bluuebunny/crossref_metadata_2025_split huggingface dataset:
PHOTOPHYSICAL STUDIES ON THE BINDING OF TETRASULFONATOPHENYLPORPHYRIN TO LENS PROTEINS
Authors: Roberts Joan E. , Atherton Stephen J. , Dillon James 
Published: January 2008

Abstract— Previous studies have shown that mesotetra(p‐sulfonatophenyl)porphine (TPPS) binds to lens proteins. This characteristic should increase the residence time of the sensitizer in the lens and therefore enhance the probability of inducing photooxidative damage to that tisue in vivo. Subsequent in vivo studies have verified that contention. The present studies were performed to determine the effect of such binding on the spectroscopy and photophysics of the porphyrins.It was found that the binding of TPPS (1) quenches the fluorescence of lens proteins, (2) causes a shift in the ground state absorption spectra, fluorescence excitation spectra and the triplet excited state spectrum of TPPS to longer wavelengths and (3) results in an increase in the triplet state lifetime of TPPS. In the presence of the isolated crystallins the average triplet lifetime increases in the following order: gamma < beta < alpha.
STUDY OF XANTHONE‐CYCLODEXTRIN INCLUSION COMPLEXES IN THE SOLID STATE USING TIME‐RESOLVED DIFFUSE REFLECTANCE‐LASER FLASH PHOTOLYSIS*
Authors: Barra Monica , Bohne Cornelia , Scaiano J. C. 
Published: January 2008

AbstractThe photochemistry of xanthone complexed with cyclodextrins (α‐, β‐ and γ‐CD) in the solid state has been examined by diffuse reflectance laser flash photolysis. The first half‐life for xanthone triplet decreases as the size of the CD cavity increases; long‐lived ketyl radicals are observed in the cases of β‐ and γ‐CD. These changes in photobehavior are attributed to the restrictions on the mobility of included xanthone imposed by the CD structure.
PHOTOPHYSICAL PROPERTIES AND CONFORMATIONAL EQUILIBRIUM OF trans‐6‐STYRYLQUINOXALINE
Authors: Kim Maeng Sup , Shim Sang Chul 
Published: January 2008

AbstractThe wavelength dependent fluorescence spectra and bi‐exponential fluorescence decays of trans‐6‐styrylquinoxaline (6‐StQx) indicate that two conformers exist in equilibrium in solution. When comparing the conformationally restricted analogues (5Me‐6‐StQx and 7Me‐6‐StQx) with 6‐StQx, the short‐wavelength absorbing conformer of 6‐StQx can be assigned to conformer(A) and the long‐wavelength absorbing component to conformer(B). The temperature effects on the fluorescence lifetime indicate that the short‐lived conformer(A) is the more stable conformer in non‐polar solvents, while the long‐lived conformer(B) is the stable component in polar solvents. The results of semiempir‐ical AMI and CNDO/S CI calculations on both the ground and excited states are consistent with the conclusions drawn from the spectral data.
ORGANIZATION OF PIGMENT‐PROTEIN COMPLEXES INTO MACRODOMAINS IN THE THYLAKOID MEMBRANES OF WILD‐TYPE and CHLOROPHYLL fo‐LESS MUTANT OF BARLEY AS REVEALED BY CIRCULAR DICHROISM
Authors: Garab G. , Kieleczawa J. , Sutherland J. C. , Bustamante C. , Hind G. 
Published: January 2008

AbstractThe organization of pigment‐protein complexes into large chiral macrodomains was investigated in wild‐type and chlorophyllb‐less mutant thylakoid membranes of barley. The variations in the anomalous circular dichroism bands and in the angular‐dependence of circular intensity differential scattering showed that in wild‐type chloroplasts, the formation of macrodomains was governed by interactions of the light‐harvesting chlorophyllalbcomplexes (LHCII). Two external factors could be identified which regulate the parameters of the anomalous circular dichroism signal: (i) electrostatic screening by divalent cations under conditions that favor membrane stacking and (ii) the osmotic pressure of the medium, which is suggested to affect the lateral interactions between complexes and influence the packing‐density of particles. These two factors governed preferentially the negative and the positive anomalous circular dichroism signals, respectively. In thechlorina f‐2mutant thylakoid membranes, deficient in most chlorophyllbbinding proteins, the formation of macrodomains which gave rise to the anomalous circular dichroism signals was still regulated by these same external factors. However, in the absence of major LHCII polypeptides the formation of macrodomains was apparently mediated by other complexes having weaker interaction capabilities. As a consequence, the size of the macrodomains under comparable conditions appeared smaller in the mutant than in the wild‐type thylakoid membranes.Circular dichroism is a valuable probe for examining the long‐range interactions between pigment‐protein complexes which participate in the formation and stabilization of membrane ultrastruc‐ture. A functional role of macrodomains in long‐range energy migration processes is proposed.
RESISTANCE TO PHOTODYNAMIC THERAPY IN RADIATION INDUCED FIBROSARCOMA‐1 and CHINESE HAMSTER OVARY‐MULTI‐DRUG RESISTANT CELLS in vitro
Authors: Singh Gurmit , Wilson Brian C. , Sharkey Sheila M. , Browman George P. , Deschamps Paula 
Published: January 2008

AbstractA degree of resistance to photodynamic therapy (PDT) has been induced in radiation‐induced fibrosarcoma‐1 (RIF‐1) tumor cells by repeated photodynamic treatment with Photofrin (4 or 18 h incubation) in vitro to the 0.1‐1% survival level, followed by regrowth from single surviving colonies. The resistance is shown as increased cell survival in the strain designated RIF‐8A, compared to the wild‐type RIF‐1 cells, when exposed to increasing Photofrin concentration for 18 h incubation and fixed light exposure. No difference was found between RIF‐1 and RIF‐8A in the uptake of Photofrin per unit cell volume at 18 h incubation.Resistance to PDT was also observed in Chinese hamster ovary‐multi‐drug resistant (CHO‐MDR) cells compared to the wild‐type CHO cells, possibly associated with decreased cellular concentration of Photofrin in the former. By contrast, the PDT‐resistant RIF‐8A cells did not show any cross‐resistance to Adriamycin, nor was there any significant drug concentration difference between RIF‐1 and RIF‐8A. These findings suggest that different mechanisms are responsible for PDT‐induced resistance and multi‐drug resistance.
ROOM TEMPERATURE TIME‐RESOLVED IN μs RANGE DELAYED LUMINESCENCE OF CHLOROPHYLL a AND CHLOROPHYLL‐LUTEIN MIXTURE SOLUTIONS
Authors: Planner Alfons , Frackowiak Danuta 
Published: January 2008

ReferencesUsing time‐resolved in μS range luminescence spectroscopy, we observed at 20°C the emission of chlorophylla,pheophytinaand chlorophyll a‐lutein mixture solutions. This delayed emission exhibits several maxima in the650–750 nm region. The positions and kinetics of decay of delayed emission bands depend on chlorophyll concentration, and vary as a result of pheophytinization and addition of lutein. Our results can be explained by supposition that upon excitation, charge transfer species are formed in various pigment complexes. The back electron transfer reactions yield chlorophyll excited singlet states contributing to observed delayed emission. Delay in emission seems to be due also to the trapping of excitation on the triplet states of various forms of pigment and its detrapping with the participation of thermal energy followed by energy transfer to the forms of pigment characterized by different decay times.
ENERGY DISSIPATION AND PHOTOPROTECTION MECHANISMS DURING CHLOROPHYLL PHOTOBLEACHING IN THYLAKOID MEMBRANES
Authors: Miller Nathalie , Carpentier Robert 
Published: January 2008

AbstractThe kinetics of chlorophyll photobleaching were followed in whole thylakoid membranes as well as in photosystem I and photosystem II submembrane fractions. The onset of photobleaching was characterized by a slow rate which indicated the presence of energy traps implicated in the photoprotection of the bulk pigments. The pigments in photosystem I submembrane fractions bleached at a faster rate than those in photosystem II counterparts, the latter being more sensitive towards photoinhibition. An analysis of the pigment‐protein complexes isolated from whole thylakoid membranes during the course of a photobleaching experiment has shown that the core‐antenna complexes, including CP29, are more sensitive to illumination than the peripheral complexes. The absorption spectra of the CPI and CP29 complexes presented a blue shift of the red absorption maximum after partial photobleaching, indicative of a non‐homogeneous bleaching of the holochromes in these complexes. An analysis of these data points towards the involvement of CP29 in a photoprotection mechanism at the level of photosystem II. The weaker resistance of photosystem I to photobleaching relative to photosystem II and its stronger resistance to photoinhibition is discussed in terms of an energy dissipation pathway in thylakoid membranes.
A NEW REDUCING AGENT OF FLAVINS AND ITS APPLICATION TO THE ASSAY OF BACTERIAL LUCIFERASE
Authors: Lei Ben‐Fang , Becvar James E. 
Published: January 2008

ReferencesCopper(I) plus ethylenediaminetetraacetic acid, Cu(I)‐EDTA, reduces flavins. Using Cu(I)‐EDTA reduction of riboflavin 5′‐phosphate, a new assay method for bacterial luciferase is established. In previous assay methods, flavin and aldehyde substrates for luciferase have been routinely added to luciferase at different times; the new assay permits aldehyde and Cu(I)‐reduced flavin to be injected simultaneously into air‐saturated buffer containing luciferase. In the new assay method using Cu(I), bovine serum albumin is not required, the initial emission intensity is more than twice and the overall yield is about twice of that in the so‐called standard assay for luciferase.
PHOTOCHEMICAL REACTIVITY OF MOLECULES TRAPPED IN SOL‐GEL GLASSES*
Authors: Slama‐Schwok Anny , Avnir David , Ottolenghi Michael 
Published: January 2008

AbstractPhotosensitizers trapped in porous sol‐gel glasses are shown to undergo photoinduced electron transfer with molecules present in the intra‐pore liquid phase. The phenomenon appears to be general, independent of molecular charge and size. The predominant mechanism involves long range electron transfer from, or to, an adsorbed solute molecule and a photosensitizer embedded in the glass. Such long range interactions are also the primary factor leading to a residual photogenerated radical ion pair which is extremely long lived (4–5orders of magnitude longer with respect to the same process in homogeneous solutions). The results bear on artificial photosynthetic devices in which solar energy conversion and storage depends on inhibition of the energy‐wasting back electron transfer reaction.
THE REACTIVITY OF CITRONELLOL and α‐THUJENE WITH SINGLET OXYGEN. RATE CONSTANTS OF CHEMICAL REACTION and PHYSICAL QUENCHING*
Authors: Bouamri M. El , Gorrichon J. P. , Braun A. M. , Oliveros E. 
Published: January 2008

AbstractThe quantum yields of Rose Bengal sensitized photooxidation of citronellol and α‐thujene have been determined as a function of added acceptor and compared with those of furfuryl alcohol as a standard. The results permitted the calculation of the corresponding rate constants of chemical reaction(kT)and physical quenching (Kq) of singlet oxygen. The sum(kT+ kq)has been verified independently by a Stern‐Volmer analysis of the singlet oxygen luminescence quenching. α‐Thujene reacts faster with singlet oxygen than citronellol, physical quenching being negligible in both cases.
BUTYL CONFORMATIONAL REORGANIZATION AS A POSSIBLE EXPLANATION FOR THE LONGITUDINAL FLEXIBILITY OF THE BINDING SITE OF BACTERIORHODOPSIN. THE AZULENE and C‐22 RETINOID ANALOGS*
Authors: Liut Robert S. H. , Liu Corey W. , Li Xiao‐Yuan , Asato Alfred E. 
Published: January 2008

AbstractThe UV‐VIS absorption data of four bacteriorhodopsin (BR) analogs formed from azulene‐retinals of varying polyene chain length show that the one‐bond‐shortened to one‐bond‐lengthened analogs possess comparable opsin shift values to that of BR. A two‐bond‐shortened analog exhibited a much smaller opsin shift. These data, combined with those reported for the C‐22 retinal analog (Tokunaga et al., 1977, Biophys. J. 19,191–198) were analyzed by molecular modelling and computer graphics in terms of a model where conformational flexibility of the appended butyl is the controlling factor in determining ease of pigment formation and protein/substrate interaction.
LONG‐TERM VARIATIONS IN ULTRAVIOLET SUNLIGHT REACHING THE BIOSPHERE: . CALCULATIONS FOR THE PAST THREE DECADES
Authors: Frederick J. E. , Weatherhead E. C. , Haywood E. K. 
Published: January 2008

AbstractThe long‐term data base on atmospheric ozone combined with a set of radiative transfer calculations provides estimates of the variability in ultraviolet (UV) sunlight that should have occurred over the period1957–1988 under clear, pollution‐free skies. Results refer to the earth's surface at specific locations in the Northern Hemisphere and to averages over collections of sites located in three latitude bands from 30 to 64°N. For any one year the annually integrated solar irradiance, weighted by the action spectrum for erythema, typically lies within3–4% of the 32‐year mean. No statistically significant trends span the entire 32‐year time frame. However, over the shorter time period1970–1988 the annually integrated erythemal irradiance shows an upward trend of +2.1 ± 1.2% per decade based on all ozone data at latitudes from 40 to 52°N. No trends exist in lower (30‐39°N) and higher (53‐64°N) latitude bands. We caution that a trend line provides a very simple index of the variability in UV sunlight, and these results should not necessarily be extrapolated into the future.
CHLOROPHYLL PHOTOSENSITIZED ELECTRON TRANSFER REACTIONS IN LIPID VESICLES:ENHANCEMENT IN YIELD OF VECTORIAL ELECTRON TRANSFER ACROSS THE BILAYER FROM REDUCED CYTOCHROME c TO OXIDIZED FERREDOXIN BY ADDITION OF VALINOMYCIN PLUS POTASSIUM ION
Authors: Zhao Zhan‐Gong , Tollin Gordon 
Published: January 2008

AbstractChlorophyll photosensitized electron transfer across a vesicle bilayer from reduced cytochromecin the inner compartment to oxidized ferredoxin in the outer compartment, using propylene diquat as a mediator, has been investigated using both steady‐state and laser flash photolysis methods. One of the factors limiting the quantum yield is the transmembrane potential, which is formed during sample preparation and is increased by the electron transfer process across the membrane bilayer. This limitation can be diminished by the incorporation of valinomycin into the bilayer in the presence of potassium ion. The overall quantum yield can be approximately doubled (up to a total of 22% based on the chlorophyll triplet which is quenched, and 2.8% based on the absorbed quanta) by valinomycin addition. Another quantum yield limitation arises from the accumulation of oxidized cytochrome c in the inner aqueous compartment, which is formed as a consequence of the transbilayer electron transport process and can quench triplet chlorophyll on the inner side of the vesicle. The chlorophyll cation radical generated in this way can participate in the electron exchange equilibrium between chlorophyll molecules located within the bilayer, and thus inhibit electron flow from inside to outside. This acts to limit the extent of cytochromecoxidation to ≤ 50% of the original amount.
DETECTION OF PORPHYRIN EXCITED STATES IN THE INTACT BOVINE LENS
Authors: Roberts Joan E. , Atherton Stephen J. , Dillon James 
Published: January 2008

AbstractPrevious steady state and time resolved spectroscopic studies on porphyrins have shown that the triplet lifetimes of those sensitizers that bind to lens proteins are lengthened by several orders of magnitude. Presented here is an extension of this experiment to measure these transients in an intact bovine lens. As demonstrated by steady state fluorescence spectroscopy and flash photolysis, mesotetra (p‐sulfonatophenyl)porphyrin (TPPS) binds to lens proteins. In air‐saturated aqueous solution, TPPS has a triplet lifetime of 2 μs. In an intact bovine lens the triplet state decayed via biexponential kinetics with lifetimes of 0.16 and 1.6 μs. In addition to a lengthening of the lifetime there was a red shift in the triplet transient spectra of10–20 nm of the porphyrin in the intact lenses.
ENHANCED EXPRESSION OF PROTEIN KINASE C GENE CAUSED BY SOLAR RADIATION
Authors: PEAK JENNIFER G. , WOLOSCHAK GAYLE E. , PEAK MEYRICK J. 
Published: January 2008

Abstract—Natural solar radiation (5 min of midday exposure in mid July, latitude 42°N) induces protein kinase C mRNA almost two‐fold in human epithelioid P3 cells in culture. This response is the same as that following tumor promotion by chemicals. The result indicates a possible role of promotion by solar UV radiation.
PHOTOCONTROL OF HYPOCOTYL ELONGATION IN LIGHT‐GROWNCucumis sativusL. PHOTOSYNTHETIC REQUIREMENT FOR A FLUENCE RATE DEPENDENT PHYTOCHROME RESPONSE
Authors: GABA VICTOR , BLACK MICHAEL , CANAANI ORA , ATTRIDGE TERENCE H. 
Published: January 2008

Abstract—We investigated the role of photosynthesis in the photocontrol of extension growth of the hypocotyl of light‐grownCucumis sativusL. Previous work [Gaba and Black (1985b)Plant Physiol.79, 1011] demonstrated that the inhibition of cucumber hypocotyl elongation is a fluence rate dependent response in red light. However, the relative contributions of phytochrome and photosynthesis to the photon flux dependent inhibition response were not clear. Here we have shown that photoperception by the foliar cotyledons as well as the hypocotyl itself are responsible for fluence rate dependence in red light. The inhibitor of photosynthesis diuron [3‐(3,4‐dichlorophenyl)‐1, 1‐dimethylurea] reduced both the magnitude of inhibition and the fluence rate dependency in red light, indicating an involvement of photosynthesis. Furthermore, the growth of non‐pigmented seedlings (treated with the herbicide norflurazon) was less inhibited by red light, with no fluence rate dependency. In particular, inhibition due to cotyledon photoperception was completely lost in non‐pigmented (norflurazon‐treated) plants, and much reduced by diuron treatment. Hypocotyl‐perceived red light inhibition was only slightly reduced by treatment with norflurazon and diuron. Photosynthesis was compared directly to photo‐inhibition of growth: the photon flux response curve of oxygen evolution of greenCucumiscotyledons was distinctly different from that of hypocotyl inhibition. In conclusion, photosynthesis is an essential requirement for the cotyledon‐perceived inhibition, but the response itself is not due to photosynthesis.
TANNING SALON EXPOSURE SUPPRESSION OF DNA REPAIR CAPACITY AND MITOGEN‐INDUCED DNA SYNTHESIS
Authors: LARCOM L. L. , MORRIS T. E. , SMITH M. E. 
Published: January 2008

Abstract—Mitogen responsiveness and the capacity to repair genetic damage were measured in lymphocytes collected from young, healthy, adult Caucasians immediately before exposure in commercial tanning salons and again 24 h after exposure. For every individual studied, tanning exposure produced significant inhibition of phytohemagglutinin‐induced mitogenesis or of the ability to repair DNA lesions by unscheduled DNA synthesis. The results imply that such exposure could: (1) pose a significant hazard for individuals who are already immunosuppressed (e. g. cancer patients, AIDS patients or carriers of latent HIV) and (2) increase the carcinogenic effects of environmental mutagens.
INHIBITORY EFFECT OF 8‐METHOXYPSORALEN PLUS ULTRAVIOLET‐A ON INTERLEUKIN‐1 PRODUCTION BY MURINE KERATINOCYTES
Authors: TOKURA YOSHIKI , YAGI JUNJI , EDELSON RICHARD L. , GASPARRO FRANCIS P. 
Published: January 2008

Abstract—We report the effects of 8‐methoxypsoralen (8‐MOP) plus ultraviolet‐A (UV‐A) irradiation on interleukin‐1 (IL‐1) production by murine epidermal keratinocytes, correlating its effect on IL‐1 with cell viability, DNA synthesis, and 8‐MOP‐DNA photoadduct formation. Freshly isolated murine keratinocytes were treated with various doses of 8‐MOP (5–100 ng/mL; incubation time, 30 min) plus 1 J/cm2 UV‐A and cultured for 1–3 days. The IL‐1/epidermal cell‐derived thymocyte‐activating factor (ETAF) activity in both supernatant and cell extract was reduced proportionately with increasing doses of 8‐MOP/UV‐A. Interleukin‐1 inhibitors induced by 8‐MOP plus UV‐A were not detected in either supernatant or cell extract. A clear reduction of the IL‐1 production was induced by the treatment as low as 15 ng/mL 8‐MOP plus 1 J/cm2 UV‐A, which led to the formation of 0.52 8‐MOP photoadducts per million DNA bases and affected neither cell viability nor DNA synthesis of the treated cells. Cells treated with 100 ng/mL 8‐MOP and 1 J/cm2 UV‐A exhibited 57% suppression of IL‐1 production in both 2‐ and 3‐day culture samples. This treatment resulted in the formation of 3.8 photoadducts per million bases as well as significant abrogation of DNA synthesis although cell viability was unchanged. These observations provide some insights into the phototoxicity mechanisms of 8‐MOP and the effect of PUVA therapy on the cytokine regulation in keratinocytes.
SIMULTANEOUS SATURATION OF VARIABLE FLUORESCENCE YIELD AND PHOTOACOUSTICALLY MONITORED THERMAL EMISSION IN THYLAKOID MEMBRANES
Authors: CARPENTIER ROBERT , OWENS THOMAS G. , LEBLANC ROGER M. 
Published: January 2008

Abstract—Thermal and fluorescence emission from thylakoid membranes were monitored simultaneously in a photoacoustic cell. A close relationship existing between variable fluorescence and variable thermal emissions is demonstrated. The modulated measuring beam of the photoacoustic spectrophotometer was used to study the effect of light intensity on the energy storage yield and on the variable fluorescence yield. The half‐saturation light intensities obtained for both parameters were 8.5 and 9.1 W m−2, respectively. The similar sensitivity of energy storage and variable fluorescence yield to light intensity indicates that electron transfer with plastoquinone as last acceptor is probably responsible for the photoacoustically monitored energy storage.
QUENCHING OF SINGLET OXYGEN BY HUMAN RED CELL GHOSTS
Authors: KANOFSKY JEFFREY R. 
Published: January 2008

Abstract— Time resolved measurements of singlet oxygen phosphorescence at 1270 nm were made from unsealed red cell ghosts, labeled with 5‐(N‐hexadecanoyl)aminoeosin and suspended in deuterium oxide buffer. The singlet oxygen emission lifetime was long, 23 ± 1 μs. The lifetime of the singlet oxygen phosphorescence from intact unsealed ghosts was not a measure of the singlet oxygen lifetime within the red cell ghost membrane, however. The prolonged singlet oxygen emission was due to singlet oxygen escaping from the thin membrane into the buffer, since the emission lifetime was significantly shortened by adding azide ion or water to the deuterium oxide buffer.The lifetime of singlet oxygen within the red cell ghosts membrane was estimated by dispersing the ghosts with detergent and then measuring the singlet oxygen lifetime in deuterium oxide buffers containing various dilutions of the dispersed ghosts. Apparent singlet‐oxygen quenching constants were measured using four different photosensitizing dyes and two different detergents. The apparent quenching constant was independent of the dye used, but varied significantly with different detergents. Extrapolation of this data to “100%” ghost concentration gave a singlet oxygen lifetime from 24 and 130 ns. A ghost concentration of “100%” was defined as that concentration of red cell ghost molecules which would be contained within a red cell ghost membrane pellet containing no buffer solutions. Most of the singlet oxygen quenching was due to proteins. Lipids extracted from red cell ghosts accounted for only 2‐7% of the total singlet oxygen quenching.