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1.
SINGLET OXYGEN: A MAJOR REACTIVE SPECIES IN THE FUROCOUMARIN PHOTOSENSITIZED INACTIVATION OF E. COLI RIBOSOMES 总被引:5,自引:0,他引:5
Abstract— The skin photosensitizing furocoumarins, 8-methoxypsoralen (MOP) and 4,5',8-trimethylpsoralen (TMP), inactivate E. coli ribosomes in vitro , on UV irradiation at 313 nm. Purging the solutions with N2 protects the ribosomes considerably against photoinactivation (75% with MOP and 80% with TMP). In air, the ribosome photoinactivation is mainly due to singlet oxygen (1 O2 ), since the presence of NaN3 and other 1 O2 quenchers protects the system and the inactivation is enhanced in D2 O. Although 1 O2 dominates as the inactivating species, the possibility of additional (∼15%) minor mechanisms involving free radicals exists. However, O- 2 does not appear to be the damaging species, since superoxide dismutase does not provide any protection.
Photosensitization of the partially purified enzyme, phe-tRNA-synthetase with MOP or TMP shows inactivation and protection curves similar to those seen with the ribosomes. On the other hand, unfrac-tionated tRNAphc is not photosensitized under similar conditions, although it shows self-photosensitization. It is likely that in the furocoumarin-sensitized ribosomes, the primary events of photoinactivation are associated with the proteins. 相似文献
Photosensitization of the partially purified enzyme, phe-tRNA-synthetase with MOP or TMP shows inactivation and protection curves similar to those seen with the ribosomes. On the other hand, unfrac-tionated tRNA
2.
Abstract —In vivo participation of singlet excited oxygen (1 O2 , 1 Δ9) in the photodynamic inactivation and induction of genetic changes (gene conversion) in acridine orange-sensitized yeast cells was investigated by using N3 - , an efficient 1 O2 quencher, and D2 O, a known agent for the enhancement of the lifetime of 1 O2 . The addition of N3 - protected the cells from both photodynamic actions. From an analysis of the concentration-dependent protection, about 80% of the induction of the genetic change is explainable on the basis of 1 O2 mechanism. The quantitative estimation of the N3 - protection in the inactivation was not possible because of the sigmoidal nature of the inactivation curve. The replacement of H2 O with D2 O during illumination was effective in enhancing the photodynamic inactivation but almost completely ineffective for the gene conversion induction. The deuterium effect with the cell system was clearly not as large as would be expected from in vitro experiments. This, however, could be explained from the kinetic consideration that natural quenchers of l O2 in the cell would mask the deuterium effect. By experiments with different cell stages it was demonstrated that these two modifying effects were dependent on the intracellular reaction environment. The conclusion is that 1 O2 must be the major intermediate responsible for the photodynamic actions in acridine orangesensitized yeast cells. 相似文献
3.
LUMIFLAVIN-SENSITIZED PHOTOOXYGENATION OF INDOLE 总被引:1,自引:0,他引:1
Abstract— The lumiflavin-sensitized photooxygenation of indole in aqueous solutions has been investigated by means of steady light photolysis and flash photolysis. The semiquinone of lumiflavin and the half-oxidized radical of indole were formed by the reaction between triplet lumiflavin and indole (3.7 times 109 M -1 s-1 ). The semiquinone anion radical of lumiflavin reacted with oxygen to form superoxide radical. The triplet state of lumiflavin also reacted with oxygen forming singlet oxygen, 1 O2 . But the reaction between 1 O2 and indole (7 times 107 M_l s_1 ; estimated from steady light photolysis using Rose Bengal as a sensitizer) was far less efficient than the reaction between indole and triplet lumiflavin. The quantum yield of the lumiflavin-sensitized photooxygenation of dilute indole via radical processes was much higher than that via 1 O2 processes, though appreciable 1 O2 was formed. 相似文献
4.
N. J. de Mol G. M. J. Beijersbergen van Henegouwen B. Weeda C. N. Knox T. G. Truscott 《Photochemistry and photobiology》1986,44(6):747-756
The photobinding of radiolabeled psoralen and 8-methoxypsoralen (8-MOP) to biological macromolecules under conditions that affect the lifetime of singlet oxygen (1 O2 ) is reported. These conditions are: increase of 1 O2 lifetime in D2 O and 1 O2 quenching with DABCO. The photobinding to calf thymus DNA was studied in vitro and the covalent photobinding to DNA and other biological macromolecules (RNA, proteins) was also studied in intact bacteria. The results of the DNA photobinding experiments have been related to the induction of genetic damage in a bacterial test system. In addition, laser flash photolysis has been used to measure the effect of D2 O and DABCO on the psoralen and 8-MOP triplet lifetimes. In general D2 O increases the triplet lifetimes and DABCO quenches the triplet states with the probable formation of radicals. The results suggest that the covalent photobinding of 8-MOP to various biological macromolecules in situ is a basis for cell damage occurring at various cellular targets. Analysis of the results of the mutagenicity test suggests that in the presence of D2 O the mechanism of induction of genetic lesions is not changed and therefore largely seems to be independent of singlet oxygen. 相似文献
5.
Abstract— In view of the increasing attention to 1 O2 (1 Δg ) participation in the photodynamic action, different types of genetic changes in Saccharomyces cerevisiae by acridine orange sensitization were compared with respect to the response to N3 - , a well known quencher of 1 O2 . The induction of mitotic crossing over with respect to ade 2 locus and mitotic gene conversion at trp 5 locus were suppressed by the addition of N3 - suggesting the involvement of 1 O2 as a major intermediate. However, the induction of reverse mutation at ilv 1 was only slightly suppressed. These results may indicate that there are two types of photodynamic DNA damage; one is produced via 1 O2 and the other via non-1 O2 reaction pathway which lead to mitotic gene conversion and mitotic crossing over, and to mutation, respectively. 相似文献
6.
Abstract— A very efficient quenching of singlet oxygen (1 O2 ) by N3 - ions has been applied to the determination of rate constants of reactions of 1 O2 with various substrates (A). This determination has been made possible by choosing experimental conditions which give simple competition between N3 - and A for 1 O2 formed in the steady state irradiation of convenient sensitizing dye (S). The consumption of oxygen by the substrate, as followed with an oxygen analyzer, decreases in the presence of low concentrations of N3 - . Using neutral air saturated aqueous solutions containing the dye phenosafranine + A and varying concentrations of N3 - , the 1 O2 rate constants for reactions with biological substrates and some radiation protective agents have been determined. 相似文献
7.
Abstract— The production of free radicals by reaction of 2,2,6,6-tetramethyl-4-piperidinol with singlet oxygen was studied by EPR spectroscopy. The rate constant of the amine was found to be equal to 8 ×105 M -1 s-1 in ethanol and to 4 × 107 M-1 s-1 in phosphate buffer (pH 8). Competition experiments were performed with singlet oxygen quenchers such as NaN3 , DABCO and the quenching rate constants were found to be consistent with the literature values. The EPR method proved to be a valuable technique to study the reaction of singlet O2 with the sterically hindered amine without any interfering effect. 相似文献
8.
SINGLET OXYGEN FORMATION BY SENSITIZATION OF FUROCOUMARINS COMPLEXED WITH, OR BOUND COVALENTLY TO DNA 总被引:1,自引:0,他引:1
N. J. de Mol G. M. J. Beijersbergen van Henegouwen B. van Beele 《Photochemistry and photobiology》1981,34(6):661-666
Abstract— The formation of singlet molecular oxygen (1 O2 ) by sensitization of the furocoumarins 5-methoxypsoralen (5-MOP), 8-methoxypsoralen (8-MOP) and psoralen complexed with DNA was investigated. From the results it is concluded that 5-MOP complexed with native DNA is able to generate 1 O2 , even in a larger extent than 5-MOP free in solution. Also, with 8-MOP and especially with psoralen, 1 O2 formation by the complexed compound could be observed. The 1 O2 formation sensitized by covalently bound furocoumarin was demonstrated with psoralen as a model compound. 4',5'-Dihydropsoralen, a model compound for the UVA light absorbing 4',5'monoadducts of furocoumarins to DNA, is also able to generate 1 O2 . 相似文献
9.
STEADY-STATE NEAR-INFRARED DETECTION OF SINGLET MOLECULAR OXYGEN: A STERN-VOLMER QUENCHING EXPERIMENT WITH SODIUM AZIDE 总被引:2,自引:1,他引:2
Abstract— A sensitive near-infrared detection system incorporating improvements to existing methodologies has been used to characterize the sodium azide quenching of the steady-state luminescence of singlet molecular oxygen at 1270 nm. Stern-Volmer plots which were linear up to 80% quenching of the 1 O2 generated by rose bengal and eosin Y yielded a rate constant of 5.8 ± 0.1 times 108 M −1 s−1 for the quenching of 1 O2 in water, while the rate constants obtained in deuterium oxide with the same sensitizers were 6.28 times 108 M −1 s−1 and 6.91 times 108 M −1 s−1 respectively. A flow system minimized the effects of photobleaching of the rose bengal. With a mercury arc light source, the instrument can be used in photosensitization experiments to detect low levels of 1 O2 production in aqueous media. 相似文献
10.
Abstract— The autoxidation of the catecholamine neurotoxin 6-hydroxydopamine (20 μ M ) gave rise to a chemiluminescence which was greatly stimulated by FeSO4 (20 μ M ) or by hydrogen peroxide addition (20 μ M to 2 m M ). The luminescence of both 6-hydroxydopamine alone or 6-hydroxydopamine plus hydrogen peroxide was strongly inhibited by catalase and by superoxide dismutase (both at 10 μg/m/); bovine serum albumin at 10 μg/m/ had no inhibitory effect. The luminescence was also strongly inhibited by several potent hydroxyl radical trapping agents and also by low concentrations of the 1 O2 quencher DABCO (l,4-diazabicyclo-2.2.2.-octane). Chemiluminescence was greatly enhanced in D2 O, a solvent in which 1 O2 has a prolonged lifetime. These data demonstrate the involvement of hydrogen peroxide, the superoxide radical and the hydroxyl radical in the chemiluminescence. The data are also consistent with some role for 1 O2 . 相似文献
11.
Abstract— A novel method for the determination of singlet oxygen reaction rate constants is described and applied to studies of cyclohexadiene in methanol and gelatins in H2 O and D2 O. The technique uses tris (2,2'-bipyridine) ruthenium(II) dication (Ru(bipy)32+ ) as both singlet oxygen sensitizer and in situ oxygen concentration monitor during irradiation of sealed samples. Because of the high efficiency with which the luminescence of Ru(bipy)3 2+* can be detected, and the fact that emission lifetimes are used, the method offers some advantages over those previously described. The advantages and disadvantages of the method are discussed. A rate constant of 2.1 (±0.3) x 106 mol-1 dm3 s-1 has been determined for the reaction of 1 O2 with cyclohexadiene in methanol. For two different photographic gelatins the sums of reaction and quenching rate constants are 2.0 (±0.4) x 106 and 3.1 (±2.0) x 105 mol-1 dm3 s-1 ; for swine skin gelatin this value is 3.9 (±2.4) × 105 mol-1 dm3 s-1 . Chemical reaction, rather than physical quenching, is the dominant reaction route for gelatins and 1 O2 . 相似文献
12.
M. Delmelle 《Photochemistry and photobiology》1978,27(6):731-734
Abstract— All -trans retinal is dissolved in alcohols and illuminated at 365 nm in the presence of a singlet oxygen acceptor, 2,5-dimethylfuran. Illumination produces the photosensitized oxidation of the acceptor which is measured by the disappearance of its 215 nm absorption band. A kinetic study is carried out and βDMF is 1.6 × 10- -4 M . The quantum yield of 1 O2 production from the light-excited retinal is estimated to 0.096. The retinal sensitized photooxidation of dimethylfuran is inhibited by a 1 O2 quencher, 1,4-diazabicyclo(2,2,2)-octane, and enhanced by deuteration of the solvent. Deuterated solvents are known to increase 1 O2 lifetime.
The production of1 O2 from retinal is briefly discussed in relation to the damage which may be induced by light in the visual cells. 相似文献
The production of
13.
Abstract In the presence of the photosensitizer riboflavin at high fluence rates a photoproduct, most probably H2 O2 , is formed which causes negative phototaxis in the colorless flagellate Polytomella magna . The aim of this study was to find out whether H2 O2 is produced in a type I or II reaction. As has been shown, 1 O2 quenchers either do not influence the photodynamic action of riboflavin (furfuryl ethanol, DPBF, l -histidine, crocetin) or show slight quenching effects only at very high concentrations ≧ 10−2 M (DABCO, DMF, imidazole). D2 O is toxic to P. magna even in 1:1 and 1:2 mixtures with H2 O. On the other hand, the quenching effect of 1,4-benzoquinone, highly indicative for the type I pathway, is more than two orders of magnitude stronger than the one of the above mentioned 1 O2 quenchers. The results suggest that H2 O2 is produced in a type I reaction. Superoxide does not seem to be involved since superoxide dismutase does not diminish the photodynamic effect of riboflavin. 相似文献
14.
Abstract— In experiments on the interception of reactive intermediates of strongly oxidizing character in dye (S) sensitized photooxidations using p -nitrosodimethylaniline (RNO) as a selective scavenger, it has been observed that some substrates (A) or 1 O2 acceptors (like imidazole derivatives) induce the bleaching of RNO as followed spectrophotometrically at 440 nm. Since singlet oxygen (1 O2 ) does not react chemically with RNO, this bleaching is a consequence of 1 O2 capture by the imidazole ring which results in the formation of a trans-annular peroxide intermediate [1 O2 ] capable of inducing the bleaching of RNO (-RNO). In the absence of RNO, [1 O2 ] decomposes or rearranges into the final oxygenation product 1 O2 : 1 Δg Thus, the system imidazole plus RNO can be used as a sensitive and selective test for the presence of 1 O2 in aqueous solutions. The method can also be applied in the presence of sensitizing dyes which, under visible irradiation, can partially bleach RNO even in the absence of imidazole derivatives. In such a case, the bleaching of RNO is strongly increased by the presence of imidazoles with a characteristic dependence on their concentration. The separation of the product of RNO bleaching by thin layer chromatography can serve as additional proof of the presence of 1 O2 in the system. The imidazole plus RNO method has been applied to a number of sensitizing and non-sensitizing dyes. 相似文献
15.
The photooxidation of N,N -diethylhydroxylamine (DEHA) by Rose Bengal (RB) has been investigated in micellar and nonmicellar aqueous solutions. We measured the quantum yield of oxygen consumption forming H2 O2 and monitored two intermediates, the superoxide and diethylnitroxide radicals. When the pH was vaned, the quantum yield of oxidation remained constant for 6 < pH < 10.5, decreased in acidic pH, and increased considerably in NaOH solution; these changes could be attributed to the protonation and dissociation processes of the >N-OH moiety of DEHA. The formation of diethylnitroxide radical was enhanced by superoxide dismutase or strong alkaline solution. Around neutral pH, the oxidation proceeded mainly via electron transfer from DEHA to the RB triplet ( k q = 107 M -1 s-1 ) with little 1 O2 participation ( kq < 105 M -1 s-1 ). However, when RB was incorporated into micelles in alkaline solution, the contribution of the singlet oxygen pathway increased at the expense of electron transfer, which was inhibited by the less polar micellar environment. Dark autoxidation of DEHA was accelerated by heavy metal impurities and increased very strongly in NaOH solution. 相似文献
16.
THE CHROMOPHORES AS ENDOGENOUS SENSITIZERS INVOLVED IN THE PHOTOGENERATION OF SINGLET OXYGEN IN SPINACH THYLAKOIDS 总被引:1,自引:0,他引:1
Abstract— The photogeneration of singlet oxygen (1 O2 ) from thylakoids and the chromophores involved as endogenous sensitizers were investigated using chloroplasts and thylakoids isolated from spinach. The blue light-induced inhibition kinetics of photosynthetic electron transport and that of CTvCF, ATPase were also studied. The spectral dependence of the generation of 1 O2 from thylakoid membranes, measured by the imidazole plus RNO method, clearly demonstrated that the Fe-S centers play an important role in 1 O2 generation, acting as sensitizers in thylakoids. The photoinhibition of the electron transport in isolated chloroplasts was strikingly depressed by a lipid-soluble '02 quencher and enhanced by deuterium oxide substitution, indicating that the inhibition processes are mainly mediated by 1 O2 which is produced via photodynamic activation. The involvement of chloroplast cytochromes in the production of 1 O2 was deduced from the action spectrum for the photodynamic inhibition of the electron carrier chain. The results obtained from the kinetic studies appear consistent with the involvement of some components such as the Fe-S centers and cytochrome chromophores of the carrier chain in the generation of 1 O2 . 相似文献
17.
S. R. Fahrenholtz F. H. Doleiden A. M. Trozzolo A. A. Lamola 《Photochemistry and photobiology》1974,20(6):505-509
Abstract —D-α-tocopherol was found to be an effective quencher of 1 O2 molecules ( k = 2.5 times 108 →mol-1 s-1 in pyridine) by measuring its effect on the autosensitized photooxidation of rubrene. The quenching process was shown to be almost entirely 'physical', that is, α-tocopherol deactivated about 120 1 O2 molecules before being destroyed. The results suggest that this process may be a mechanism for the protective effect of α - tocopherol in photodynamic action. 相似文献
18.
Abstract— The self-sensitized photooxidation of mesodiphenylhelianthrene in various solvents has been investigated. The involvement of 1 O2 as the reactive intermediate in the formation of the endoperoxide has been demonstrated by the quenching of the photooxidation by the efficient 1 O2 -quencher β-carotene. The rate constant for the addition of 1 O2 to mesodiphenylhelianthrene has been determined to be k R ≅ 1010 M -1 s-1 , which is the highest value hitherto known in the literature. The probability factor p , which describes the concentration independent part of the overall quantum yield, has been measured to be p =0.17. 相似文献
19.
Abstract— Yeast cells are inactivated by treatment with hematoporphyrin and light. The inactivation, which is mediated by singlet oxygen (1 O2 ), is enhanced by the presence of phosphate and chloride. Neither phosphate nor chloride has any influence on the yield of 1 O2 . Possible mechanisms for the enhancement are briefly discussed. 相似文献
20.
Abstract— The use of cyclic 1,3-dienes and polycyclic aromatic hydrocarbons as xenobiotic substrates for the interception of electronically excited (singlet) molecular oxygen (1 O2 ) in biological systems is reviewed and criticized, and the possibility of utilization of reactive endogenous substrates for 1 O2 interception is considered. The common sterols, cholesterol, 5α-cholest-7-en-3β-ol, and 5α-lanost-8-en-3β-ol each give oxidation products with 1 O2 different from those with ground-state molecular oxygen that can be distinguished from one another by simple chromatographic means. 相似文献