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International Journal of Molecular... Dec 2023In the retina, retinoids involved in vision are under constant threat of oxidation, and their oxidation products exhibit deleterious properties. Using pulse radiolysis,...
In the retina, retinoids involved in vision are under constant threat of oxidation, and their oxidation products exhibit deleterious properties. Using pulse radiolysis, this study determined that the bimolecular rate constants of scavenging cation radicals of retinoids by taurine are smaller than 2 × 10 Ms whereas lutein scavenges cation radicals of all three retinoids with the bimolecular rate constants approach the diffusion-controlled limits, while zeaxanthin is only 1.4-1.6-fold less effective. Despite that lutein exhibits greater scavenging rate constants of retinoid cation radicals than other antioxidants, the greater concentrations of ascorbate in the retina suggest that ascorbate may be the main protectant of all visual cycle retinoids from oxidative degradation, while α-tocopherol may play a substantial role in the protection of retinaldehyde but is relatively inefficient in the protection of retinol or retinyl palmitate. While the protection of retinoids by lutein and zeaxanthin appears inefficient in the retinal periphery, it can be quite substantial in the macula. Although the determined rate constants of scavenging the cation radicals of retinol and retinaldehyde by dopa-melanin are relatively small, the high concentration of melanin in the RPE melanosomes suggests they can be scavenged if they are in proximity to melanin-containing pigment granules.
Topics: Retinoids; Vitamin A; Melanins; Retinaldehyde; Lutein; Zeaxanthins; Taurine; Cations
PubMed: 38203675
DOI: 10.3390/ijms25010506 -
The Journal of Physical Chemistry. B Feb 20235-Azidomethyl-2'-deoxyuridine (5-AmdU, ) has been successfully employed for the metabolic labeling of DNA and fluorescent imaging of live cells. 5-AmdU also demonstrated...
5-Azidomethyl-2'-deoxyuridine (5-AmdU, ) has been successfully employed for the metabolic labeling of DNA and fluorescent imaging of live cells. 5-AmdU also demonstrated significant radiosensitization in breast cancer cells via site-specific nitrogen-centered radical (π-aminyl (U-5-CH-NH), , and σ-iminyl (U-5-CH═N), ) formation. This work shows that these nitrogen-centered radicals are not formed via the reduction of the azido group in 6-azidomethyluridine (6-AmU, ). Radical assignments were performed using electron spin resonance (ESR) in supercooled solutions, pulse radiolysis in aqueous solutions, and theoretical (DFT) calculations. Radiation-produced electron addition to leads to the facile N loss, forming a stable neutral C-centered allylic radical (U-6-CH, ) through dissociative electron attachment (DEA) via the transient negative ion, TNI (U-6-CH-N), in agreement with DFT calculations. In contrast, TNI (U-5-CH-N) of , via facile N loss (DEA) and protonation from the surrounding water, forms radical . Subsequently, undergoes rapid H-atom abstraction from and produces the metastable intermediate α-azidoalkyl radical (U-5-CH-N). U-5-CH-N converts facilely to radical . N loss from U-6-CH-N is thermodynamically controlled, whereas N loss from U-5-CH-N is dictated by protonation from the surrounding waters and resonance conjugation of the azidomethyl side chain at C5 with the pyrimidine ring.
Topics: Nitrogen; Nucleosides; Azides; Electrons; Electron Spin Resonance Spectroscopy; Water; Free Radicals
PubMed: 36780335
DOI: 10.1021/acs.jpcb.2c08257 -
L'Actualite Chimique Apr 2020DNA damage caused by the dissociative electron attachment (DEA) has been well-studied in the gas and solid phases. However, understanding of this process at the...
DNA damage caused by the dissociative electron attachment (DEA) has been well-studied in the gas and solid phases. However, understanding of this process at the fundamental level in solution is still a challenge. The electrons, after losing their kinetic energy via ionization and excitation events, are thermalized and undergo a multistep hydration process with a time constant of ca. ≤1 ps, to becoming fully trapped as a hydrated or solvated electron (e or e ). Prior to the formation of e , the electron exists in its presolvated (or prehydrated) state (e ) with no kinetic energy. We used picosecond pulse radiolysis to generate electrons in water or in liquid diethylene glycol (DEG) to observe the dynamics of capture of these electrons by DNA/RNA bases, nucleosides, and nucleotides. Contrary to the hypotheses in the literature that the presolvated electrons (e ) are captured well by the DNA-nucleosides/tides and the transient negative ions (TNIs) cause strand breaks, we first show that the quasi-free electrons with kinetic energy (e ) or e cannot be captured by guanine and adenine at very long distances in aqueous solutions with concentrations lower than 50 mM. However, the observation of a substantial decrease in the initial yield of e as a function of nucleoside/nucleotide concentrations accompanied by the formation of the nucleotide anion radicals provides direct evidence of an ultrafast step involving radiation-produced electron-mediated DNA damage via DEA. Transient signal analysis suggests that the dissociation channel of TNIs in nucleotide solutions is not even probable up to 0.25 M. On the other hand, in diethylene glycol, we demonstrate that unlike e and e , e effectively attaches itself to the RNA-nucleoside, ribothymidine, forming the TNI in the excited state (TNI*) that undergoes the N1-C1' glycosidic bond dissociation. Thanks to DEA, this process induced by e , in fact, leads to an oxidation of the parent molecule similar to the hydroxyl radical (OH) leading to the same glycosidic bond (N1-C1') cleavage.
PubMed: 32747845
DOI: No ID Found -
Molecular Vision 2014To study the comparative structural and functional changes between wild-type (wt) and N-terminal congenital cataract causing αA-crystallin mutants (R12C, R21L, R49C,... (Comparative Study)
Comparative Study
PURPOSE
To study the comparative structural and functional changes between wild-type (wt) and N-terminal congenital cataract causing αA-crystallin mutants (R12C, R21L, R49C, and R54C) upon exposure to different dosages of gamma rays.
METHODS
Alpha A crystallin N-terminal mutants were created with the site-directed mutagenesis method. The recombinantly overexpressed and purified wt and mutant proteins were used for further studies. A (60)Co source was used to generate gamma rays to irradiate wild and mutant proteins at dosages of 0.5, 1.0, and 2.0 kGy. The biophysical property of the gamma irradiated (GI) and non-gamma irradiated (NGI) αA-crystallin wt and N-terminal mutants were determined. Oligomeric size was determined by size exclusion high-performance liquid chromatography (HPLC), the secondary structure with circular dichroism (CD) spectrometry, conformation of proteins with surface hydrophobicity, and the functional characterization were determined regarding chaperone activity using the alcohol dehydrogenase (ADH) aggregation assay.
RESULTS
αA-crystallin N-terminal mutants formed high molecular weight (HMW) cross-linked products as well as aggregates when exposed to GI compared to the NGI wt counterparts. Furthermore, all mutants exhibited changed β-sheet and random coil structure. The GI mutants demonstrated decreased surface hydrophobicity when compared to αA-crystallin wt at 0, 1.0, and 1.5 kGy; however, at 2.0 kGy a drastic increase in hydrophobicity was observed only in the mutant R54C, not the wt. In contrast, chaperone activity toward ADH was gradually elevated at the minimum level in all GI mutants, and significant elevation was observed in the R12C mutant.
CONCLUSIONS
Our findings suggest that the N-terminal mutants of αA-crystallin are structurally and functionally more sensitive to GI when compared to their NGI counterparts and wt. Protein oxidation as a result of gamma irradiation drives the protein to cross-link and aggregate culminating in cataract formation.
Topics: Base Sequence; Chromatography, Gel; Chromatography, High Pressure Liquid; Circular Dichroism; Cross-Linking Reagents; Densitometry; Gamma Rays; Humans; Hydrophobic and Hydrophilic Interactions; Molecular Sequence Data; Mutant Proteins; Protein Structure, Quaternary; Protein Structure, Secondary; Pulse Radiolysis; Reproducibility of Results; alpha-Crystallin A Chain
PubMed: 25018622
DOI: No ID Found -
The Journal of Biological Chemistry Jan 2015The functional and structural significance of the intrasubunit disulfide bond in copper-zinc superoxide dismutase (SOD1) was studied by characterizing mutant forms of...
The functional and structural significance of the intrasubunit disulfide bond in copper-zinc superoxide dismutase (SOD1) was studied by characterizing mutant forms of human SOD1 (hSOD) and yeast SOD1 lacking the disulfide bond. We determined x-ray crystal structures of metal-bound and metal-deficient hC57S SOD1. C57S hSOD1 isolated from yeast contained four zinc ions per protein dimer and was structurally very similar to wild type. The addition of copper to this four-zinc protein gave properly reconstituted 2Cu,2Zn C57S hSOD, and its spectroscopic properties indicated that the coordination geometry of the copper was remarkably similar to that of holo wild type hSOD1. In contrast, the addition of copper and zinc ions to apo C57S human SOD1 failed to give proper reconstitution. Using pulse radiolysis, we determined SOD activities of yeast and human SOD1s lacking disulfide bonds and found that they were enzymatically active at ∼10% of the wild type rate. These results are contrary to earlier reports that the intrasubunit disulfide bonds in SOD1 are essential for SOD activity. Kinetic studies revealed further that the yeast mutant SOD1 had less ionic attraction for superoxide, possibly explaining the lower rates. Saccharomyces cerevisiae cells lacking the sod1 gene do not grow aerobically in the absence of lysine, but expression of C57S SOD1 increased growth to 30-50% of the growth of cells expressing wild type SOD1, supporting that C57S SOD1 retained a significant amount of activity.
Topics: Amyotrophic Lateral Sclerosis; Apoproteins; Calorimetry, Differential Scanning; Disulfides; Electron Spin Resonance Spectroscopy; Humans; Mass Spectrometry; Metals; Mutant Proteins; Mutation; Oxidative Stress; Protein Binding; Protein Conformation; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Spectrometry, Mass, Electrospray Ionization; Spectrophotometry; Superoxide Dismutase; Superoxides; Zinc
PubMed: 25433341
DOI: 10.1074/jbc.M114.588798 -
Chemosphere Nov 2017The absolute temperature-dependent kinetics for the reaction between hydroxyl radicals and the chloramine water disinfectant species monochloramine (NHCl), as well as...
The absolute temperature-dependent kinetics for the reaction between hydroxyl radicals and the chloramine water disinfectant species monochloramine (NHCl), as well as dichloramine (NHCl) and trichloramine (NCl), have been determined using electron pulse radiolysis and transient absorption spectroscopy. These radical reaction rate constants were fast, with values of 6.06 × 10, 2.57 × 10, and 1.67 × 10 M s at 25 °C for NHCl, NHCl, and NCl, respectively. The corresponding temperature dependence of these reaction rate constants, measured over the range 10-40 °C, is well-described by the transformed Arrhenius equations:giving activation energies of 8.57 ± 0.58, 6.11 ± 0.40, and 5.77 ± 0.72 kJ mol for these three chloramines, respectively. These data will aid water utilities in predicting hydroxyl radical partitioning and chemical contaminant removal efficiencies under real-world advanced oxidation process treatment conditions.
Topics: Chloramines; Chlorides; Disinfectants; Hydroxyl Radical; Kinetics; Nitrogen Compounds; Oxidation-Reduction; Spectrum Analysis; Temperature; Water
PubMed: 28843670
DOI: 10.1016/j.chemosphere.2017.08.053 -
International Journal of Molecular... Jan 2021The azide radical (N) is one of the most important one-electron oxidants used extensively in radiation chemistry studies involving molecules of biological significance....
The azide radical (N) is one of the most important one-electron oxidants used extensively in radiation chemistry studies involving molecules of biological significance. Generally, it was assumed that N reacts in aqueous solutions only by electron transfer. However, there were several reports indicating the possibility of N addition in aqueous solutions to organic compounds containing double bonds. The main purpose of this study was to find an experimental approach that allows a clear assignment of the nature of obtained products either to its one-electron oxidation or its addition products. Radiolysis of water provides a convenient source of one-electron oxidizing radicals characterized by a very broad range of reduction potentials. Two inorganic radicals (SO, CO) and Tl ions with the reduction potentials higher, and one radical (SCN) with the reduction potential slightly lower than the reduction potential of N were selected as dominant electron-acceptors. Transient absorption spectra formed in their reactions with a series of quinoxalin-2-one derivatives were confronted with absorption spectra formed from reactions of N with the same series of compounds. Cases, in which the absorption spectra formed in reactions involving N differ from the absorption spectra formed in the reactions involving other one-electron oxidants, strongly indicate that N is involved in the other reaction channel such as addition to double bonds. Moreover, it was shown that high-rate constants of reactions of N with quinoxalin-2-ones do not ultimately prove that they are electron transfer reactions. The optimized structures of the radical cations (7-R-3-MeQ), radicals (7-R-3-MeQ) and N adducts at the C2 carbon atom in pyrazine moiety and their absorption spectra are reasonably well reproduced by density functional theory quantum mechanics calculations employing the ωB97XD functional combined with the Dunning's aug-cc-pVTZ correlation-consistent polarized basis sets augmented with diffuse functions.
Topics: Azides; Electrons; Free Radicals; Quinoxalines; Water
PubMed: 33435233
DOI: 10.3390/ijms22020633 -
Physical Chemistry Chemical Physics :... May 2018In irradiated DNA, by the base-to-base and backbone-to-base hole transfer processes, the hole (i.e., the unpaired spin) localizes on the most electropositive base,...
In irradiated DNA, by the base-to-base and backbone-to-base hole transfer processes, the hole (i.e., the unpaired spin) localizes on the most electropositive base, guanine. Phosphate radicals formed via ionization events in the DNA-backbone must play an important role in the backbone-to-base hole transfer process. However, earlier studies on irradiated hydrated DNA, on irradiated DNA-models in frozen aqueous solution and in neat dimethyl phosphate showed the formation of carbon-centered radicals and not phosphate radicals. Therefore, to model the backbone-to-base hole transfer process, we report picosecond pulse radiolysis studies of the reactions between H2PO4˙ with the DNA bases - G, A, T, and C in 6 M H3PO4 at 22 °C. The time-resolved observations show that in 6 M H3PO4, H2PO4˙ causes the one-electron oxidation of adenine, guanine and thymine, by forming the cation radicals via a single electron transfer (SET) process; however, the rate constant of the reaction of H2PO4˙ with cytosine is too low (<107 L mol-1 s-1) to be measured. The rates of these reactions are influenced by the protonation states and the reorganization energies of the base radicals and of the phosphate radical in 6 M H3PO4.
Topics: Base Sequence; Cytosine; DNA; Free Radicals; Kinetics; Oxidation-Reduction; Phosphates; Thermodynamics
PubMed: 29786710
DOI: 10.1039/c8cp00352a -
International Journal of Molecular... Jun 2020Gold nanoparticle (GNP) enhanced proton therapy is a promising treatment concept offering increased therapeutic effect. It has been demonstrated in experiments which...
Modelling Spatial Scales of Dose Deposition and Radiolysis Products from Gold Nanoparticle Sensitisation of Proton Therapy in A Cell: From Intracellular Structures to Adjacent Cells.
Gold nanoparticle (GNP) enhanced proton therapy is a promising treatment concept offering increased therapeutic effect. It has been demonstrated in experiments which provided indications that reactive species play a major role. Simulations of the radiolysis yield from GNPs within a cell model were performed using the Geant4 toolkit. The effect of GNP cluster size, distribution and number, cell and nuclear membrane absorption and intercellular yields were evaluated. It was found that clusters distributed near the nucleus increased the nucleus yield by 91% while reducing the cytoplasm yield by 7% relative to a disperse distribution. Smaller cluster sizes increased the yield, 200 nm clusters had nucleus and cytoplasm yields 117% and 35% greater than 500 nm clusters. Nuclear membrane absorption reduced the cytoplasm and nucleus yields by 8% and 35% respectively to a permeable membrane. Intercellular enhancement was negligible. Smaller GNP clusters delivered near sub-cellular targets maximise radiosensitisation. Nuclear membrane absorption reduces the nucleus yield, but can damage the membrane providing another potential pathway for biological effect. The minimal effect on adjacent cells demonstrates that GNPs provide a targeted enhancement for proton therapy, only effecting cells with GNPs internalised. The provided quantitative data will aid further experiments and clinical trials.
Topics: Cells; Gold; Metal Nanoparticles; Models, Biological; Monte Carlo Method; Proton Therapy; Pulse Radiolysis; Radiation-Sensitizing Agents
PubMed: 32580352
DOI: 10.3390/ijms21124431 -
Molecules (Basel, Switzerland) Oct 2014Thermal decomposition of cellulose can be upgraded by means of an electron-beam irradiation to produce valuable organic products via chain mechanisms. The samples being...
Thermal decomposition of cellulose can be upgraded by means of an electron-beam irradiation to produce valuable organic products via chain mechanisms. The samples being irradiated decompose effectively at temperatures below the threshold of pyrolysis inception. Cellulose decomposition resembles local "explosion" of the glucopyranose unit when fast elimination of carbon dioxide and water precede formation of residual carbonyl or carboxyl compounds. The dry distillation being performed during an irradiation gives a liquid condensate where furfural and its derivatives are dominant components. Excessively fast heating is adverse, as it results in a decrease of the yield of key organic products because pyrolysis predominates over the radiolytic-controlled decomposition of feedstock. Most likely, conversion of cellulose starts via radiolytic formation of macroradicals do not conform with each other, resulting in instability of the macroradical. As a consequence, glucosidic bond cleavage, elimination of light fragments (water, carbon oxides, formaldehyde, etc.) and formation of furfural take place.
Topics: Cellulose; Electrons; Gamma Rays; Hot Temperature; Pulse Radiolysis; Volatile Organic Compounds; Wood
PubMed: 25338178
DOI: 10.3390/molecules191016877