are not benign species, with evidence for pro-inflammatory actions. In this article the mechanisms and role of nitration, and particularly that on proteins within the artery wall, in cardiovascular disease is discussed, together with emerging data suggesting that low levels of nitration occur within biological systems in the absence of added oxidants. Both stimulated and endogenous nitration may play a role in modulating cell signaling, alter the structure and function of both cellular- and extracellular proteins, and contribute to various inflammatory pathologies, including atherosclerosis.

Nitro-oxidative stress affects DNA, leading to special chemical modifications of nucleobases and deoxyribose, impacting DNA integrity and stability. Because of the importance of the topic, the state of the knowledge on purine, nucleoside, and DNA nitration by the reactive nitrogen species peroxynitrite was reviewed. Following a description of the chemical and physicochemical characteristics of purines and peroxynitrite, purine nitro-oxidation and its products, the reaction mechanisms, and the recently reported kinetic behavior of 8-NitroGua formation are discussed. Moreover, novel computational studies report structural and conformational DNA changes resulting from the formation of guanine nitration products. Given the relevance of the subject, surprisingly few publications deal with this topic, even considering the past five years.