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At least 721 records · Page 40Linked to original sources
PubMed2003

Singlet oxygen (1deltag) production by pterin derivatives in aqueous solutions.

Six compounds of the pterin family (pterin, 6-carboxypterin, 6-formylpterin, folic acid, biopterin and neopterin) have been investigated for their efficiencies of singlet oxygen (O2(1deltag)) production and quenching in aqueous solutions. The quantum yields of 1O2 production (phidelta) have been determined by measurements of the 1O2 luminescence in the near-infrared (1270 nm) upon continuous excitation of the sensitizer. Under our experimental conditions, all studied compounds (except folic acid) are relatively efficient 1O2 sensitizers with phidelta values of up to 0.47. Results show that the nature of the substituent at position 6 on the pterin moiety, as well as the pH, affect considerably the capacity of pterins to produce 1O2. All compounds investigated are efficient 1O2 quenchers: the rate constant of 1O2 total quenching (kt) by folic acid (3.0(+/- 0.3) x 10(7) M(-1) s(-1)) is one order of magnitude larger than those for the other pterin derivatives investigated (1.4(+/- 0.1) x 10(6) M(-1) s(-1) to 2.9(+/- 0.3) x 10(6) M(-1) s(-1)).

Hydrogen-Ion Concentration↗
PubMed2003

Enantiopure lanthanide complexes incorporating a tetraazatriphenylene sensitiser and three naphthyl groups: exciton coupling, intramolecular energy transfer, efficient singlet oxygen formation and perturbation by DNA binding.

In cationic nine-coordinate chiral terbium and europium complexes incorporating exciton-coupled naphthyl groups and a tetraazatriphenylene sensitising chromophore, efficient intramolecular energy transfer occurs leading to population of the naphthyl triplet state. With the terbium complex, the absolute quantum yield of singlet oxygen formation is 51% (lambda(exc) 355 nm), and for the Eu complex the intensity of metal-based emission increases by up to 350% on binding to poly(dGdC) or calf-thymus DNA, and was greater for the delta-isomer.

Animals↗
PubMed2003

Reactive species formed on proteins exposed to singlet oxygen.

Singlet oxygen ((1)O(2)) is believed to be generated in biological systems by a range of endogenous processes (e.g. enzymatic and chemical reactions) and exogenous stimuli (e.g. UV or visible light in the presence of a sensitiser). Kinetic data is consistent with proteins being a major target for (1)O(2), with damage occurring preferentially at Trp, His, Tyr, Met, and Cys side-chains. Reaction with each of these residues gives rise to further reactive species. In the case of Trp and Tyr, initial poorly characterised endoperoxides are believed to undergo ring-opening reactions to give hydroperoxides, which can be reduced to the corresponding alcohols; other products arising from radical intermediates can also be generated, particularly in the presence of UV light and metal ions. With His side-chains, poorly characterised peroxides are also formed. Reaction with Met and Cys has been proposed to occur via zwitterionic peroxy intermediates. Peroxides are also generated on isolated proteins, and protein within intact cells, via(1)O(2)-mediated reactions. The peroxides formed on Trp, Tyr, and His peptides, as well as on proteins, have been shown to induce damage to other targets, with molecular oxidation of thiol residues an important reaction. This can result in the inactivation of cellular enzymes and the oxidation of other biological targets. Protein cross-linking and aggregation can also be induced by reactive species formed on photo-oxidised proteins, though the nature of the species that participate in such reactions is poorly understood. These secondary reactions, and particularly those involving hydroperoxides, may play a key role in the induction of secondary damage (bystander effects) in systems subject to photo-oxidation.

Amino Acids↗
PubMed2004

Are dietary carotenoids beneficial? Reactions of carotenoids with oxy-radicals and singlet oxygen.

Carotenoids play diverse roles in biology and medicine. Both the quenching of singlet oxygen (energy transfer) and interaction with oxy-radicals (electron transfer, H-atom transfer and addition reactions) are key processes in understanding many of these roles. Much previous work in 'simple' solvents is reviewed and new results in cell membrane models are presented. The possible consequences of using carotenoids as dietary supplements are discussed.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2006

Deactivation of the first excited singlet state of thiophenols.

On the bases of picosecond and nanosecond laser flash photolysis with detection by emission and absorption spectroscopy, a quantitative description is given of all deactivation channels of the first excited singlet state of thiophenols ArSH(S(1)) such as fluorescence, intersystem crossing (ISC), chemical dissociation into radicals, and radiation-less internal conversion (IC). For this purpose, the photolysis of thiophenol and its methyl-, methoxy-, and chloro-substituted derivatives was studied in solvents of increasing polarity: 1-chlorobutane, ethanol, and acetonitrile. The fluorescence lifetime of the thiophenols was found to range from some hundreds of picoseconds up to a few nanoseconds, correlating with fluorescence quantum yields between 0.001-0.040, at room temperature. Depending on the substitution pattern of the aromatic ring, the quantum yield of the S-H bond dissociation was found to be between 0.3-0.5, irrespective of the solvent polarity. In laser photolysis, no triplet formation of the investigated compounds could be observed neither by the direct way nor by subsequent sensitization with beta-carotene. As a difference to the total, the radiation-less internal conversion (Phi(IC)>or= 0.5) was found to be the dominating process.

Antioxidants↗
PubMed2007

Immunogenicity of DNA modified by singlet oxygen: implications in systemic lupus erythematosus and cancer.

Activation, proliferation and programmed cell death of immune cells are dependent on controlled production of ROS (reactive oxygen species). However, under chronic inflammatory conditions, large amounts of ROS generated are a major cause of many human degenerative diseases. ROS are known to cause DNA damage, leading to strand breaks, base damage and conformational changes. (1)O(2) (singlet oxygen), being one of the most potent ROS, is known to selectively react with the deoxyguanosine moiety in DNA. The effect of (1)O(2), generated by UV irradiation of Methylene Blue, on plasmid DNA was studied by UV spectroscopy and electrophoresis. The antibodies raised against the modified DNA in experimental animals induced a high titre. IgG was purified on a Protein A-Sepharose matrix, and oxidative lesions in DNA of SLE (systemic lupus erythematosus) and cancer patients were probed using anti-((1)O(2)-plasmid DNA) [anti-((1)O(2)-modified plasmid DNA)]. The DNA isolated from the sera of SLE and cancer patients was found to inhibit anti-(1)O(2)-plasmid DNA IgG activity, reiterating the results obtained with serum samples. These binding results indicate the presence of oxidative lesions in the SLE and cancer patients' genome caused by excessive production of ROS. The results confirm the damaging effect ROS has on DNA. The excessive production of reactive oxygen intermediates may be one of the factors responsible for the induction of autoimmune response seen in SLE and cancer.

Animals↗
PubMed2005

A transcriptional response to singlet oxygen, a toxic byproduct of photosynthesis.

The ability of phototrophs to convert light into biological energy is critical for life on Earth. However, there can be deleterious consequences associated with this bioenergetic conversion, including the production of toxic byproducts. For example, singlet oxygen (1O2) can be formed during photosynthesis by energy transfer from excited triplet-state chlorophyll pigments to O2. By monitoring gene expression and growth in the presence of 1O2, we show that the phototrophic bacterium Rhodobacter sphaeroides mounts a transcriptional response to this reactive oxygen species (ROS) that requires the alternative sigma factor, sigma(E). An increase in sigma(E) activity is seen when cells are exposed to 1O2 generated either by photochemistry within the photosynthetic apparatus or the photosensitizer, methylene blue. Wavelengths of light responsible for the generating triplet-state chlorophyll pigments in the photosynthetic apparatus are sufficient for a sustained increase in sigma(E) activity. Continued exposure to 1O2 is required to maintain this transcriptional response, and other ROS do not cause a similar increase in sigma(E)-dependent gene expression. When a sigma(E) mutant produces low levels of carotenoids, 1O2 is bacteriocidal, suggesting that this response is essential for protecting cells from this ROS. In addition, global gene expression analysis identified approximately 180 genes (approximately 60 operons) whose RNA levels increase > or = 3-fold in cells with increased sigma(E) activity. Gene products encoded by four newly identified sigma(E)-dependent operons are predicted to be involved in stress response, protecting cells from 1O2 damage, or the conservation of energy.

Carotenoids↗
PubMed2005

Linoleic acid hydroperoxide reacts with hypochlorous acid, generating peroxyl radical intermediates and singlet molecular oxygen.

The reaction of hypochlorous acid (HOCl) with hydrogen peroxide is known to generate stoichiometric amounts of singlet molecular oxygen [O2 (1Deltag)]. This study shows that HOCl can also react with linoleic acid hydroperoxide (LAOOH), generating O2 (1Deltag) with a yield of 13 +/- 2% at physiological pH. Characteristic light emission at 1,270 nm, corresponding to O2 (1Deltag) monomolecular decay, was observed when HOCl was reacted with LAOOH or with liposomes containing phosphatidylcholine hydroperoxides, but not with cumene hydroperoxide or tert-butyl hydroperoxide. The generation of O2 (1Deltag) was confirmed by the acquisition of the spectrum of the light emitted in the near-infrared region showing a band with maximum intensity at 1,270 nm and by the observation of the enhancing effect of deuterium oxide and the quenching effect of sodium azide. Mechanistic studies using 18O-labeled linoleic acid hydroperoxide (LA18O18OH) showed that its reaction with HOCl yields 18O-labeled O2 (1Deltag) [18O2 (1Deltag)], demonstrating that the oxygen atoms in O2 (1Deltag) are derived from the hydroperoxide group. Direct analysis of radical intermediates in the reaction of LAOOH with HOCl by continuous-flow electron paramagnetic resonance spectroscopy showed a doublet signal with a g-value of 2.014 and a hyperfine coupling constant from the alpha-hydrogen of a(H) = 4.3 G, indicating the formation of peroxyl radicals. Taken together, our results clearly demonstrate that HOCl reacts with biologically relevant lipid hydroperoxides, generating O2 (1Deltag). In addition, the detection of 18O2 (1Deltag) and peroxyl radicals strongly supports the involvement of a Russell mechanism in the generation of O2 (1Deltag).

Hydrogen Peroxide↗
PubMed2002

Mechanism for antibody catalysis of the oxidation of water by singlet dioxygen.

Wentworth et al. [Wentworth, P., Jones, L. H., Wentworth, A. D., Zhu, X. Y., Larsen, N. A., Wilson, I. A., Xu, X., Goddard, W. A., Janda, K. D., Eschenmoser, A. & Lerner, R. A. (2001) Science 293, 1806-1811] recently reported the surprising result that antibodies and T cell receptors efficiently catalyze the conversion of molecular singlet oxygen (1O2) plus water to hydrogen peroxide (HOOH). Recently, quantum mechanical calculations were used to delineate a plausible mechanism, involving reaction of 1O2 with two waters to form HOOOH (plus H2O), followed by formation of HOOOH dimer, which rearranges to form HOO-HOOO + H2O, which rearranges to form two HOOH plus 1O2 or 3O2. For a system with 18O H2O, this mechanism leads to a 2.2:1 ratio of 16O:18O in the product HOOH, in good agreement with the ratio 2.2:1 observed in isotope experiments by Wentworth et al. In this paper we use docking and molecular dynamics techniques (HierDock) to search various protein structures for sites that stabilize these products and intermediates predicted from quantum mechanical calculations. We find that the reaction intermediates for production of HOOH from 1O2 are stabilized at the interface of light and heavy chains of antibodies and T cell receptors. This inter Greek key domain interface structure is unique to antibodies and T cell receptors, but is not present in beta2-microglobulin, which does not show any stabilization in our docking studies. This result is consistent with the experimentally observed lack of HOOH production in this system. Our results provide a plausible mechanism for the reactions and provide an explanation of the specific structural character of antibodies responsible for this unexpected chemistry.

Antibodies, Catalytic↗
PubMed2002

The gas phase reaction of singlet dioxygen with water: a water-catalyzed mechanism.

Stimulated by the recent surprising results from Wentworth et al. [Wentworth, A. D., Jones, L. H., Wentworth, P., Janda, K. D. & Lerner, R. A. (2000) Proc. Natl. Acad. Sci. USA 97, 10930-10935] that Abs efficiently catalyze the conversion of molecular singlet oxygen ((1)O(2)) plus water to hydrogen peroxide (HOOH), we used quantum chemical methods (B3LYP density functional theory) to delineate the most plausible mechanisms for the observed efficient conversion of water to HOOH. We find two reasonable pathways. In Pathway I, (i) H(2)O catalyzes the reaction of (1)O(2) with a second water to form HOOOH; (ii) two HOOOH form a dimer, which rearranges to form the HOO-HOOO + H(2)O complex; (iii) HOO-HOOO rearranges to HOOH-OOO, which subsequently reacts with H(2)O to form H(2)O(4) + HOOH; and (iv) H(2)O(4) rearranges to the cyclic dimer (HO(2))(2), which in turn forms HOOH plus (1)O(2) or (3)O(2). Pathway II differs in that step ii is replaced with the reaction between HOOOH and (1)O(2), leading to the formation of HOO-HOOO. This then proceeds to similar products. For a system with (18)O H(2)O, Pathway I leads to a 2.2:1 ratio of (16)O:(18)O in the product HOOH, whereas Pathway II leads to 3:1. These ratios are in good agreement with the 2.2:1 ratio observed in isotope experiments by Wentworth et al. These mechanisms lead to two HOOH per initial (1)O(2) or one, depending on whether the product of step iv is (1)O(2) or (3)O(2), in good agreement with the experimental result of 2.0. In addition to the Ab-induced reactions, the hydrogen polyoxides (H(2)O(3) and H(2)O(4)) formed in these mechanisms and their decomposition product polyoxide radicals (HO(2), HO(3)) may play a role in combustion, explosions, atmospheric chemistry, and the radiation chemistry in aqueous systems.

Antibodies, Catalytic↗
PubMed2006

Cross-talk between singlet oxygen- and hydrogen peroxide-dependent signaling of stress responses in Arabidopsis thaliana.

Upon a dark-to-light shift, the conditional fluorescent (flu) mutant of Arabidopsis releases singlet oxygen (1O2) within the plastid compartment. Distinct sets of nuclear genes are activated that are different from those induced by superoxide (O2*-)) and/or hydrogen peroxide (H2O2), suggesting that different types of reactive oxygen species activate distinct signaling pathways. It is not known whether the pathways operate separately or interact with each other. We have addressed this problem by modulating noninvasively the level of H2O2 in plastids by means of a transgenic line that overexpresses the thylakoid-bound ascorbate peroxidase (tAPX). The overexpression of the H2O2-specific scavenger reduced strongly the activation of nuclear genes in plants treated with the herbicide paraquat that in the light leads to the enhanced generation of O2*- and H2O2. In the flu mutant overexpressing tAPX, the intensity of 1O2-mediated cell death and growth inhibition was increased when compared with the flu parental line. Also, the expression of most of the nuclear genes that were rapidly activated after the release of 1O2 was significantly higher in flu plants overexpressing tAPX, whereas in wild-type plants, overexpression of tAPX did not lead to visible stress responses and had only a very minor impact on nuclear gene expression. The results suggest that H2O2 antagonizes the 1O2-mediated signaling of stress responses as seen in the flu mutant. This cross-talk between H2O2- and 1O2-dependent signaling pathways might contribute to the overall stability and robustness of wild-type plants exposed to adverse environmental stress conditions.

Arabidopsis↗
PubMed2000

The decomposition of peroxynitrite to nitroxyl anion (NO-) and singlet oxygen in aqueous solution.

The mechanism of decomposition of peroxynitrite (OONO(-)) in aqueous sodium phosphate buffer solution at neutral pH was investigated. The OONO(-) was synthesized by directly reacting nitric oxide with superoxide anion at pH 13. The hypothesis was explored that OONO(-), after protonation at pH 7.0 to HOONO, decomposes into (1)O(2) and HNO according to a spin-conserved unimolecular mechanism. Small aliquots of the concentrated alkaline OONO(-) solution were added to a buffer solution (final pH 7.0-7.2), and the formation of (1)O(2) and NO(-) in high yields was observed. The (1)O(2) generated was trapped as the transannular peroxide (DPAO(2)) of 9, 10-diphenylanthracene (DPA) dissolved in carbon tetrachloride. The nitroxyl anion (NO-) formed from HNO (pKa 4.5) was trapped as nitrosylhemoglobin (HbNO) in an aqueous methemoglobin (MetHb) solution. In the presence of 25 mM sodium bicarbonate, which is known to accelerate the rate of decomposition of OONO(-), the amount of singlet oxygen trapped was reduced by a factor of approximately 2 whereas the yield of trapping of NO(-) by methemoglobin remained unaffected. Because NO(3)(-) is known to be the ultimate decomposition product of OONO(-), these results suggest that the nitrate anion is not formed by a direct isomerization of OONO(-), but by an indirect route originating from NO(-).

Animals↗
PubMed1995

Singlet oxygen and peroxyl radicals regulate carotenoid biosynthesis in Phaffia rhodozyma.

Carotenoids have recently received considerable interest because of their potential in delaying or preventing degenerative diseases such as arteriosclerosis, cancer, and aging. In this study we show that the active oxygen species singlet oxygen (1O2) and peroxyl radicals differently affect carotenoid composition and biosynthesis in the yeast Phaffia rhodozyma. Photochemical generation of 1O2 with rose bengal or alpha-terthienyl induced carotenoid accumulation. In contrast, peroxyl radicals derived from t-butylhydroperoxide (tBOOH) or H2O2 decreased the content of astaxanthin and increased beta-carotene by approximately 4-fold, suggesting end product feedback regulation by astaxanthin or inhibition of biosynthetic enzymes. 14C labeling of carotenoids during oxidative stress supported the possibility of end product regulation. Carotenoids were bleached by 8 mM tBOOH within 6 h when carotenogenesis was inhibited by thymol. When treated with peroxides, a previously unreported pigment in P. rhodozyma was formed. The carotenoid had a mass of 580 Da and a molecular formula of C40H52O3. Chemical derivatizations combined with mass and absorbance spectroscopy tentatively identified the carotenoid as dehydroflexixanthin (3,1'-dihydroxy-2,3,3',4'-tetradehydro-1',2'-dihydro-beta,psi-caro tene-4-one). This study provides the first report of induction of astaxanthin biosynthesis by 1O2, probable feedback control by astaxanthin, and the oxidative degradation of astaxanthin to novel pigments in P. rhodozyma.

Carotenoids↗
PubMed1997

Singlet oxygen produced by photodynamic action causes inactivation of the mitochondrial permeability transition pore.

We have studied the effects of singlet oxygen produced by photodynamic action on the cyclosporin A-sensitive permeability transition (PT) in isolated rat liver mitochondria. Mitochondria were incubated with 3 microM hematoporphyrin and irradiated at 365 nm with a fluence rate of 25 watts/m2. For short durations of irradiation (60 s) the adenine nucleotide translocase was inactivated, but mitochondria retained their ability to form a proton electrochemical gradient and accumulated Ca2+ and Pi at the same rate as non-irradiated controls. Strikingly, however, the oxidative effects of photodynamic action prevented opening of the PT pore which is normally induced by Ca2+ plus Pi or by treatment with diethyl pyrocarbonate (a histidine reagent) or diamide (a thiol oxidant). We show that the most likely targets for photodynamic action are critical histidines that undergo degradation. Irradiated, hematoporphyrin-loaded mitochondria treated with diethyl pyrocarbonate or diamide still undergo the PT when treated with phenylarsine oxide, which reacts with a critical dithiol involved in pore modulation (Petronilli, V., Costantini, P., Scorrano, L., Colonna, R., Passamonti, S., and Bernardi, P. (1994) J. Biol. Chem. 269, 16638-16642). These data suggest (i) that the dithiol cysteines are not oxidized by photodynamic action, but rather became inaccessible to oxidants; and (ii) that irradiation of hematoporphyrin-loaded mitochondria does not lead to pore denaturation, but rather to site-selective inactivation of discrete pore functional domains.

Animals↗
PubMed2006

Nordihydroguaiaretic acid is a potent in vitro scavenger of peroxynitrite, singlet oxygen, hydroxyl radical, superoxide anion and hypochlorous acid and prevents in vivo ozone-induced tyrosine nitration in lungs.

The antioxidant nordihydroguaiaretic acid (NDGA) has recently become well known as a putative anticancer drug. In this paper, it was evaluated the in vitro peroxynitrite (ONOO(-)), singlet oxygen ((1)O(2)), hydroxyl radical (OH(v)), hydrogen peroxide (H(2)O(2)), superoxide anion and hypochlorous acid (HOCl) scavenging capacity of NDGA. It was found that NDGA scavenges: (a) ONOO(-) (IC(50) = 4 +/- 0.94 microM) as efficiently as uric acid; (b) (1)O(2) (IC(50) = 151 +/- 20 microM) more efficiently than dimethyl thiourea, lipoic acid, N-acetyl-cysteine and glutathione; (c) OH(v) (IC(50) = 0.15 +/- 0.02 microM) more efficiently than dimethyl thiourea, uric acid, trolox, dimethyl sulfoxide and mannitol, (d) (IC(50) = 15 +/- 1 microM) more efficiently than N-acetyl-cysteine, glutathione, tempol and deferoxamine and (e) HOCl (IC(50) = 622 +/- 42 microM) as efficiently as lipoic acid and N-acetyl-cysteine. NDGA was unable to scavenge H(2)O(2). In an in vivo study in rats, NDGA was able to prevent ozone-induced tyrosine nitration in lungs. It is concluded that NDGA is a potent in vitro scavenger of ONOO(-), (1)O(2), OH(v), and HOCl and is able to prevent lung tyrosine nitration in vivo.

Animals↗