bluuebunny/crossref_metadata_2025 huggingface dataset:
PHOTOADDITION OF p‐AMINOBENZOIC ACID TO THYMINE AND THYMIDINE
Authors: Shaw Anthony A. , Wainschel Larry A. , Shetlar Martin D.
Published: July 2010

Abstract— Several studies in the literature have shown that DNA is damaged after UV irradiation in the presence of the sunscreen agent p‐aminobenzoic acid (PABA), both in vivo and in vitro. One type of damage has been shown to be the result of increased yields of pyrimidine cyclobutane dimer formation. However, it has been suggested that other types of lesions are produced as well. We have studied the photochemistry of the thymine‐PABA and thymidine‐PABA systems and report here the isolation and characterization of thymine‐PABA and thymidine‐PABA photoadducts. These products have been identified, respectively, as 5‐(2‐amino‐5‐carboxyphenyl)‐5,6‐dihydrothymine and isomeric forms of 5‐(2‐amino‐5‐carboxyphenyl)‐5,6‐dihydrothymidine. The quantum yields for the formation of these adducts in deaerated aqueous solutions at pH 7.0 have been determined to be 9.5 × 10–4 and 4.3 × 10–3 for the thymine and thymidine based adducts respectively. A pH profile for the thymine‐PABA system indicated a maximum quantum yield for adduct formation at pH 6.5, although it could be detected over the whole pH range studied (pH 3.5–11.0).
THE INWARD H+ PATHWAY IN BACTERIORHODOPSIN: THE ROLE OF M412 AND P(N)560 INTERMEDIATES*
Authors: Danshina S. V. , Drachev L. A. , Kaulen A. D. , Skulachev V. P.
Published: July 2010

Abstract— In purple bacteriorhodopsin sheets adsorbed onto the phospholipid‐impregnated collodion film, electrogenic stages are identified correlating with decays of the M and N(P)‐type intermediates. It is concluded that both M → N and N → bR transitions are electrogenic.

The M decay is shown to be of a complex kinetics. In purple sheets, the lower the light intensity, the higher the rate of “slow M” decay. Such a dependence, which is absent from monomeric bacteriorhodopsin in proteoliposomes and from Triton X‐100‐solubilized protein, may be explained by the inhibiting effect of a light‐induced conformation change in a bacteriorhodopsin molecule upon the M decay in some other bacteriorhodopsin molecules within the same sheet.

The light intensity‐independent “slow M” decay in solubilized bacteriorhodopsin is shown to correlate with the decay of the N intermediate and H+ uptake after the flash. In contrast to “fast M”, “slow M” is pH dependent, closely resembling in this respect the N intermediate. It is suggested that there is a fast light‐independent equilibration between M and N so that “slow M” represents the portion of the M pool that monitors the N concentration. The M → N equilibrium is assumed to be involved in the effect of the light‐induced electric field on the M decay. No direct effect of light on the equilibrium was found.
DETERMINATION OF CYTOSINE‐CYTOSINE PHOTODIMERS IN THE DNA OF CLOUDMAN S91 MELANOMA CELLS USING HIGH PRESSURE LIQUID CHROMATOGRAPHY
Authors: Niggli Hugo J.
Published: July 2010

Abstract— I measured the induction of cytosine‐cytosine dimer (C‐C) densities after UV‐C (< 290 nm) and UV‐B irradiation (290–320 nm) in the 2′‐deoxy‐[3H]cytidine labeled DNA of Cloudman S91 mouse melanoma cells using a new, sensitive high pressure liquid chromatography procedure. UV‐B exposure resulted in 0.000034% C‐C/J m‐2 of the total cytosine radioactivity which is 10 times less than the rate during UV‐C irradiation. Previous work with these melanoma cells showed a 4‐fold lower rate of induction of thymine‐containing pyrimidine dimers by UV‐B than UV‐C light (Niggli Photochem. Photobiol. 52, 519–524, 1990). Based on these results, the calculated ratios for the pyrimidine dimer subspecies showed no significant difference following UV‐C and UV‐B exposure. However, UV‐C and UV‐B light induce 10–20 times more thymine‐containing pyrimidine dimers than C‐C in the DNA of S91 cells.
A FLUORESCENCE STUDY OF TRYPTOPHAN‐HISTIDINE INTERACTIONS IN THE PEPTIDE ANANTIN AND IN SOLUTION
Authors: Vos Rita , Engelborghs* Yves
Published: July 2010

Abstract—Anantin is a heptadecapeptide in which the C‐terminal peptide chain pierces the covalently cyclized peptide ring formed by an amide link between the α‐NH2 end group and the β‐carboxyl group of Asp(8). It contains a tryptophan and a histidine at positions 5 and 12, respectively. Des‐Phe(17)‐anantin lacks the C‐terminal phenylalanine.

Fluorescence emission intensity as a function of pH follows the ionization of a single residue. The pKa amounts to 7.23 ± 0.03 for anantin and is attributed to His(12). At pH 9 the quantum yield is 0.12 ± 0.01 for anantin, whereas at pH 4.5 the quantum yield decreases more than two‐fold (0.05 2 0.01). Practically identical parameters are observed for des‐Phe(17)‐anantin. This pH dependency reveals intramolecular quenching of the excited indole ring of Trp(5) by the imidazole of His(12), which results in a marked decrease of the tryptophan fluorescence at low pH. In a multifrequency phase fluorometric study the fluorescence lifetimes for both peptides at pH 4.5 and pH 9 are determined. At both, pH fluorescence decay is well described by a sum of two exponentials. For anantin at pH 4.5 the lifetimes are 0.72 ± 0.07 ns and 1.67 ± 0.07 ns. At pH 9 the lifetimes are 1.11 ±0.12 ns and 2.55 ± 0.03 ns. In methanol we find two lifetimes for anantin: 0.68 ± 0.01 ns and 2.57 ± 0.01 ns. The lifetimes are found to be slightly dependent upon emission wavelength. For des‐Phe(17)‐anantin practically the same values are observed.

The quenching of tryptophan fluorescence by histidine is further studied in solution using N‐acetyl‐tryptophanamide in the presence of increasing concentrations of imidazole in the protonated (pH 4.5) and unprotonated (pH 9) state and in methanol. At both pH values and in methanol, a linear increase in both the inverse of the steady‐state fluorescence Fo/F and the inverse of the lifetime 1/τ with increasing imidazole concentration indicates that a collisional mechanism is at the root of the observed quenching. The quenching efficiency values, γ, are calculated and amount to about 0.32 at pH 4.5, 0.02 at pH 9 and 0.002 in methanol, showing that protonated imidazole is a better quencher than the unprotonated form, and that the nature of the solvent is involved even in the quenching by unprotonated imidazole. Tryptophan‐histidine interactions in solution and in the peptide are compared.
PHOTOCHEMISTRY OF 5‐S‐CYSTEINYLDOPA
Authors: Costantini Claudio , d'Ischia Marco , Palumbo Anna , Prota Giuseppe
Published: July 2010

Abstract‐The photochemical behavior of 5‐S‐cysteinyldopa (5‐S‐CD), a colorless product of melanocyte metabolism, was investigated in neutral phosphate buffer with biologically relevant UV radiation. Exposure of 5‐S‐CD to pyrex‐filtered UV light (wavelengths > 320 nm) was found to induce an oxygen‐dependent reaction, leading to, besides abundant polymeric materials, the benzothiazine derivatives I and II (two diastereoisomers). Superoxide dismutase exerted a small inhibitory effect on 5‐S‐CD consumption, whereas other active oxygen scavengers had no effect on the reaction course. Addition of glutathione as a hydrogen donor completely suppressed the reaction. With UVB light (wavelength range 280–320 nm) photolysis of 5‐S‐CD proceeded mainly with formation of 3,4‐dihydroxy‐phenylalanine, arising presumably by photohomolytic cleavage of the S‐CH2 bond followed by desulfuration. These results are of interest in relation to the high susceptibility of fair‐complexioned individuals to actinic damage and skin cancer.
pH DEPENDENCE OF THE ABSORPTION SPECTRA AND PHOTOCHEMICAL TRANSFORMATIONS OF THE ARCHAERHODOPSINS
Authors: Lukashev E. P. , Govindjee R. , Kono Masahiro , Ebrey T. G. , Sugiyama Yasuo , Mukohata Yasuo
Published: July 2010

Abstract—Two strains of archaebacteria have been found to contain light‐driven proton pumping pigments analogous to bacteriorhodopsin (bR) in Halobacterium salinarium. These proteins are called archaerhodopsin‐1 (aR‐1) and archaerhodopsin‐2 (aR‐2). Their high degree of sequence identity with bR within the putative proton channel enables us to draw some conclusions about the roles of regions where differences in amino acids exist, and in particular the surface residues, on the structure and function of retinal‐based proton pumps. We have characterized the spectral and photochemical properties of these two proteins and compared them to the corresponding properties of bR. While there are some differences in absorbance maxima and kinetics of the photocycle, most of the properties of aR‐1 and aR‐2 are similar to those of bR. The most striking differences of these proteins with bR are the lack of an alkaline‐induced red‐shifted absorption species and a dramatic (apparent) decrease in the light‐induced transient proton release. In membrane sheet suspensions of aR‐1 at 0.15 M KCI, the order of proton release and uptake appears opposite that of bR, in which proton release precedes uptake. The nature of this behavior appears to be due to differences in the amino acid sequence at the surfaces of the proteins. In particular, the residue corresponding to the lysine at position 129 of the extracellular loop region of bR is a histidine in aR‐1 and could regulate the efficient release of protons into solution in bR.
PHOTODEGRADATION OF NIFEDIPINE UNDER in vivo‐RELATED CIRCUMSTANCES
Authors: Vries Henk de , Henegouwen Gerard M. J. Beijersbergen van
Published: July 2010

In view of light‐induced side effects of the drug nifedipine (NIF), its photodegradation was studied under in Wvo‐related conditions. There proved to be no difference between UVA and daylight. In phosphate buffer, the nitroso derivative of NIF was the only photoproduct. In the presence of glutathione (GSH), in plasma and in blood, the nitroso derivative is a short‐lived intermediate, which proved to be very reactive. With GSH, both the photodegradation of NIF and the incubation of the nitroso derivative in the dark quantitatively produced a lactam. The implications of the photodegradation under in vivo‐related conditions for light‐induced side effects of NIF are discussed.
DIETARY FAT MODULATES IMMUNORESPONSIVENESS IN UV‐IRRADIATED MICE
Authors: Black Homer S. , Okotie‐Eboh Goodluck , Gerouis Janette , Urban Julie I. , Thornby John I.
Published: July 2010

Previous studies have shown that a high level of dietary lipid (corn oil) exacerbates UV‐carcinogenic expression in hairless mice. Furthermore, it was demonstrated that this effect occurs at the postinitiation, or promotion, stage of UV‐carcinogenesis‐a stage believed to be modulated immunologically. Thus, we sought to examine the influence of dietary lipid on specific immune parameters at various times within a UV‐carcinogenic protocol, with the purpose of detecting potential relationships to UV carcinogenesis. Hairless mice were fed either a high‐ (12%, wt/wt, corn oil) or low‐fat (0.75%, wt/wt, corn oil) diet for 2 weeks prior to start of the UV or experimental protocols. Animals were sensitized to dinitrochlorobenzene (DNCB) hapten and delayed‐type hypersensitivity (DTH) was assessed. Delayed‐type hypersensitivity was significantly suppressed (P= 0.01) in the high‐fat group, even before UV irradiation. Although both groups exhibited UV‐induced suppression of this response, the high‐fat group was totally suppressed after 3 weeks of UV, whereas the low‐fat group exhibited reactivity through week 8. The splenic T‐lymphocyte (Thy 1.2+) population had declined by about 50% at the time of UV termination (11 weeks). Dietary lipid exerted no apparent influence upon this T‐cell population. However, after 6 weeks of UV, I‐J+ cells (a marker shown to be acquired adaptively by suppressor T lymphocytes) began to increase. By week 15 (4 weeks post‐UV) I‐J+ cells had increased by about 65% in the high‐fat group, twice the % increase that occurred in the low‐fat group. When UV‐induced tumors were transplanted to recipient animals receiving various periods (0, 6, 11 weeks) of UV irradiation, no significant differences in median tumor rejection times between the two dietary groups occurred at 0 or 6 weeks. After 11 weeks of UV, the low‐fat group exhibited a tumor rejection time that was comparable to that of nonirradiated animals, i.e. 21 days. However, median tumor rejection time for the high‐fat group was greater than 63 days, significantly (P= 0.01) longer than that of the low‐fat group. Thus, suppression of tumor rejection by high fat occurred at a time when high fat had been shown to exacerbate carcinogenic expression and when I‐J+ cells had markedly increased. These data demonstrate that level of dietary lipid modulates immunoresponsiveness in UV‐irradiated animals and is compatible with the thesis that immune suppression may account for the exacerbation of carcinogenic expression elicited by high dietary fat.
PHOTOINDUCED ELECTRON TRANSFER IN A CAROTENOBUCKMINSTERFULLERENE DYAD
Authors: Imahori Hiroshi , Cardoso Sergio , Tatman Dereck , Lin Su , Noss Lori , Seely Gilbert R. , Sereno2 Leonides , Silber Juana Chessa de , Moore Thomas A. , Moore Ana L. , Gust Devens
Published: July 2010

A carotenoid‐fullerene dyad has been synthesized by condensing a carotenoid amine with an acid group attached to C60 by a cyclopropane‐based linkage. The lowest excited singlet state of the fullerene is strongly quenched by electron transfer from the carotenoid moiety to generate the charge‐separated species Car+‐C60.‐. In CS2 solution Car+‐C60.‐ has a rise time of 0.8 ps and decays by charge recombination in 534 ps. Light absorbed by either chromophore produces a high yield of Car+‐C60.‐, which implies that internal conversion in the carotenoid is negligible. The lowest triplet level in the dyad is localized on the carotenoid and is populated in low yield from the charge‐separated species. The sensitization of singlet oxygen by the fullerene component is effectively curtailed in the dyad.
SUBCELLULAR DAMAGE KINETICS WITHIN CO‐CULTIVATED WI38 and VA13‐TRANSFORMED WI38 HUMAN FIBROBLASTS FOLLOWING 5‐AMINOLEVULINIC ACID‐INDUCED PROTOPORPHYRIN IX FORMATION
Authors: ÜBerriegler K. P. , Banieghbal E. , Krammer B.
Published: July 2010

The generation of the photosensitizer protoporphyrin IX (PpIX) in cells can be induced by externally applied 5‐aminolevulinic acid (ALA), with that bypassing the feedback control mechanism. The aim of the present study was to investigate the onset of destructive changes in living cocultivated WI38 and VA13‐transformed WI38 human fibroblasts following ALA incubation, PpIX production and subsequent irradiation by white halogen light with a dose of 2.2 kJ/m2. Specific fluorescence markers such as 3,3′‐dihexyloxacarbocyanine iodide for endoplasmic reticulum (ER) staining and dihydrorhodamine for intact mitochondria mapping combined with a low light imaging system are a versatile and sensitive tool to examine the photoinduced destruction of organelles in living cells, while artifacts are minimized. Mitochondria as primary targets of PpIX undergo a condensation under irradiation and are finally destroyed. Photodynamic treatment induces further a significant decomposition of ER, although PpIX localization could not be determined. Initial destabilization and vesiculation of ER is followed by a porous network with large cisternae (indicating the breakdown of cell integrity and cell/nucleus membrane damage). Normal cocultivated lung fibroblasts showed a delay in destruction compared to the transformed WI38‐VA13 cells. The observed decomposition pattern resembles the morphological pattern of apoptosis.
ULTRAVIOLET ACTION SPECTRA FOR PHOTOBIOLOGICAL EFFECTS IN CULTURED HUMAN LENS EPITHELIAL CELLS
Authors: Andley Usha P. , Weber1 Jennifer G.
Published: July 2010

Abstract— The action spectrum for cell killing by UV radiation in human lens epithelial (HLE) cells is not known. Here we report the action spectrum in the 297–365 nm region in cultured HLE cells with an extended lifespan (HLE B‐3 cells) and define their usefulness as a model system for photobiological studies. Cells were irradiated with monochromatic radiation at 297, 302, 313, 325, 334 and 365 nm. Cell survival was determined using a clonogenic assay. Analysis of survival curves showed that radiation at 297 nm was six times more effective in cell killing than 302 nm radiation; 297 nm radiation was more than 260, 590, 1400 and 3000 times as effective in cell killing as 313, 325, 334 and 365 nm radiation, respectively. The action spectrum was similar in shape to that for other human epithelial cell lines and rabbit lens epithelial cells. The effect of UV radiation on crystallin synthesis was also determined at different wavelengths. To determine whether exposure to UV radiation affects the synthesis of β‐crystallin, cells were exposed to sublethal fluences of UV radiation at 302 and 313 nm, labeled with [35S]methionine and the newly synthesized βY‐crystallin was analyzed by immunoprecipitation and western blotting using an antibody to β‐crystallin. The results show a decrease in crystallin synthesis in HLE cells irradiated at 302 and 313 nm at fluences causing low cytotoxicity. The effect of radiation on membrane perturbation was determined by measuring enhancement of synthesis of prostaglandin E2 (PGE2). Synthesis of PGE2 occurs at all UV wavelengths tested in the 297–365 nm region. The slope of the PGE2 response curves was higher than that of cell killing curves in cultured HLE cells. These data show that cultured HLE cells with extended lifespan are a suitable system for investigating photobiological responses of cells to UV radiation.
In situ COMPARISON OF 665 nm and 633 nm WAVELENGTH LIGHT PENETRATION IN THE HUMAN PROSTATE GLAND
Authors: Lee L. K. , Whitehurst1 C. , Pantelides M. L. , Moore J. V.
Published: July 2010

Abstract— The depth of treatment in photodynamic therapy (PDT) of tumors varies with the wavelength of light activating the photosensitizer. New generation photosensitizers that are excited at longer wavelengths have the potential for increasing treatment depths. Tin ethyl etiopurpurin (SnET2), a promising second‐generation photosensitizer is maximally activated at 665 nm, which may be significantly more penetrating than 633 nm light currently used with porphyrins in PDT. The penetration of 665 nm and 633 nm wavelength red light in the prostate gland was compared in 11 patients undergoing prostatic biopsies for suspected prostatic cancer. Interstitial optical fibers determined the light attenuation within the prostate gland. Of the 11 patients, 7 had dual wavelength and 4 had single wavelength studies. The mean attenuation coefficients, μeff, for 665 nm and 633 nm wavelength light were 0.32 ± 0.05 mm‐1 and 0.39 ± 0.05 mm‐1, respectively, showing a statistically significant difference (P= 0.0003). This represented a 22% increase in the mean penetration depth and at 10 mm from the delivery fiber there was 1.8 times as much 665 nm light fluence than 633 nm. The mean μeff at 665 nm for benign and malignant prostate tissue were similar (P = 0.42), however, there was significant interpatient variation (μeff ranging from 0.24 to 0.42 mm‐1) reflecting biological differences of therapeutic importance. The enhanced light fluence and penetration depth with 665 nm light should allow significantly larger volumes of prostatic tissue to be treated with SnET2‐mediated PDT.
CHROMOPHORE‐ASSISTED LASER INACTIVATION OF SUBUNITS OF THE T‐CELL RECEPTOR IN LIVING CELLS IS SPATIALLY RESTRICTED
Authors: Liao Joseph C. , Berg Leslie J. , Jay Daniel G.
Published: July 2010

Abstract— Chromophore‐assisted laser inactivation (CALI) is a molecular photoablation technique that has been used to elucidate the in vivo roles of specific proteins in neural development. The interpretation of its effects on proteins in living cells relies on knowing how spatially restricted the CALI‐induced damage is in vivo. To determine the spatial specificity of CALI in living cells, we have applied CALI to individual subunits of the T‐cell receptor (TCR) complex on the surface of 2B4 hybridoma cells in culture and have examined the consequent structural and functional integrity of the TCR‐α, TCR‐β and CD3‐α. The CALI of TCR‐β resulted in the disruption of the β subunit and also resulted in a small effect on antibody binding alone to the neighboring TCR‐α but caused no effect on another subunit, CD3‐ε. Reciprocal experiments directing CALI to TCR‐α and CD3‐ε gave consistent results. No effects other than a simple loss of function were observed for any of these CALI experiments. These data demonstrate the extent of CALI‐induced damage within a multisubunit complex in living cells and provide greater confidence for the future application of this technique to understanding in vivo function of proteins during complex cellular processes.
FUNCTIONAL MAPPING OF THE BRANCHED SIGNAL TRANSDUCTION PATHWAY THAT CONTROLS SPORULATION IN Physarum polycephalum
Authors: Starostzik Christine , Marwan Wolfgang
Published: July 2010

Abstract— Sporulation of starving plasmodia of Physarum polycephalum was found to be induced by far‐red light, blue light or heat shock, each of which is perceived by a different input receptor system. The branched signal transduction pathway was mapped and the time‐dependent formation of some of its components analyzed.
Photophysical Studies on Antimalariai Drugs
Authors: Morten Ann G. , Martinez Lydia J. , Holt Nathan , Sik Robert H. , Reszka Krzysztof , Chignell Colin F. , Tonnesen Hanne H. , Roberts Joan E.
Published: July 2010

Abstract— Most drugs used in the treatment of malaria produce phototoxic side effects in both the skin and the eye. Cutaneous and ocular effects that may be caused by light include changes in skin pigmentation, corneal opacity, cataract formation and other visual disturbances including irreversible retinal damage (retinopathy) leading to blindness. The mechanism for these reactions in humans is unknown. We irradiated a number of antimalarial drugs (amodiaquine, chloroquine, hydroxychloroquine, mefloquine, primaquine and quinacrine) with light (Λ > 300 nm) and conducted electron paramagnetic resonance (EPR) and laser flash photolysis studies to determine the possible active intermediates produced. Each antimalarial drug produced at least one EPR adduct with the spin‐trap 5,5‐dimethyl‐l‐pyrroline N‐oxide in benzene: superoxide/hydroperoxyl adducts (chloroquine, mefloquine, quinacrine, amodiaquine and quinine), carbon‐centered radical adducts (all but primaquine), or a nitrogen‐centered radical adduct only (primaquine). In ethanol all drugs except primaquine produced some superoxide/hydroperoxyl adduct, with quinine, quinacrine, and hydroxychloroquine also producing the ethoxyl adduct. As detected with flash photolysis and steady‐state techniques, mefloquine, quinine, amodiquine and a photoproduct of quinacrine produced singlet oxygen (τ= 0.38; τ= 0.36; τ= 0.011; τ= 0.013 in D2O, pD7), but only primaquine quenched singlet oxygen efficiently (2.6 × 108M−1 s1 in D2O, pD7). Because malaria is a disease most prevalent in regions of high light intensity, protective measures (clothing, sunblock, sunglasses or eye wraps) should be recommended when administering antimalarial drugs.
A Comparative Study of the Cellular Uptake and Photodynamic Efficacy of Three Novel Zinc Phthalocyanines of Differing Charge
Authors: Ball D. J. , Mayhew S. , Wood S. R. , Griffiths J. , Vernon D. I. , Brown S. B.
Published: July 2010

Abstract— Three novel substituted zinc (II) phthalocyanines (one anionic, one cationic and one neutral) were compared to two clinically used photosensitizers, 5,10,15,20‐tetra(m‐hydroxyphenyl)chlorin (m‐THPC) and polyhematoporphyrin (PHP), as potential agents for photodynamic therapy (PDT). Using the RIF‐1 cell line, photodynamic efficacy was shown to be related to cellular uptake. The cationic phthalocyanine (PPC, pyridinium zinc [II] phthalocyanine) had improved activity over the other two phthalocyanines and slightly unproved activity over PHP and m‐THPC. The initial subcellular localization of each photosensitizer was dependent upon the hydrophobicity and plasma protein binding. The phthalocyanines had a punctate distribution indicative of lysosomes, whereas m‐THPC and PHP had a more diffuse cytoplasmic localization. A relocalization of phthalocyanine fluorescence was observed in some cases following low‐level light exposure, and this was charge dependent The anionic phthalocyanine (TGly, tetraglycine zinc [II] phthalocyanine) relocalized to the nuclear area, the localization of the hydrophobic phthalocyanine (TDOPc, tetradioctylamine zhic [II] phthalocyanine) was unchanged, whereas the distribution of the cationic phthalocyanine (PPC) became more cytoplasmic. This suggests that relocalization following low‐level irradiation is a critical factor governing efficacy, and a diffuse cytoplasmic distribution may be a determinant of good photodynamic activity.
A2E: A Component of Ocular Lipofuscin¶
Authors: Lamb Laura E. , Simon John D.
Published: July 2010

The presence of lipofuscin in post mitotic cells is considered a hallmark of the aging process. In the retinal pigment epithelium (RPE), lipofuscin is found as micrometer‐sized spherical particles and characterized by its yellow autofluorescence when exposed to blue light. This exposure to light is also known to produce reactive oxygen intermediates (ROI), but the particular molecular constituent(s) responsible for this phototoxicity have yet to be completely identified. Resulting mostly from the autophagocytosis of intracellular organelles, the composition of lipofuscin is poorly defined but known to contain protein, lipids and several fluorophores. The subsequent identification of one of the fluorophores in lipofuscin, A2E, generated much interest and resulted in a variety of studies to understand its potential role in the phototoxicity of lipofuscin. Several modes of toxicity have been suggested through which A2E can affect the health of RPE cells. These modes include photoinduced production of ROI, which places additional oxidative stress on RPE cells, the disruption of membrane integrity through its natural role as an amphiphilic detergent and inhibition of key cellular functions. This article presents the current understanding of the photochemistry of A2E and its involvement as a phototoxic agent in RPE cells.
Photoisomerization of Arylstilbazolium Ligands in the Presence of DNA¶
Authors: Juskowiak Bernard , Chudak Malgorzata
Published: July 2010

The ability of the DNA duplex to behave as an efficient organized medium for trans‐cis photoisomerization has been explored. The presence of DNA affected isomerization in a variety of ways depending on the aryl moiety properties of the ligand and its DNA‐binding mode. Contrary to intercalating ligands, 9‐[2‐(N‐methylpyridinium‐4‐yl)vinyl)phenanthrene (2) and 9‐[2‐(N‐methylpyridinium‐4‐yl)vinyl]anthracene (3), which gave only cis and trans isomers, the additional products‐cyclobutane photodimers‐were detected for 2‐[2‐(N‐methylpyridinium‐4‐yl)vinyl]naphthalene (1), which binds cooperatively to the minor groove of DNA. Photostationary states (pss) for all ligands were seriously affected by the presence of DNA. A trans isomer‐rich pss and restriction of trans→cis process, observed for ligands 1 and 2, were explained in terms of a different binding affinity of DNA toward particular isomers. On the contrary, 9‐anthryl derivative 3 isomerized against the isomer‐binding preferences, showing cis isomer‐rich pss and enhanced quantum yield of isomerization. The unique behavior of ligand 3‐DNA complex was attributed to different isomerization mechanism that consists in quantum chain isomerization from an excited singlet state possessing a charge transfer character. This is the first example of ligand, which undergoes DNA‐mediated cis‐trans isomerization in the opposite direction than expected from DNA‐binding preferences. The analysis of pss data based on two alternative pathways of photoisomerization showed that investigated ligands follow the model that allows isomerization of both free and DNA‐bound ligands.
Elevated Ultraviolet‐B Radiation Induces Cross‐protection to Cold in Leaves ofRhododendronUnder Field Conditions¶
Authors: Chalker‐Scott Linda , Scott James D.
Published: July 2010

Previously, we have shown a cold‐hardening response inRhododendron‘English Roseum’ exposed to elevated ultraviolet‐B radiation (UV‐B, 280–320 nm) under growth chamber conditions. We have conducted the present study under field conditions to provide for a higher ratio of photosynthetically active radiation to UV‐B (PAR:UV‐B) than is possible in the laboratory and to more accurately reflect natural conditions of solar irradiance. Leaf disks taken after 3 months from UV‐B‐exposed plants exhibited a greater tolerance to freezing temperatures than those from control plants that received no supplemental UV‐B exposure during this time. Leaf disks taken from UV‐B‐irradiated plants survived temperatures below −8°C, whereas control disks were killed at −6°C. Cold hardiness did not significantly increase until September, when environmental cues such as decreasing day length and night temperatures also may have enhanced hardening. Our field findings confirm our previous laboratory study, demonstrating that elevated UV‐B induces cross‐protection to cold inRhododendronleaf tissues.
Larval and Adult Emission Spectra of Bioluminescence in Three European Firefly Species¶
Authors: De Cock Raphaël
Published: July 2010

We studied the spectral characteristics of the larvae of three sympatric Belgian species of fireflies, Lampyris noctiluca, Phosphaenus hemipterus and Lamprohiza splendidula. An in vivo spectral study was performed to compare bioluminescence spectra. The emission spectrum of a laboratory reared female L. noctiluca was recorded by a different, more exact method. The mean peak wavelength (λmax= 546 nm) and shapes of the unimodal emission spectra are visually similar for the larvae of all three species. The emission spectrum of the adult female L. noctiluca peaked in the same range as the larval bioluminescence between 546 and 551 nm. The bandwidth at half‐maximum intensity was slightly greater for larval L. noctiluca (77 ± 4 nm) compared with P. hemipterus (70 ± 10 nm). The bandwidth of larval L. splendidula (77 ± 8 nm) was not different compared with the other larvae, whereas the females' bandwidth was somewhat narrower (68 nm). The ecological significance of the color of bioluminescence and conservancy of green emission in larval fireflies and other luminescent beetle larvae is discussed.
Photodynamic Actinometry Using Microspheres: Concept, Development and Responsivity ¶
Authors: Bisland Stuart K. , Austin James W. , Hubert Daniel P. , Lilge Lothar
Published: July 2010

Photodynamic therapy (PDT) relies on three main ingredients, oxygen, light and photoactivating compounds, although the PDT response is definitively contingent on the site and level of reactive oxygen species (ROS) generation. This study describes the development of a novel, fluorescent‐based actinometer microsphere system as a means of discerning spatially resolved dosimetry of total fluence and ROS production. Providing a high resolution, localized, in situ measurement of fluence and ROS generation is critical for developing in vivo PDT protocols. Alginate‐poly‐l‐lysine‐alginate microspheres were produced using ionotropic gelation of sodium alginate droplets, ranging from 80 to 200 μm in diameter, incorporating two dyes, ADS680WS (ADS) and Rhodophyta‐phycoerythrin (RPE), attached to the spheres' inside and outside layers, respectively. To test the responsivity and dynamic range of RPE for ROS detection, the production of ROS was initiated either chemically using increasing concentrations of potassium perchromate or photochemically using aluminum tetrasulphonated phthalocyanine. The generation of singlet oxygen was confirmed by phosphorescence at 1270 nm. The resulting photodegradation and decrease in fluorescence of RPE was found to correlate with increased perchromate or PDT treatment fluence, respectively. This effect was independent of pH (6.5–8) and could be inhibited using sodium azide. RPE was not susceptible to photobleaching with light alone (670 nm; 150 Jcm−2). ADS, which absorbs light between 600 and 750 nm, showed a direct correlation between radiant exposure (670 nm; 0–100 Jcm−2) and diminished fluorescence. Photobleaching was independent of irradiance (10–40 mW cm−2). We propose that actinometer microspheres may provide a means for obtaining high spatial resolution information regarding delivered PDT dose within model systems during investigational PDT development and dosimetric information for clinical extracorporeal PDT as in the case of ex vivo bone marrow purging.
Ecosystem Consequences of Enhanced Solar Ultraviolet Radiation: Secondary Plant Metabolites as Mediators of Multiple Trophic Interactions in Terrestrial Plant Communities¶
Authors: Bassman John H.
Published: July 2010

The potential role of ultraviolet‐B (UV‐B)‐induced secondary plant metabolites as mediators of multiple trophic responses in terrestrial ecosystems is considered through review of the major classes of secondary metabolites, the pathways for their biosynthesis, interactions with primary and secondary consumers and known UV effects on their induction. Gross effects of UV‐B radiation on plant growth and survival under realistic spectral balances in the field have been generally lacking, but subtle changes in carbon allocation and partitioning induced by UV‐B, in particular production of secondary metabolites, can affect ecosystem‐level processes. Secondary metabolites are important in plant‐herbivore interactions and may affect pathogens. They act as feeding or oviposition deterrents to generalists and nonadapted specialists, but adapted specialists are stimulated to feed by these same compounds, which they detoxify and often sequester for use against their predators. This provides a route for tritrophic effects of enhanced UV‐B radiation whereby herbivory may be increased while predation on the herbivore is simultaneously reduced. It is in this context that secondary metabolites may manifest their most important role. They can be the demonstrable mechanism establishing cause and effect at higher trophic levels because the consequences of their induction can be established at all trophic levels.
UV Radiation Effects on Plant Growth and Forage Quality in a Shortgrass Steppe Ecosystem¶
Authors: Milchunas Daniel G. , King Jennifer Y. , Mosier Arvin R. , Moore John C. , Morgan Jack A. , Quirk Meghan H. , Slusser James R.
Published: July 2010

Levels of UV were manipulated in a native shortgrass steppe using open‐sided structures with tops that either passed or blocked wavelengths shorter than ∼370 nm. Precipitation was controlled to create a drought or a very wet year. Subplots were either nondefoliated or defoliated to simulate grazing by livestock, which is the primary land use. Plant community productivity and forage quality were assessed in response to the two climate change variables (UV, precipitation) and grazing stress. Productivity and seasonal standing biomass of the dominant grass species were negatively affected by passing versus blocking UV, but only in the dry year. Another species was negatively affected by passing UV in the wet year, indicating the potential for future shifts in species composition. Forage quality for ruminants increased when UV was passed compared with blocked, as determined by in vitro digestible dry matter, depending on species and precipitation. Nitrogen concentrations and soluble and fiber components of vegetation also displayed some UV effects, but they were generally small and depended on species, season or amount of precipitation (or all). Grazing treatment had large positive effects on current‐year productivity only in the wet year and some small positive effects on quality in both wet and dry years. Interactions between UV and grazing treatment were not observed.
Interactive Effects of Ultraviolet‐B Radiation and Temperature on Cotton Physiology, Growth, Development and Hyperspectral Reflectance¶
Authors: Reddy K. Raja , Kakanl Vijaya Gopal , Zhao Dull , Kotl Sallaja , Gao Wel
Published: July 2010

Current conditions of 2–11 kJ m−2 day−1 of UV‐B radiation and temperatures of >30°C during flowering in cotton cultivated regions are projected to increase in the future. A controlled environment study was conducted in sunlit growth chambers to determent the effects of UV‐B radiation and temperature on physiology, growth, development and leaf hyperspectral reflectance of cotton. Plants were grown in the growth chambers at three day/night temperatures (24/16° C, 30/22° C and 36/28° C) and three levels of UV‐B radiation (0, 7 and 14 kJ m−2 day−1) at each temperature from emergence to 79 days under optimum nutrient and water conditions. Increases in main stem node number and the node of first fruiting branch and decrease in duration to first flower bud (square) and flower were recorded with increase in temperature. Main effects of temperature and UV‐B radiation were significant for net photosynthetic rates, stomatal conductance, total chlorophyll and carotenoid concentrations of uppermost, fully expanded leaves during squaring and flowering. A significant interaction between temperature and UV‐B radiation was detected for total biomass and its components. The UV‐B radiation of 7 kJ m−2 day−1 reduced boll yield by 68% and 97% at 30/22°C and 36/28° C, respectively, compared with yield at 0 kJ m−2 day−1 and 30/22° C. No bolls were produced in the three temperature treatments under 14 kJ m−2 day−1 UV‐B radiation. The first‐order interactions between temperature, UV‐B radiation and leaf age were significant for leaf reflectance. This study suggests a growth‐ and process‐related temperature dependence of sensitivity to UV‐B radiation.
The Complex of Apomyoglobin with the Fluorescent Dye Coumarin 153¶
Authors: Chowdhury P. K. , Halder M. , Sanders L. , Arnold R. A. , Liu Y. , Armstrong D. W. , Kundu S. , Hargrove M. S. , Song X. , Petrich J. W.
Published: July 2010

Understanding a protein's dielectric response requires both a theoretical model and a well‐defined experimental system. The former has already been proposed by Song (J. Chem. Phys. 116, 9359 [2002]). We suggest that the latter is provided by the complex of coumarin 153 (C153) with apomyoglobin (ApoMb). C153 has been exhaustively studied and has proven to be an excellent probe of the solvation dynamics of polar solvents. Myoglobin is one of the most thoroughly studied proteins. Myoglobins from a wide range of species have been subject to X‐ray structural analysis and site‐directed mutagenesis. Here, we demonstrate the existence of a robust C153‐apomyglobin system by means of molecular dynamics simulations, equilibrium binding studies using a Job's plot and capillary electrophoresis, circular dichroism and time‐resolved fluorescence. The reorganization energy of C153 bound to ApoMb is compared with that of C153 in bulk solvent using the method of Jordanides et al. (J. Phys. Chem. B 103, 7995 [1999]).
Evaluation of 15 Polymerases and Phosphorothioate Primer Modification for Detection of UV‐induced C:G to T:A Mutations by Allele‐specific PCR¶
Authors: Gale James M. , Tafoya Gregory B.
Published: July 2010

Allele‐specific polymerase chain reaction is based on polymerase extension from primers that contain a 3′end base that is complementary to a specific mutation and inhibition of extension with wild‐type DNA due to a 3′end mismatch.Taqpolymerase is commonly used for this assay, but because of the high rate of nucleotide extension from primer 3′base mismatches documented forTaqpolymerase, high sensitivity is difficult to achieve. To determine whether other polymerases might improve assay sensitivity, 15 polymerases were tested with mutation‐specific primers for two ultravioletinduced mutations in the human 5S ribosomal RNA genes. Of the 15 polymerases tested, six were capable of discriminating these mutations at levels equivalent to or better thanTaqpolymerase. All primers were phosphorothioate modified on the 3′end to block removal of the critical 3′mutation‐specific base by polymerases containing 3′→ 5′exonuclease “proofreading” activity. The effectiveness of phosphorothioate modification was measured in mock polymerase chain reaction reactions and a time course. All six enzymes containing this exonuclease activity showed some ability to digest phosphorothioate‐modified primers and could be divided into two groups, showing fast and slow digestion kinetics. Of the three enzymes that showed slow digestion kinetics, two also showed significantly slower digestion kinetics of unmodified primers.
Mitochondria‐derived Reactive Oxygen Species Mediate Blue Light‐induced Death of Retinal Pigment Epithelial Cells¶
Authors: King Ayala , Gottlieb Eyal , Brooks David G. , Murphy Michael P. , Dunaief Joshua L.
Published: July 2010

Throughout the lifetime of an individual, light is focused onto the retina. The resulting photooxidative stress can cause acute or chronic retinal damage. The pathogenesis of age‐related macular degeneration (AMD), the leading cause of legal blindness in the developed world, involves oxidative stress and death of the retinal pigment epithelium (RPE) followed by death of the overlying photoreceptors. Evidence suggests that damage due to exposure to light plays a role in AMD and other age‐related eye diseases. In this work a system for lightinduced damage and death of the RPE, based on the human ARPE‐19 cell line, was used. Induction of mitochondriaderived reactive oxygen species (ROS) is shown to play a critical role in the death of cells exposed to short‐wavelength blue light (425 ± 20 nm). ROS and cell death are blocked either by inhibiting the mitochondrial electron transport chain or by mitochondria‐specific antioxidants. These results show that mitochondria are an important source of toxic oxygen radicals in blue light‐exposed RPE cells and may indicate new approaches for treating AMD using mitochondria‐targeted antioxidants.
Structural Heterogeneity of Cryotrapped Intermediates in the Bacterial Blue Light Photoreceptor, Photoactive Yellow Protein¶
Authors: Anderson Spencer , Šrajer Vukica , Moffat Keith
Published: July 2010

We investigate by X‐ray crystallographic techniques the cryotrapped states that accumulate on controlled illumination of the blue light photoreceptor, photoactive yellow protein (PYP), at 110 K in both the wild‐type species and its E46Q mutant. These states are related to those that occur during the chromophore isomerization process in the PYP photocycle at room temperature. The structures present in such states were determined at high resolution, 0.95–1.05Å. In both wild type and mutant PYP, the cryotrapped state is not composed of a single, quasitransition state structure but rather of a heterogeneous mixture of three species in addition to the ground state structure. We identify and refine these three photoactivated species under the assumption that the structural changes are limited to simple isomerization events of the chromophore that otherwise retains chemical bonding similar to that in the ground state. The refined chromophore models are essentially identical in the wild type and the E46Q mutant, which implies that the early stages of their photocycle mechanisms are the same.
Metronomic Photodynamic Therapy as a New Paradigm for Photodynamic Therapy: Rationale and Preclinical Evaluation of Technical Feasibility for Treating Malignant Brain Tumors¶
Authors: Bisland Stuart K. , Lilge Lothar , Lin Annie , Rusnov Robert , Wilson Brian C.
Published: July 2010

The concept of metronomic photodynamic therapy (mPDT) is presented, in which both the photosensitizer and light are delivered continuously at low rates for extended periods of time to increase selective tumor cell kill through apoptosis. The focus of the present preclinical study is on mPDT treatment of malignant brain tumors, in which selectivity tumor cell killing versus damage to normal brain is critical. Previous studies have shown that low‐dose PDT using 5‐aminolevulinic acid (ALA)‐induced protoporphyrin IX(PpIX) can induce apoptosis in tumor cells without causing necrosis in either tumor or normal brain tissue or apoptosis in the latter. On the basis of the levels of apoptosis achieved and model calculations of brain tumor growth rates, metronomic delivery or multiple PDT treatments, such as hyperfractionation, are likely required to produce enough tumor cell kill to be an effective therapy. In vitro studies confirm that ALA‐mPDT induces a higher incidence of apoptotic (terminal deoxynucleotidyl transferase‐mediated 2′‐deoxyuridine 5′‐triphosphate, sodium salt nick‐end labeling positive) cells as compared with an acute, high‐dose regimen (ALA‐αPDT). In vivo, mPDT poses two substantial technical challenges: extended delivery of ALA and implantation of devices for extended light delivery while allowing unencumbered movement. In rat models, ALA administration via the drinking water has been accomplished at very high doses (up to 10 times therapeutic dose) for up to 10 days, and ex vivo spectro‐fluorimetry of tumor (9L gliosarcoma) and normal brain demonstrates a 3–4 fold increase in the tumor‐to‐brain ratio of PpIX concentration, without evidence of toxicity. After mPDT treatment, histological staining reveals extensive apoptosis within the tumor periphery and surrounding microinvading colonies that is not evident in normal brain or tumor before treatment. Prototype light sources and delivery devices were found to be practical, either using a laser diode or light‐emitting diode (LED) coupled to an implanted optical fiber in the rat model or a directly implanted LED using a rabbit model. The combined delivery of both drug and light during an extended period, without compromising survival of the animals, is demonstrated. Preliminary evidence of selective apoptosis of tumor under these conditions is presented.
A Multicomponent Model of Chromophoric Dissolved Organic Matter Photobleaching¶§
Authors: Goldstone Jared V. , Del Vecchio Rossana , Blough Nell V. , Voelker Bettina M.
Published: July 2010

Light absorption by chromophoric dissolved organic matter (CDOM) plays a number of roles in natural waters, including both control of the underwater light field and the initiation of many photochemical reactions. A multicomponent analysis was used to describe the effects of UV and visible radiation on the optical absorption spectra of two natural water samples, a Suwannee River fulvic acid standard (SRFA) and a Delaware Bay water sample. This analysis used a constrained minimization technique to fit independent spectral components to the observed bleaching behavior of the water samples under monochromatic irradiation. Spectra derived from these fits were used to predict the bleaching behavior of both samples under polychromatic irradiation (λ< 320 nm). This approach reproduces the kinetics and spectral behavior of polychromatic photobleaching very well at times <48 h, but underpredicts the bleaching at longer time periods.