bluuebunny/crossref_metadata_2025_split huggingface dataset:
CONTRASTING STRUCTURAL IMPACTS INDUCED BY cis‐syn CYCLOBUTANE DIMER AND (6–4) ADDUCT IN DNA DUPLEX DECAMERS: IMPLICATION IN MUTAGENESIS AND REPAIR ACTIVITY
Authors: Kim Jong‐Ki , Patel Dinshaw , Choi Byong‐Seok 
Published: January 2008

Abstract—The relative biological importance of cis‐syn cyclobutane dimer and pyrimidine(6–4)pyr‐imidone photoadduct ([6–4] photoadduct) appears to be dependent on the biological species, dipyrimidine sites and the local conformational variation induced at the damaged sites. The single‐stranded deoxyn‐ucleotide 10‐mers containing the site‐specific (6–4) adduct or cis‐syn cyclobutane dimer of thymidylyl (3'‐5')‐thymidine were generated by direct photolysis of d(CGCATTACGC) with UVC (220–260 nm) irradiation or UVB (260–320 nm) photosensitization. Three‐dimensional structures of the duplex cis‐syn and (6–4) decamers of d(CGCATTACGC)d(GCGTAATGCG) were determined by NMR spectroscopy and the relaxation matrix refinement method. The NMR data and structural calculations establish that Watson‐Crick base pairing is still intact at the cis‐syn dimer site while the hydrogen bonding is absent at the 3'‐side of the (6–4) lesion where the T → C transition mutation is predominantly targeted. Overall conformation of the duplex cis‐syn decamer was B‐DNA and produced a 9° bending in the DNA helix, but a distinctive base orientation of the (6–4) lesion provided a structural basis leading to 44° helical bending. The observed local structure and conformational rigidity at the (6–4) adduct of the thymidylyl(3'‐5')‐thymidine (T‐T [6–4]) lesion site suggest the potential absence of hydrogen bonding at the 3' sides of the (6–4) lesion with a substituted nucleotide during replication under SOS conditions. Contrasting structural distortions induced by the T‐T (6–4) adduct with respect to the T‐T cis‐syn cyclobutane pyrimidine photodimer may explain the large differences in mutation spectrum and repair activities between them.
PHOTOPHYSICS OF METHYLENE BLUE‐POLYNUCLEOTIDE COMPLEXES IN THE PICOSECOND TIME RANGE: INFLUENCE OF THE LOCAL STRUCTURE OF THE POLYNUCLEOTIDE
Authors: Enescu Mironel , Lindqvist Lars 
Published: January 2008

Abstract—The photophysics of methylene blue (MB) complexed with 2'‐deoxycytidylyl‐2'‐deoxygua‐nosine, polydeoxyguanylic‐deoxycytidylic acid, polydeoxyguanylic‐polydeoxycytidylic acid and poly‐guanylic acid, respectively, was investigated by transient absorption spectroscopy with a time resolution of ˜1 ps. The decays of the transient difference spectra indicate that the radiationless process responsible for the strong shortening of the S, state lifetime of MB associated with a guanine in the polynucleotide chain is similar to that already observed in the case of the MB—guanosine‐5'‐monophosphate complex, that is, the excited state decays by return of molecules to the ground state without formation of a detectable intermediate state. The local structure of the polynucleotide apparently does not change the nature of the deactivation process but influences significantly the deactivation rate. Thus, the intercalation of MB between guanosine and cytosine increases this rate constant (as compared to that of the MB—guanosine‐5'‐monophosphate complex) while the interaction of MB intercalated with a supplementary guanine has an opposite effect. The results are discussed in connection with the photosensitizing effect of MB in nucleic acid damage.
DECAY KINETICS OF N, N, N', N‐TETRAMETHYLBENZIDINE PHOTOCATIONS IN FROZEN MICELLAR SOLUTION OF CETYLTRIMETHYLAMMONIUM BROMIDE
Authors: Wolff Thomas , Weber Susanne , Böhm Britta , Schütz Andreas 
Published: January 2008

Abstract—After UV irradiation of rapidly frozen solutions of N, N, N', N'‐tetramethylbenzidine (TMB) in dilute aqueous micellar cetyltrimethylammonium bromide at 80 K, the ESR signal corresponding to the TMB+ cation was detected indicating photoionization. This signal was monitored as a function of time at various temperatures between 80 K and 260 K. On a timescale of a few days the signal decayed to a plateau value that was stable for months. Two distinct second‐order processes for the decay from the initial to the plateau value were observed: one prevailing at low temperatures with an activation energy of 0.6 kJ/mol, and one prevailing at T > 220 K with an activation energy of 13 kJ/mol. By means of spin probe investigations the latter process was shown to be connected with a local softening of the region adjacent to the micellar surface.
P840‐Reaction Centers from Chlorobium tepidum–Quinone Analysis and Functional Reconstitution into Lipid Vesicles
Authors: Frankenberg Nicole , Hager‐Braun Christine , Feiler Ute , Fuhrmann Markus , Rogl Hans , Schneebauer Nikolaus , Nelson Nathan , Hauska Günter 
Published: January 2008

AbstractMembranes of Chlorobium tepidum contain about 35, 45 and2–10 molecules of menaquinone‐7, chlorobium quinone (1′‐oxo‐menaquinone‐7) and of the polar menaquinone (probably 1′‐OH‐menaquinone‐7) per reaction center, respectively. None of these quinones was retained during the isolation of P840‐reaction centers beyond the detection limit of about 0.2 quinones per reaction center, neither in the core complex nor in functionally intact reaction center preparations. The latter is shown to catalyze the formation of an electrochemical proton gradient in the presence of ascorbate and phenazinium methosulfate, when it is incorporated into lipid vesicles.
Photophysical Properties of Some Methyl‐Substituted Angelicins: Fluorometric and Flash Photolytic Studies
Authors: Elisei F. , Aloisi G. G. , Lattarini C. , Dall'Acqua F. , Guiotto A. 
Published: January 2008

AbstractThis paper describes the results of a study of the photophysical properties of various methyl‐angelicins (MA) in solvents of different polarity and proticity. The behavior of their excited singlet and triplet states was investigated by fluorometry and nanosecond laser flash photolysis. On the basis of semiempirical (ZINDO/S‐CI) calculations and the solvent effect on the absorption and fluorescence properties, the lowest excited singlet state (S1) is assigned to a partially allowed π, π* state. The close lying S2state is n,π* in nature. The efficiency of the decay pathways of S1(fluorescence, intersystem crossing and internal conversion) strongly depends on the energy gap between the S1and S2states consistent with the manifestation of “proximity effect.” Thus, MA in cyclohexane decay only through S1→ S0internal conversion, while in acetonitrile and ethanol, where the n, π* state is located at higher energy, their fluorescence and intersystem crossing increase significantly. The lowest excited triplet states (T1) were characterized in terms of their absorption spectra, decay kinetics, molar absorption coefficients and formation quantum yields. The interaction of T1MA with molecular oxygen leads to an efficient formation of singlet oxygen, as evidenced by the appearance of characteristic IR phosphorescence centered at 1269 nm.
Role of Calcium in Photodynamically Induced Cell Damage of Human Fibroblasts
Authors: Hubmer Alexander , Hermann Anton , Überreigler Karl , Krammer Barbara 
Published: January 2008

AbstractPhotodynamically induced changes in the cytoplasmic free calcium concentration ([Ca2+]i) and its role in cell damage were investigated in human skin fibroblasts using confocal laser microscopy. Fluorescence and absorbance spectrophotometry measurements indicate that the photosensitizer aluminum phthalocyanine tetrasulfonate (AlPcS4) binds to the plasma membrane and only after irradiation is able to enter the cells, causing massive morphologic alterations. Upon irradiation of sensitizer‐treated cells, the increase in [Ca2+]i is related to the amount of light and extracellular [Ca2+]e. The increase in [Ca2+]i was substantially reduced in the absence of [Ca2+]e. Cell damage or death after photodynamic treatment was prevented and shifted toward higher fluence by increasing [Ca2+]i at high [Ca2+]e and was greater at low [Ca2+]e. Application of Ca2+ channel blockers, such as Co2+, Cd2+ or verapamil, could not prevent the increase of [Ca2+]i. Our results indicate that activation of the photosensitizer, AlPcS4, causes an influx of Ca2+, which protects cells from photodamage. At low [Ca2+]e and high fluence values, release of Ca2+ from internal stores probably as a protective measure occurs in order to increase the [Ca2+]i.
Effect of Low‐Dose Gamma Radiation on HIV Replication in Human Peripheral Blood Mononuclear Cells
Authors: Xu Y. , Conway B. , Montaner J. S. G. , O'Shaughnessy M. V. , Greenstock C. L. 
Published: January 2008

AbstractRecent studies have demonstrated that UV light and x‐irradiation enhance human immunodeficiency virus (HIV) gene expression. There are few published data on related effects of γ‐radiation. This may be of clinical relevance, as radiotherapy has been used extensively for the treatment of acquired immunodeficiency syndrome associated conditions. With this in mind, we have studied the effects of γ‐radiation on HIV replication in mononuclear cells (MC). These cells were obtained from five seronegative healthy donors, exposed to0–200 cGy γ‐radiation, stimulated with phytohemagglutinin‐P (PHA‐P) for 24 h, infected with a laboratory strain of HIV (HTLV‐IIIB, multiplicity of infection = 0.001), then carried in culture for 14 days. Overall, when considering p24 antigen levels on days 7 and 11 in cultures established from cells exposed to 50 cGy, the maximal levels were significantly higher than those measured in the parallel control cultures taken as a whole (P < 0.05), with viral replication enhanced as much as 1000‐fold in one case. No significant cytotoxicity was observed following exposure to doses up to 50 cGy. The mechanism of the observed effect remains unknown but may relate to direct gene activation and/or free radical generation, leading to such activation. To date, there is no evidence that viral stimulation occurs following therapeutic radiation in a clinical setting.
PUVA Therapy is Preferable to UVB Phototherapy in the Management of HIV‐Associted Dermatoses
Authors: Morison Warwick L. 
Published: January 2008

AbstractBoth methoxsalen plus UVA (PUVA) therapy and UVB phototherapy are commonly used in the management of human immunodeficiency virus‐associated dermatoses but UVB phototherapy appears to be the preferred treatment. There are several considerations, in particular therapeutic efficacy and therapeutic profile, which suggest that PUVA therapy might be more effective, This needs to be established in clinical trials.
Risk Assessment of UVB Effects on Resistance to Infectious Diseases
Authors: Garssen Johan , Goettsch Wim , Gruijl Frank de , Loveren Henk Van 
Published: January 2008

AbstractThe aim of this study was to develop a qunatitiative risk assessment of lowered resistance to Infections in humans due to (solar) ultraviolet B (UVB) exposure. We followed the steps for risk assessment as defined by the U. S. National Academy of Sciences: (1) hazard identification, (2) dose‐response assessment, (3) exposure assessment, and (4) risk characterization. For step 1, the suppressory effects of UVB radiation on the immune system have been reviewed, suplemented with new data, and analyzed. Experiments on UV‐induced immunosuppression cannot be performed with humans for ethical reasons, but herpes simplex virus infection appears to be the human paradigm. Thus, UVB radiation appears to be a potential hazard to immunologic functions, Step 2 is crucial, but dose‐response relationships for infections have never been measured in humans. We used our earlier doseresponse rat data for suppression of lymphocyte stimulation and computed that the UVB dose resulting in a 50% reduction of lymphocyte stimulation by Listeria monocytogenes is 6.800 J/m2. Using mixed skin lymphocyte response assays we found that humans are 3.8 times less sensitive than rats (interspeices variation (IEVI). To account for the 2.5 percentile of most susceptible individuals in a population, and additional factor (intraspecies varations (IAV) was introduced (0.5 for humans). Using these data, we computed that 13.100 J/m2 of UVB radiation emitted by FS40 lamps would suppress 50% of the proliferative response of lymphocytes to L. monocytogenes in most sensitive skin type 2 humans. In step 3, we assumed the action spectrum for the responses analyzed by us as indentical to an action spectrum for suppression of contact hypersensitivity that is available in the literature. This led us to step 4, where we calculated that approximately 100 min of solar exposure at around noon in Italy or Spain would suppress the resistance to infections by L. monocytogenes in the most sensitive humans.
Kinetic Analysis of Apoptosis Induction in Human Cell Lines by UVA and 8‐MOP
Authors: Vowels Benjamin R. , Yoo Elisa K. , Gasparro Francis P. 
Published: January 2008

ABSTRACTWhereas previous studies have indicated that DNA damage as a result of 8‐methoxypsoralen (8‐MOP) and UVA treatment leads to cell death, this study establishes the minimum concentrations of 8‐MOP and UVA necessary to induce apoptosis in human T‐lymphocytic and mono‐cytic cell lines. In order to assess apoptosis, we used fluorescent microscopy to examine changes in light scattering as well as internucleosomal DNA fragmentation. Generation of a dose response curve showed that the minimum combination of UVA and 8‐MOP that was necessary to induce greater than background levels of apoptosis within 24 h of treatment was 0.5 J/cm2 UVA and 12.5 ng/mL of 8‐MOP. A striking observation was that UVA alone at doses 1.0 J/cm2, but not 8‐MOP alone (6300 ng/mL), induced significant apoptosis in the Sup‐T1 cell line within 24 h. Although the percentage of apoptotic Sup‐T1 cells induced by UVA alone was not as great as that of 8‐MOP and UVA in combination, a highly significant correlation between the product of the concentration of 8‐MOP (ng/mL) times the dose of UVA (J/ cm2) and the percentage of apoptotic cells was observed. This correlation provides an important tool for studying the relationship of UVA‐induced DNA damage to apoptosis induction. Moreover, it will provide a means by which early events in the apoptotic pathway can be dissected.
Solvent Polarity and pH Effects on the Spectroscopic Properties of Neutral Red: Application to Lysosomal Microenvironment Probing in Living Cells
Authors: Sousa Cristina , Sá e Melo Teresa , Gèze Marc , Gaullier Jean‐Michel , Mazière Jean Claude , Santus René 
Published: January 2008

ABSTRACTNeutral red is a lysosomal probe and a biological pH indicator. In aqueous solutions, the protonated (NRW) and neutral (NR) forms of monomeric neutral red exhibit distinct absorption maxima (535 and 450 nm, respectively) but have the same fluorescence with a maximum at 637 nm and a quantum yield of 0.02. The similarity of the fluorescence spectra at acidic and basic pH suggests deprotonation of cationic species in the first singlet excited state. The NR fluorescence strongly depends on the solvent polarity as shown by addition of increasing amounts of water to pure dioxane, which gradually shifts the fluorescence maximum from 540 nm in pure dioxane to 637 nm in water. The fluorescence quantum yield increases from 0.17 in dioxane to 0.3 upon addition of 7% water and then decreases, reaching 0.02 in pure water. Immediately after incubation of human skin fibroblasts with neutral red, excitation with 435 nm light produces a fluorescence whose maximum is recorded at 575 nm. This fluorescence is located in the perinuclear region and originates from large fluorescent intracytoplasmic spots, suggesting staining of the endoplasmic reticulum‐Golgi complex. At longer times, this fluorescence is shifted to 606 nm, suggesting slow diffusion of the lysosomotropic dye toward the more hydrated and acidic interior of ly‐sosomes. Addition of a lysosomotropic detergent to cells previously incubated with neutral red shifts the fluorescence to the blue. Thus, in complex biological systems, this probe cannot be a good pH indicator but is a very sensitive probe of lysosomal rnicroenvironrnents.
Fourier Transform Multipixel Spectroscopy and Spectral Imaging of Protoporphyrin in Single Melanoma Cells
Authors: Malik Zvi , Dishi Michal , Garini Yuval 
Published: January 2008

AbstractFourier transform multipixel spectroscopy was applied to subcellular localization of endogenous protoporphyrin (endo‐PP) in single living B16 melanoma cells during photosensitization. Continuous fluorescence spectra for each pixel were recorded using a Sagnac interferometer coupled to a charge‐coupled device camera. Multiple frames of data were acquired for each pixel composing the image, then they were stored as interferometric data and resolved as spectra for every pixel (103‐−4 × 103 point pixels in a single cell). The net result was the intensity I (x, y, λ), for each pixel of the image (x, y), at any wavelength (λ). The present study demonstrates the application of Fourier transformed multipixel spectroscopy for spectral imaging of melanoma cells incubated with 5‐aminolevulinic acid (ALA). The fluorescence image of ALA‐treated cells revealed endo‐PP all over the cytosol with a vesicular distribution, which represent mitochondria and endoplasmic reticulum compartments. Two main spectral fluorescence peaks were demonstrated at 630 and 670 nm, of monomeric and aggregated protoporphyrin, with intensities that differed from one sub‐cellular site to another. Photoirradiation of the cells induced point‐specific subcellular fluorescence spectrum changes and demonstrated photoproduct formation. Spectral‐image reconstruction revealed the subcellular distribution of porphyrin species in single photosensitized cells. Multipixel spectroscopy of exogenous protoporphyrin revealed an endosomal‐lysosomal compartment in aggregated states, whereas monomeric porphyrin species were localized mainly on the outer membrane. Photo‐products could be visualized at sites of formation in suhcellular compartments.
Erythemal Ultraviolet Insolation in New Zealand at Solar Zenith Angles of 30° and 45°
Authors: Ryan K. G. , Smith G. J. , Rhoades D. A. , Coppell R. B. 
Published: January 2008

ABSTRACTSolar UV radiometers with spectral responsivities that are close to the erythemaVcarcinogenic action spectrum of skin have been installed at several centers of population in New Zealand, including Auckland, 37°S, Wellington, 41°s and Christchurch, 43.5°S. The data set covers the period from the time the radiometry program commenced in 1988/1989 to the end of the southern summer, March 1995. The radiometers were recalibrated annually and the data were corrected for changes in the absolute responsivity of the radiometers. Erythemally effective UV irradiances at solar zenith angles of 30° and 45° were then extracted from the data set. No monotonic trend in these data is apparent, although there are statistically significant differences in mean irradiances from one year to the next. An example of this is the decrease observed in all sites following the Mt. Pinatubo eruption in June 1991. The maximum erythemally effective insolations at solar zenith angles of 30° and 45° were consistently lower in Christchurch than in the other two New Zealand sites. This could arise from higher levels of atmospheric turbidity andlor tropospheric ozone at this location. Also, a seasonal increase in erythemally effective UV insolation from spring to autumn was observed each year in all three New Zealand sites.
Quantitation of the Reactive Oxygen Species Generated by the UVA Irradiation of Ascorbic Acid‐Glycated Lens Proteins
Authors: Linetsky Mikhail , Ortwerth Beryl J. 
Published: January 2008

ABSTRACTThe oxidation products of ascorbic acid rapidly glycate proteins and produce protein‐bound, advanced glycation endproducts. These endproducts can absorb UVA light and cause the photolytic oxidation of proteins (Ortwerth, Linetsky and Olesen, Photochem. Photobiol. 62, 454–463, 1995), which is mediated by the formation of reactive oxygen species. A dialyzed preparation of calf lens proteins, which had been incubated for 4 weeks with 20 mM ascorbic acid in air, was irradiated for 1 h with 200 mW/ cm2 of absorbed UVA light (λ > 338 nm), and the concentration of individual oxygen free radicals was measured. Superoxide anion attained a level of 76 μM as determined by the superoxide dismutase (SOD)‐depen‐dent increase in hydrogen peroxide formation and of 52 μM by the SOD‐inhibitable reduction of cytochrome c. Hydrogen peroxide formation increased linearly to 81 μM after 1 h. Neither superoxide anion nor hydrogen peroxide, however, could account for the UVA photolysis of Trp and His seen in this system.Singlet oxygen levels approached 1.0 mM as measured by the oxidation of histidine, which was consistent with singlet oxygen measurements by the bleaching of N,N‐dimethyl‐4‐nitrosoaniline. High concentrations of sodium azide, a known singlet oxygen quencher, inhibited the photolytic destruction of both His and Trp. Little or no protein damage could be ascribed to hydroxyl radical based upon quenching experiments with added mannitol. Therefore, superoxide anion and H2O2 were generated by the UVA irradiation of ascorbate advanced glycation endproducts, however, the major reactive oxygen species formed was singlet oxygen.
The Relative UV Sensitizer Activity of Purified Advanced Glycation Endproducts
Authors: Ortwerth B. J. , Prabhakaram Malladi , Nagaraj R. H. , Linetsky Mikhail 
Published: January 2008

Abstract— The oxidation products of ascorbic acid react with lens proteins to form advanced glycation endproducts (AGE) that are capable of generating reactive oxygen species when irradiated with UVA light. L‐Threose, the most active of these oxidation products, was reacted with N‐acetyl lysine and six AGE peaks were isolated by RP‐HPLC. Each peak exhibited fluorescence and generated superoxide anion and singlet oxygen in response to UV light. Solutions of these AGE peaks (50 μg/mL) generated5–10 nmol/mL of superoxide anion during a 30 min irradiation. This activity was 100‐fold less than the superoxide anion generated by kynurenic acid and 400‐fold less than riboflavin.Ultraviolet irradiation generated from 1.2 to 2.7 μmol/mL of singlet oxygen with the purified threose AGE compounds. This activity was similar to that seen with other purified AGE compounds (pentosidine, LM‐1 and Ac‐FTP) and with kynurenine and 3‐OH kynurenine. This considerable singlet oxygen formation, however, was still 40‐fold less than that obtained with kynurenic acid and 100‐fold less than riboflavin under the same irradiation conditions. In spite of this lower sensitizer efficiency, the purified AGE generated20–60‐fold more singlet oxygen on a weight basis than either crude ascorbic acid glycated proteins or a preparation of water‐insoluble proteins from aged normal human lenses. On a molar basis, therefore, AGE could account for the sensitizer activity in these protein preparations if they represented less than 1% of the total amino acids.
UV Light‐induced Crosslinking of the Complementary Strands of Plasmid pUC19 DNA Restriction Fragments
Authors: Pospíšilová Šáka , Kypr Jaroslav 
Published: January 2008

ABSTRACTRestriction fragments of pUC19 DNA were irradiated by various doses of UV light and analyzed by denaturing (alkaline) agarose gel electrophoresis. The irradiation generated retarded species whose mobility indicated two crosslinked DNA strands. Quantitative analysis of the experimental data provided an empirical equation relating the fraction of crosslinked DNA molecules to their length and to the dose of their irradiation by UV light. This equation can be used to predict the crosslinking behavior of pUC19‐like DNA molecules whose primary structures do not much differ from a random nucleotide sequence. The amount of interstrand crosslinks increased with the (A+T) content of the pUC19 DNA fragments but the dependence was not clear‐cut to indicate that oligonucleotide composition of DNA played a significant role as well.