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PubMed2003

Rapid induction of distinct stress responses after the release of singlet oxygen in Arabidopsis.

The conditional fluorescent (flu) mutant of Arabidopsis accumulates the photosensitizer protochlorophyllide in the dark. After a dark-to-light shift, the generation of singlet oxygen, a nonradical reactive oxygen species, starts within the first minute of illumination and was shown to be confined to plastids. Immediately after the shift, plants stopped growing and developed necrotic lesions. These early stress responses of the flu mutant do not seem to result merely from physicochemical damage. Peroxidation of chloroplast membrane lipids in these plants started rapidly and led to the transient and selective accumulation of a stereospecific and regiospecific isomer of hydroxyoctadecatrieonic acid, free (13S)-HOTE, that could be attributed almost exclusively to the enzymatic oxidation of linolenic acid. Within the first 15 min of reillumination, distinct sets of genes were activated that were different from those induced by superoxide/hydrogen peroxide. Collectively, these results demonstrate that singlet oxygen does not act primarily as a toxin but rather as a signal that activates several stress-response pathways. Its biological activity in Arabidopsis exhibits a high degree of specificity that seems to be derived from the chemical identity of this reactive oxygen species and/or the intracellular location at which it is generated.

Acclimatization↗
PubMed2005

Concurrent activation of cell death-regulating signaling pathways by singlet oxygen in Arabidopsis thaliana.

Upon a dark/light shift the conditional flu mutant of Arabidopsis starts to generate singlet oxygen ((1)O(2)), a non-radical reactive oxygen species that is restricted to the plastid compartment. Immediately after the shift, plants stop growing and develop necrotic lesions. We have established a protoplast system, which allows detection and characterization of the death response in flu induced by the release of (1)O(2). Vitamin B6 that quenches (1)O(2) in fungi was able to protect flu protoplasts from cell death. Blocking ethylene production was sufficient to partially inhibit the death reaction. Similarly, flu mutant seedlings expressing transgenic NahG were partially protected from the death provoked by the release of (1)O(2), indicating a requirement for salicylic acid (SA) in this process, whereas in cells depleted of both, ethylene and SA, the extent of cell death was reduced to the wild-type level. The flu mutant was also crossed with the jasmonic acid (JA)-depleted mutant opr3, and with the JA, OPDA and dinor OPDA (dnOPDA)-depleted dde2-2 mutant. Analysis of the resulting double mutants revealed that in contrast to the JA-induced suppression of H(2)O(2)/superoxide-dependent cell death reported earlier, JA promotes singlet oxygen-mediated cell death in flu, whereas other oxylipins such as OPDA and dnOPDA antagonize this death-inducing activity of JA.

Arabidopsis↗
PubMed1990

The hemolysis of erythrocytes by singlet oxygen generated in the gas phase.

Many sensitizers cause photodynamic hemolysis of erythrocytes. As these sensitizers usually participate in Type I as well as Type II processes, the determination of the mechanism(s) of photosensitized hemolysis is always ambiguous. Here, human erythrocytes were proved to hemolyze upon treatment with singlet oxygen (1 delta g) generated with fluoranthene in the gas phase. These conditions rigorously exclude the participation of superoxide anion. The standard diagnostic tests for singlet oxygen (enhanced effect in D2O and protection by NaN3) gave the anticipated results when the erythrocytes were treated with 1O2 generated in the gas phase. When the erythrocytes were irradiated in a buffer solution containing fluoranthene, the results of the diagnostic tests depended on the sensitizer concentration.

Hemolysis↗
PubMed1992

Photoacoustic detection of triplet state and singlet oxygen in highly absorbing samples.

A photoacoustic (PA) effect theory taking into account two heat sources corresponding to the radiationless relaxation processes of two states of different lifetimes and to the heat diffusion across the sample is herewith presented. Results obtained demonstrate that the amplitude and the phase of the PA signal depend on the sample's thermal properties, on its optical absorption coefficient, on the lifetime of the long-lived excited state, and on the ratio of the two heat sources. This ratio can be expressed as a function of the product of the energy of the excited state times the quantum yield of its production. Simulations of PA amplitude and phase variations vs light modulation frequency exhibit new features of the PA signal:phase inversion and fast decrease of the amplitude. Experimental verifications were carried out on solutions and gels. Fitting of the amplitude and phase variations allow us to measure the lifetime and conversion yield of the intermediate state which can be a triplet state or singlet oxygen, O2(1 delta g). The addition of an acceptor, specific to O2(1 delta g), induces changes in the amplitude of the PA signal which can be used to study the production and deactivation of this excited form of oxygen. This work demonstrates the usefulness of PA in the detection of metastable excited states such as the triplet state and singlet oxygen and in their quantitative analysis.

Coloring Agents↗
PubMed1992

Synthetic carotenoids, novel polyene polyketones and new capsorubin isomers as efficient quenchers of singlet molecular oxygen.

Novel synthetic polyene polyketones and new synthetic capsorubin isomers were examined for their ability to quench singlet molecular oxygen (1O2) generated by the thermodissociation of the endoperoxide of 3,3'-(1,4-naphthylene) dipropionate (NDPO2). C28-polyene-tetrone (1) exhibits the highest physical quenching rate constant with 1O2 (kq = 16 x 10(9) M-1 s-1). For comparison, the rate constant for the most efficient biological carotenoid, lycopene (3) is kq = 9 x 10(9) M-1 s-1 and that of beta-carotene (5) kq = 5 x 10(9) M-1 s-1. The presence of two oxalyl chromophores at the ends of the polyene chain seems to enhance the 1O2 quenching ability in the C28-polyene-tetrone (1). C28-polyene-tetrone-diacetal (2) (kq = 9 x 10(9) M-1 s-1) and C40-epiisocapsorubin (4) (kq = 8 x 10(9) M-1 s-1) also have high 1O2 quenching abilities. Two carotenoids from plants, phytoene and phytofluene, were much less efficient, kq values being below 10(7) M-1 s-1. Due to the very high singlet oxygen quenching abilities, C28-polyene-tetrone (1), C28-polyene-tetrone-diacetal (2) and C40-epiisocapsorubin (4) may have potential use in preventing 1O2-induced damage in biological and non-biological systems.

Carotenoids↗
PubMed1993

Hydrogen peroxide-dependent generation of singlet molecular oxygen by human saliva: its detection by chemiluminescence from a Cypridina luciferin analog.

By the addition of hydrogen peroxide to human saliva, chemiluminescence from Cypridina luciferin analog (CCLA) and oxygen evolution were observed. Chemiluminescence was inhibited by inhibitors of salivary peroxidase, azide and cyanide and by a singlet oxygen quencher, crocin. Deuterium oxide (99.75%) stimulated the initial increase of CCLA by 15-50% and the integrated CCLA 2.1-3.6-fold. The results suggest that the generation of singlet oxygen by peroxidase in human saliva depends on hydrogen peroxide.

Azides↗
PubMed1994

Reaction and quenching of singlet molecular oxygen with esters of polyunsaturated fatty acids.

The rate constants for the reactive (kR) and unreactive (kQ) interaction of singlet molecular oxygen with three esters of polyunsaturated fatty acids (PUFA: cis-methyl oleate, MO; cis-methyl linoleate, MLA and cis-ethyl linolenate, ELN) are determined. The values of the ratio kQ/kR are 0.51, 0.26 and 0.20 for MO, MLA and ELN, respectively. This variation results principally from that of kR because the values of kQ are only slightly different (1.24 x 10(4) M-1 s-1 for MO and approximately 1.0 x 10(4) M-1 s-1 for MLA and ELN). It is shown that the rate constant kQ characterizes mainly an interaction with the unreactive part of the molecule rather than with the double bonds (solventlike quenching). Contrary to the already reported case of 1,5-polyenes for which kQ << kR, the present results and those obtained from a number of literature data show that for PUFA and their esters, neither kR+kQ nor kR are proportional to the total number of double bonds or of methylene groups adjacent to the double bonds. Instead, a linear correlation is observed by plotting kR vs the number of methylene groups adjacent to two double bonds. It is deduced that contrary to a common assumption, biallylic hydrogens have a reactivity higher than that of singly allylic hydrogens (reactivity ratio 1.19). The consequence of this result on the estimation of relative contributions of singlet oxygen and radical mechanisms to oxidation processes is discussed. Moreover, the whole of these results allows prediction of the values of kR and kQ for all unsaturated fatty acids (and their esters) of similar structure.

Esters↗
PubMed1994

Doubly allylic hydroperoxide formed in the reaction between sterol 5,7-dienes and singlet oxygen.

Ergosterol and 7-dehydrocholesterol, common 5,7-conjugated diene sterols, react with photochemically produced singlet oxygen very efficiently to yield, in parallel pathways, the corresponding 5,8-endoperoxides and the 7 beta-hydroperoxy-5,8(9),22-trienol or -5,8(9)-dienol, respectively. The hydroperoxides decompose in an acid-catalyzed reaction to generate hydrogen peroxide and the 5,7,9(11),22-tetraenol or 5,7,9(11) trienol, respectively, with 1:1 stochiometry. The molar ratio of endoperoxide to hydroperoxide was constant (16:5) with two different reaction solvents, two different photosensitizers, and at all time points between 5 min and 3 h from the start of irradiation. Ergosterol did not react with either hydrogen peroxide or superoxide ion under our reaction conditions. Inhibition studies with nitrogen, 2,5-dimethylfuran, beta-carotene, and tert-butanol confirmed the involvement of singlet oxygen in these reactions. The unstable hydroperoxide would be expected to have undesirable biological consequences if formed in vivo.

Allyl Compounds↗
PubMed1995

Reactivity of singlet oxygen toward large peptides.

The reactions of singlet oxygen, 1O2, with amino acids and their derivatives have been studied previously. It was found that only five amino acid residues interact readily with 1O2. Here we describe its reactions with the large peptides melittin, neuropeptide Y (NPY) and insulin in their native and in their denatured forms. The singlet oxygen quenching by a polypeptide was compared with that of a solution at the same concentration as those of its constituent amino acids, which are known to react efficiently with 1O2. It was found that the quenching rate by such a mixture exceeded that of the polypeptides in their native form. The ratio of the rate constants for NPY to that of the corresponding amino acid mixture in solution was 0.75. For melittin in its monomeric form it was 0.83 and for a tetramer of melittin (at high ionic strength) it was 0.70. For native insulin the ratio of the rate constants was 0.55. For oxidized insulin with its -S-S- bridges opened the figure became 0.80. However, the quenching by all the polypeptides in their fully denatured form (in the presence of 6 M urea) equalled that of the corresponding amino acid mixtures. Although polypeptides are generally supposed not to possess a stable secondary structure in solution the effects are explained by shielding of some of the reactive amino acid residues in the chain by temporary folding or incipient secondary structures of the native polypeptide.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1997

Quantitation of the singlet oxygen produced by UVA irradiation of human lens proteins.

Ultraviolet irradiation of aged human lens proteins in vitro causes extensive photolytic damage of His and Trp residues. Protection by sodium azide argues for a process mediated by singlet oxygen (1O2). In the work described here, the synthesis of 1O2 was measured by the bleaching of N,N-dimethyl-4-nitrosoaniline (RNO), the oxidation of added histidine and the oxidation of furfuryl alcohol. To obtain a more accurate value for 1O2 generation, a known quantity of 1O2 was generated by the thermal dissociation of 3-(4-methyl-naphthyl)propionic acid endoperoxide, and the efficiency of each assay method to report on the 1O2 generated was determined. The values obtained were 0.003 mol of RNO bleached/mol of 1O2 generated, 0.55 mol of furfuryl alcohol oxidized/mol 1O2 and 0.5 mol of His oxidized/mol 1O2 generated. Irradiation of the human lens proteins with UVA light produced from 2.1 to 2.4 mM of 1O2 by RNO bleaching, 2.6-2.8 mM 1O2 by furfuryl alcohol oxidation and up to 1.9 mM of 1O2 by histidine oxidation during a 1 h irradiation period. The average value (2.2 mM of 1O2) corresponds to the theoretical production of 30 nmol of singlet oxygen at UVA light intensities equivalent to a 1 h exposure to sunlight at noon in the northern hemisphere.

Aged↗
PubMed2003

Phosphadioxirane: a peroxide from an ortho-substituted arylphosphine and singlet dioxygen.

We prepared the primary adduct for the reaction of singlet dioxygen (1O2) with an arylphosphine by using the sterically hindered arylphosphine tris(o-methoxyphenyl)phosphine. The resulting phosphadioxirane has a dioxygen molecule triangularly bound to the phosphorus atom. Olefin trapping experiments show that the phosphadioxirane can undergo nonradical oxygen atom-transfer reactions. Under protic conditions, two different intermediates are formed during the reaction of singlet dioxygen with tris(o-methoxyphenyl)phosphine, namely, the corresponding hydroperoxy arylphosphine and a hydroxy phosphorane. Experiments with other arylphosphines possessing different electronic and steric properties demonstrate that the relative stability of the tris(o-methoxyphenyl)phosphadioxirane is due to both steric and electronic effects.

Chemical Phenomena↗
PubMed2004

The genetic basis of singlet oxygen-induced stress responses of Arabidopsis thaliana.

Plants under oxidative stress suffer from damages that have been interpreted as unavoidable consequences of injuries inflicted upon plants by toxic levels of reactive oxygen species (ROS). However, this paradigm needs to be modified. Inactivation of a single gene, EXECUTER1, is sufficient to abrogate stress responses of Arabidopsis thaliana caused by the release of singlet oxygen: External conditions under which these stress responses are observed and the amounts of ROS that accumulate in plants exposed to these environmental conditions do not directly cause damages. Instead, seedling lethality and growth inhibition of mature plants result from genetic programs that are activated after the release of singlet oxygen has been perceived by the plant.

Amino Acid Sequence↗
PubMed1989

Singlet oxygen-induced arrhythmias. Dose- and light-response studies for photoactivation of rose bengal in the rat heart.

In a study of aerobically perfused rat hearts, the in situ photoactivation (530-590 nm) of rose bengal (a process that leads to the production of singlet oxygen and superoxide) has been shown to lead to the rapid development of electrocardiographic abnormalities and arrhythmias. With rose bengal concentrations of 1,000, 500, 250, 100, and 50 nmol/l (n = 6/group), photoactivation (3,600 lx) led to electrocardiographic changes (inversion of the T wave, Q-T prolongation, or both) after 3.8 +/- 0.9, 4.5 +/- 0.7, 11.8 +/- 2.1, 24.8 +/- 3.9, and 65.3 +/- 6.0 seconds), respectively; ventricular premature beats occurred in 100% of hearts after 0.5 +/- 0.2, 1.1 +/- 0.3, 2.2 +/- 0.7, 4.4 +/- 0.8, and 6.6 +/- 1.2 minutes, respectively. Ventricular tachycardia occurred in 83%, 83%, 83%, 67%, and 50% of hearts after 2.1 +/- 0.2, 2.1 +/- 0.4, 2.8 +/- 0.7, 5.7 +/- 2.0, and 11.2 +/- 1.9 minutes, respectively, and complete atrioventricular block in 100%, 100%, 100%, 100%, and 67% of hearts after 3.8 +/- 0.7, 6.5 +/- 1.0, 5.5 +/- 0.9, 13.8 +/- 1.0, and 14.1 +/- 0.9 minutes, respectively. With a fixed concentration (250 nmol/l) of rose bengal, similar light-response relations were observed. Photoactivation of rose bengal had no effect on heart rate but caused a transient (0-4 minutes) vasodilation followed by a progressive vasoconstriction. In further studies in which rose bengal was washed out for 10 minutes before photoactivation, several arrhythmias still developed, indicating that rose bengal binds strongly to tissue and acts as a cellular level rather than in the vascular compartment. To assess the reversibility of rose bengal-induced effects, hearts (n = 6/group) were perfused with rose bengal (250 nmol/l) for 1, 2, 4, 6, and 20 minutes followed by perfusion in the dark for 19, 18, 16, 14, and 0 minutes, respectively. During dark perfusion, the incidence of arrhythmias declined and any decrease in coronary flow was reversed. However, analysis of contents of adenosine triphosphate, creatine phosphate, lactate, and creatine kinase leakage indicated the occurrence of severe injury that did not abate on termination of photoactivation. Finally, although many arrhythmias developed before the onset of vasoconstriction, the reduction in flow with consequent ischemia was shown to exacerbate vulnerability to arrhythmias. In conclusion, short-lived reactive oxygen intermediates such as singlet oxygen and superoxide, which are produced during the photoactivation of rose bengal, can cause rapid and major damage to the heart and its function.

Animals↗
PubMed2007

Effects of edaravone on singlet oxygen released from activated human neutrophils.

The effects of edaravone, a curative agent for acute brain infarction, on singlet oxygen ((1)O2) released from activated human neutrophils were examined, and the effects were compared to those of histidine, a (1)O2 singlet oxygen scavenger. The neutrophils, stimulated with opsonized zymosan, released (1)O2 that was detected by chemiluminescence using a (1)O2 specific probe, trans-1-(2'-methoxyvinyl)pyrene. Edaravone dose-dependently suppressed the (1)O2 release with an IC(50) of approximately 0.3 microM, while the IC(50) of histidine was approximately 1 mM. This (1)O2 scavenging activity of edaravone might be involved in its curative effects on acute brain infarction.

Adult↗
PubMed2000

Green fluorescent protein photobleaching: a model for protein damage by endogenous and exogenous singlet oxygen.

Characterization of protein damage during photosensitization of chlorin e6-treated cells was performed using the green fluorescent protein (GFP). The GFP-chromophore damage caused by singlet oxygen was studied in COS 7 kidney cells and E. coli bacteria following light irradiation. Electron spin resonance (ESR) revealed the generation of endogenous singlet oxygen (1O2) by photoactivated GFP, an effect similar to that produced by the exogenous photosensitizer chlorin e6. A light dose-dependent photobleaching effect of GFP was pronounced at low pH or upon photosensitization with chlorin e6. However, the 1O2 quenchers beta-carotene and sodium azide minimized GFP photo-bleaching. Gel electrophoresis of photosensitized GFP followed by fluorescence multi-pixel spectral imaging revealed the binding of chlorin e6 to GFP, affecting the photobleaching efficacy. Fluorescence multi-pixel spectral imaging of GFP-transfected COS 7 cells demonstrated the presence of GFP in the cytoplasm and nucleus, while chlorin e6 was found to be concentrated in the perinuclear vesicles. Exposure of the cells to light induced GFP photobleaching in the close vicinity of chlorin e6 vesicles. We conclude that photoactivated GFP generates endogenous 1O2, inducing chromophore damage, which can be enhanced by the cooperation of exogenous chlorin e6.

Animals↗
PubMedDate not supplied

Photosensitized effects of furocoumarins: the possible role of singlet oxygen.

The capacity of various furocoumarins to generate singlet oxygen in aqueous solution has been determined. The antiproliferative and the skin-photosensitizing activities of the same furocoumarins did not show any correlation with the capacity to generate the singlet oxygen, while these photobiological properties could be correlated with the capacity of furocoumarins to induce photolesions to the DNA.

Animals↗
PubMed2003

Tuning the singlet oxygen quantum yield of near-IR-absorbing porphyrazines.

We report the quantum yields for singlet oxygen production by a series of porphyrazines (pz) of the form M[pz(An;B4-n)] (Scheme 1), where the peripheral substituent A is [S-R]2 with R = (CH2CH2O)3H, B is a fused alpha,alpha'-dialkoxybenzo group and M = 2H, Mg or Zn. These compounds show intense near-IR absorbance/emission (longest wavelength emission, approximately 830 nm). Their solubilities vary with R, whereas their optical properties do not. We show that singlet oxygen sensitization by these luminescent compounds can be "tuned" from essentially off to on by varying n and selection among M = 2H, Mg or Zn. The quantum yields vary ca 60-fold within the set of compounds studied, from phidelta = 0.007 for compound 3 to phidelta = approximately 0.4 for compound 11.

Infrared Rays↗
PubMedDate not supplied

Energy dissipation processes of singlet-excited 1-hydroxyfluorenone and its hydrogen-bonded complex with N-methylimidazole.

Effects of solvent, pH and hydrogen bonding with N-methylimidazole (MIm) on the photophysical properties of 1-hydroxyfluorenone (1HOF) have been studied. Fluorescence lifetime, fluorescence quantum yield and triplet yield measurements demonstrated that intersystem crossing was the dominant process in apolar media and its rate constant significantly diminished with increasing solvent polarity. The acceleration of internal conversion in alcohols paralleled the strength of intermolecular hydrogen bonding. The faster energy dissipation from the singlet-excited state in cyclohexane was attributed to intramolecular hydrogen bonding. The pK(a) of 1HOF decreased from 10.06 to 5.0 on light absorption, and H(3)O(+) quenched the singlet-excited molecules in a practically diffusion-controlled reaction. On addition of MIm in toluene, dual fluorescence was observed, which was attributed to reversible formation of excited hydrogen-bonded ion pair. Rate constants for the various deactivation pathways were derived from the combined analysis of the steady-state and the time-resolved fluorescence results.

Fluorenes↗