摘要:

Abstract—The recent results of stationary‐state and time‐resolved absorption, fluorescence and Raman spectroscopies of some typical carotenoids are summarized. Theoretical analyses of carotenoid singlet states and of carotenoid‐to‐bacteriochlorophyll singlet‐energy transfer are also included. On the bases of the energies, the lifetimes and other properties of singlet excited states of the carotenoids in solution and bound to the light‐harvesting complexes, the energetics and the dynamics of the light‐harvesting function in purple photosynthetic bacteria are discussed with emphasis on the 2

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03021.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03022.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract—Fluorescence recovery after photobleaching (FRAP) measurements on air‐saturated aqueous solutions of fluorescein made viscous with glycerol or sucrose revealed a rapid component of fluorescence recovery with exponential time constants of 30‐120 μs at viscosities of 15‐300 cP. The rapid recovery process was not related to fluorophore translational diffusion and was insensitive to fluorophore concentration and the additive used to increase solution viscosity. At constant viscosity, the rate of reversible photobleaching recovery increased 2.5‐fold in an O2‐vsN2‐saturated solution. The relative efficiency of reversible‐to‐irreversible photobleaching decreased with increasing photobleaching time and/or beam intensity. Reversible photobleaching was also detected for conjugates of fluorescein with dextrans and proteins in viscous media. In screening triplet state quenchers that might influence the reversible recovery, it was found that tryptophan enhanced the rate of reversible photobleaching recovery (two‐fold increase at 8 mM) and quenched the fluorescein singlet state (Stern‐Volmer constant, 12M−1). Analysis of fluorescein lifetimes and photobleaching parameters for a series of fluorescein‐labeled proteins with different numbers of tryptophans were also carried out. The results provide evidence for an oxygen‐dependent, reversible photobleaching mechanism for the fluorescein chromophore involving triplet state relaxation. The identification of reversible fluorescein photobleaching has important implications for FRAP measurements of rapid solute dif

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03023.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract—The aim of this investigation is the evaluation of DNA interaction of with tetraruthenated porphyrin (TRP) and of DNA damage in the presence of light. Direct‐fluorescence and electronic absorption measurements after incubation of DNA with TRP indicate strong binding between pBR322 DNA or calf thymus DNA with the modified porphyrin. Exposure of pBR322 DNA to TRP (up to 3 μM) and light leads to single‐strand break formation as determined by the conversion of the supercoiled form (form I) of the plasmid into the nicked circular form (form II). Oxidative DNA base damage was evaluated by the detection of 8‐oxo‐7,8‐dihydro‐2′‐deoxyguanosine (8‐oxodGuo) after irradiation of calf thymus DNA in the presence of the TRP. The data demonstrated a dose and time dependence with each type of DNA damage. These data indicate (1) a specificity of the binding mode and (2) type I and II photoinduced mechanisms leading to strand scission activity and 8‐oxodGuo formation. Accordingly, singlet molecular oxygen formation, after TRP excitation, was confirmed by near‐infrared emission. From these investigations a potential application of TRP in photodyn

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03024.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract—A novel algorithm (QUENCH) is described that resolves fluorescence spectra into components differing in the accessibility (the Stern‐Volmer constants) for small quencher molecules. In contrast to the known algorithms, QUENCH first evaluates Stern‐Volmer constants of the components using the total set of intensities in spectra measured at several quencher concentrations and then calculates contributions of each component in the emission intensities at every wavelength value. The component spectra, revealed with QUENCH in the tryptophan fluorescence of ribosomal S7 protein, are very similar to the log‐normal components calculated using the SIMS program (Abornev, S. M. and E. A. BursteinMol. Biol.[Engl, transl.] 26, 890‐897 1992). The QUENCH method is applicable for the component resolution of fluorescence spectra of any liquid system containing fluorophores of different accessibility to small

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03025.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract—We compared the DNA damage produced by radiation from two UV laser wavelengths, 213 nm and 193 nm, with that produced by noncoherent 254 nm radiation. Following irradiation ofEscherichia coliBR339, a bacteriophage lambda lysogen containing the lacZ gene, prophage induction was measured by assaying for β‐galactosidase. Because of the limited penetration by UV laser wavelengths an agar overlay of the lysogen was used as the irradiation target. Irradiation of 254 nm was performed in buffer suspension followed by transfer of 5 μL spots onto assay plants. Computer image analysis was used to monitor the rate of product formation, observed as an increase in optical density of the irradiated zones on assay plates. We found that the rate of product formation was a more reproducible unit of comparison than the optical density present at the end of the reaction. Although the rate of product formation was not linearly related to enzyme concentration, the data could be fit to a simple logarithmic function. Using this method, we concluded that the DNA damaging ability of 213 nm radiation was 10 times more efficient than 193 nm radiation and about 100 times less efficient than 254 nm noncoherent radi

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03026.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract—Calf thymus DNA was irradiated with low‐intensity UVA (main output at 365 nm, 2 mW cm−2or 36 kj m2for 30 min), and the role of metal ions, hydrogen peroxide and reactive oxygen species (ROS) was examined. DNA damage was measured as thiobarbituric acid‐reactive substances (possibly from degradation of deoxyribose) and as changes in ethidium bromide‐DNA fluorescence due to unwinding from strand breaks. Under the present experimental conditions, UVA alone or in the presence of H202had no effect on DNA but slightly enhanced the damage by iron/EDTA. Ultraviolet A strongly enhanced DNA damage (ca four‐ to five‐fold) by the Fenton reaction system (50μMFe2+/100 μM EDTA + 0.5 mM H202). The results suggest that the Fenton reaction system was “photosensitized” to damage DNA by low‐intensity UVA radiation. The enhanced damage by UVA was attributed in part to the reduction of Fe3+to Fe2+. Ultraviolet A had no effect when iron (ferric or ferrous) ions were replaced by Cu2+, Zn2+, Mn2+or Cd2+. The ROS involved in the UVA‐enhanced damage to DNA by the Fenton reagents were OH and, to a lesser extent, superoxide anions. The UVA‐potentiated DNA damage by the Fenton reaction system was then used to examine the protective effect ofpara‐aminobenzoate (PABA), a UVB‐absorbing sunscreen that protects against photocarcinogenesis in hairless mice. The results show that PABA and mannitol dose‐dependently inhibited the damage with concentrations required for 50% inhibition at 0.1 mM and 3mM, respectively. The protection by PABA was attributed to its radical‐scavenging ability because PABA does not absorb light in the UVA region. These findings may be relevant to the biological damage by UVA and suggest that PABA is useful in protection against photocarcinog

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03027.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract—The (6‐4) photoproduct DNA photolyase was detected in two vertebrate animalsCrotalus atrox(rattlesnake) andXenopus laevis(South African clawed toad). The enzyme was extensively purified fromX. laevisand characterized. The highly purified enzyme is fluorescent with an excitation maximum at 420‐440 nm and emission maximum at 460‐480 nm. The photorepair action spectrum matches the fluoresoence excitation spectrum with a 430 nm

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03028.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract—The photoacoustic (PA) signal at the modulation frequency of 35 Hz was studied in MV‐treated barley leaves or leaves preheated at different temperatures. Saturating illumination enhanced the magnitude of the PA signal in MV‐treated leaves in contrast with the opposite result usually found in untreated intact leaves where saturating illumination abolishes the photobaric component of the PA signal due to oxygen evolution and thus decreases the total PA signal. A linear relationship was found between the changes induced by continuous background light in the negative response of PA signal to saturating light in intact leaves and in the positive response in MV‐treated leaves. A linear relationship was also observed in MV‐treated leaves between the positive changes in the PA signal and the changes in the rate of electron transport through photosystem II (PSII) calculated from chlorophyll fluorescence data. The conclusion was drawn that only the thermal component contributes to the PA signal measured at low modulated frequency in MV‐treated leaves because the enhanced O2 uptake provides a zero net oxygen exchange by superimposing with O2 evolution. The leaves preheated at temperatures above 43°C demonstrated the positive response of the PA signal to saturating light at 35 Hz. In leaves preheated at 41.5°C, the first and second saturating pulses induced the enhancement of PA signal, whereas other pulses decreased the PA signal due to onset of oxygen evolution. The energy storage activity measured in the absence of oxygen evolution in heat‐treated leaves is proposed to be associated with cyclic electron transport activities arou

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03029.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract—Trans‐urocanic acid (UCA) is found in the upper layer of the skin and UV irradiation induces its photoisomerization tocis‐UCA.Cis‐UCA mimics some of the immunosuppressive properties of UV exposure. The wavelength dependence forin vitrophotoisomerization oftrans‐UCA(15 μM) over the spectral range 250 nm‐340 nm (10 nm intervals) was determined. The action spectrum revealed that maximal cis‐UCA production occurred at 280 nm, which is red‐shifted by 10‐12 nm from its absorption peak at 268 nm and differs markedly from the reported action spectra forcis‐UCAproduction in mouse skinin vivo, which peaks at 300‐310 nm. The reasons for the red shift between thein vitroandin vivoaction spectra are not clear. There is limited evidence suggesting that the UV absorption maximum oftrans‐UCA red shifts from 268 nmin vitroto 310 nm on interaction with stratum corneum proteinsin vivo.This phenomenon was investigated by applyingtrans‐UCA(2.5 mg/cm2) in an oil emulsion to isolated human stratum corneum. After incubation at 37°C for 1 h, the absorption spectra of stratum corneum with UCA and with oil only were compared using a Xe arc source and a spectrora‐diometer. A moderate red shift intrans‐UCAabsorption from ∼268 nm to 280 nm was observed. In summary, we suggest that the 10‐12 nm red shift between the UCA absorption spectrum peak and the action spectrum peakin vitromay be accounted for by the wavelength dependence of quantum yields reported over the 254‐313 nm range. The red shift between thein vitroandin vivophotoisomerization action spectra may result from the 10 to 12 nm red shift in the absorption of UCA in association with stratum corneum proteins, combined with increasing qua

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1996.tb03030.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY