bluuebunny/crossref_metadata_2025_split huggingface dataset:
UV‐INDUCED DNA DEGRADATION IN THE CYANOBACTERIUM SYNECHOCYSTIS PCC 6308
Authors: O'Brien Philip A. , Houghton James A. 
Published: January 2008

AbstractUltraviolet radiation‐induced DNA degradation has been demonstrated in the unicellular cyanobacterium Synechocystis PCC 6308. The extent of DNA degradation was greatly reduced by inhibition of DNA replication by preirradiation dark incubation and degradation was completely inhibited by exposure of irradiated cells to photoreactivating wavelengths. DNA degradation was not observed when irradiated cells were incubated in the presence of the excision repair inhibitors caffeine and acriflavin, suggesting that degradation is a manifestation of excision repair of pyrimidine dimers in Synechocystis. Increasing UV fluences resulted in an increase in the final extent of DNA degradation. However, at higher fluences degradation was inhibited, suggesting saturation of the excision repair system. Incubation of irradiated cells under conditions which inhibit protein synthesis greatly increased the extent of DNA degradation and the time over which it occurred. Exposure of cells to a sublethal fluence of UV greatly reduced the extent of DNA degradation produced by a challenge fluence administered after 24 h incubation providing evidence for inducible DNA repair activity in cyanobacteria.
MODE OF ACTION OF α‐TERTHIENYL ON ESCHERICHIA COLI: EVIDENCE FOR A PHOTODYNAMIC EFFECT ON MEMBRANES
Authors: Downum K. R. , Hancock R. E. W. , Towers G. H. N. 
Published: January 2008

AbstractThe photodynamic effects of α‐terthienyl (αT) in near‐UV light (UV‐A) onEscherichia colishowed close agreement with the light absorption of αT at different wavelengths suggesting that αT is the primary absorbing molecule responsible for the photosensitized reaction. Studies with DNA repair deficient mutants ofE. coliindicated that the bactericidal action of αT/UV‐A was not mediated by DNA damage, in direct contrast to the well‐known photosensitizer, 8‐methoxypsoralen. By using a closed borosilicate glass reaction vessel and various gas mixtures, it was demonstrated that photosensitization of bothE. coliand a more resistant bacterium,Pseudomonas aeruginosa, was absolutely dependent on the presence of oxygen. The rate of killing by αT/UV‐A showed a rather small dependence on preincubation temperatures, with quite rapid killing at 5°C, suggesting that the movement of αT across the cytoplasmic membrane ofE. coliis not the rate limiting step in killing and perhaps is not even necessary for killing. Sodium dodecyl sulphate‐polyacrylamide gels of cell membrane proteins after 15 and 30min of treatment with αT/UV‐A showed substantial random crosslinking of these proteins. The results taken overall suggest that αT is a photodynamic photosensitizer which exerts its primary effect at the level of the cytoplasmic membrane.
PHOTO ACTIVATION OF ISOFLAVONOID PHYTOALEXINS: INVOLVEMENT OF FREE RADICALS
Authors: Bakker J. , Gommers F. J. , Smits L. , Fuchst A. , Vries F. W. de 
Published: January 2008

Abstract— Upon irradiation with ultraviolet light the isoflavonoid phytoalexins phaseollin, 3,6a, 9‐trihydroxypterocarpan, glyceollin, tuberosin and pisatin, but not medicarpin, brought about inactivation ofglucose–6‐phosphate dehydrogenase in an in vitro assay system. Photoinactivation of the enzyme by photoactivated pisatin in air‐saturated solutions was hardly affected by singlet oxygen quenchers such as NaN3, bovine serum albumin, histidine or methionine. Neither addition of the hydroxyl radical scavengers mannitol, Na‐benzoate and ethanol nor the presence of catalase or supcroxide dismutase protected the enzyme against photoinactivation, suggesting that OH, H2O2 and O2 are not the reactive oxygen species involved. However, the free radical scavenger S‐(2‐amino‐ethyl)isothiouronium bromide hydrobromide (AET) protected the enzyme against inactivation by photoactivated pisatin. Direct evidence for the generation of free radicals was obtained by ESR measurements of solutions of phaseollin, pisatin and medicarpin in hexane irradiated with ultraviolet light in the presence or absence of O2. Phaseollin produced the most stable free radicals, whereas medicarpin hardly gave rise to free radical formation; pisatin took a somewhat intermediate position by producing a strong ESR signal which, however, decayed rather quickly. Photodegradation of all phytoalexins, except for medicarpin, was accompanied with loss of fungitoxicity, as shown in thin‐layer chromatographic bioassays, and formation of new products.These results indicate free radical formation as the causative process for photoinactivation of enzymes by photoactivated isoflavonoid phytoalexins.
OXIDATIVE DEGRADATION OF LIGNIN BY PHOTOCHEMICAL AND CHEMICAL RADICAL GENERATING SYSTEMS
Authors: Gold Michael H. , Kutsuki Hidetoshi , Morgan Meredith A. 
Published: January 2008

Abstract—Oxidation of specifically radiolabeled 14C‐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] and 14C‐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] and 14C‐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 of 14C‐methoxy labeled lignin and significant degradation of 2‐(14C‐sidechain] and 14C‐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 heterogeneous, optically inactive and random biopolymer.
DETERMINATION OF THEIN VIVOABSORPTION AND PHOTOSYNTHETIC PROPERTIES OF THE LICHENAcarospora schleicheriUSING PHOTO ACOUSTIC SPECTROSCOPY
Authors: O'Hara Ellen P. , Tom Roderick D. , Moore Thomas A. 
Published: January 2008

Abstract—Photoacoustic spectroscopy was used to determine thein vivospectra of the stratified components of the lichenAcarospora schleicheri.There were three pigmented layers observed by the photoacoustic method: an absorption band associated with the pigment rhizocarpic acid, a bulk cytochrome absorption, and the absorption of the algal chloroplast. Due to the different absorption properties of these distinct layers, the photoacoustic technique was able to monitor the physical effect of hydration on the lichen. Hydration of the lichen reduced the scatter of the sample, increasing the effective incident light intensity within the sample. Hydration also resulted in an increase in the optical absorption coefficient of the algal layer, which was interpreted as a movement of the algal chloroplast in response to low light fluence and hydrated conditions.The photoacoustic technique was also used to monitor the relative photosynthetic activity of the algae within the lichen in a hydrated and dehydrated state. The photosynthetic assay could detect photosynthetic activity in the hydrated state but not in the dehydrated state. In addition, the photosynthetic response was found to be induced and repressed with light and dark periods respectively and its detection was limited at high frequencies by the damping of the thermal wave from the algal layer.
THE ROLE OF A PHOTOCHEMICAL REACTION ON THE DEACTIVATION OF EXCITED 4,5′,8‐TRIMETHYLPSORALEN IN ETHANOL
Authors: Ishikawa Mitsuru , Kikuchi Koichi , Kokubun Hiroshi 
Published: January 2008

Abstract—The transient absorption of an intermediate R which is formed from an excited state higher than the lowest triplet state was observed in an ethanol solution of 4,5′,8‐trimethylpsoralen (TMP). The temperature effects on the fluorescence yield φF for TMP and on the initial absorbance DR of R were studied and it was found that DR increases with increasing temperature whereas φF decreases. These results indicate that a photochemical reaction plays an important role on the deactivation of TMP in the excited singlet state
THE DECONVULATION OF ABSORPTION SPECTRA OF GREEN PLANT MATERIALS—IMPROVED CORRECTIONS FOR THE SIEVE EFFECT
Authors: Latimer Paul 
Published: January 2008

Abstract—The extinction (absorbance, optical density) of a suspension of algal cells or chloroplasts, etc. can be an a linear function of the absorption coefficient of the cell contents, even when the effects of scattering are negligible. The deviation from linearity is Duysens' sieve effect. The heights of absorption maxima of suspensions are depressed as compared with those of the “particle” contents. Duysens proposed an expression for correcting for this distortion; that expression proves to be a special approximate case of a more general one. This paper proposes an improved method of correction which utilizes this general expression, conventional expressions for particle absorption based on the Lorentz‐Mie and Aden and Kerker equations for scattering and absorbing, and iterative methods for numerically deducing particle absorption coefficients from suspension parameters. The procedure is illustrated by applying it to previous experimental spectra of Chlorellu cells and spinach chloroplasts.
DESTRUCTION OF MICROSOMAL CYTOCHROME P‐450 BY REACTIVE OXYGEN SPECIES GENERATED DURING PHOTOSENSITIZATION OF HEMATOPORPHYRIN DERIVATIVE
Authors: Dixit Rakesh , Mukhtar Hasan , Bickers David R. 
Published: January 2008

AbstractRat liver microsomal cytochrome P‐450 undergoes rapid destruction in the presence of hematoporphyrin derivative (HpD) and solar radiation (∼ 400 nm). Destruction of cytochrome P‐450 is associated with the formation of cytochrome P‐420 and significant loss of microsomal haem. Quenchers of singlet oxygen including 2,5‐dimethylfuran, histidine, ß‐carotene, and ascorbic acid and inhibitors of the hydroxyl radical such as benzoate, mannitol, and ethanol prevent deterioration of the microsomal haem‐protein, whereas superoxide dismutase and catalase are ineffective in this regard. These results indicate that generation of singlet oxygen during hematoporphyrin photosensitization is associated with destruction of microsomal cytochrome P‐450 and haem.
IN VIVO FLUORESCENCE SPECTROSCOPY OF CHLOROPHYLL IN VARIOUS UNRIPE AND RIPE FRUIT
Authors: Gross Jeana , Ohad Itzhak 
Published: January 2008

Abstract—Low temperature (77 K) fluorescence emission spectra of slices obtained from the peel and various layers of the pericarp were recorded for fruits which remain green or undergo color break during ripening.Fluorescence emission peaks characteristic of the photosystem II antennae (λF 686 nm) and reaction center (λF 696 nm), as well as of the photosystem I antenna (λF 730‐740 nm), were present in the peel and all parts of the green pericarp of ripe kiwi, avocado and cantaloupe, as well as in ripe tomato and tangerine after color break. The pattern of the fluorescence emission spectra of all samples except that of the kiwi fruit was similar to that obtained from green photosynthetic tissue of leaves, indicating a normal organization of the chlorophyll‐containing complexes of thylakoidal membranes. This pattern is characterized by a significantly higher emission at 730‐740 nm relative to that of the 696 and 686 nm peaks. In contradistinction, the fluorescence emission at 686 and 696 nm was higher than that at 730 nm in the kiwi fruit, indicating a reduction in the size of the photosystem I antenna chlorophyll. In the innermost yellowish layers of the kiwi pericarp, a further loss of this antenna occurred, as well as disorganization of the photosystem II complex. The above conclusions are suggested also by measurements of variable fluorescence kinetics.The results presented here indicate that fluorescence spectroscopy might be used as a tool for the study of chlorophyll organization during the growth and ripening periods of fruit.
POSSIBLE INVOLVEMENT OF MEMBRANE DAMAGE IN THE IN ACTIVATION BY BROAD‐BAND NEAR‐UV RADIATION IN Saccharomyces cerevisiae CELLS
Authors: Ito Atsushi , Ito Takashi 
Published: January 2008

AbstractMultiple cellular effects of near‐UV radiation (300‐380 nm) on inactivation, disruption of the permeability barrier and induction of gene conversion at the trp 5 locus were simultaneously measured in the same culture of a diploid strain of the yeast Saccharomyces cerevisiae in order to assess the critical lethal damage. Inactivation of exponential phase cells in water appeared to be closely related to the disruption of the permeability barrier. Inactivation and membrane damage were remarkably oxygen dependent, whereas the induction of genetic changes was very low and dependent much less on oxygen. The dependence on the temperature for inactivation and membrane damage was both low, conforming with the expectation that the processes are mainly photochemical and not enzymatic. These features are very contrasted with the characteristics of far‐UV radiation effects. Possible involvement of membrane damage in near‐UV inactivation of exponential phase yeast cells is discussed.
PICOSECOND FLUORESCENCE KINETICS and ENERGY TRANSFER IN THE ANTENNA CHLOROPHYLLS OF GREEN ALGAE*
Authors: Haehnel Wolfgang , Holzwarth Alfred R. , Wendler Joachlm 
Published: January 2008

AbstractSingle‐photon timing measurements on flowing samples of Chlorella vulgaris and Chlamydomonas reinhardtii at low excitation intensities at room temperature indicate two main kinetic components of the fluorescence at open reaction centers (F0) of photosystem II with lifetimes of approx. 130 and 500 ps and relative yields of about 30 and 70%. Closing the reaction centers progressively by preincubation of the algae with increasing concentrations of 3‐(3′,4′‐dichlorophenyl)‐l,l‐dimethylurea (DCMU) and hydroxylamine gave rise to a slow component with a lifetime increasing from 1.4 to 2.2 ns (Fmax) The yield of the slow component increased to 65‐68% of the total fluorescence yield in parallel to a decrease in the yield of the fast component to a value close to zero at the fmax‐level. The 130 ps lifetime of the fast component remained unchanged. The middle component showed an increase of its lifetime from 500 to 1100 ps and of its yield by a factor of 1.5. Spacing of the ps laser pulses by 12 μs allowed us to resolve a new long‐lived fluorescence component of very small amplitude which is ascribed to a small amount of chlorophyll not connected to functional antennae.The opposite dependence of the yield of the fast and the slow component on the state of the reaction centers at almost constant lifetimes is consistent with a mechanism of energy conversion in largely separately functioning photosystem II units. Yields and lifetimes of these two components are in agreement with the high quantum yield of photosynthesis. The lower lifetime limit of 1.4 ns of the slow component is assigned to the average transfer time of an excited state from a closed to a neighboring open reaction center and the increase in the lifetime to 2.2 ns is evidence for a limited energy transfer between photosystems II.Relative effects of changing the excitation wavelength from 630 to 652 nm on the relative fluorescence yields of the kinetic components were studied at the fluorescence wavelengths 682, 703 and 730 nm. Our data indicate that (i) the middle component has its fluorescence maximum at shorter wavelength than the fast component and (ii) that the antennae chlorophylls giving rise to the middle component are preferentially excited by 652 nm light. It is concluded that the middle component originates from the light‐harvesting chlorophyll alb protein complexes and the major portion of the fast component from the chlorophyll a antennae of open photosystem II reaction centers.
TEMPERATURE DEPENDENCE OF INDUCTION OF CYCLOBUTANE‐TYPE PYRIMIDINE PHOTODIMERS IN HUMAN FIBROBLASTS BY 313 nm LIGHT
Authors: Niggli Hugo J. , Cerutti Peter A. 
Published: January 2008

AbstractThe rate of cyclobutane‐type pyrimidine photodimerization with 313 nm light was determined in confluent cultures of xeroderma pigmentosum cells of group A. A new method was developed for the determination of sodium borohydride reduced thymine‐thymine (TT) and cytosine‐thymine (CT) dirners by high pressure liquid chromatography. It was found that the yield of dimerization andtheratioof CT/TT depended on the irradiation temperature in the physiological fluence range of 2.25 to 15 kJ m−2. Both were significantly higher at 37 than at 0°C.
A MODULATED LAMP SYSTEM FOR SOLAR UV‐B (280‐320 nm). SUPPLEMENTATION STUDIES IN THE FIELD
Authors: Caldwell M. M. , Gold W. G. , Harris G. , Ashurst C. W. 
Published: January 2008

AbstractPrecise control and modulation of fluorescent sunlamps are necessary for ecologically valid simulation of solar UV‐B (280‐320 nm) radiation enhancement which would correspond to ozone reduction. A control system is described which allows lamp emittance to be modulated over a large dynamic range (50:1), permits stable lamp operation and starting at low temperatures, and provides a sensitive feedback loop to compensate for both atmospheric conditions, such as cloud cover, as well as changes in radiant emittance from the lamps resulting from factors such as temperature and lamp age.
CAROTENOID PIGMENT ADMINISTRATION and DELAY IN DEVELOPMENT OF UV‐B‐INDUCED TUMORS
Authors: Mathews‐Roth Micheline M. 
Published: January 2008

Abstract—The results of two studies are reported. In the first study, the carotenoid pigments, β‐carotene. canthaxanthin and phytoene were administered to mice after one UV‐B‐induced skin tumor had developed, to see if carotenoid administration would delay the development of subsequent tumors. Canthaxanthin significantly delayed the development of subsequent tumors. In the second study, the same pigments were administered starting 10 weeks before, and for 24 weeks after, exposure to a large single fluence (8 × 104J/m2) of UV‐B radiation, to determine the effect of the pigments on tumor development. Phytoene significantly prevented the development of tumors to this fluence of radiation.
TYROSINE DOES NOT ENHANCE TANNING IN PIGMENTED HAIRLESS MICE
Authors: Agin Patricia Poh , Wilson Diane K. , Shorter Gwendolyn G. , Sayre Robert M. 
Published: January 2008

AbstractPre‐tan products claiming to enhance pigmentation contain tyrosine as an‘active’ ingredient. Tyrosine is said to penetrate into the cell's metabolic pool, increasing the concentration of precursors essential to melanin formation, so that subsequent melanogenesis will be intensified. To address this theory, female pigmented hairless mice were irradiated three times weekly using FS‐20 lamps while receiving 0.01% tyrosine or 0.01% glycine either as a diet supplement or topically daily for 4 weeks. Control groups received the supplement or topical application without irradiation. Two additional groups were treated with a commercial pre‐tan enhancing product for 2 weeks prior to use of one group as a control, and the other irradiated as above. At the end of the experiment whole skin sections were taken for histological evaluation. Forward scattering absorbance spectrophotometry was performed on whole skin and separated epidermis.Comparison of averaged forward scattering absorbance spectra for each group revealed that there was no significant difference in the skin optics of any of the irradiated groups, while each irradiated group was significantly different from its non‐irradiated control. The spectra of all treated controls fell within pre‐established normal control limits. Histological evaluation by Fontana‐Masson staining showed that all irradiated groups had developed noticeable pigmentation not present in the controls. Of the groups receiving topical applications, the irradiated tyrosine group developed strikingly less pigmentation than did the irradiated glycine group. The irradiated pre‐tan product treated group was intermediate in the development of pigmentation. Melanocytes were visible throughout the dermis and epidermis of the irradiated groups, whereas only scattered dermal melanocytes were found in the controls. It appears that oral or topical tyrosine did not enhance pigmentation present with or without irradiation, detected optically or histologically.
ACTINIC RETICULOID–AN IDIOPATHIC PHOTODERMATOSIS WITH CELLULAR SENSITIVITY TO NEAR ULTRAVIOLET RADIATION
Authors: Botcherby P. K. , Magnus I. A. , Marimo B. , Giannelli F. 
Published: January 2008

Abstract— Long wavelength UV radiations (320–400 nm) cause persistent inhibition of RNA synthesis and marked cytopathic changes in fibroblasts from patients with actinic reticuloid (AR) but not in those from patients with Bloom syndrome or xeroderma pigmentosum. Furthermore, the AR cells show abnormal DNA fragmentation when they are irradiated at temperatures compatible with enzyme activity. Germicidal UVR (ca. 95% 254 nm) stimulates DNA repair synthesis and inhibits DNA replication to a normal extent in the AR cells.Thus, actinic reticuloid, a severe photodermatosis, characterised by skin sensitivity to UV‐B, UV‐A and part of the visible spectrum and by infiltrates reminiscent of mycosis fungoides, is a human disease with in vitro cellular sensitivity to UV‐A and, to our knowledge, is also the first to be reported.We advance the hypothesis that inefficient cellular neutralisation of free radicals may explain the cellular phenotype of actinic reticuloid and contribute to the establishment of a vicious circle that would favour the chronic clinical course and persistent lympho‐histiocytic skin infiltrates characteristic of the disease.
THE PHOTOCHEMISTRY OF PIPERAZINE‐2,5‐DIONE IN AQUEOUS SOLUTION
Authors: Coyle J. D. , Hill R. R. , Randall D. 
Published: January 2008

Abstract The aqueous photochemistry of deoxygenated solutions of piperazine‐2,5‐dione was investigated and three products were isolated in low yield using preparative high‐performance liquid chromatography: 3,3′‐bis(piperazine‐2,5‐dione) (1), oxamide and N‐methyloxamide. The structure of 1 was established by infrared, mass and high‐field proton magnetic resonance spectroscopy, and by the synthesis of its meso diastereoisomer. A 1:2 mixture of meso and racemic diastereoisomers of 1 was formed in good yield in thermally or photochemically initiated reactions of piperazine‐2,5‐dione with t‐butyl peroxide in aqueous t‐butanol.The rate of photolysis of aqueous piperazine‐2,5‐dione was markedly enhanced in the presence of iron(II) ions, copper(II) ions or powdered titanium dioxide. A diastereomeric mixture of 1, oxamide and N‐methyloxamide were isolated from the reaction with iron(II) ions. The possibility that oxamides were formed in these reactions via reaction with atmospheric oxygen was eliminated in a series of control experiments.The results suggest α‐carbon radicals are important in the photolysis of peptides in fluid aqueous media, possibly as a consequence of photoinduced electron transfer. No significant adduct formation could be detected when mixtures of piperazine‐2,5‐dione and uracil or thymine were irradiated in frozen aqueous solution.
A PORPHYROPSIN‐LIKE ACTION SPECTRUM FROM Xenopus MELANOPHORES
Authors: Lythgoe J. N. , Thompson M. 
Published: January 2008

AbstractLight causes an aggregation of the melanosomes in the melanophores of isolated dark adapted Xenopus tadpole tails. Dose response curves for 6 wavelengths of light were measured, and using a standard response, an action spectrum was derived that can be fitted to a porphyropsin absorbance curve.