bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of the UV Modification of α‐Crystallin on Its Ability to Suppress Nonspecific Aggregation
Authors: Ellozy Aziza R. , Ceger Patricia , Wang Ren H. , Dillon James 
Published: January 2008

AbstractRecent studies have shown that structural modifications of α‐crystallin during lens aging decrease it's effectiveness as a molecular chaperone. Some of these posttranslational modifications have been linked to UV radiation, and this study was undertaken to investigate the effect of UV irradiation on the ability of α‐crystallin to suppress nonspecific aggregation. The effect of 3‐hydroxykynurenine (3‐HK) was also investigated as a model for its glucoside (3‐HKG), a main lens chromophore that has been linked to photochemical changes in the human lens. Alpha‐ and γ‐crystallin solutions (1 mg/mL, 1:0.125 wt/wt) were photolyzed (transmission above 295 nm) for various time intervals. Thermal denaturation of γ‐crystallin with or without α‐crystallin was carried out at 70°C and increases in light scattering were measured at 360 nm. We found that (1) irradiation of γ‐crystallin increased its susceptibility to heat‐induced scattering. The addition of α‐crystallin protects it against thermal denaturation, although its ability to do so decreases the longer γ‐crystallin is irradiated and (2) irradiation of α‐crystallin decreases its ability to suppress nonspecific aggregation and the presence of 3‐HK during irradiation decreases it further. Our results indicate that posttranslational modifications of α‐crystallin due to UV irradiation affect the sites and mechanisms by which it interacts with γ‐crystallin. The kinetics of γ‐crystallin unfolding during thermal denaturation were also analyzed. We found that a simple two state model applies for nonirradiated γ‐crystallin. This model does not hold when γ‐crystallin is irradiated in the presence or absence of α‐crystallin. In these cases, two step or multistep mechanisms are more likely.
Action Spectra for Photoinhibition of Sexual Development in Phycomyces blakesleeanus
Authors: Yamazaki Y. , Kataoka H. , Miyazakl A. , Watanabe M. , Ootakl T. 
Published: January 2008

AbstractThe sexual development of the fungus Phycomyces is inhibited by light. The action spectra for this photoinhibitory effect were determined for 48 h continuous exposure between 350 and 700 nm wavelengths during the mating process. Effective wavelengths were shorter than 490 nm, but the most effective wavelengths depended on the stage of sexual development. In early stages of progametangium formation, the major peaks appeared near 360 nm with small shoulders at 410 nm, but in later stages, after gametangium formation, only single peaks were detected in the UVA range (350–390 nm). Low‐fluence irradiation in the later stage, however, revealed inhibitory effectiveness at 370–410 nm, implying the existence of a dual photoresponse and multiple regulatiory systems in the mating process of Phycomyces.
The Protective Effect of N‐Acetylcysteine on UVB‐Induced Immunosuppression by Inhibition of the Action of Cis‐Urocanic Acid
Authors: Hemelaar Peter J. , van Henegouwen Gerard M. J. Beijersbergen 
Published: January 2008

Abstract— A recent study has shown that N‐acetylcysteine (NAC) not only has sun‐protective properties but also inhibits the UVB‐induced suppression of contact hypersensitivity (CHS) in mice. Because NAC does not absorb any UVA (320‐400 nm radiation) or UVB (290‐320 nm radiation) we have studied the underlying mechanism of protection. Irradiation of solutions of plasmid DNA with UVC (200‐290 nm radiation) (10 J m‐2) resulted in the formation of cyclobutane pyrimidine dimers, but the extent to which this occurred was not affected by the presence of NAC as was determined by an in vitro T4 endonuclease assay. N‐acetylcysteine proved not to have any effect on the photoisomerization of trans‐urocanic acid (UCA) to its cis‐form in vitro; at equilibrium, approximately 55% cis‐UCA was formed. The same percentage was also found in vivo on exposure of mice to UVB (15 kj m‐2). Topical application of NAC 30 min prior to irradiation did not have any influence as well on the photoisomerization of trans‐ to cis‐UCA. These in vivo experiments were performed under the same conditions used previously to show the protective effect of NAC against UVB‐induced suppression of CHS.We conclude that this protection of NAC is at least partly based on interference in the role of cis‐UCA in UVB‐induced suppression of CHS. This conclusion is supported by the observation that NAC completely inhibits the suppression of CHS by cis‐UCA administered to mice that were always kept in the dark. In the same range of doses as used in the present study, it was shown in our previous study that NAC alone does not affect the CHS response.
Singlet‐Oxygen Generation from Liposomes: A Comparison of 6β‐Cholesterol Hydroperoxide Formation with Predictions from a One‐Dimensional Model of Singlet‐Oxygen Diffusion and Quenching
Authors: Fu Yingxian , Sima Paul D. , Kanofsky Jeffrey R. 
Published: January 2008

Abstract— We measured 6β‐cholesterol hydroperoxide (6β‐CHP), a specific singlet‐oxygen (O2(δg)) product, during irradiation of unilamellar dimyristoyl 1‐α‐phosphatidylcholine liposomes containing cholesterol and zinc phthalocyanine (ZnPC). The effects of liposome size, the hydrophobic (O2(1δg)) quencher, β‐carotene, and hydrophilic O2(1δg) quenchers upon the amount of 6β‐CHP formed were determined and interpreted in terms of a one dimensional model of 2(1δg) quenching and diffusion. The model correctly predicted (1) that the amount of 6β‐CHP was increased with increasing liposome size, (2) that P‐carotene was more effective at reducing 6β‐CHP formation in 400 nm diameter liposomes than 100 nm diameter liposomes and (3) that the hydrophilic quencher, water, was also more effective in large liposomes than in small liposomes.The hydrophobic quencher, β‐carotene, was more effective at reducing the formation of 6β‐CHP than at reducing the 1270 nm O2(1δg) emission. This difference was found to be due to the size distribution present in the liposome preparations because the difference between the 6β‐CHP data and the 1270 nm emission data was much smaller in liposome preparations with a narrow size distribution. When a significant size distribution was present, the 6β‐CHP data were weighted more heavily with large‐diameter liposomes, while the 1270 nm emission data were weighted more heavily with small‐diameter liposomes.
Mutation of Arginine 134 to Lysine Alters the pKas of Key Groups Involved in Proton Pumping by Bacteriorhodopsin
Authors: Misra Saurav , Martin Charles , Kwon Oh‐Hoon , Ebrey Thomas G. , Chen Ning , Crouch Rosalie K. , Menick Donald R. 
Published: January 2008

Abstract— Arginine 134 is located near the extracellular surface of bacteriorhodopsin (bR) and may interact with one or more nearby glutamate residues. In the bR mutant R134K, light‐induced Schiff‐base deprotonation (formation of the M intermediate) exhibits several kinetic components and has a complex pH dependence. The kinetics and pH dependence of M formation were analyzed using the following general guidelines for interpreting M formation: (1) The fastest component of M formation reflects the redistribution of the Schiff‐base proton to D85, the usual proton acceptor, in response to the change in the proton affinities of the Schiff base and D85 early in the photocycle; (2) Two additional components of M formation reflect transitions between spectroscopically similar substates of M. By applying these guidelines, supplemented by information about the pKas of D85 and the proton release group from acid (purple‐to‐blue) and alkaline titrations of the absorption spectra of the unphotolyzed R134K pigment, we explain the pH dependence of M formation as being due to titration of the counter‐ion, D85, and of the proton release group. We calculate, in R134K, that the pKa of D85 is 4.6 in the unphotolyzed state, while the pKa of the proton release group is 8.0 in the unphotolyzed state but drops to ?5.8 in the M intermediate. The same value for the pKa of the proton release group in the M intermediate is obtained when we use photocurrent measurements to monitor proton release.The altered values of these pKas relative to the corresponding values in wild‐type bR suggest that D85 and the proton release group are coupled more weakly in R134K than in the wild type.
Sunscreen Protection Against Ultraviolet Radiation‐induced Pyrimidine Dimers in Mouse Epidermal DNA
Authors: Ley Ronald D. , Fourtanier Anny 
Published: January 2008

ABSTRACTPyrimidine dimers were measured in epidermal DNA of SKH:HRI mice following exposure to solar‐simulated UV radiation (SSUV, 290–400 nm) or to UVA (320–400 nm). Mice were exposed to SSUV or UVA after topical application (2 mg/cm2) of vehicle, a UVB absorber (5% 2‐ethylhexyl p‐methoxycinnamate [2‐EHMC]), or a broad‐spectrum UVA absorber (5% Mexoryl®SX). The rates of induction of pyrimidine dimers in untreated animals were 5.4 ± 0.57 times 10‐4 (mean ± SEM) and 7.6 ± 0.95 times 10‐6 dimers per 108 Da of epidermal DNA per J/m2 of SSUV and UVA, respectively. Topical application of Mexoryl®SX reduced the rate of induction of pyrimidine dimers in SSUV‐exposed animals to 4.7 ± 0.44 times 10‐5 dimers per 108 Da per J/m2 for a dimer induction protection factor (PF) of 11.5 (5.4 times 10 4/4.7 times 10‐5). The rate of dimer induction in Mexoryl®SX‐treated, UVA‐ex‐posed mice was 0.95 ± 0.2 times 10‐6 dimers per 108 Da per J/m2 (PF = 8.0). The 2‐EHMC at a concentration of 5% (wt/wt) was significantly less effective than Mexoryl®SX in preventing the induction of pyrimidine dimers in animals exposed to either SSUV or UVA. The rates of dimer induction in 2‐EHMC‐treated mice were 8.2 ± 1.1 times 10‐5 and 3.8 ± 0.33 times 10‐6 dimers per Da per J/m2 of SSUV (PF = 6.6) and UVA (PF = 2.0), respectively. Upon normalizing to the efficacy for edema induction, UVA induced approximately one‐fourth the number of pyrimidine dimers per equivalent edematous response when compared to SSUV.
Light‐dependent Oxygen Consumption in Bacteriochlorophyll‐Serine‐treated Melanoma Tumors: On‐line Determination Using a Tissue‐inserted Oxygen Microsensor
Authors: Zilberstein Judith , Bromberg Avraham , Frantz Anatol , Rosenbach‐Belkin Varda , Kritzmann Amnon , Pfefermann Reuven , Salomon Yoram , Scherz Avigdor 
Published: January 2008

ABSTRACTSuccessful application of anticancer therapy, and especially photodynamic therapy (PDT) mediated by type II (PDTII) processes, depends on the oxygen content within the tumor before, during and after treatment. The high consumption of oxygen during type II PDT imposes constraints on therapy strategies. Although rates of oxygen consumption and repletion during PDTII were suggested by theoretical studies, direct measurements have not been reported. Application of a novel oxygen sensor allowed continuous and direct in situ measurements (up to a depth of 8–9 mm from the tumor surface and for several hours) of temporal variations in the oxygen partial pressure (pO2) during PDT. Highly pigmented M2R mouse melanoma tumors implanted in CD1 nude mice were treated with bacteriochlorophyll‐serine (Bchl‐Ser; a new photodynamic reagent) and were subjected to fractionated illumination (700 < λ. < 900 nm) at a fluence rate of 12 mW cm‐2. This illumination led to total oxygen depletion with an average consumption rate of 7.2 uAf(O2) s‐1. Spontaneous reoxygenation (at an average rate of 2.5 µM(O2)/s) was observed during the following dark period. These rates are in good agreement with theoretical considerations (Foster et al., Radiat. Res. 126, 296,1991 and Henning et al, Radiat. Res. 142, 221, 1995). The observed patterns of oxygen consumption and recovery during prolonged periods of light/dark cycles were interpreted in terms of vasculature damage and sensitizer clearance. The presented data support the previously suggested advantages of fractionated illumination for type II photodynamic processes.
Safety Analysis: Relative Risks of Ultraviolet Exposure from Fluorescence Spectroscopy and Colposcopy Are Comparable*
Authors: Brookner Carrie K. , Agrawal Anant , Trujillo E. Vanessa , Mitchell Michele Follen , Richards‐Kortum Rebecca R. 
Published: January 2008

ABSTRACTFluorescence spectroscopy is a promising tool for use in the diagnosis of disease in human tissue. However, few published reports have evaluated the safety of this technique, despite the fact that many spectroscopic systems use UV illumination. This study determined the relative risk associated with light exposure from spectroscopic systems compared with the traditional light sources that are used to illuminate tissue and direct biopsies. We compared spectroscopic detection systems for the cervix to the colposcope, a low‐power microscope routinely used to illuminate the cervix, which does not cause any known photochemical damage. We measured the average spectral irradiance (W/[cm2nm]) and the average tissue exposure time during a diagnostic colposcopy examination. To quantify the relative risks, we multiplied illumination spectra by several action spectra from the literature and compared the areas under the curves corresponding to each procedure. The risk associated with the average power colposcope served as our basis for comparison. We conclude that the risks of illumination using spectroscopic systems are lower than or comparable to those already encountered in routine diagnostic procedures such as colposcopy with an average power colposcope. Spectroscopic examination can be associated with a somewhat higher risk than a colposcopy with the lowest power colposcope or a shorter than average colposcopy. The analysis presented can be repeated to estimate the magnitude of risks associated with other spectroscopic diagnostic devices.
Photophysical Properties of Pyrazinocoumarin Derivatives
Authors: Shim Sang Chul , Han Gyu Seok 
Published: January 2008

AbstractPyrazinocoumarin (PzC), 7‐methoxypyrazinocoumarin (7‐MOPzC) and 5,7‐dimethoxypyrazinocoumarin (5,7‐DMPzC) show the similar UV‐visible absorption spectra as the corresponding coumarins except for more distinct shoulders in the near UV absorption band (300–350 nm), probably due to n * transition. Fluorescence excitation spectra of PzC derivatives in nonpolar solvents have the lowest energy maxima in the region of the shoulders of UV‐visible absorption, indicating the lowest fluorescent state to have the same energy as these shoulders. Fluorescence quantum yields (ρF) of pyrazinocoumarins are on the order of 10 2‐10‐4, much lower than the corresponding coumarins. The activation energies (Ea(nr)) for nonradiative processes (internal conversion, intersystem crossing, etc.) determined by the temperature effect on the fluorescence are 10.2, 6.35 and 6.57 kj/mol for PzC, 7‐MOPzC and 5,7‐DMPzC, respectively. Phosphorescence emission spectra of PzC and 7‐MOPzC are structureless with φP of 0.12 and 0.17, respectively
Anthraquinone Photonucleases: A Surprising Role for Chloride in the Sequence‐Neutral Cleavage of DNA and the Footprinting of Minor Groove‐Bound Ligands
Authors: Armitage Bruce , Schuster Gary B. 
Published: January 2008

AbstractIrradiation of water‐soluble anthraquinone (AQ) reagents in the presence of chloride ions results in the spontaneous, sequence‐neutral cleavage of DNA. Mechanistic studies indicate that cleavage is initiated by chlorine atoms, produced by charge transfer interaction between chloride anion and AQ triplet states. High‐resolution gel electrophoresis suggests that cleavage arises from abstraction of a hydrogen atom from C‐4′ of deoxyribose units. The targeting of this hydrogen, which is located in the minor groove of duplex DNA, can be effectively blocked by netropsin and, to a lesser degree, berenil, leading to photofootprinting of these minor groove‐binding drugs.
Continuous Photoreduction of Methyl Viologen Using Disubstituted Terthiophenes and EDTA in Aqueous Solution
Authors: Kim Young‐Sug , McNiven Scott , Ikebukuro Kazunori , Karube Isao 
Published: January 2008

AbstractThe continuous photoreduction of methyl viologen by 5,5″‐bis(aminomethyl)‐2,2′:5′,2″‐terthiophene (AT) and 2,2′:5′,2″‐terthiophene‐5,5″‐dicarboxylic acid (CT), using EDTA as a sacrificial electron donor, has been investigated in aqueous solution at various pH. Apparent rates and efficiencies of production of the methyl viologen radical cation (MV+) were found to be dependent on the pH, the concentrations of all three components and the intensity of the incident light. The highest conversion efficiency (77%) was shown by the bis(aminoniethyI (‐substituted terthiophene AT at pH 7.7. The quantum yield for the formation of MV+ under these conditions was 0.24, which is comparable with other common systems
Characterization of Two Light‐Harvesting Subunits Isolated from the Brown Alga Pelvetia canaliculata: Heterogeneity of Xanthophyll Distribution
Authors: Martino Alessandra De , Douady Dominique , Rousseau Bernard , Duval Jean Claude , Caron Lise 
Published: January 2008

AbstractThe main light‐harvesting fraction from Pelvetia canaliculata was isolated on a sucrose density gradient from digitonin‐solubilized chloroplasts. After further solubilization by dodecyl maltoside, the bulk fraction was separated into two subunits by preparative isoelectric focusing. The more acidic brown fraction was mainly composed of 22 kDa polypeptides having an apparent pI of 4.55. Its pigment composition was very simple, containing chlorophyll (Chi) a, Chi c and fucoxanthin. The in vivo spectral properties of fucoxanthin, namely a shift in light absorption to the green and efficient energy transmission to Chi a, were conserved in this subunit. No xanthophyll associated with photoprotection was found in this band, even when obtained from photoinhibited thalli. The less acidic green band contained predominantly 22 kDa polypeptides that were resolved into numerous components by denaturing isoelectric focusing. Its pigment composition was more complex, containing, in addition, pigments of the so‐called xanthophyll cycle. In photoinhibited thalli, about half of the violaxanthin was converted into antheraxanthin and zeaxanthin. All the pigments of the xanthophyll cycle were specifically associated with this subunit, and it may thus have a central role in the thermal dissipation of the absorbed light energy as postulated for light‐harvesting complex II isolated from green plants.
Effectiveness of the Accessory Yellow Fluorescent Protein in the Bacterial Luciferase Reaction Correlates with the Lifetime of the Peroxyhemiacetal Intermediate: The Stereochemistry of the Reaction
Authors: Sirokman Geza , Hastings J. Woodland 
Published: January 2008

AbstractIn the in vitro reaction of Vibrio fischeri Y‐1 luciferase, the dependence of the initial luminescence intensity (Io) and its rate of decay (kd) on the chain‐length of the aliphatic aldehyde are greatly altered by the presence of yellow fluorescent protein (YFP), which functions as an accessory emitter. Whereas with no YFP both kd and Io are maximum for chain lengths ≥ 12, the fraction of the light emitted from the accessory chromophore, measured as the ratio of yellow to blue light (Y/B), is greater with shorter chain‐length aldehydes. Thus, aldehydes that are least efficient in the absence of YFP are more efficient for causing yellow emission in its presence. These results are interpreted on the basis of the expected lifetimes of the peroxyhem‐iacetals with which YFP interacts: high values of kd reflect short peroxyhemiacetal lifetimes, hence less chance of interaction with YFP. The critical dependence on aldehyde chain‐length underlines the importance of stereochemical factors in the bacterial reaction, which are discussed here in the framework of a chemically initiated electron exchange luminescence model.
Chemiluminescence of Cypridina Luciferin Analogs. Part 3. MCLA Chemiluminescence with Singlet Oxygen Generated by the Retro‐Diels‐Alder Reaction of a Naphthalene Endoperoxide
Authors: Fujimori Ken , Komiyama Tomoko , Tabata Hideo , Nojima Takayuki , Ishiguro Katsuya , Sa‐waki Yasuhiko , Tatsuzawa Hidetaka , Nakano Minoru 
Published: January 2008

AbstractThe chemiluminescence of the Cypridina luciferin analog, 2‐methyl‐6‐(p‐methoxyphenyl)‐3,7‐dihydroirnidazo[1,2‐a]pyrazin‐3‐one (MCLA), with O2 (1Δg) generated by the retro‐Diels‐Alder reaction of 3‐(4′‐methyI‐l'‐naphthyl)‐propionic acid endoperoxide was studied in an aqueous solution with pH 7.12 at 37°C. The retro‐Diels‐Alder reaction occurs with a first‐order rate constant of (4.16 ± 0.13) × 10−4/s to quantitatively yield O2 (1Δg) and 3‐(4′‐methyl‐l'‐naphthyl (‐propionic acid. MCLA consumed equimolar amounts of O2 (1Δg) with a second‐order rate constant (6.96 ± 0.27) × 108/M/s to emit light in an aqueous solution with pH 7.12 at 37°C. The chemiluminescence spectrum was identified as the fluorescence spectrum of 2‐acetylamino‐5‐(p‐methoxyphenyl)pyrazine (OMCLA), a major chemiluminescence reaction. Chemiluminescence spectra and product yields for MCLA reactions with O21Δg, with O2 (3Σ−g) and with superoxide anion radicals are identical, suggesting that all of these reactions occur via a common MCLA‐2‐hydrope‐roxide intermediate formed by a combination of MCLA radicals and superoxide anion radicals. We have established practical use of NEPO as an O2 (1Δg) source and MCLA as a biological probe for detecting O2 (1Δg).
Photosensitized Oxidation of Oxopurines by Rose Bengal†
Authors: Murgida Daniel H. , Aramendía Pedro F. , Balsells Rosa Erra 
Published: January 2008

AbstractPhotosensitized oxidations of oxopurines (OP) as caffeine, theophylline, theobromine and 1,3,7‐trimethyluric acid (TMU) by Rose Bengal were investigated. In all cases photooxidations occur by a type II mechanism. Reactive and nonreactive 1O2 quenching rate constants by OP were determined in different solvents. Based on the correlations of the rate constants with different solvent parameters (α, β, ET[30], AN, DN, *,), the initial formation of an exciplex between 1O2 and OP is proposed that evolves to a zwitterionic transition state. Some reaction products were characterized, among them 3‐mefh‐yl‐5‐(methylamine)‐1,5‐dehydrohydantoin was obtained as the main photooxidation product of TMU. A reaction mechanism is proposed for the formation of this and other reaction products.
Assessment of the Effects of Various UV Sources on Inactivation and Photoproduct Induction in Phage T7 Dosimeter
Authors: Fekete A. , Vink A. A. , Gaspar S. , Berces A. , Modos K. , Ronto Gy. , Roza L. 
Published: January 2008

AbstractThe correlation between the biologically effective dose (BED) of a phage T7 biological dosimeter and the induction of cyclobutane pyrimidine dimers (CPD) and (6‐4) photoproducts ((6‐4)PD) in the phage DNA was determined using seven various UV sources. The BED is the inactivation rate of phage T7 expressed in HT7 units. The CPD and (6‐4)PD were determined by lesion‐specific monoclonal antibodies in an immunodot‐blot assay. The various lamps induced these lesions at different rates; the relative induction ratios of CPD to (6‐4)PD increased with increasing effective wavelength of irradiation source. The amount of total adducts per phage was compared to the BED of phage T7 dosimeter, representing the average number of UV lesions in phage. For UVC (200–280nm radiation) and unfiltered TL01 the number of total adducts approximates the reading; however, UV sources having longer effective wavelengths produced fewer CPD and (6‐4)PD. A possible explanation is that although the most relevant lesions by UVC are the CPD and (6‐4)PD, at longer wavelengths other photoproducts can contribute to the lethal damage of phages. The results emphasize the need to study the biological effects of solar radiation because the lesions responsible for the lethal effect may be different from those produced by various UV sources.