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At least 829 records · Page 46Linked to original sources
PubMed1994

Filtering methods for selection of singlet and doublet signals in NMR spectra of DNA oligomers.

The base proton (purine H8 and pyrimidine H6) resonances are key signals for the assignment of the proton resonances of DNA oligomers. They are classified into two groups, i.e., cytosine H6 signals, observed as doublets, and the other base proton signals, observed as singlets. Here we propose some experiments for distinguishing the cytosine H6 signals from the other base proton signals. Moreover, the ability of signal selection and the sensitivity as to signal detection were compared for all experiments, and the optimum conditions for spectral measurements were surveyed. Some of the experiments were employed as the NOESY detection pulse. Previously proposed experiments, such as HOENOE and HAL, were also used in the comparison.

Cytosine↗
PubMed1992

Lidocaine: a hydroxyl radical scavenger and singlet oxygen quencher.

Lidocaine, a local anaesthetic, has been shown to reduce ventricular arrhythmias associated with myocardial infarction and ischemic myocardial injury and its protective effects has been attributed to its membrane stabilizing properties. Since oxygen radicals are known to be produced during ischemia induced tissue damage, we have investigated the possible antioxidant properties of lidocaine and found that lidocaine does not scavenge O2-. radicals at 1 to 20 mM concentrations. However, lidocaine was found to be a potent scavenger of hydroxyl radicals and singlet oxygen. Hydroxyl radicals were produced in a Fenton type reaction and detected as DMPO-OH adducts by electron paramagnetic resonance spectroscopic techniques. Lidocaine inhibited DMPO-OH adduct formation in a dose dependent manner. The amount of lidocaine needed to cause 50% inhibition of that rate was found to be approximately 80 microM and at 300 microM concentration it virtually eliminated the DMPO-OH adduct formation. The production of OH.-dependent TBA reactive products of deoxyribose was also inhibited by lidocaine in a dose dependent manner. Lidocaine was also found to inhibit the 1O2-dependent 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO) formation in a dose dependent manner. 1O2 was produced in a photosensitizing system using Rose Bengal or Methylene Blue as photosensitizers and was detected as TEMP-1O2 adduct by EPR spectroscopy. The amount of lidocaine required to cause 50% inhibition of TEMP-1O2 adduct formation was found to be 500 microM. These results suggest that the protective effect of lidocaine on myocardial injury may, in part, be due to its reactive oxygen scavenging properties.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclic N-Oxides↗
PubMed1977

Retinal damage by light: possible implication of singlet oxygen.

A new hypothesis is proposed in an attempt to explain the mechanism of the irreversible damage which can be induced in the retina by visible light. Upon illumination, retinal generates singlet oxygen and this reactive species can produce lipid peroxidation which in turn may induce membrane instability.

Light↗
PubMed1983

Lack of singlet oxygen formation by photoexcited promazine derivatives in aqueous and ethanolic solutions.

The EPR detection of nitroxide formation and the observation by thin layer chromatography of the specific 1O2 oxidation product of cholesterol, have been used to appreciate singlet oxygen production by promazine and four of its derivatives during irradiation with near-UV light of ethanolic and aqueous solutions. Within the range of sensitivity of the methods, no 1O2 had been detected.

Acepromazine↗
PubMed1993

Degradation of methyl and ethyl mercury by singlet oxygen generated from sea water exposed to sunlight or ultraviolet light.

Photodegradation of methyl mercury (MeHg) and ethyl Hg (EtHg) in sea water was studied by sunlight or ultraviolet (UV) light exposure, and by determining inorganic Hg produced by degradation. Sea water containing 1 microM MeHg or EtHg was exposed to sunlight or UV light. N-Acetyl-L-cysteine was added to the solution for preventing Hg loss during the light exposure. MeHg and EtHg in sea water were degraded by sunlight (> 280 nm), UV light A (320-400 nm) and UV light B (280-320 nm), though the amounts of inorganic Hg produced from MeHg were 1/6th to 1/12th those from EtHg. Inorganic Hg production was greater with increasing concentration of sea water. Degradation of MeHg and EtHg by the UV light A exposure was inhibited by singlet oxygen (1O2) trappers such as NaN3, 1,4-diazabicyclo[2,2,2]octane, histidine, methionine and 2,5-dimethylfuran. On the other hand, inhibitors or scavengers of superoxide anion, hydrogen peroxide or hydroxyl radical did not inhibit the photodegradation of alkyl Hg. These results suggested that 1O2 generated from sea water exposed to sunlight, UV light A or UV light B was the reactive oxygen species mainly responsible for the degradation of MeHg and EtHg.

Ethylmercury Compounds↗
PubMed1977

ESR and optical absorption evidence for free radical involvement in the photosensitizing action of furocoumarin derivatives and for their singlet oxygen production.

Frozen aqueous solutions of thymine and its derivatives were irradiated with visible light (lambda greater than 320 nm) in the presence of various furocoumarins. ESR analysis revealed the induction of hydrogen adduct free radicals at C-6 position of thymine, only with those furocoumarin derivatives which show a skin-photosensitizing ability. It has been shown, moreover, that the photocycloaddition of psoralen to thymine, which is responsible for the biological effects of this dye, is inhibited when the induction of free radicals in thymine moiety has been prevented by electron scavengers. It is suggested that the free radicals observed could be involved in the biological photosensitization. The mechanism of free radical generation and singlet oxygen production by furoccoumarins were also investigated.

Coumarins↗
PubMed1983

Production of singlet oxygen and superoxide radicals by psoralens and their biological significance.

We have investigated a series of linear and angular furocoumarins, capable of forming either the monofunctional adducts (single strand) or bifunctional adducts (interstrand cross-links) with DNA with a view to examine the relationship of their skin photosensitizing potency, their ability to produce singlet oxygen (1O2) or superoxide radicals (O-.2 or HO.2), and their carcinogenic activity. The significance of photochemical interactions of psoralens and DNA is well known in skin photosensitization and skin carcinogenesis. Our data suggest that both monofunctional and bifunctional psoralens produce 1O2 and O-.2, and these reactive forms of oxygen may contribute to the development of skin cancer and membrane-damaging effects of these furocoumarins.

Cross-Linking Reagents↗
PubMed1989

ESR evidence for superoxide, hydroxyl radicals and singlet oxygen produced from hydrogen peroxide and nickel(II) complex of glycylglycyl-L-histidine.

ESR studies using spin traps, 5,5-dimethylpyrroline-N-oxide and alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone, revealed that hydroxyl radical adducts are produced by the decomposition of hydrogen peroxide in the presence of nickel(II) oligopeptides. Order of catalytic activities of nickel(II) oligopeptides used in the production of hydroxyl radical adducts was tetraglycine greater than pentaglycine greater than triglycine greater than GlyGly, GlyHis. Ni(II) GlyGlyHis plus hydrogen peroxide produced superoxide in addition to hydroxyl radical adduct. Trapping experiments with 2,2,6,6-tetramethyl-4-piperidone suggested that singlet oxygen was generated by the reaction of hydrogen peroxide with Ni(II) GlyGlyHis, but not in the case of tetraglycine, pentaglycine, triglycine, GlyGly or GlyHis.

Catalysis↗
PubMed1980

The induction of benzo[a]pyrene-3-mono-oxygenase by singlet oxygen in liver cell culture is mediated by oxidation products of histidine.

The photochemical generation of excited states of oxygen by the mild illumination of culture medium containing 15 microM riboflavin results in a typical induction of benzo[a]pyrene-3-mono-oxygenase in cell lines derived from liver. However, the induction of the mono-oxygenase is not due to an excited state of oxygen directly activating the inducing mechanism inside the cell but is due to the oxidation of a component of the culture medium forming a stable inducer. The present work unequivocably shows that the component oxidised is histidine. The mild illumination of culture medium containing riboflavin therefore converts a physiological component of the medium which is not normally an inducer of the mono-oxygenase into a compound which is as effective an inducer as the classical inducer. The finding that singlet oxygen will oxidise a cell constituent into a powerful inducer is compatible with the hypothesis that excited states of oxygen and their oxidation products may play a central role in the induction of cytochrome P-450 and associated enzyme activities by many chemically unrelated inducers.

Amino Acids↗
PubMed1990

Singlet oxygen and myocardial injury: ultrastructural, cytochemical and electrocardiographic consequences of photoactivation of rose bengal.

Photoactivation of rose bengal leads to the generation of reactive oxygen intermediates (predominantly singlet oxygen with some superoxide anion) which are potentially injurious to biological systems. Isolated rat hearts were perfused aerobically at 37 degrees C with bicarbonate buffer for 10 min without rose bengal and for 10 min with rose bengal (500 nM). During the last 5 min of perfusion with rose bengal, hearts were globally illuminated (5500 lux) with light (530 to 590 nm) and electrocardiographic changes were detected within 2.7 +/- 0.3 s (approximately 15 beats) of the onset of illumination. All hearts developed ventricular premature beats, ventricular tachycardia and complete atrioventricular block after 20.2 +/- 6.6, 68.0 +/- 29.7 and 184.3 +/- 20.9 s, respectively. Photoactivation by rose bengal also resulted in severe ultrastructural damage including intracellular clarifications, swelling of mitochondria with disruption and clumping of cristae and the development of contraction band necrosis. Extensive degranulation of mast cells was also observed. These changes were most evident in myocytes adjacent to large epicardial blood vessels. Cytochemical studies demonstrated that there was a loss of the calcium which is normally localized at the inner sarcolemmal surface, and the appearance of intramitochondrial calcium precipitates. In control hearts (no illumination and/or no rose bengal), arrhythmias did not develop and tissue morphology and calcium distribution remained normal. In additional studies, rose bengal-perfused hearts were illuminated regionally for 10 min over an area (approximately 6 mm2) of the left ventricle. Extensive tissue injury and calcium overload developed in the area of maximum illumination.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1981

On the involvement of singlet oxygen in mutation induction by 8-methoxypsoralen and UVA irradiation in Escherichia coli K-12.

The possible mutagenic effects induced by single oxygen, which is formed during UVA irradiation of bacterial cells pretreated with 8-methoxypsoralen (8-MOP), were investigated. As genetic endpoint, black mutation from arg-56 to arg+ was assayed in strain Escherichia coli K-12/343/113/uvrB; this system, in preliminary experiments, was rather sensitive to 8-MOP-induced photodynamic effects. To assess the involvement of singlet oxygen (1O2) in the mutation induction process, 2 tests were applied, namely, comparative mutation induction in D2O and H2O media (pH 7.0) and quenching of 1O2 with 1,4-diazabicyclo[2.2.2]octane (DABCO). When photodynamy was performed with the indicator cells suspended in D2O buffer, the mutagenic effect was substantially higher than that obtained with cells suspended in H2O buffer; this increase was even more pronounced when the incubation mixtures were thoroughly oxygenated before irradiation. D2O itself was not mutagenic under th present experimental conditions. Addition of DABCO in concentrations of 0.1--10 mM to the irradiation mixtures effectively reduced the number of 8-MOP-induced mutant yields by about 40%. DABCO itself had no effect on cell viability or on spontaneous mutation frequency under our experimental conditions. From these 2 sets of results, and from the preliminary findings that the photomutagenic effect of 8-MOP is higher in the uvrB derivative than in the corresponding excision-repair-proficient parent strain, which is in concordance with previous observations in other E coli strains, it can be concluded that 1O2 generated upon UVA irradiation of 8-MOP solutions is probably responsible for part of the observed genetic effects.

DNA Repair↗
PubMed1991

Characteristics of mutagenesis by glyoxal in Salmonella typhimurium: contribution of singlet oxygen.

The characteristics of mutagenesis by glyoxal in Salmonella tester strains TA100 and TA104, and particularly a possible role of active oxygen species, were investigated. Glyoxal was converted into a non-mutagenic chemical with glutathione (GSH) by glyoxalase I, and the mutagenic activity was enhanced by the depletion of intracellular GSH. Glyoxal caused the reduction of nitro blue tetrazolium, which was suppressed by the addition of 2,5-diphenylfuran, superoxide dismutase (SOD) and catalase (CAT), scavengers of singlet oxygen (1O2), superoxide radical (O2-) and hydrogen peroxide (H2O2), respectively. However, only the 1O2 scavenger almost completely suppressed the mutagenic activity of glyoxal. Mutagenicity assays using strains pretreated with N,N-diethyldithiocarbamate of a SOD inhibitor and strains with low levels of SOD and CAT indicated that the mutagenesis by glyoxal was independent of intracellular levels of SOD and CAT, though glyoxal itself repressed them. Therefore, all the results suggest that 1O2 formed from glyoxal is related to its mutagenesis, but that neither O2- nor H2O2 is intracellularly predominantly related to it. The action of glyoxal against SOD and CAT, and the formation of glyoxal adducts with amino acids as their components are also discussed.

Amino Acids↗
PubMed1991

Singlet oxygen induced single-strand breaks in plasmid pBR322 DNA: the enhancing effect of thiols.

The biologically occurring thiols, glutathione, cysteamine and cysteine, significantly enhance the single-strand breaks in plasmid pBR322 DNA induced by singlet molecular oxygen (1O2) generated by the thermodissociation of the endoperoxide of 3,3'-(1,4-naphthylidene)dipropionate. The enhancing effect was also observed with chemically related sulfhydryl compounds but not by disulfides. In contrast, dihydrolipoate and its disulfide lipoate protected the plasmid DNA. Metal chelators as well as superoxide dismutase or catalase had no effect, whereas mannitol or sodium azide, decreased the thiol-1O2-induced strand breaks. It is concluded that the observed effects are mediated by reactive oxidation products arising from the 1O2-oxidation of thiols.

Chelating Agents↗
PubMed1980

Activation of polycyclic aromatic hydrocarbons to mutagens by singlet oxygen: an enhancing effect of atmospheric pollutants?

Chrysene and 3-methylcholanthrene are transformed to direct-acting mutagens by photodynamically generated singlet oxygen. In view of the presence of this species of oxygen in the polluted atmosphere, the possible conversion of environmental polycyclic aromatic hydrocarbons to mutagens and to potential direct-acting ('ultimate') carcinogens deserves consideration.

Carcinogens, Environmental↗
PubMed1987

Singlet oxygen intermediacy in the photodynamic action of membrane-bound hematoporphyrin derivative.

The cell-damaging photochemistry of hematoporphyrin derivative (HPD) has been investigated using isolated erythrocyte membranes as a test system. Irradiation of membranes in the presence of the tumor-localizing fraction of HPD resulted in formation of singlet molecular oxygen (1O2) as measured by the phosphorescence at 1268 nm. The authentic product of 1O2 attack on cholesterol, 3 beta-hydroxy-5 alpha-cholest-6-ene-5-hydroperoxide, was identified in this system. Relatively insignificant amounts of free radical-derived hydroperoxides were detected. These results suggest that 1O2 plays a major role in the HPD-sensitized photokilling of tumor cells in vivo.

Cholesterol↗
PubMed1978

Chemically shifted singlet oxygen spectrum.

The estimated light emission spectrum was determined for a singlet oxygen (1O2)-producing system, NaOCl + H2O2, alone and in the presence of tryptophan and bovine serum albumin. Tryptophan and bovine serum albumin caused a decrease in the red emission of 1O2 and an increase in the amount of shorter wavelength light. This effect was due to chemiluminescence rather than fluorescence. Arachidonic acid caused a similar spectral shift, while guanosine demonstrated a late chemiluminescent reaction of predominantly short wavelength light in the presence of 1O2.

Hydrogen Peroxide↗