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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 -
Anticancer Research 2004Steady-state radiolysis of aqueous procarbazine (PC) was studied in air-free, aerated and solutions saturated with N2O. The corresponding Gi(-PC)-values obtained at...
Steady-state radiolysis of aqueous procarbazine (PC) was studied in air-free, aerated and solutions saturated with N2O. The corresponding Gi(-PC)-values obtained at pH=7.4 were: 2.85, 5.60 and 3.45, respectively. The investigations in vitro, using E. coli (AB 1157) as a model for living systems, demonstrated that PC acts as a cytostatic in air-free as well as in aerated media. However, it shows radiation protecting ability in the presence of N2O, where OH-radicals are the predominant reactants. Similar results were observed at pH=6.2. The experimental data contribute to a better understanding of the many-sided and frequently contradictory behavior of PC.
Topics: Air; Antineoplastic Agents; Escherichia coli; Hydrogen-Ion Concentration; Nitrous Oxide; Procarbazine; Pulse Radiolysis; Radiation-Sensitizing Agents; Solutions
PubMed: 15274327
DOI: No ID Found -
The Journal of Biological Chemistry Sep 1987Transferrin and the transferrin model compound Fe(III)-EHPG (Fe(III)-ethylenediamine-N,N'-bis[2-(2-hydroxyphenyl)acetic acid] were found not to react with superoxide, as...
The reaction of superoxide, formate radical, and hydrated electron with transferrin and its model compound, Fe(III)-ethylenediamine-N,N'-bis[2-(2-hydroxyphenyl)acetic acid] as studied by pulse radiolysis.
Transferrin and the transferrin model compound Fe(III)-EHPG (Fe(III)-ethylenediamine-N,N'-bis[2-(2-hydroxyphenyl)acetic acid] were found not to react with superoxide, as pulse radiolysis and kinetic spectroscopy revealed no transient species and no bleaching of the 465-nm absorption. However, transferrin was found to react with the formate radical, CO-.2, and the hydrated electron, e-aq, with second-order rate constants of 3.8 X 10(8) and 1.1 X 10(10) M-1 S-1, respectively. These reactions produced a transient species (lambda max = 420 nm) which subsequently decayed by a second-order process. However, no reduction of the Fe(III) in transferrin was detected. Fe(III)-EHPG was also found to react with CO-.2 and e-aq, k = 7.3 X 10(6) and 1.1 X 10(9) M-1 S-1, respectively. The reactions of CO-.2 and e-aq with Fe(III)-EHPG resulted in no transient species but rather in reduction of the iron. These results are consistent with the inability of transferrin and Fe(III)-EHPG to catalyze the Haber-Weiss reaction.
Topics: Chemical Phenomena; Chemistry; Electrons; Ethylenediamines; Formates; Free Radicals; Humans; Kinetics; Pulse Radiolysis; Superoxides; Transferrin
PubMed: 3040725
DOI: No ID Found -
Free Radical Biology & Medicine Oct 2013Hypochlorous acid and its acid-base counterpart, hypochlorite ions, produced under inflammatory conditions, may produce chloramides of glycosaminoglycans, these being...
Hypochlorous acid and its acid-base counterpart, hypochlorite ions, produced under inflammatory conditions, may produce chloramides of glycosaminoglycans, these being significant components of the extracellular matrix (ECM). This may occur through the binding of myeloperoxidase directly to the glycosaminoglycans. The N-Cl group in the chloramides is a potential selective target for both reducing and oxidizing radicals, leading possibly to more efficient and damaging fragmentation of these biopolymers relative to the parent glycosaminoglycans. In this study, the fast reaction techniques of pulse radiolysis and nanosecond laser flash photolysis have been used to generate both oxidizing and reducing radicals to react with the chloramides of hyaluronan (HACl) and heparin (HepCl). The strong reducing formate radicals and hydrated electrons were found to react rapidly with both HACl and HepCl with rate constants of 1-1.7 × 10(8) and 0.7-1.2 × 10(8)M(-1)s(-1) for formate radicals and 2.2 × 10(9) and 7.2 × 10(8)M(-1)s(-1) for hydrated electrons, respectively. The spectral characteristics of the products of these reactions were identical and were consistent with initial attack at the N-Cl groups, followed by elimination of chloride ions to produce nitrogen-centered radicals, which rearrange subsequently and rapidly to produce C-2 radicals on the glucosamine moiety, supporting an earlier EPR study by M.D. Rees et al. (J. Am. Chem. Soc.125: 13719-13733; 2003). The oxidizing hydroxyl radicals also reacted rapidly with HACl and HepCl with rate constants of 2.2 × 10(8) and 1.6 × 10(8)M(-1)s(-1), with no evidence from these data for any degree of selective attack on the N-Cl group relative to the N-H groups and other sites of attack. The carbonate anion radicals were much slower with HACl and HepCl than hydroxyl radicals (1.0 × 10(5) and 8.0 × 10(4)M(-1)s(-1), respectively) but significantly faster than with the parent molecules (3.5 × 10(4) and 5.0 × 10(4)M(-1)s(-1), respectively). These findings suggest that these potential in vivo radicals may react in a site-specific manner with the N-Cl group in the glycosaminoglycan chloramides of the ECM, possibly to produce more efficient fragmentation. This is the first study therefore to conclusively demonstrate that reducing radicals react rapidly with glycosaminoglycan chloramides in a site-specific attack at the N-Cl group, probably to produce a 100% efficient biopolymer fragmentation process. Although less reactive, carbonate radicals, which may be produced in vivo via reactions of peroxynitrite with serum levels of carbon dioxide, also appear to react in a highly site-specific manner at the N-Cl group. It is not yet known if such site-specific attacks by this important in vivo species lead to a more efficient fragmentation of the biopolymers than would be expected for attack by the stronger oxidizing species, the hydroxyl radical. It is clear, however, that the N-Cl group formed under inflammatory conditions in the extracellular matrix does present a more likely target for both reactive oxygen species and reducing species than the N-H groups in the parent glycosaminoglycans.
Topics: Electron Spin Resonance Spectroscopy; Electrons; Extracellular Matrix; Glycosaminoglycans; Heparin; Hyaluronic Acid; Hydroxyl Radical; Hypochlorous Acid; Inflammation; Kinetics; Oxidation-Reduction; Pulse Radiolysis
PubMed: 23684776
DOI: 10.1016/j.freeradbiomed.2013.05.012 -
Biochimica Et Biophysica Acta Apr 2010Superoxide reductase SOR is an enzyme involved in superoxide detoxification in some microorganisms. Its active site consists of a non-heme ferrous center in an unusual...
Superoxide reductase SOR is an enzyme involved in superoxide detoxification in some microorganisms. Its active site consists of a non-heme ferrous center in an unusual [Fe(NHis)(4) (SCys)(1)] square pyramidal pentacoordination that efficiently reduces superoxide into hydrogen peroxide. In previous works, the reaction mechanism of the SOR from Desulfoarculus baarsii enzyme, studied by pulse radiolysis, was shown to involve the formation of two reaction intermediates T1 and T2. However, the absorption spectrum of T2 was reported with an unusual sharp band at 625 nm, very different from that reported for other SORs. In this work, we show that the sharp band at 625 nm observed by pulse radiolysis reflects the presence of photochemical processes that occurs at the level of the transient species formed during the reaction of SOR with superoxide. These processes do not change the stoichiometry of the global reaction. These data highlight remarkable photochemical properties for these reaction intermediates, not previously suspected for iron-peroxide species formed in the SOR active site. We have reinvestigated the reaction mechanism of the SOR from D. baarsii by pulse radiolysis in the absence of these photochemical processes. The T1 and T2 intermediates now appear to have absorption spectra similar to those reported for the Archaeoglobus fulgidus SOR enzymes. Although for some enzymes of the family only one transient was reported, on the whole, the reaction mechanisms of the different SORs studied so far seem very similar, which is in agreement with the strong sequence and structure homologies of their active sites.
Topics: Bacterial Proteins; Catalytic Domain; Deltaproteobacteria; Kinetics; Oxidoreductases; Photochemical Processes; Pulse Radiolysis; Recombinant Proteins; Spectrophotometry; Superoxides
PubMed: 19962458
DOI: 10.1016/j.bbapap.2009.11.019 -
The Biochemical Journal Nov 1979Reduction of fully oxidized Clostridium pasteurianum 8-Feox.,ox. ferredoxin by using pulse-radiolysis techniques yields the half-reduced species 8-Feox.,red. ferredoxin....
Mechanism of formation, spectrum and reactivity of half-reduced eight-iron Clostridium pasteurianum ferredoxin in pulse-radiolysis studies and the non-co-operativity of the four-iron clusters.
Reduction of fully oxidized Clostridium pasteurianum 8-Feox.,ox. ferredoxin by using pulse-radiolysis techniques yields the half-reduced species 8-Feox.,red. ferredoxin. The subsequent oxidation of 8-Feox.,red. ferredoxin with Co(NH3)5Cl2+ was studied. From a comparison with stopped-flow studies on the 2:1 Co(NH3)5Cl2+ oxidation of 8-Fered.,red. ferredoxin to the 8-Feox.,ox. form it is concluded that there is no redox co-operativity between the two 4-Fe centres in these reactions.
Topics: Chemical Phenomena; Chemistry; Clostridium; Ferredoxins; Kinetics; Oxidation-Reduction; Pulse Radiolysis
PubMed: 534509
DOI: 10.1042/bj1830471 -
The Journal of Biological Chemistry Sep 1982The temperature and pH dependence of the reaction of the superoxide radical anion with ferricytochrome c have been measured using the pulse-radiolysis technique. The...
The temperature and pH dependence of the reaction of the superoxide radical anion with ferricytochrome c have been measured using the pulse-radiolysis technique. The temperature dependence of the reaction at low ionic strength yields an activation energy of 31 +/- 5 kJ/mol as compared to 14 +/- 3 kJ/mol for the reaction of CO2.(-) under the same conditions. The pH dependence fits the single pK'a of ferricytochrome c of 9.1. The bimolecular rate constant for the reaction of the superoxide anion with ferricytochrome c at pH 7.8, 21 +/- 2 degrees C, in the presence of 50 mM phosphate and 0.1 mM EDTA is (2.6 +/- 0.1) X 10(5) M-1 s-1. Using this value, 1 unit of superoxide dismutase activity (McCord, J. M., and Fridovich, I. (1969) J. Biol. Chem. 244, 6049-6055) is calculated to be 3.6 +/- 0.3 pmol of enzyme if the assay is performed in a total volume of 3.0 ml. Copper ions reduce the yield of the reaction of ferricytochrome c with CO2.(-). The reactivities of native and singly modified 4-carboxy-2,4-dinitrophenyllysine cytochromes c towards the superoxide anion radical are in the order native greater than 4-carboxy-2,4-dinitrophenyllysine 60 greater than lysine 13 greater than lysine 87 greater than lysine 27 greater than lysine 86 greater than lysine 72, indicating that electron transfer takes place at or close to the solvent accessible heme edge. The mechanism of the reaction is discussed in terms of the approach of superoxide anion radicals to the heme edge and the available molecular orbitals of both heme and free radicals.
Topics: Animals; Cytochrome c Group; Horses; Hydrogen-Ion Concentration; Kinetics; Myocardium; Oxidation-Reduction; Oxygen; Superoxides; Temperature
PubMed: 6286671
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 -
Bioscience, Biotechnology, and... Mar 2000The antioxidant property of tetrahydrocurcumin (THC), a reduced derivative of curcumin, was examined by its ability to inhibit radiation-induced lipid peroxidation in...
The antioxidant property of tetrahydrocurcumin (THC), a reduced derivative of curcumin, was examined by its ability to inhibit radiation-induced lipid peroxidation in rat liver microsomes and compared with curcumin. The lipid peroxidation caused by irradiation of N2O-purged and aerated buffered aqueous solutions was found to be inhibited by THC in a dose- and concentration-dependent manner. In order to understand the actual reaction mechanisms involved in the inhibition process, pulse radiolysis investigation of THC with radiolytically produced radicals like hydroxyl, model peroxyl radicals, and azide radicals were done and the transients were detected by kinetic spectrophotometry. The reaction of THC with hydroxyl and azide radicals gave rise to transient absorption in the region 200-400 nm with two peaks at 310 nm and 390 nm. From the spectral properties and kinetics of these radicals, a suitable mechanism is discussed to explain the antioxidant actions of THC.
Topics: Animals; Antioxidants; Curcumin; Gamma Rays; Lipid Peroxidation; Male; Microsomes, Liver; Molecular Structure; Pulse Radiolysis; Rats; Rats, Wistar
PubMed: 10803946
DOI: 10.1271/bbb.64.503 -
The Journal of Biological Chemistry Jul 2003We have studied the reaction kinetics of ten manganese porphyrins, differing in their meso substituents, with peroxynitrite (ONOO-) and carbonate radical anion (CO3.)...
We have studied the reaction kinetics of ten manganese porphyrins, differing in their meso substituents, with peroxynitrite (ONOO-) and carbonate radical anion (CO3.) using stopped-flow and pulse radiolysis, respectively. Rate constants for the reactions of Mn(III) porphyrins with ONOO- ranged from 1 x 10(5) to 3.4 x 10(7) m(-1) s(-1) and correlated well with previously reported kinetic and thermodynamic data that reflect the resonance and inductive effects of the substituents on the porphyrin ring. Rate constants for the reactions of Mn(III) porphyrins with CO3. ranged from 2 x 10(8) to 1.2 x 10(9) m(-1)s(-1) at pH
Topics: Anions; Carbon; Hydrogen-Ion Concentration; Kinetics; Manganese; Models, Chemical; Oxygen; Peroxynitrous Acid; Porphyrins; Spectrophotometry; Temperature; Thermodynamics
PubMed: 12700236
DOI: 10.1074/jbc.M213302200