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PubMed1991

Singlet oxygen production from the reactions of ozone with biological molecules.

The reaction of ozone with a number of biological molecules was found to produce singlet oxygen in high yield. At pH 7.0, the reaction of ozone with an equimolar amount of biological molecule produced the following singlet oxygen yields (mole of singlet oxygen/mole of ozone): cysteine, 0.49 +/- 0.02; methionine, 1.13 +/- 0.11; reduced glutathione, 0.33 +/- 0.02; albumin, 1.00 +/- 0.05; uric acid, 0.64 +/- 0.09; ascorbic acid, 0.96 +/- 0.007; NADPH, 1.07 +/- 0.07; NADH, 0.95 +/- 0.01. Thus, singlet oxygen may be an important intermediate in the biochemical damage caused by ozone.

Antioxidants↗
PubMed1982

Human red blood cell membrane oxidase and horseradish peroxidase cleavage of folic acid: evidence for formation of singlet oxygen.

1. Human red blood cell membrane oxidase catalyzes the transformation of folic acid to pterin-6-aldehyde and p-aminobenzoyl glutamic acid provided hydrogen peroxide, a xanthine oxidase inhibitor, is present. Horseradish peroxidase produces the same product in the absence of hydrogen peroxide. 2. The oxidation of folic acid by horseradish peroxidase is accompanied by photon emission. Several lines of evidence suggest that singlet oxygen is the emitting species and is generated directly: a) the effects of singlet oxygen traps such as bilirubin, and of singlet oxygen enhancers such as 1,4-diazobicyclo 2.2.2 octane (DABCO) and eosin; b) the emission spectrum maximum of the unsensitized reaction was greater than 560 nm; c) enhancement of photon emission when the reaction was carried out in D2O, and d) no enhancement of the emission was observed when anthracenic energy acceptors were present. 3. Singlet oxygen production and the inactivation of xanthine oxidase may be important when considering folic acid metabolism by cancer cells, in view of the fact that the level of this enzyme is low in these cells.

Animals↗
PubMed1996

Formation of singlet oxygen in the thermal decomposition of 3-hydroxymethyl-3,4,4-trimethyl-1,2-dioxetane, a chemical source of triplet-excited ketones.

Triplet-excited carbonyl species can be generated by photoexcitation of carbonyl compounds or alternatively by thermal decomposition of 1,2-dioxetanes. Such electronically excited species are involved in the oxidative modification of biologically important molecules such as DNA. This study demonstrates that thermal decomposition of 3-hydroxymethyl-3,4,4-trimethyl-1,2-dioxetane (HTMD), which is a chemical source of triplet-excited ketones, is accompanied by infrared photoemission at 1270 nm characteristic for singlet oxygen monomol emission. The intensity of infrared photoemission at 1270 nm was solvent-dependent, in agreement with the reported lifetime of singlet oxygen in the employed solvents. Calibration of monomol emission with the endoperoxide of 1,4-dimethylnaphthalene (DMNO2) showed that HTMD (30 mM) produced 25 microMs of singlet oxygen. Thus, the yield of singlet oxygen production in the thermal decomposition of HTMD in carbon tetrachloride is about 0.1%.

Heating↗
PubMed1989

Near infrared emission of singlet oxygen generated in the dark.

Singlet oxygen generation is reported from (1) enzymatic reaction and (2) electron transfer reactions of the superoxide anion measured directly with an ultrasensitive near-IR emission spectrophotometer by monitoring the O2(1 delta g)----O2 (3 sigma g-) transition at 1268 nm. Near-IR emission spectra from the myeloperoxidase and lactoperoxidase enzymatic systems show only emission of singlet oxygen at 1268 nm. The lipoxygenase/Na-linoleate enzymatic reaction exhibits two emissions, 1268 nm and 1288 nm. The latter emission is identified as originating from a peroxy radical. Spectral and kinetic data giving evidence of singlet oxygen generation is obtained from the reaction of potassium superoxide solubilized by 18-crown-6-ether in acetonitrile with a series of organometallic coordination compounds.

Chloride Peroxidase↗
PubMed1999

Compounds capable of generating singlet oxygen represent a source of artifactual data in scintillation proximity assays measuring phosphopeptide binding to SH2 domains.

We developed scintillation proximity assays (SPA) to discover compounds which inhibit phosphopeptide binding to Src homology 2 (SH2) domain proteins Grb2 and Syk. An assay artifact is reported here as a caveat to others. The SPA used an antibody to couple glutathione-S-transferase SH2 domain fusion proteins to scintillant beads coated with protein A. A pyrazoloquinolone and indolocarbazole inhibited [3H]phosphopeptide binding in both assays. Their potency in the SPA increased with prolonged (2 to 24 h) assay exposure to ambient light. They were inactive in absence of light and in an alternate binding assay. Both compounds absorbed visible light and generated singlet oxygen based on 2-methylfuran-trapping experiments. Their inhibitory activity was suppressed by the singlet oxygen scavengers sodium azide and dithiothreitol. The results suggest that compounds, not previously considered photosensitizers, generated enough singlet oxygen to damage oxidant-sensitive SPA components. Therefore, this SPA should be protected from light to minimize occurrence of false positives.

Adaptor Proteins, Signal Transducing↗
PubMed1994

Hunt for singlet oxygen under in vivo conditions.

It is widely accepted that applying exogenous photosensitizers in living organism the photodynamic effect is mediated by singlet oxygen formed by energy transfer from excited sensitizer to oxygen present in the cells (Type II mechanism). Though in homogeneous solutions singlet oxygen was detected during sensitization, efforts to observe it in vivo failed, so far. Kinetic considerations based on the assumption that triplet sensitizer molecules interact with (doublet) free radicals accumulated in the tissue as well as on literature data indicate that the steady state concentration of singlet oxygen can decrease by more than one order of magnitude at transition from homogeneous systems to in vivo conditions making it undetectable.

Kinetics↗
PubMed2000

Hypotaurine protection on cell damage by singlet oxygen.

Singlet oxygen (1O2), generated by irradiating methylene blue, is toxic to melanoma cell cultures. Hypotaurine is known to scavenge efficiently singlet oxygen; the addition of hypotaurine (800 microM) to the medium during irradiation of the dye produces a greater protective effect on cells than taurine added at the same concentration. The assay of some detoxifying enzymatic activities indicate a different mechanism of protection of the two molecules: taurine induces an efficient detoxifying enzymatic action with respect to the control; hypotaurine exerts its effect greatly by specifically scavenging singlet oxygen.

Antioxidants↗
PubMed2006

Synthesis and characterization of new fluorene-based singlet oxygen sensitizers.

The synthesis, photophysical characterization, and determination of singlet oxygen quantum yields (Phi(Delta)) for a class of fluorene derivatives with potential application in two-photon photodynamic therapy (PDT) is reported. It has been demonstrated that these compounds possess the ability to generate singlet oxygen (1O2) upon excitation. A photochemical method, using 1,3-diphenylisobenzofuran (DPBF) as 1O2 chemical quencher, was employed to determine the singlet oxygen quantum yields (Phi(Delta)) of the fluorene-based photosensitizers in ethanol. Phi(Delta) values ranged from 0.35 to 0.75. These derivatives may have potential application as two-photon photosensitizers when pumped via two-photon excitation in the near-IR spectral region.

Benzofurans↗
PubMed1992

Photodynamic effects of chloroaluminum phthalocyanine tetrasulfonate are mediated by singlet oxygen: in vivo and in vitro studies utilizing hepatic microsomes as a model membrane source.

Chloroaluminum phthalocyanine tetrasulfonate (AlPcTS) is a promising photosensitizer for the photodynamic therapy (PDT) of cancer. In this study, we investigated the in vivo and in vitro photodestruction of hepatic microsomal membranes by AlPcTS and studied the role of reactive oxygen species in this process. Irradiation of hepatic microsomes prepared from AlPcTS-pretreated SENCAR mice to approximately 675 nm light resulted in rapid destruction of cytochrome P450 and associated monooxygenase activities, and enhancement of lipid peroxidation in a light-dose-dependent manner. The specificity of AlPcTS and light dependency on photodestruction of microsomal membranes was confirmed by Western blot analysis. Similar results were obtained when AlPcTS was added in vitro to a suspension of hepatic microsomes prepared from control animals followed by irradiation to approximately 675 nm light. Among the quenchers of singlet oxygen, superoxide anion, hydrogen peroxide, and hydroxyl radical, only the quenchers of singlet oxygen such as sodium azide, histidine, and 2,5-dimethyl furan afforded substantial protection in a dose-dependent manner against AlPcTS-mediated photodestruction of cytochrome P450 and associated monooxygenase activities, and photoenhancement of lipid peroxidation under both in vivo and in vitro conditions. These results suggest that lipid-rich microsomal membranes may be the potential targets of cell injury by AlPcTS-based PDT and that this process is mediated by singlet oxygen.

Animals↗
PubMed1987

Water induced dismutation of superoxide anion generates singlet molecular oxygen.

Direct spectroscopic measurement of 1268 nm singlet oxygen emission from KO2 suspensions at room temperature in three non-protonic solvents--CCl4, Cl2FCCClF2, and C6F14 by the action of water is reported. The results clearly show that the singlet oxygen generation is due to a water induced reaction, and suggest that one role of the enzyme superoxide dismutase may be the protection of biological structures, for example, lipid membranes, from degradation by singlet oxygen.

Carbon Tetrachloride↗
PubMed1989

Singlet oxygen production from the peroxidase catalyzed formation of styrene glutathione adducts.

Recently, Stock et al. (J. Biol. Chem. 261, 15915-15922 [1986]) described a model enzyme system composed of horseradish peroxidase, hydrogen peroxide, phenol, glutathione and styrene. This system forms glutathione-styrene conjugates. Glutathione radicals and carbon-centered radicals are intermediates in this process. In the present study, this model enzyme system was also shown to generate singlet oxygen, probably via a Russell mechanism. No singlet oxygen was generated in the absence of styrene. Thus, contrary to prior suggestions, the reaction of glutathione radical with oxygen to produce a thiyl peroxyl radical is not a significant source of singlet oxygen.

Glutathione↗
PubMedDate not supplied

Cytotoxic and genotoxic effects of extracellular generated singlet oxygen in human lymphocytes in vitro.

The induction of sister-chromatid exchanges (SCE) together with the proliferation rate index (PRI) were studied in human lymphocytes in vitro after treatment with singlet oxygen. When produced outside the cells, singlet oxygen can increase the duration of the cellular cycle as measured by an enhancement of the differences between the proliferation rate indexes of the control and the treated cells. A dose-dependent increase in the SCE rate per chromosome was also detected after contact between the singlet oxygen and lymphocytes.

Cells, Cultured↗
PubMed1992

Biological inactivation by singlet oxygen: distinguishing O2(1 delta g) and O2(1 sigma g+)

Experiments were performed to determine whether bacterial inactivation in the separated-surface-sensitizer system for singlet oxygen generation is due to O2(1 delta g) or O2(1 sigma g+). The rates of inactivation of Gram-negative Salmonella typhimurium LT-2 and a nonpigmented strain of Gram-positive Sarcina lutea were found to increase linearly with the concentration of 1 delta g. The gas phase lifetime of the inactivating agent was found to be within the range of values expected for the gas phase lifetime of 1 delta g rather than 1 sigma g+. These measurements conclusively demonstrate that bacterial inactivation in this system is due predominantly to 1 delta g. Therefore, studies of bacterial inactivation with this singlet oxygen generating system can be used to assess the role of singlet oxygen in various biological and medically relevant situations.

Acetonitriles↗
PubMed1996

Sod and catalase inactivation by singlet oxygen and peroxyl radicals.

Both superoxide dismutase and catalase are readily deactivated by singlet oxygen and by the radicals produced in the pyrolysis of 2,2'-azo-bis-(2-amidinpropano) under aerobic conditions. The rate constant for the loss of enzymatic activity induced by singlet oxygen are 3.9 x 10(7) and 2.5 x 10(7) M-1 sec-1 for SOD and catalase, respectively. The similarity between these values implies that in systems where SOD and catalase are exposed to similar singlet oxygen concentrations, it can be expected a parallel inactivation of both enzymes. The inactivation of both enzymes by the radicals produced by 2,2'-azo-bis-(2-amidinopropane) pyrolysis under aerobic conditions follows a first-order kinetics at low enzyme concentrations and a zero-order kinetics at higher concentrations. Although at low enzymatic concentrations the rate of inactivation of both enzymes is similar, this results from a compensation of effects because there are wide differences in the reactivity of both enzymes towards peroxyalkyl radicals. Catalase is considerably more reactive, but a large number of protein/radical reactive interactions are needed to inactivate one enzyme. On the other hand, the reactivity of SOD is smaller, but the average enzyme activity decreases by nearly 20% in each SOD/radical reactive interaction.

Animals↗
PubMed2005

Specific inactivation of cysteine protease-type cathepsin by singlet oxygen generated from naphthalene endoperoxides.

Singlet oxygen is a causal factor in light-induced skin photoaging and the cytotoxic process of tumor cells in photodynamic chemotherapy. To develop a better understanding of the functional consequences of protein modification by singlet oxygen, the effects of naphthalene endoperoxide on lysosomal protease, cathepsin, were examined. When the soluble fraction of normal human fetal skin fibroblast cells was treated with the endoperoxide, the activities of cysteine proteases, cathepsins B and L/S, were inhibited, but that of aspartate protease, cathepsin D/E, was not. The reduction of the endoperoxide-treated soluble fractions by treatment with dithiothreitol barely recovered the activities. Cathepsin B, purified from normal human liver, exhibited similar profiles to that in cytosol. These data suggest that singlet oxygen oxidatively modifies an amino acid residue essential for catalysis and consequently results in the irreversible inactivation of cysteine protease-type cathepsin.

Cathepsin B↗
PubMed1983

Role of singlet oxygen in the degradation of hyaluronic acid.

To investigate the effect of singlet oxygen on the molecular properties of hyaluronic acid, the polymer was irradiated in the presence of a dye sensitizer for singlet oxygen. Viscosity and circular dichroism techniques were used to monitor these changes. The relative viscosity of the polymer solution decreased steadily with increasing duration of irradiation, indicating an apparent decrease in molecular weight of hyaluronic acid. Circular dichroism measurements of the irradiated sample, however, did not show any appreciable change in the secondary structure, but do suggest that the generated singlet oxygen changes the tertiary structure and that this change is followed by a minor depolymerization.

Circular Dichroism↗
PubMed1983

L-ascorbic acid quenching of singlet delta molecular oxygen in aqueous media: generalized antioxidant property of vitamin C.

L-ascorbic acid quenches singlet (1 delta g) molecular oxygen in aqueous media (pH 6.8 for [1H]H2O and pD 7.2 for [2H]D2O) as measured directly by monitoring (0,0) 1 delta g leads to 3 sigma-g emission at 1.28 micron. Singlet oxygen was generated at room temperature in the solutions via photosensitization of sodium chrysene sulfonate; this sulfonated polycyclic hydrocarbon was synthesized to provide a water soluble chromophore inert to usual dye-ascorbate photobleaching. A marked isotope effect is found; kHQ2O is 3.3 times faster than kDQ2O, suggesting ascorbic acid is chemically quenching singlet oxygen.

Ascorbic Acid↗
PubMed1984

Myeloperoxidase singlet molecular oxygen generation detected by direct infrared electronic emission.

Myeloperoxidase in micromolar concentrations reacting with half-millimolar stock solution H2O2 in acetate buffer containing KBr and in 50% D2O (pH + pD = 4.5) at 298 K is shown to generate singlet delta molecular oxygen efficiently. The near infrared electronic emission of singlet oxygen at 1268 nm is detected directly by novel ultrasensitive IR spectrophotometer equipment. The quantum efficiency of singlet oxygen generation by the MPO X Br- X H2O2 reaction is shown to be comparable with that of the standard chemical reaction OCl- X H2O2 at identical peroxide concentrations.

Animals↗