bluuebunny/crossref_metadata_2025 huggingface dataset:
PHOTOCHEMICAL SENSITIZATION BY AZATHIOPRINE AND ITS METABOLITES. PART 3. A DIRECT EPR AND SPIN‐TRAPPING STUDY OF LIGHT‐INDUCED FREE RADICALS FROM 6‐MERCAPTOPURINE AND ITS OXIDATION PRODUCTS
Authors: Moore Douglas E. , Sik Robert H. , Bilski Piotr , Chignell Colin F. , Reszka Krzysztof J.
Published: January 2008

Abstract Sunlight has been implicated in the high incidence of skin cancer found in patients receiving 6‐mercaptopurine (PSH) in the form of its pro‐drug azathioprine. In this study we have used EPR spectroscopy in conjunction with the spin‐trapping technique to determine whether PSH and its metabolic or photochemical oxidation products generate highly reactive free radicals upon UV irradiation. When an aqueous anaerobic solution (pH 5 or 9) of PSH (pK2= 7.7) and either 2‐methyl‐2‐nitrosopropane (MNP) or nitromethane (NM) were irradiated (λ > 300 nm) with a Xe arc lamp, the corresponding purin‐6‐thiyl (PS.) radical adduct and the reduced form of the spin trap (MNPIH’or CH3N02) were observed. However, no radical adducts were detected when PSH and 5,5‐dimethyl‐1‐pyrroline‐N‐oxide (DMPO) were irradiated (λ= 320 nrn) in oxygen‐free buffer. These findings suggest that PSH does not photoionize but that instead MNP and NM are reduced by direct electron transfer from excited state PSH, 1,3(PSH)*. In aerobic solution, oxygen can act as an electron acceptor and the O2*‐ and PS radicals are formed and trapped by DMPO. 6‐Mercaptopurine did photoionize when irradiated with a Nd:YAG laser at 355 nm as evidenced by the appearance of the DMPO/H (eeq+ H+) adduct, which decreased in intensity in the presence of N2O. 1,3(6‐Mercap‐topurine)* oxidized ascorbate, formate and reduced glutathione to the corresponding ascorbyl, CO2.‐ or glutathiyl radicals. The photochemical behavior of 6‐thioxanthine and 6‐thiouric acid was similar to PSH. However, the excited states of these metabolic oxidation products exhibited stronger reducing properties than 1,3(PSH)*. Photolysis of PSH photoproducts purine‐6‐sulfonate or purine‐6‐sulfinate resulted in homolysis of the C‐S bond and the appearance of the SO3′‐ and SO2−‐‐ radicals, respectively, which were detected by direct EPR. These studies demonstrate that UV irradiation of PSH, its photoproducts and metabolites generates a variety of free radicals that may be involved in the etiology of skin cancer induced by azathioprine.
PHOTOSENSITIZED INHIBITION OF PHOTOSYNTHETIC 14 CO2 FIXATION BY α‐TERTHIENYL and ULTRAVIOLET‐A*
Authors: Brennan Thomas M.
Published: January 2008

Abstract –A variety of naturally occurring photosensitizers of plant origin were tested for their ability to cause ultraviolet‐A (UVA)‐dependent inhibition of photosynthetic 14CO2 fixation in leaf disks of Pisum sativum L. At 0.1 mM concentrations and 60 min UVA irradiation, α‐terthienyl was strongly inhibitory, harmine and sanguinarine inhibited to a lesser degree, and curcumin, 8‐methoxypsoralen and nordihydroguaiaretic acid had no effect under the conditions tested. Alpha‐terthienyl + UVA treatments that fully inhibited 14CO2 fixation had no effect on fresh weight, chlorophyll or protein content of the tissue. Chloroplast malate dehydrogenase and glyceraldehyde‐3‐phosphate dehydrogenase were inhibited 45% and 29%, respectively, by α‐terthienyl + UVA treatment. Electron transport from H2O to the reducing side of photosystem I was inhibited to a similar extent, suggesting interference with the reductive activation of chloroplast enzymes. Alpha‐terthienyl + UVA‐treated tissue exhibited a seven‐fold increase in leakage of labeled photosynthate into the external medium. Treated leaf disks showed no ability to recover 14CO2 fixing ability over a 24 h period. These results indicate photosensitized damage at the level of the thylakoid membranes resulting in partial loss of electron transport capability and more general damage to chloroplast and cell membranes.
A MULTITHERAPY RESISTANCE FACTOR FROM MELANOMA REVEALS THAT KILLING BY NEAR UV IS DIFFERENT FROM GENOTOXIC AGENTS
Authors: Hill Helene Z. , Hill George J. , Cieszka Krystyna , Azure Michael , Chowdhary Indu , Sayre Robert M.
Published: January 2008

A diffusible multitherapy resistance factor (MTRF) is produced by Cloudman S91 melanoma cells in vitro. The MTRF decreases sensitivity of the target cell line, S91/amel, to γ‐irradiation, UVC (200–280nm) and mitomycin C (MMC). In the present study, we demonstrate that MTRF also increases the survival of S91/amel after exposure to actinomycin D (AMD) and vinblastine (VBL). The MTRF is thus effective when target cells have been exposed to five genotoxic agents that act by different mechanisms. It does not alter the response to the same five agents of the S91/13 producer cells, which are presumably saturated with the factor. The factor has no effect on the survival of S91/amel cells that have been exposed to lethal doses of near monochromatic UVB (280–320nm) or UVA (320–400nm) or to polychromatic FS20 lamps. The lack of effectiveness of MTRF after cells have been exposed to near (300–400nm) UV radiation indicates that in this wavelength range, S91 melanoma cells are killed by mechanisms that are different from the lethal effects of the five genotoxic agents (γ‐irradiation, UVC, MMC, AMD and VBL) to which the target cells demonstrate a response.
QUENCHING OF METHYLCYCLOHEXANE FLUORESCENCE BY METHANOL*
Authors: Gryczynski Ignacy , Lakowicz Joseph R.
Published: January 2008

Abstract—

We measured the fluorescence emission spectrum and intensity decays of methylcyclohexane (MCH) when excited by simultaneous absorption of two photons at 298 nm. The steady‐state intensities and lifetimes were both decreased by methanol, which was found to be an efficient quencher of MCH fluorescence. Methanol quenching of MCH is clearly dynamic, but the exact mechanism of quenching is unclear. Dynamic quenching of MCH was also observed by water and n‐propanol. These results suggest that alkane fluorescence from biopolymers, if observable, will only occur from regions of the macromolecules that are not exposed to water.
USE OF TRIS (2,2‘‐BIPYRIDINE) RUTHENIUM(II) DICATION IN A NOVEL METHOD FOR THE DETERMINATION OF SINGLET OXYGEN REACTION RATES: APPLICATION TO STUDIES OF GELATIN
Authors: Douglas Peter , Evans Philippa C. , Henbest Kevin
Published: January 2008

Abstract— A novel method for the determination of singlet oxygen reaction rate constants is described and applied to studies of cyclohexadiene in methanol and gelatins in H2O and D2O. The technique uses tris (2,2′‐bipyridine) ruthenium(II) dication (Ru(bipy)32+) as both singlet oxygen sensitizer and in situ oxygen concentration monitor during irradiation of sealed samples. Because of the high efficiency with which the luminescence of Ru(bipy)32+* can be detected, and the fact that emission lifetimes are used, the method offers some advantages over those previously described. The advantages and disadvantages of the method are discussed. A rate constant of 2.1 (±0.3) x 106 mol‐1 dm3 s‐1 has been determined for the reaction of 1O2 with cyclohexadiene in methanol. For two different photographic gelatins the sums of reaction and quenching rate constants are 2.0 (±0.4) x 106 and 3.1 (±2.0) x 105 mol‐1 dm3 s‐1; for swine skin gelatin this value is 3.9 (±2.4) × 105 mol‐1 dm3 s‐1. Chemical reaction, rather than physical quenching, is the dominant reaction route for gelatins and 1O2.
REGULATORY CIRCUITRY CONTROLLING LUMINESCENCE AUTOINDUCTION IN Vibrio fischeri
Authors: Ulitzur S. , Dunlap P. V.
Published: January 2008

Abstract— Luminescence in the marine symbiotic bacterium Vibrio fischeri is subject to control by autoinduction, a regulatory mechanism that activates light production at high population density and suppresses light production at low population density. Several genetic, physiological and environmental factors contribute to autoinduction. Primary among these are a self‐produced, membrane‐permeable compound, N‐3‐oxohexanoyI‐L‐homoserine lactone, called autoinducer, which accumulates in a population density‐dependent manner during growth of V. fischeri, and a transcriptional activator protein, LuxR, which with autoinducer activates transcription of the luminescence (lux) genes (luxICDABEG; encoding proteins for autoinducer synthesis and light production). Additional genetically defined regulatory elements involved in autoinduction include 3′:5′‐cyclic AMP (cAMP), which via cAMP receptor protein activates transcription of luxR, and the GroESL proteins, which stabilize LuxR in its active form. Evidence exists also for the involvement of LexA protein, for a second autoinducer, N‐octanoyl‐l‐homoserine lactone, and under anaerobic conditions for Fnr protein. Besides these regulatory elements, nutrient limitation, presence of glucose, availability of iron and oxygen, temperature, salts and an au‐toinducer‐LuxR protein‐independent modulation also contribute to the autoinduction phenomenon. The multiplicity of genetic, physiological and environmental factors indicates that luminescence autoinduction is mediated by a complex regulatory circuitry, one that is highly integrated with and responsive to the physiological and ecological status of the cells. Long thought to be unique to V. fischeri and certain closely related marine luminous bacteria, luminescence autoinduction is now viewed as a model for understanding population density‐responsive control of gene expression in a wide variety of terrestrial and marine bacteria in which N‐acyl‐l‐homoserine lactones and homologs of Luxl and LuxR recently have been found.
SYMBIOTIC LUMINOUS SOIL BACTERIA: UNUSUAL REGULATION FOR AN UNUSUAL NICHE
Authors: Hosseini Pamela K. , Nealson Kenneth H.
Published: January 2008

Abstract— Analysis of the patterns of luminescence in Photorhabdus luminescens suggests that the factors that regulate light emission may be fundamentally different in this organism from those known in its marine luminous counterparts. Patterns of light emission seen in strain Hm, in response to the mRNA synthesis inhibitor, rifampicin (RIF), suggest that regulation may be at a posttranscriptional level. When RIF is added at concentrations that inhibit but do not totally stop growth, an increase in luminescence activity is seen approximately two generations later, independent of the rate of growth, or the cell density at which RIF is added. Furthermore, in secondary variants of this strain, which are strongly repressed for luminescence, the addition of RIF results in virtually complete expression of the luminous system. This is apparently the first demonstration of the phenotypic reversion of a trait associated with the primary/secondary transition in this organism.
SPECTRAL ALBEDO MEASUREMENTS IN THE UV and VISIBLE REGION OVER DIFFERENT TYPES OF SURFACES
Authors: Feister Uwe , Grewe Rolf
Published: January 2008

Abstract— The spectral albedo of the earth's surface, i.e. the ratio between spectral irradiance reflected by the ground to all directions and global irradiance, was measured by a spectroradiometer in the UV and visible region from 290 nm to 800 nm with a spectral resolution of 1.5 nm at steps of 2 nm in the UV (290–400 nm) and 10 nm in the visible (400–800 nm) region. The measurements were performed over bare fertile soil, sand at the beach, concrete (autobahn) and snow as well as over different types of vegetation (grass, oats, rye, sugar‐beet, stubble). As the albedo increases with increasing wavelengths for most types of surfaces considered, it is smaller in the UV than in the visible region. In the UVB region (λ < 315 nm) the measured albedo is as small as 0.016‐0.017 over vegetation, 0.04‐0.05 over bare fertile soil, 0.07‐0.10 over concrete (“autobahn”) and 0.62‐0.76% over polluted snow with a small wavelength dependence. A somewhat higher albedo occurs in the UVA region (315 < λ < 400 nm) with values ranging from 0.02 over vegetation to 0.05 to 0.08 over bare soil. The albedo over dry bright sand, which is typically found at the beach, is significantly higher (0.14 at 300 nm to 0.24 at 400 nm) than over other snow‐free surfaces, thus leading to an enhanced dose of biologically effective radiation at the beach.
Phospholipases Induce Melanogenesis in Organ‐Cultured Skin
Authors: Maeda* Kazuhisa , Tomita Yasushi , Naganuma Masako , Tagaml Hachiro
Published: January 2008

Guinea pig skin becomes more pigmented following exposure to UV rays. This melanization was accompanied by enhanced intensity of tyrosinase‐staining and increased number of tyrosinase‐positive melanocytes (MELty+), with resultant enhancement of melanin synthesis. To clarify the regulatory mechanism for melanization following UV irradiation, organ‐cultured guinea pig skins have been used to examine their melanogenic responses to exogenous stimulation. This organ culture system responded well to UV irradiation, by increasing melanogenic activity. Also, in this system, phospholipases (PL), arachidonic acid, interleukin‐1α and melanocytestimulating hormone, but not endothelin‐1 or phosphatidylinositol‐specific PLC (PI‐PLC), stimulated melanogenesis to various extents as indicated by the number of MELty+ and morphological changes. Among them, the PLA2 and PLD were found to have a potent stimulatory property for melanocytes. They might affect melanocytes directly or indirectly through an effect on keratinocytes. These results suggest that PLA2 and PLD play a key role in epidermal hyperpigmentation after UV irradiation or inflammation.
Protochlorophyllide Reductase III: Synthesis of a Protochlorophyllide‐Dihydroflavin Complex
Authors: Nayar Parmesh , Begley Tadhg P.
Published: January 2008

Abstract— A mild and efficient method of linking a dihydroflavin to the C‐17 carboxylic acid side chain of protochlorophyllide, without degradation of the sensitive E ring or loss of magnesium, is described. The appended dihydroflavin was shown to quench the fluorescence of protochlorophyllide. In contrast, a dihydronicotinamide moiety was unable to effect fluorescence quenching. The relevance of these findings to a possible mechanism of action of the enzyme protochlorophyllide reductase is discussed.
Effect of Delivery System on the Pharmacokinetics and Tissue Distribution of bis(Di‐lsobutyl Octadecylsiloxy)Silicon 2,3‐Naphthalocyanine (isoBOSINC), a Photosensitizer for Tumor Therapy
Authors: Zuk Maria M. , Rihter Boris D. , Kenney Malcolm E. , Rodgers Michael A. J. , Kreimer‐Birnbaum Martha
Published: January 2008

Abstract— Bis(di‐isobutyl octadecylsiloxy)silicon 2,3‐naphthalocy‐anine (isoBOSINC) is a representative of a group of naphthalocyanine derivatives with spectral and photophysical properties that make them attractive candidates for photodynamic therapy (PDT). Tissue distributions were studied in tumor‐bearing rats as a function of delivery system and time following administration. The tumor model was an N‐(4‐[5‐nitro‐2‐furyl]‐2‐thiazolyl) formamide (FANFT)‐induced urothelial cell carcinoma transplanted into one hind leg of male Fischer 344 rats; isoBOSINC was delivered to the rats by intravenous injection of 0.50 mg/kg of body weight as a suspension either in 10% Tween 80 in saline (Tween) or 10% (Cremophor® EL + propylene glycol) in saline (Cremophor). The isoBOSINC was isolated from several tissues and organs, as well as tumors and peritumoral muscles and skin. Quantitation was by a high‐performance liquid chromatographic technique with detection that utilizes the native fluorescence of the naphthalocyanine derivative. Independent of the delivery system, the dye was retained in tumors at higher concentrations than in normal tissues, except for spleen and liver. The isoBOSINC retention in tumors was high and was vehicle dependent. For Tween, the maximal ratio of dye in tumor versus peritumoral muscle occurred 12 h after injection; for Cremophor, the maximal ratio occurred later, 336 h postinjection. When the drug was delivered in Tween, isoBOSINC in serum showed two compartment kinetics: half‐lives of about 2 and 11 h were found for the distribution and the elimination phases, respectively. When Cremophor was the vehicle, the elimination half‐life was about 20 h, and one compartment kinetics was observed. The latter findings may explain the generally higher levels of the dye attained by the tissues at later times with Cremophor as the vehicle. An interesting exception wasthat after 7 and 14 days postinjection in Tween, the levels of dye found in testes were six‐ to seven‐fold higher than those found after Cremophor delivery. Levels of dye were very low or not detectable in the brain. Optimal parameters for PDT of tumors with this novel photosensitizer are clearly time‐ and vehicle‐dependent, and future PDT studies will need to incorporate these modulators.
Denaturation of a Recombinant Cutinase from Fusarium solani in AOT‐iso‐Octane Reverse Micelles: a Steady‐State Fluorescence Study
Authors: Melo E. Pinho , Costa Silvia M. B. , Cabral Joaquim M. S.
Published: January 2008

Abstract— Near UV absorbance and fluorescence spectroscopy show conformational changes of a recombinant cutinase from Fusarium solani incorporated in sodium‐di‐2‐ethylhexyl sulfosuccinate (AOT)‐iso‐octane reversed micelles with W0= [H2O]/[AOT] = 20. Excitation spectra were used to decompose cutinase absorbance in its Trp and Tyr components, showing that the latter absorb red‐shifted in the native cutinase in aqueous solution as compared to free Tyr, whereas in reverse micelles and denatured cutinase no shift is detected. Emission maxima variations (λmax 303, 311 and 335 nm, respectively in aqueous, reverse micelles and thermally denatured cutinase) reflect progressive changes in the micropolarity of the environment and exposure of Trp residues at the protein surface. The encapsulation of cutinase in AOT‐iso‐octane reversed micelles induces a time‐dependent denaturation measured by fluorescence intensity changes at 330 nm, which match the profile of enzyme activity loss in this media.
A Comparison of Functional Bladder Damage after Intravesical Photodynamic Therapy with Three Different Photosensitizers
Authors: Post J. G. , te Poele J. A. M. , Schuitmaker J. J. , Stewart F. A.
Published: January 2008

Abstract— The influence of type of photosensitizer, drug and light dose, and time interval between photosensitizer and illumination on the extent of photodynamic therapy (PDT)‐induced bladder damage and recovery was investigated using a mouse model. The three photosensitizers studied were Photofrin, meso‐tetrahydroxyphenylchlorin (m‐THPC) and bacteriochlorin a (BCA). Functional bladder damage was quantitatively assessed from increases in urination frequency index (FI) at 1‐35 weeks after illumination and histological damage was qualitatively assessed at 1 day, 1, 2 and 12 weeks.

Photofrin‐mediated PDT caused an acute increase in FI at 1 week, with recovery within 2‐8 weeks after light doses of 2.7‐8.2 J/cm2. After higher light doses there was only partial recovery. Previous results indicated that the acute response and rate of recovery was the same whether Photofrin was given at 1 day or up to 7 days before illumination. The m‐THPC‐mediated PDT at drug doses of 0.3 mg/kg also resulted in a marked acute response with good recovery, even after 10.8 J/cm2. Lower drug doses in combination with 5.4 J/cm2 did not result in acute or late damage. There was no significant difference in acute response when m‐THPC was given 1, 3 or 7 days before illumination, although recovery was faster for the longer illumination intervals (3 or 7 days). Illumination at 1 h after 20 mg/kg BCA induced an acute response within 2 days after illumination, with recovery within 4‐8 weeks. Lower drug doses did not result in damage. The most prominent histological changes during the acute period with all three photosensitizers were submucosal edema and vessel dilation, with epithelial denudation (depending on drug/light dose).

We conclude that BCA and m‐THPC are both potent new photosensitizers. They can induce a moderate to severe acute bladder response with complete healing over a period of a few weeks. The photosensitizer m‐THPC is very effective with low doses of photosensitizer and light, whereas relatively high doses of BCA and light are required to obtain equivalent functional bladder damage in our mouse model.
Effects of Moderately Low Temperature (20°C) on Phytochrome Responses During Preirradiation: Anthocyanin Synthesis in Sorghum bicolor at High‐ and Low‐Pfr/Ptot Ratios
Authors: Shichijo Chizuko , Hamada Tohru , Johnson Christopher B. , Hashimoto Tohru
Published: January 2008

Abstract—Effects on phytochrome‐mediated anthocyanin synthesis of moderately low temperature (MLT) given during the preirradiation culture period were studied with seedlings of broom sorghum (Sorghum bicolorMoench, cvs. Acme Broomcorn and Sekishokuzairai‐Fukuyama). Seedlings were grown in the dark at 20°C (MLT) and 24°C (control). The MLT treatment strikingly enhanced the action induced by a red light (R) pulse aboveca200 μmol m−2and suppressed the action induced by an R pulse belowca30 μmol m−2and by a far‐red light (FR) pulse alone. We refer to these MLT‐affected distinct responses as “high‐Pfr/Ptot response” and “low‐Pfr/Ptot response,” as they have features different from the high‐irradiance and very‐low‐fluence responses, respectively. The destruction rate of spectroscopically detectable phytochrome (phyA) and the time course of escape of anthocyanin synthesis from FR reversibility did not match, and hence the possibility of phyA being involved in high‐Pfr/Ptot response was rejected, although it might be involved in low‐Pfr/Ptot response. Possible mechanisms for the two distinct phytochrome responses are discussed.
Light Reflected from Colored Mulches to Growing Turnip Leaves Affects Glucosinolate and Sugar Contents of Edible Roots
Authors: Antonious George F. , Kasperbauer Michael J. , Byers Matthew E.
Published: January 2008

Abstract— Plastic mulches are widely used to conserve water and control weeds with less applied herbicides in production of food crops. Both yield and quality are important and can be affected by reflected blue (B), red (R) and far‐red (FR) light combinations received during growth and development. Photosynthate allocation among growing plant parts and flavor of edible roots were studied in turnip (Brassica rapa L.) grown in trickle‐irrigated field plots with blue, green and white mulches. The blue and green mulches reflected different amounts of B, but they both reflected FR/R ratios higher than the ratio in incoming sunlight. The white mulch reflected more photosyn‐thetic light and a lower FR/R ratio than the blue or green mulches. Plants grown with blue and green mulches did not differ significantly in leaf length, root size and shoot/ root biomass ratio. Those grown with white had shorter leaves and larger roots. Taste testers found that plants grown with blue mulch developed roots with a sharp flavor, and roots from plants grown with green mulch had a mild flavor. Those grown with white had a less distinct flavor. Roots grown with blue mulch had the greatest concentrations of total glucosinolates (GSL) and ascorbic acid. Reducing sugar concentrations were higher in roots grown with green than in those grown with blue mulches. The comparison of chemical composition of roots from plants grown with blue versus green mulches is important because the main difference was the amount of reflected B, suggesting that B influenced an enzyme involved in the pathway from glucose to GSL. We conclude that the spectrum of light reflected from mulch on the soil surface can influence not only shoot/root biomass ratio but also flavor‐related chemical composition of field‐grown food crop plants.
Photogenotoxicity of Skin Phototumorigenic Fluoroquinolone Antibiotics Detected Using the Comet Assay
Authors: Reavy Helen J. , Traynor Nicola J. , Gibbs Neil K.
Published: January 2008

Abstract— The fluoroquinolone(FQ) antibiotics photosensitize human skin to solar UV radiation and are reported to photosensitize tumor formation in mouse skin. As tumor initiation will not occur without genotoxic insult, we examined the potential of ciprofloxacin, lomefloxacin, fle‐roxacin, BAYy3118 (a recently developed monofluori‐nated quinolone) and nalidixic acid to photosensitize DNA damage in V79 hamster fibroblasts in vitro. Cells were exposed to 37.5 kj/m2 UVA (320‐400 nm; glass filtered Sylvania psoralen + UVA (PUVA) tubes; calibrated Waldmann radiometer) at 4AoC in the presence of FQ and immediately afterwards embedded in agarose, lysed and placed in an electrophoretic field at pH 12. Under these denaturing conditions, the presence of DNA single‐strand breaks (SSB), alkali‐labile sites (ALS) and double‐strand breaks (DSB) can be visualized as DNA migrating away from the nucleus (characteristic “comet” appearance) after staining with a specific fluorochrome. At FQ concentrations that induced minimal loss of cell viability (neutral red uptake assay) the compounds tested induced comets with a rank order of BAYy3118 norfloxacin ciprofloxacin lomefloxacin fleroxacin nalidixic acid. If cells were incubated after treatment for 1 h at 37oC, the comet score decreased, suggesting efficient removal of SSB/ALS/DSB. Addition of the DNA polymerase, inhibitor, aphidicolin, to cells treated with either ciprofloxacin alone or ciprofloxacin + UVA resulted in an accumulation of SSB due to the endo/exonuclease steps of excision repair. We have demonstrated that the FQ are photogenotoxic in mammalian cells but that FQ‐pho‐tosensitized SSB are efficiently repaired. Preliminary evidence that ciprofloxacin photosensitizes the formation of DNA lesions warranting excision repair may indicate production of more mutagenic lesions.
Kinetics of Stem Elongation in Light‐Grown Tomato Plants. Responses to Different Photosynthetically Active Radiation Levels by Wild‐Type and aurea Mutant Plants
Authors: Bertram Lise , Lercari Bartolomeo
Published: January 2008

Abstract— In this research, we measured the short‐ and long‐term, stem elongation responses of wild‐type and aurea(au) mutant tomato plants to different photosynthetically active radiation (PAR) levels by using linear voltage transducers. Stem elongation was continuously measured in green tomato plants over 2.75 days, under 12 h light/12 h dark photoperiods or in darkness after a 6 h irradiation period. There is no significant difference in stem elongation between wild‐type plants pregrown at either LOO or 400 μmol m−2 s−1 and then exposed to 12 h photoperiods. However, in the au mutant there is a very large difference between plants pregrown under 100 or 400 umol m −2 s−1 and then exposed either to 12 h photoperiods or to continuous darkness. Total stem elongation of the wild type appears to be maximal at 100 umol m−2 s−1, while that of the au mutant appears to be maximal with PAR 400 umol m−2 s−1. Wild‐type plants displayed PAR‐dependent (in the range 100‐800 umol m−2 s−1) inhibition of growth both during the day and during the night. In contrast, the au mutant showed a fluence‐rate‐dependent promotion of growth during the dark periods in the range of 10‐400 umol m−2 s−1. Large, fast and opposite changes in stem elongation rate at the light/dark and dark/light transitions were present in both genotypes. Internode elongation rate in the first half of the night was always modest in wild‐type tomato, whereas it increased rapidly in the au mutant. Stem elongation rate of wild type starts to increase after about 6 h in darkness, showing the typical time course of escape from Pfr‐mediated inhibition of elongation by an end‐of‐day response. The role of phytochrome level and type in sensing light quantity is discussed.
The Importance of Charge Transfer between the Retinal Chromophore and the Protein Environment in Bacteriorhodopsin: A Theoretical Analysis on Reduced and Oxidized Chromophores
Authors: Sakar K. , Vacek G. , Luthi H. P. , Nagashima U.
Published: January 2008

Abstract— The importance of charge transfer(CT) between the retinal chromophore and the protein environment in the ground state of bacteriorhodopsin(BR) has been verified by using ab initio and semiempirical molecular orbital methods. We hypothesize that the chromophore is stabilized in BR by highest occupied molecular orbital‐lowest unoccupied molecular orbital(HOMO‐LUMO) interaction with the protein environment. If sufficient charge is transferred between two sites due to the strong HOMO‐LUMO interaction, the chromophore might be treated as a one‐electron reduced species(when it behaves as an electron acceptor), or as a one‐electron oxidized one (when it acts as an electron donor).In both optimized geometries, the ‐conjugated systems exhibit a drastic decrease in bond alternation. To estimate the rotational barrier for thermal isomerization between the al‐trans and the 13,15‐dicis form, the potential energy curve around these two bonds was computed. The first ‐* transition energy was also calculated for an inspection of the opsin shift. The barrier height and the transition energy became much lower as a result of the chromophore reduction. The site selectivity in photo‐ and thermal isomerization and the opsin shift in BR can be well explained by considering CT from the protein environment to the chromophore.
Thermodynamic and Kinetic Study of the Interaction between Alkylpyridinium Ions and Pyrene Derivatives in Aqueous Solution
Authors: Rosenbluth H. , Weiss‐Lopez B. , Olea A. F.
Published: January 2008

Abstract— The kinetics of fluorescence quenching of pyrene and three of its derivatives by a series of n ‐alkylpyridinium ions has been studied. The quenching process is diffusion controlled for all the systems studied, independent of the charge in the aromatic molecule and the size of the alkyl chain in the pyridinium ions. Pyrensulfonate, PS, and pyranine form ground‐state complexes with these quenchers. The association constants were determined by using a kinetic scheme where both dynamic and static quenching were included. A linear relationship between the free energy change and number of carbon atoms was found for PS, and a methylene contribution equal to ‐1.1 kJ/mol was determined from the slope. A similar correlation was established for pyranine, but a slope change was observed when the alkyl chain has more than 10 carbon atoms. From the initial slope, an incremental free energy of ‐0.35 kJ/mol was obtained. The ground‐state complex formation is determined mainly by an electrostatic interaction, but there is a hydrophobic effect on the value of the measured association constants.
m‐THPC‐Mediated Photodynamic Therapy (PDT) Does Not Induce Resistance to Chemotherapy, Radiotherapy or PDT on Human Breast Cancer Cells In Vitro
Authors: Hornung René , Walt Heinrich , Crompton Nigel E. A. , Keefe Kristin Anne , Jentsch Brigitte , Perewusnyk Gloria , Haller Urs , Köchli Ossi R.
Published: January 2008

Photodynamic therapy (PDT) uses laser light to activate a photosensitizer that has been absorbed preferentially by cancer cells after systemic administration. A photo‐toxic reaction ensues resulting in cell death and tissue necrosis. Some cells, however, may survive PDT. This study was performed to determine if surviving human breast cancer cells (MCF‐7) can become resistant to PDT, chemotherapy or radiotherapy. The MCF‐7 cells were cultured under standard conditions prior to being exposed to the photosensitizer, 5,10,15,20‐meta‐tet‐ra(hydroxyphenyl)chlorin (zn‐THPC), for 24 h and then irradiated with laser light (652 nm). Surviving cells were allowed to regrow by allowing a 2 week interval between each additional PDT. After the third and final treatment, colony formation assays were used to evaluate the sensitivity of cultured cells to ionizing radiation and PDT and the ATP cell viability assay tested in vitro chemosen‐sitivity. Flow cytometry was used to analyze the cell cycle. No alterations in the cell cycle were observed after three cycles of PDT with m‐THPC. Similar responses to chemotherapy and ionizing radiation were seen in control and treatment groups. The m‐THPC‐sensitized PDT did not induce resistance to subsequent cycles of PDT, chemo‐ or radiotherapy. Photodynamic therapy with m‐THPC may represent a novel adjunctive treatment of breast cancer that may be combined with surgery, chemotherapy or ionizing radiation.
Suppression of Delayed and Contact Hypersensitivity Responses in Mice Have Different UV Dose Responses
Authors: Kim Tae Heung , Ullrich Stephen E. , Ananthaswamy Honavara N. , Zimmerman Stuart , Kripke Margaret L.
Published: January 2008

Although acute exposure to UV radiation suppresses the induction of delayed‐type (DTH) and contact (CHS) hypersensitivity in mice, it is not clear whether the photo‐biological mechanism(s) involved in suppressing these closely related immune reactions is the same. A careful examination of the UV dose responses and wavelength dependencies involved in suppressing CHS and DTH may provide important insights into the mechanisms involved. We compared the UV dose‐response curves for suppressing four closely related immune reactions, local and systemic suppression of CHS to dinitrofluorobenzene, systemic suppression of DTH to Candida albicans and systemic suppression of DTH to alloantigen using three different UV spectra (FS40 sunlamps, Kodacel‐filtered FS40 sunlamps and solar‐simulated light). For each immune response studied, the amount of UVB radiation required to induce 50% immune suppression was lowest when FS40 sunlamps were used, highest with solar‐simulated light and intermediate when Kodacel‐filtered FS40 sunlamps were used, but the differences observed were not statistically significant. The UV dose‐response curves for immune suppression differed significantly depending on the assay used, the site of antigenic sensitization and the antigen used. These findings suggest that the mechanisms by which UV radiation induces immune suppression differ for the four immunological reactions studied.
The Effects of Octanol on the Late Photointermediates of Rhodopsin
Authors: Mah Tina L. , Szundi Istvan , Lewis James W. , Jager Stefan , Kliger David S.
Published: January 2008

Membrane suspensions of unperturbed rhodopsin and rhodopsin perturbed with 2.5 niM octanol were photo‐lyzed with 477 nm laser pulses at 20OC and 35°C. Changes in absorbance were monitored at times ranging from 1 u‐s to 80 ms after excitation. The data were analyzed using singular value decomposition, global exponential fitting and kinetic modeling. A recently proposed model involving the photointermediate Meta‐I380 (T. E. Thorgeirsson, J. W. Lewis, S. E. Wallace‐Williams, and D. S. Kliger, Biochemistry 32,13861–13872, 1993) fits data for samples with and without octanol. Comparison of the microscopic rates shows this alcohol accelerates the formation of Meta‐II via Meta‐I380. Activation and equilibrium thermodynamic parameters obtained from Ar‐rhenius plots suggest that octanol reduces the entropy increase in forming both Meta‐I3g0 and Meta‐II. It also lowers the enthalpy of Meta‐1, SI, relative to Lumi and of Meta‐II relative to Meta‐I480. To help determine whether octanol affects the protein directly or indirectly through the lipid bilayer, similar experiments were conducted using rhodopsin solubilized in 0.13% dodecyl maltoside with and without octanol. Spectral shifts in the presence of octanol suggest that a direct protein interaction exists in addition to previously reported effects dependent on membrane free volume.
Raman Spectroscopy and Fluorescence Photon Migration for Breast Cancer Diagnosis and Imaging
Authors: Manoharan Ramasamy , Shafer Karen , Perelman Lev , Wu Jun , Chen Kun , Deinum Geurt , Fitzmaurice Maryann , Myles Jonathan , Crowe Joseph , Dasarl Ramachandra R. , Feld Michael S.
Published: January 2008

We are developing optical methods based on near infra‐red Raman spectroscopy and fluorescence photon migration for diagnosis and localization of breast cancer. We demonstrate the ability of Raman spectroscopy to classify accurately normal, benign and malignant breast tissues, an important step in developing Raman spectroscopic needle probes as a tool for improving the accuracy of needle biopsy. We also show that photon migration imaging can be used to localize accurately small fluorescent objects imbedded in a thick turbid medium with realistic optical properties, thus demonstrating the potential of this technique for optical imaging.
Identification of a Single Phosphorylation Site Within Octopus Rhodopsin
Authors: Ohguro Hiroshi , Yoshida Norihiko , Shindou Hideo , Crabb John W. , Palczewski Krzysztof , Tsuda Motoyuki
Published: January 2008

Abstract— Light‐dependent phosphorylation of rhodopsin (Rho) is a first step in the desensitization of the signaling state of the receptor during vertebrate and invertebrate visual transduction. We found that only 358Ser of the photoac‐tivated octopus Rho (oRho*) was phosphorylated by octopus rhodopsin kinase (oRK). Tryptic truncation of the C‐terminal PPQGY repeats of oRho that follow the phosphorylation region did not influence spectral or G‐protein activation properties of oRho but abolished phos phorylation. Despite significant structural differences between oRK and mammalian RK, these results provide i further evidence of the importance of singly phosphorylated species of Rho* in the generation of arrestin binding sites.
Comparison of Models Used for UV Index Calculations
Authors: Koepke Peter , Bais Alkiviadis , Balis Dimitrios , Buchwitz Michael , De Backer Hugo , de Cabo Xavier , Eckert Pierre , Eriksen Paul , Gillotay Didier , Heikkilä Anu , Koskela Tapani , Lapeta Bozena , Litynska Zenobia , Lorente Jeronimo , Mayer Bernhard , Renaud Anne , Ruggaber Ansgar , Schauberger Günther , Seckmeyer Gunther , Seifert Peter , Schmalwieser Alois , Schwander Harry , Vanicek Karel , Weber Mark
Published: January 2008

Eighteen radiative transfer models in use for calculation of UV index are compared with respect to their results for more than 100 cloud‐free atmospheres, which describe present, possible future and extreme conditions. The comparison includes six multiple‐scattering spectral models, eight fast spectral models and four empirical models. Averages of the results of the six participating multiple‐scattering spectral models are taken as a basis for assessment. The agreement among the multiple‐scattering models is within ±0.5 UV index values for more than 80% of chosen atmospheric parameters. The fast spectral models have very different agreement, between ±1 and up to 12 UV index values. The results of the empirical models agree reasonably well with the reference models but only for the atmospheres for which they have been developed. The data to describe the atmospheric conditions, which are used for the comparison, together with the individual results of all participating models and model descriptions are available on the Internet: http://www.meteo.physik.uni‐muenchen.de/strahlung/cost/.
Phthalocyanine 4 (Pc 4) Photodynamic Therapy of Human OVCAR‐3 Tumor Xenografts
Authors: Colussi Valdir C. , Feyes Denise K. , Mulvihill John W. , Li Ying‐Syi , Kenney Malcolm E. , Elmets Craig A. , Oleinick Nancy L. , Mukhtar Hasan
Published: January 2008

Abstract— Photodynamic therapy (PDT) is a cancer treatment modality utilizing a photosensitizer, light and oxygen. Photodynamic therapy with Photofrin® has been approved by the US. Food and Drug Administration for treatment of advanced esophageal and early lung cancer. Because of certain drawbacks associated with the use of Photofrin, there is a need to identify new photosensitizers for human use. The photosensitizer Pc 4 (HOSiPc‐OSi[CH3]2[CH2]3N[CH3]2) has yielded promising PDT effects in many in vitro and in vivo systems. The aim of this study was to assess the usefulness of Pc 4 as a PDT photosensitizer for a human tumor grown as a xenograft in athymic nude mice. The ovarian epithelial carcinoma (OVCAR‐3) was heterotransplanted subcutaneously in athymic nude mice. Sixty mice bearing OVCAR‐3 tumors (∼80–130 mm3) were divided into six groups of 10 animals each, three for controls and three for treatment. The Pc 4 was given by tail vein injection, and 48 h later a 1 cm area encompassing the tumor was irradiated with light from a diode laser coupled to a fiberoptic terminating in a microlens (Λ= 672 nm, 150 J/cm2,150 mW/cm2). Tumors of control animals receiving no treatment, light alone or Pc 4 alone continued to grow. Of animals receiving 0.4 mg/kg Pc 4 and light, one (10%) had a complete response and was cured (no regrowth up to 90 days post‐PDT), while all others (90%) had a partial response and were delayed in regrowth. Of animals receiving 0.6 mg/kg Pc 4 and light, eight (80%) had a complete response, and two of these were cured. Of animals receiving 1.0 mg/kg Pc 4 and light, six (60%) had a complete response, and two of these were cured. In additional experiments, tumors from animals treated with Pc 4 (1 mg/kg) and light were removed 15, 30, 60 and 180 min post‐PDT, and from these tumors DNA and protein were extracted. Agarose gel electrophoresis revealed the presence of apoptotic DNA fragmentation as early as 15 min post‐PDT. Western blotting showed the cleavage of the 116 kDa native poly (ADP‐ribose) polymerase (PARP) into fragments of ∼90 kDa, another indication of apoptosis, and the presence of p21/WAFl/CIPl (p21) in all PDT‐treated tumors. These changes did not occur in control tumors. Pc 4 appears to be an effective photosensitizer for PDT of human tumors grown as xenografts in nude mice. Early apoptosis, as revealed by PARP cleavage, DNA fragmentation and p21 overexpression, may be responsible for the excellent Pc 4‐PDT response. Clinical trials of Pc 4‐PDT are warranted.
Time‐Resolved Studies of Light Propagation in Crassula and Phaseolus Leaves
Authors: Johansson Jonas , Berg Roger , Pifferi Antonio , Svanberg Sune , Björn Lars Olof
Published: January 2008

Abstract— Time‐resolved transmittance was used to extract in vivo optical properties of leaves of green plants experimentally. In time‐resolved transmittance measurements an ultrashort light pulse is directed onto the surface of the object and the transmitted light is measured with a time resolution in the range of picoseconds. A table‐top terawatt laser was used to generate 200 fs light pulses at 790 nm with a repetition rate of 10 Hz. The light pulses were focused through a cuvette filled with water to produce white light pulses and optical filters were placed in the beam path to select the wavelength of the light focused onto the leaf surface. The time profiles of the light transmitted through the leaves was recorded with a streak camera having a time resolution of about 2.5 ps. Results from Crassula falcata and Phaseolus vulgaris studied at 550, 670 and 740 nm are reported. The three selected wavelength regions represent medium, high and a low absorption of light, respectively. A library of curves was generated using Monte Carlo simulation, and the absorption and scattering coefficients were extracted by comparison of experimental curves with this library. Our results suggest that in the case of the thin (200 μm) Phaseolus leaves and certainly in the case of the thick (4 mm) Crassula leaves, light scattering plays an important role in light transport through the leaf and should also affect light flux in these leaves.
Damage to Rat Retinal DNA Induced In Vivo by Visible Light
Authors: Specht Sandra , Leffak Michael , Darrow Ruth M. , Organisciak Daniel T.
Published: January 2008

Abstract— Intense visible light can damage retinal photoreceptor cells by photochemical or thermal processes, leading to cell death. The precise mechanism of light‐induced damage is unknown; however, oxidative stress is thought to be involved, based on the protective effect of antioxidants on the light‐exposed retina. To explore the in vivo effects of light on retinal DNA, rats were exposed to intense visible light for up to 24 h and the time courses of single‐strand breaks in restriction fragments containing the opsin, insulin 1 and interleukin‐6 genes were measured. All three gene fragments displayed increasing single‐strand modifications with increasing light exposure. Treatment with the antioxidant dimethylthiourea prior to light exposure delayed the development of net damage. The time course of double‐strand DNA damage was also examined in specific genes and in repetitive DNA. The appearance of discrete 140–200 base‐pair DNA fragments after 20 h of light exposure implicated a nonrandom, possibly enzymatic damaging mechanism. The generation of nucleosome core‐sized DNA fragments, in conjunction with single‐strand breaks, suggests two phases of light‐induced retinal damage, with random attack on DNA by activated oxygen species preceding enzymatic degradation.
Visible‐light Photochemistry and Phototoxicity of Thiarubrines
Authors: Page Jonathan E. , Block Eric , Towers G. H. Neil
Published: January 2008

Abstract. Thiarubrines, a group of intensely red, sulfur‐containing pigments produced by asteraceous plants, are photola‐bile, yielding thiophenes and elemental sulfur upon exposure to UV or visible light. The mechanism of this light‐induced conversion for thiarubrines A (la), B (lb) and D (lc), isolated from the roots of Ambrosia chamis‐sonis (Asteraceae), was investigated. Visible‐light irradiation of thiarubrines resulted in the formation of novel 2,6‐dithiabicyclo[3.1.0]hex‐3‐ene polyyne photointerme‐diates (photosulfides) that rapidly undergo desulfuriza‐tion to yield thiophenes. Six photosulfides, photosulfides 3a and 3a' from thiarubrine A (la), photosulfides 3b and 3b' from thiarubrine B (lb) and photosulfides 3c and 3c' from thiarubrine D (lc) were characterized. Thiarubrine photointermediates are short‐lived and unstable, with the photosulfides formed from thiarubrine A having a half‐life of 12.3 min at room temperature. While the immediate fate of the extruded sulfur is unknown, we identified cyclooctasulfur (S8) in photolysis solutions of thiarubrine A using electron impact mass spectrometry. Visible‐light irradiation of Candida albicans cell suspensions treated with thiarubrine A led to a 99% decrease in cell viability, suggesting that the photosulfides, or other molecules generated by the exposure of thiarubrines to light, have significant toxicity.
Room Temperature Phosphorescence from Tryptophan and Halogenated Tryptophan Analogs in Amorphous Sucrose
Authors: McCaul Colin P. , Ludescher Richard D.
Published: January 2008

Abstract. Tryptophan phosphorescence lifetime and quantum yield are sensitive to the local environment. The phosphorescence from tryptophan analogs, however, has not been studied. We report here data on the room temperature phosphorescence of tryptophan, 4‐, 5‐ and 6‐fluoro‐DL‐tryptophan (4‐F‐trp, 5‐F‐trp and 6‐F‐trp) and 5‐bromo‐DL‐tryptophan (5‐Br‐trp) embedded in glassy powders of freeze‐dried sucrose. In aqueous solution, the absorption of the analogs was either blue‐shifted (4‐F‐trp), red‐shifted (5‐F‐trp and 5‐Br‐trp) or not shifted (6‐F‐trp) with respect to tryptophan. The phosphorescence emission spectra of all analogs were red‐shifted compared to trp (442 nm) with maxima at 446 nm (5‐F‐trp), 451 mn (6‐F‐trp), 452 nm (5‐Br‐trp) and 469 nm (4‐F‐trp). The 5‐F‐trp and 6‐F‐trp analogs had emission intensities similar to tryptophan (relative quantum yields of 0.68 and 0.91, respectively, compared to tryptophan), while the intensities of the 4‐F and 5‐Br analogs were lower (relative quantum yields of 0.039 and 0.022, respectively). All analogs exhibited complex decay behavior requiring several exponentials for an adequate fit; the average lifetimes were all lower than that of trp (1039 ms). The average lifetimes of the fluorinated analogs (5‐F, 721 ms; 6‐F, 482 ms and 4‐F, 35 ms) scaled approximately with the relative quantum yields while that of 5‐Br (0.53 ms) was significantly lower. Analysis of the individual lifetimes suggested that the fluorinated analogs differ in their sensitivity to environmental interactions, with 5‐F‐ and 6‐F‐trp quenched 1.5‐2‐fold and 4‐F‐trp about 23‐fold more efficiently than tryptophan. The red‐shifted 5‐F‐trypto‐phan analog, which has been incorporated into proteins, may provide an alternative phosphorescence probe for selective phosphorescence detection of a specific protein in a complex mixture.