摘要:

Abstract—The transient absorption spectra of aqueous solutions of adenine, 2′‐deoxyadenosine, 2′‐deoxyadenosine‐5′‐phosphate and 2′‐deoxyadenylyl‐(3′‐5′)‐2′‐deoxyadenosine have been determinated at different pH values using conventional flash photolysis. Reactives intermediates produced in the flash photolysis of these adenine derivatives present similar absorption regions: two higher intensity bands in the UV and 560–720 nm wavelength region and a third weaker band at 420–560 nm. On the basis of the effects produced by triplet quenchers and/or electron scavengers the bands have been assigned to hydrated electrons, radical cations, radical anions and/or neutral radicals resulting from neutralization reactions of the charged radicals. The results indicate that the bases photoionizeviaa

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb03593.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—This paper describes an experimental study of the photo properties of the triplet (T,) states of hematoporphyrin (HP) and coproporphyrin (CP), particularly in relation to their medium dependence and reactivity towards oxygen. Triplet‐triplet absorption spectra of HP and CP have been determined in aqueous buffer at pH = 7.4 and in water‐methanol and water‐formamide mixtures. The spectra corrected for ground state contributions show major absorption peaks near 400 nm and lesser peaks near 500 nm. Extinction coefficient measurements have been made and their dependences on solvent composition investigated. Natural lifetimes of the T1states of HP and CP and the bimolecular quenching constants with oxygen have been determined. The quantum yields of T1formation areca.0.6 in buffer rising to 0.8 and higher in predominantly organic media. Incorporation of the porphyrins into micellar phases similarly causes φT, to increase. Quantum efficiencies of O−2and O2(lΔg) formation have been determined for HP in buffer, some binary mixtures and micellar dispersions. Superoxide yields are low and may result from photo‐ionization processes. O2(lΔg) yields are large but appear to have an unexpected dependence

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb03594.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—Oxidation of specifically radiolabeled14C‐lignins by UV/H202. Fenton's reagent, photosesitizing riboflavin. UV‐ and γ‐irradiation was examined. In the presence of UV/H2O2, a hydroxyl radical (·OH) generating system.14C‐methoxy. 2‐[14C‐sidechain] and14C‐ring labeled lignin were rapidly and extensively degraded as measured by gel filtration of the reaction products on Sephadex LH‐20. This suggested that exposure to OH leads to rapid, nonspecific lignin degradation. Rapid degradation of 14C‐methoxy, 2‐[14C‐sidechain] and14C‐ring labeled lignin also occurred in the presence of the ·OH generating system, Fenton's reagent, confirming the primary role of ·OH in these reactions. Photosensitizing riboflavin, also capable of effecting transformation of organic compounds via Type I hydrogen radical abstractions, caused extensive oxidative degradation of14C‐methoxy labeled lignin and significant degradation of 2‐(14C‐sidechain] and14C‐ring labeled lignin. In addition, UV‐ and γ‐irradiation caused slower but extensive degradation of the polymers, probably via radical type mechanisms. All of these results indicate that ·OH as well as organic radical generating systems are effective agents for the purpose of degrading this heterogeneou

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb03595.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—L1210 mouse leukaemia cells were treated with psoralen [S‐methoxy‐(XMOP), 4,5′,8‐trimethyI‐(TMP), 4′‐hydroxymethyl‐4,5′,8‐trimethyl‐(HMT) or 4′‐amino‐ methyl‐4,5′,8‐trimethylpsoralen (AMT)] in combination with long wavelength ultraviolct irradiation (Λ∼ 365 nm). In order to investigate the relative photobiological activities of the psoralens, cell viability and DNA‐synthesis activity as well as psoralen‐DNA photoaddition and DNA interstrand cross‐linking were measured after the treatment. In all assays the activity ranking order was found to he: TMP>HMT>AM7>8MOP. Furthermore, a direct correlation between phototoxicity, psoralen induced DNA interstrand cross‐links and inhibition of DNA synthesis was indicated. Finally, psoralen uptake by the cells appears to be an important determinant for phototoxici

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb03596.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—Double stranded salmon sperm DNA in a chlorpromazine (CPZ) solution is damaged when irradiated with near UV light. The damage of irradiated DNA can be estimated by measuring the increase in extinction at 260 nm following incubation at 60°C of the DNA with formaldehyde. Moreover, DNA irradiated in the presence of CPZ or kept in the dark separate quite differently in an aqueous polymer two‐phase system. DNA irradiated in the presence of CPZ seemed to be susceptible to digestion by endonuclease S1, while the endonuclease ofNeurospora crassacould not digest this DNA. Irradiation under aerobic conditions seemed to be less disastrous for DNA than under anaerobic condit

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb03597.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—We have used a signal averaging laser (30 ps pulse)‐streak camera system to measure fluorescence anisotropy decays of dyes in solution and protein tryptophan chromophores with picosecond time resolution. Emission polarization as a function of time can be measured directly and simultaneously for both polarization directions and stored in an optical multichannel analyzer. The corrected anisotropy is computed after background subtraction. Rotations of free dyes in solution (Sulforhodamine 101, tryptophan) and the temperature‐dependent internal motions of human serum albumin (tryptophan emission) are disp

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb03598.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—Musk ambrette (4‐tert‐butyl‐3‐methoxy‐2,5‐dinitrotoluene), a common component of perfumes, soaps, and some food flavorings, can cause cutaneous photosensitization reactions including photoallergy. These may be mediated through free radicals formed during photolysis. When musk ambrette was photolyzed under nitrogen in basic methanol, two distinct nitro anion radicals were identified by electron spin resonance. One radical was centered on a nitro group in the plane of the aromatic ring, while the other was centered on a nitro group twisted out of the plane of the ring due to steric hindrance by bulky substituents on either side of the group: the two radicals appeared to interconvert and maintain an equilibrium concentration ratio. Two closely related compounds which are also used in perfumes, but have not been reported to cause photosensitizing reactions, also produced free radicals during photolysis. Musk xylene (2,4,6‐trinitro‐1,3‐dimethyl‐5‐tert‐butylbenzene) generated two nitro anion radicals, both of which were centered on twisted nitro groups, while musk ketone (3,5‐dinitro‐2,6‐dimethyl‐4‐tert‐butylacetophenone) produced only one nitro anion radical, which is also twisted. Athough these nitro anion radicals are probably the first step in the photolysis of these nitroarornatic molecules, it seems likely thatin vivothey will undergo further reduction to produce more reactive species including the corresponding nitroso and hydroxylamine derivatives. In addition, autoxidation of the nitro anion

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb03599.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—Dark‐grown cells ofEuglena gracilisvar.bacillariscontain low levels of protochlorophyll(ide) [Pchl(ide)] which absorbs at 635 nmin vivo.When growing cells are placed on a resting medium, cell division ceases after 3 days and the levels of total extractable and phototransformable Pchl(ide) decrease, reaching a new plateau at one‐half the original concentration by 7 days of resting. Phototransformable Pchl(ide) can be induced to regenerate to the original levels found in dark‐grown cells by treatment with light. The optimum conditions are 40 min of white light (0.2–0.3 W/m2) followed by 1 h of darkness. Although reciprocity between fluence rate and duration of illumination was not observed in this system, it was possible to determine the effectiveness of various spectral regions for the regeneration of phototransformable Pchl(ide) as a function of fluence rate. Blue light (400–510 nm) was most effective followed closely by green (490–590 nm); red light (610–720 nm) was relatively ineffective. The results suggest that phototransformable Pchl(ide) is regulated to achieve the levels ordinarily found in dark‐grown cells and that the blue photoreceptor system, rather than Pchl(ide) itself, is probably the light receptor for Pchl(

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb03600.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—Dark‐grown cells ofEuglena gracilisvar.bacillarisincubated on resting medium for 7 days lose half of their extractable and phototransformable protochlorophyll(ide) [Pchl(ide)]. The readily‐utilized substrates glutamate and malate bring about a regeneration of both pools of Pchl(ide) to the levels found in growing cells, without causing cell division during the period of regeneration. Light does not cause a regeneration of total extractable Pchl(ide) to the levels found in growing cells, and the complete regeneration of phototransformable Pchl(ide) seen probably results from conversion of non‐transformable Pchl(ide) to transformable Pchl(ide). Optimal glutamate, malate, and light in any combination are no better in causing phototransformable Pchl(ide) regeneration than any one treatment alone, indicating that the Pchl(ide) pool size is limited by other factors. The regeneration of phototransformable Pchl(ide) induced by light or substrates is insensitive to inhibitors of protein synthesis on 80 S cytoplasmic ribosomes (cycloheximide) or on 70 S chloroplast ribosomes (streptomycin). Cycloheximide, however, induces the regeneration of phototransformable Pchl(ide) in darkness in the absencc of externally‐added substrates. Since cycloheximide is known to induce paramylum breakdown under the same conditions, it is likely that this process can provide internal substrates and/or reducing power for phototransformable Pchl(ide) regeneration. Possible mechanisms of regulation of formation of Pchl(ide)635inEuglenaare discussed and compared with regulation of Pchl(ide)650in high

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb03601.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract—The accumulation of phytochrome in the dark was measured forAvena sativaseedlings after a white light pretreatment and forSorghum vulgareseedlings after continuous red or far‐red light treatments, using the herbicide Norflurazon to prevent greening under continuous irradiation. In both cases the accumulation of phytochrome depends on the state of the phytochrome at the light‐dark transition: high Pfrlevels (red light pulse) led to a slower rate of phytochrome accumulation than lower Pfrlevels (long wavelength far‐red (RG 9) light pulse). Poly‐(A+)‐RNA was isolated fromA.sativaseedlings grown for 48 h in darkness + 24 h WL + light pulse (5 min) (red, RG 9 light, red followed by RG 9 light or RG 9 followed by red light pulse) + 19 h darkness. The poly‐(A+)‐RNA was translated in a rabbit reticulocyte lysate system and the translation products were immunoprecipitated by specific anti‐phytochrome antibodies. It was demonstrated that the activity of mRNA coding for phytochrome was under ph

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1983.tb03602.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY