bluuebunny/crossref_metadata_2025 huggingface dataset:
REVERSION PROFILES OF COOL WHITE FLUORESCENT LIGHT COMPARED WITH FAR ULTRAVIOLET LIGHT: HOMOLOGIES AND DIFFERENCES
Authors: Cebula Thomas A. , Henrikson Erik N. , Hartman Philip E. , Biggley William H.
Published: January 2008

Abstract— General Electric and Sylvania 15 W coolwhite fluorescent lamps emit roughly 6% of their total irradiance as light in the UV spectrum. Illumination of sensitive Salmonella tester strains results in both lethal and mutagenic activities. In contrast, comparable Philips lamps emit lower levels of U V light, especially UVB, and exhibit no detectable lethal or mutagenic effects. The spectra of mutations induced by General Electric coolwhite lamps in histidine‐requiring base substitution mutants hisG46 and hisG428 (“reversion profiles”) resemble mutagenesis by far UV light (UVC) and differ quite markedly from the spectra of mutations that occur spontaneously. Coolwhite and UVC reversion profiles are not identical, however. The percentage of C to A transversion mutations induced in hisG46 are elevated over those found after UVC treatment, and a strong bias for one particular class of tandem base substitutions (TAA → TGT) prevails after treatment of hisG428 with coolwhite light, a bias not observed with UVC. Increased attention needs to be given to minimization of exposure to UV light from fluorescent lamps commonly used in homes and workplaces.
USING CELL‐FRACTIONATION AND PHOTOCHEMICAL CROSSLINKING METHODS TO DETERMINE THE CELLULAR BINDING SITE(S) OF THE ANTITUMOR DRUG DMP 840
Authors: Chatterjee Pradeep K. , Sternberg Nat L.
Published: January 2008

Abstract— In order to understand its mechanism of action we have begun an effort to better define the cellular target of action of the experimental antitumor agent DMP 840 (NSC D640430; (R, R)‐2,2′‐(1,2‐ethanediylbis(imino‐(1 ‐methyl‐2,1 ‐ethanediyl)))‐bis(5‐nitro‐1 H‐benz(de)isoquinoline‐1,3‐(2H)‐dione) dimethanesulfonate). Using a combination of gentle cell fractionation procedures and a previously unidentified photochemical crosslinking reaction, we have shown that after the drug is added to cultured Clone A cells, more than 80% of the drug that is found associated with cells partitions to the chromatin‐containing structural framework of the cell and that the primary target after crosslinking with 360 nm light is DNA. While DMP 840 photoreacts quite efficiently with purified RNA in vitro, no photoat‐tachment of the drug to RNA was observed in cells. In vitro photochemical studies also reveal that while GC‐rich DNA is a preferred target for drug interaction, AT‐rich DNA is more active in the photochemical crosslinking reaction. These results suggest that DMP 840 probably kills cells by interfering with DNA‐metabolic processes, and that the drug and its derivatives are likely to be useful photoactive molecular probes for investigating higher order chromatin structures in cells.
DISTRIBUTION OF TEMOPORFIN, A NEW PHOTOSENSITIZER FOR THE PHOTODYNAMIC THERAPY OF CANCER, IN A MURINE TUMOR MODEL
Authors: Whelpton Robin , Michael‐Titus Adina T. , Basra Sukhbinder S. , Grahn Michael
Published: January 2008

Abstract— The biodistribution of temoporfin (tetra[m‐hydroxyphenyl]chlorin, m‐THPC), a recently developed photosensitizer, was investigated in BALB/c mice. The drug was administered intravenously (0.35‐0.75 μmol/kg) to tumor‐free mice or to mice implanted with the Colo 26 colorectal carcinoma. Blood and tissue samples were collected for up to 96 h post‐dose. Drug concentrations were determined by HPLC coupled to photometric detection at 423 nm. Concentrations in blood and liver fell relatively rapidly such that blood concentrations at later time points were below the limit of detection. Tumor concentrations rose at first and then remained constant from 24 h. Temoporfin concentrations in some tissues, notably heart and skeletal muscle, declined only slowly when compared to blood. The tumor: tissue ratios for those organs that showed a more rapid decline in temoporfin concentrations were higher at later times, whereas in tissues such as muscle the ratio remained relatively constant. The organs with the highest tumor: tissue ratios were small intestine (8.6), liver (6.9) and skeletal muscle (5.0).
IMPACT OF UVB and 03 ON THE OXYGEN FREE RADICAL SCAVENGING SYSTEM IN Arabidopsis thaliana GENOTYPES DIFFERING IN FLAVONOID BIOSYNTHESIS
Authors: Rao Mulpuri V. , Ormrod D. P.
Published: January 2008

Abstract— The effect of UVB and ozone (O3) on growth and ascorbate‐glutathione cycle were investigated in Arabidopsis thaliana wild‐type Landsberg erecta (LER) and its transparent testa (tt5) mutant differing in UVB sensitivity. Ultraviolet‐B radiation decreased dry matter production of tt5, while the dry weight of LER remained unaltered. Ozone exposure decreased dry weight of both genotypes. Ultraviolet‐B radiation decreased the Fv/Fm ratio in tt5 but not in LER plants, while O3 exposure decreased the Fv/Fm ratio in both genotypes. Ultraviolet‐B radiation enhanced total ascorbic acid, total glutathione and their redox state and superoxide dismutase and glutathione reductase activities in both genotypes and the increases were greater in tt5 compared to UVB‐irradiated LER. Although O3 exposure enhanced total ascorbic acid and total glutathione in both genotypes, the redox state was significantly higher in tt5. Ozone exposure enhanced superoxide dismutase and glutathione reductase activities in tt5 while there were no major changes in LER. These results suggested that (1) plants blocked in flavonoid biosynthesis are sensitive to UVB in spite of their ability to maintain efficient oxygen free radical scavenging systems and (2) plants sensitive to UVB are comparatively tolerant of O3 compared to UVB‐insensitive plants. The differential responses of plants are discussed with reference to their ability to maintain high redox states of ascorbate and glutathione.
MOLYBDENUM COFACTOR BIOSYNTHESIS IN Neurospora crassa: BIOCHEMICAL CHARACTERIZATION OF PLEIOTROPIC MOLYBDOENZYME MUTANTS nit‐7, nit‐8, nit‐9A, B and C*
Authors: Heck Immanuel S. , Ninnemann Helga
Published: January 2008

Abstract— Available mutants of molybdenum cofactor (MoCo) biosynthesis of Neurospora crassa were studied for converting factor activity and for in vitro molybdate repair of nitrate reductase (NR) activity. Mutant nit‐7 was found to contain an activity that fits the functional definition of converting factor activity in Escherichia coli. Its high molecular weight fraction converts a low molecular weight compound from nit‐1 and nit‐8 into biologically active molybdopterin (MPT). Like nit‐1, mutant nit‐8 is devoid of this activity. Mutants nit‐9 A, B and C contain a protein‐bound precursor form of MoCo, which is presumed to be MPT bound to apo‐NR. It is converted into active MoCo as part of NR in the presence of reduced glutathione and high exogenous molybdate concentrations. The NR apoenzyme of nit‐1 is needed to detect the total amount of MoCo after molybdate repair, because mutants nit‐9 A, B and C build no detectable content of functional NR apoenzyme. Evidence is presented for the transfer of MPT from demolybdo‐NR to free NR apoenzyme.
Photochemistry and Photophysical Properties of Novel, Unsymmetrically Substituted Metallophthalocyanines
Authors: Lawrence David S. , Whitten David G.
Published: January 2008

Abstract— A series of novel, unsymmetrically substituted metallophthalocyanines was synthesized, along with their symmetrically substituted analogs, and the effects of structure and metal substitution on their photophysical and photoredox properties were investigated. The macrocy‐cles were synthesized using a mixed‐condensation method followed by chromatographic separation of the resulting soluble products. They possess a catechol “active site” and three tert‐butyl groups for enhanced solubility. The ground‐ and excited‐state photophysical properties of the free‐base, Zn(II) and Pd(II) macrocycles were measured and compared with their symmetrically substituted (tetra[tert‐butyl]) analogs. The efficiency with which these macrocycles sensitize the formation of singlet oxygen was determined and discussed in the context of the excited‐state photophysical properties. Several examples of photoinduced electron transfer reactions with one‐ and two‐electron acceptors are demonstrated and discussed. These soluble molecules can be tuned to optimize their photochemical and redox properties by varying the central metal, axial ligands and other substituents, thereby providing a series of molecules for the investigation of photodynamic therapy and photoinduced electron transfer mechanisms.
Photochemistry of Tetracene Adsorbed on Dry Silica: Products and Mechanism
Authors: Dabestani Reza , Nelson Mark , Sigman Michael E.
Published: January 2008

The photochemistry of tetracene (1) has been studied on dry silica at very low surface coverages (less than 3% of a monolayer). Irradiation of degassed samples of 1 adsorbed on silica surface proceeds very slowly to produce both syn (2) and anti (3) dimers. Under aerated conditions photolysis of 1 at surface coverages <1% of a monolayer gives mainly tetracene‐5, 12‐endoperoxide (4) and very little dimer. The endoperoxide slowly decomposes to form 5, 12‐tetracenequinone (5), 5, 12‐dihydroxytetracene (6) and 5, 12‐dihydro‐5, 12‐dihydroxytetracene (7), respectively. As the surface coverage is increased above 1% of a monolayer, dimerization becomes more pronounced as a result of pairing and/or aggregation. The photooxidation process is mediated by the addition of singlet molecular oxygen to 1. Tetracene also undergoes a dark oxidation reaction on the silica surface to give 5 (major), 6 and 7 (minors) as products. The first‐order rate constant for this Lewis acid‐catalyzed oxidation was determined to be 1 × 105 S−1.
The Use of UV Radiation to Control the Architecture of Salvia splendens Plants. I. Effects on Plant Growth, Water Relations and Gas Exchange
Authors: Giannini A. , Pardossi A. , Lercari B.
Published: January 2008

In experiments with Salvia splendens plants grown in the greenhouse we evaluated the possible use of irradiation with unfiltered UV (UVA + UVB + UVC) lamps for the control of plant growth. The effect of UV Irradiation on the growth of S. splendens plants in the grcenhouse was closely dependent on the growing season and the level of available photosynthetically active radiation. In summer UV treatments were ineffective, but in the low light conditions of winter UV irradiation inhibited the growth via both photomorphogenic and photosynthetic effects. The reduction of stomatal conductance and expansion growth, which in turn depressed photosynthesis and dry matter accumulation, were not a consequence of an impairment of plant water status but appeared to be a direct UV effect on stomata and cell wall rheological propertles. Our findings suggest that the use of unfiltered UV irradiation could become an effective tool for the regulation of growth in greenhouse crops, particularly during the poor light conditions of the winter season.
Photochemistry and Photobiology of lmidazole‐4(5)‐Methylidene Malonic Acid: An Analog of Both E‐ and Z‐Urocanic Acid*
Authors: Houghtaling Melissa A. , Kennedy Matthew A. , Mohammad Taj , Tessman Irwin , Morrison Harry
Published: January 2008

Imidazole‐4(5)‐methylidene malonic acid (IMMA) may be thought of as having its imidazole and carboxyl functionalities permanently fixed in a configuration that is simultaneously analogous to both E‐ (trans) and Z‐ (cis) urocanic acid (UA). Because the UA isomers affect the photoinactivation of bacteriophage single‐stranded DNA differently (E‐UA increases and Z‐UA decreases viral DNA inactivation), IMMA was similarly tested and was found to change the inactivation rate by a factor of 0.43, which is intermediate between the values for E‐ and Z‐UA (1.6 and 0.014, respectively). The IMMA likewise sensitizes double‐stranded DNA by a factor of 10.3 compared to a value of 13 for UA. In several ways the effects of IMMA parallel the distinctive effects of UA on the UV inactivation of single‐ and double‐stranded DNA, including the ability to prevent the formation of cyclobutane pyrimidine dimers in irradiated single‐stranded DNA and to sensitize a large increase in the formation of those dimers in irradiated double‐stranded DNA. The IMMA photodecarboxylates to UA with a low quantum efficiency (ca 1 × 10−3) and photochemically binds to calf‐thymus DNA.
Is Phototherapy Safe for HIV‐Infected Individuals?
Authors: Adams Melanie L. , Houpt Karen R. , Cruz Ponciano D.
Published: January 2008

Patients infected with human immunodeficiency virus (HIV) have a high prevalence of UV radiation‐responsive skin diseases including psoriasis, pruritus, eosinophilic folliculitis and eczemas. On the other hand, UV has been shown to suppress T cell‐mediated immune responses and to induce activatin and replication of HIV. These developments have prompted clinicians and investigators to question whether phototherapy is safe for HIV‐infected individuals. We have reviewed these issues and hereby provide a summary and critique of relevant laboratory and clinical evidence.
Detector‐Based Calibration Method for High‐Accuracy Solar UV Measurements
Authors: Kärhä Petri , Visuri Reijo , Leszczynski Kirsti , Manoochehrl Farshid , Jokela Kari , Ikonen Erkki
Published: January 2008

A novel method for calibrating the absolute responsivity of solar UV spectroradiometers has been developed and tested. The method is based on calibrated filter radiometers constructed from a detector, a precision aperture, a band‐pass filter and devices for temperature stabilization. The filter radiometers utilize a trap detector with very low reflectance. The filter and the detector can therefore be characterized separately. As an example the detector‐based calibration is compared at 312 nm wavelength with lamp‐based calibration by measuring the irradiance of a deuterium lamp with both the filter radiometer and the lamp‐calibrated spectroradiometer. The agreement between the results is at the level of 1%, well within the estimated uncertainties of both methods.
Effect of the UV Modification of α‐Crystallin on Its Ability to Suppress Nonspecific Aggregation
Authors: Ellozy Aziza R. , Ceger Patricia , Wang Ren H. , Dillon James
Published: January 2008

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

The sexual development of the fungus Phycomyces is inhibited by light. The action spectra for this photoinhibitory effect were determined for 48 h continuous exposure between 350 and 700 nm wavelengths during the mating process. Effective wavelengths were shorter than 490 nm, but the most effective wavelengths depended on the stage of sexual development. In early stages of progametangium formation, the major peaks appeared near 360 nm with small shoulders at 410 nm, but in later stages, after gametangium formation, only single peaks were detected in the UVA range (350–390 nm). Low‐fluence irradiation in the later stage, however, revealed inhibitory effectiveness at 370–410 nm, implying the existence of a dual photoresponse and multiple regulatiory systems in the mating process of Phycomyces.
Replication in UV‐lrradiated Caenorhabditis elegans Embryos
Authors: Jones Clark A. , Hartman Phil S.
Published: January 2008

Abstract— Replication continues in wild‐type (but not rad mutant) Caenorhabditis elegans embryos even after exposure to massive fluences of UV radiation. It is of interest to elucidate the mechanism(s) for this “damage‐resistant” DNA synthesis. In this study, DNA from unirradiated and UV‐irradiated wild‐type embryos was examined using the electron microscope. Large fluences of UV radiation (180 J m−2) had little effect on either replication bubble size or distances between bubbles in wild‐type embryos, indicating that the damage‐resistant DNA synthesis was not grossly aberrant. Conversely, UV irradiation significantly decreased center‐to‐center distances between bubbles in excision‐repair‐deficient rad‐3 embryos. This suggests that the decreased DNA synthesis observed after UV irradiation in rad‐3 embryos is due largely to blockage of elongation of DNA synthesis.
Induction of Lambda Prophage by 213 nm Laser Radiation: A Quantitative Comparison with 193 nm Excimer Radiation Using Image Analysis
Authors: Matchette L. S. , Grossman L. W. , Hahn D. W. , Cooney C.
Published: January 2008

Abstract— We compared the DNA damage produced by radiation from two UV laser wavelengths, 213 nm and 193 nm, with that produced by noncoherent 254 nm radiation. Following irradiation of Escherichia coli BR339, a bacteriophage lambda lysogen containing the lacZ gene, prophage induction was measured by assaying for β‐galactosidase. Because of the limited penetration by UV laser wavelengths an agar overlay of the lysogen was used as the irradiation target. Irradiation of 254 nm was performed in buffer suspension followed by transfer of 5 μL spots onto assay plants. Computer image analysis was used to monitor the rate of product formation, observed as an increase in optical density of the irradiated zones on assay plates. We found that the rate of product formation was a more reproducible unit of comparison than the optical density present at the end of the reaction. Although the rate of product formation was not linearly related to enzyme concentration, the data could be fit to a simple logarithmic function. Using this method, we concluded that the DNA damaging ability of 213 nm radiation was 10 times more efficient than 193 nm radiation and about 100 times less efficient than 254 nm noncoherent radiation.
The Protective Effect of N‐Acetylcysteine on UVB‐Induced Immunosuppression by Inhibition of the Action of Cis‐Urocanic Acid
Authors: Hemelaar Peter J. , van Henegouwen Gerard M. J. Beijersbergen
Published: January 2008

Abstract— A recent study has shown that N‐acetylcysteine (NAC) not only has sun‐protective properties but also inhibits the UVB‐induced suppression of contact hypersensitivity (CHS) in mice. Because NAC does not absorb any UVA (320‐400 nm radiation) or UVB (290‐320 nm radiation) we have studied the underlying mechanism of protection. Irradiation of solutions of plasmid DNA with UVC (200‐290 nm radiation) (10 J m‐2) resulted in the formation of cyclobutane pyrimidine dimers, but the extent to which this occurred was not affected by the presence of NAC as was determined by an in vitro T4 endonuclease assay. N‐acetylcysteine proved not to have any effect on the photoisomerization of trans‐urocanic acid (UCA) to its cis‐form in vitro; at equilibrium, approximately 55% cis‐UCA was formed. The same percentage was also found in vivo on exposure of mice to UVB (15 kj m‐2). Topical application of NAC 30 min prior to irradiation did not have any influence as well on the photoisomerization of trans‐ to cis‐UCA. These in vivo experiments were performed under the same conditions used previously to show the protective effect of NAC against UVB‐induced suppression of CHS.

We conclude that this protection of NAC is at least partly based on interference in the role of cis‐UCA in UVB‐induced suppression of CHS. This conclusion is supported by the observation that NAC completely inhibits the suppression of CHS by cis‐UCA administered to mice that were always kept in the dark. In the same range of doses as used in the present study, it was shown in our previous study that NAC alone does not affect the CHS response.
Light Effects on Cyclic Nucleotide Levels and Phase Shifting of the Circadian Clock in Neurospora crassa
Authors: Kallies Andreas , Gebauer Gerd , Rensing Ludger
Published: January 2008

Abstract— Mycelia of Neurospora crassa (band [bd] mutant) were exposed to white light (blue light intensity 3.5 μ.mol s−1 m−2) of different durations during constant darkness. The concentrations of different second messenger molecules and the phase shifting of the circadian rhythm were determined during light exposures at circadian time (ct) 12 and thereafter. These light exposures elicited 8‐12 ct units delay phase shifts but did not change the amount of inositol 1,4,5‐triphosphate (InsP3). In contrast, significant effects of light were observed on cyclic adenosine 3′,5′‐monophosphate (cAMP) levels, which increased transiently about 30‐90 s after the onset of light. The same kinetics was observed under continued exposure to light as well as after 10 s and 2 s of light followed by darkness. The relative amount of the cAMP‐dependent protein kinase A (PKA) in the form of its catalytic sub‐units was determined in isolated nuclei of the bd strain in relation to total nuclear proteins by means of western blot analysis, using a heterologous antibody. The nuclear PKA content changed parallel to the cAMP changes. The transient increase of cAMP did not occur in the “blind”white collar mutant (wc‐2). Long‐term kinetics of cAMP changes after different light pulses in bd showed the initial increase and a return to control levels about 10 min after the onset of the light pulse and a subsequent longer lasting decrease. Light‐induced cAMP changes and light‐induced phase shifts showed different duration dependencies, thus indicating that cAMP may not play a role in the signal transduction pathway to the clock. Light exposures, furthermore, led to a significant decrease of the cyclic guanosine 3′,5′‐monophosphate (cGMP) level. Long‐term kinetics of the cGMP content again showed the immediate decrease after 2 min and a slow recovery to (or above) control values after several hours. Various calcium channel blockers (nickel, cobalt, nifedipine, dantrolene, lanthanum) and the calcium calmodulin inhibitor chlorpromazine did not affect the phase shifting by light nor did they significantly phase shift the circadian rhythm in the dark themselves (again determined at ct 12). The data showed that InsP3 did not change after exposure to light, whereas cAMP increased and cGMP decreased. There was no evidence, however, that these changes play a role in light signal transmission to the clock.
Photolysis of Retinol in Liposomes and Its Protection with Tocopherol and Oxybenzone
Authors: Young Anne M. , Gregoriadis Gregory
Published: January 2008

Abstract— In this work the stabilities of retinol in methanolic solutions and liposomal suspensions exposed to UV light were compared using absorbance spectroscopy and the ability of a‐tocopherol and the sunscreen additive, oxybenzone, to reduce the rate of retinol decomposition assessed. Retinol in methanol decolorized almost completely within a few minutes of exposure to a 6 W 350 nm wavelength lamp. From the concentration dependence of the reaction rates it appears that retinol activated by light can decompose either directly or after collision with a second retinol molecule. Several reaction products are formed, α‐Tocopherol solutions were unaffected by 350 nm light but they did darken when irradiated with 250 nm wavelength light. Addition of a‐tocopherol or removal of oxygen from the retinol in methanol solutions reduced only slightly the rates of retinol photolysis. When dispersed in water within liposomes made of equimolar egg phosphatidylcholine (PC) and cholesterol, up to six‐fold increases in the decomposition rate of the retinol were observed. The reaction rate could be reduced but only slightly by increasing the ratio of PC to retinol. A mechanism that explains the concentration dependence of the retinol photolysis is that the reduction in reaction rate on diluting the retinol concentration within a given liposome was due to the prevention of the reaction between one light‐activated retinol molecule with another within the same liposome. Incorporation of oxybenzone into the liposomes reduced the reaction rates. The results suggested that most of the protection in this case arises through the oxybenzone closest to the light source absorbing the light, thereby preventing it reaching retinol much further into the sample. Incorporation of a‐tocopherol into the liposomes could also reduce substantially the photolysis rate of co‐entrapped retinol. The mechanism of protection in this case appears to be via the tocopherol quenching activated retinol molecules. The close proximity of the tocopherol to the retinol within a single liposome has shown to be important in this case. Only slight protection of retinol in one liposome by tocopherol in another was observed under the conditions studied. This means that the protection by tocopherol will still be observed if the liposome dispersions are diluted considerably or if only thin samples are exposed to light.
Singlet‐Oxygen Generation from Liposomes: A Comparison of 6β‐Cholesterol Hydroperoxide Formation with Predictions from a One‐Dimensional Model of Singlet‐Oxygen Diffusion and Quenching
Authors: Fu Yingxian , Sima Paul D. , Kanofsky Jeffrey R.
Published: January 2008

Abstract— We measured 6β‐cholesterol hydroperoxide (6β‐CHP), a specific singlet‐oxygen (O2(δg)) product, during irradiation of unilamellar dimyristoyl 1‐α‐phosphatidylcholine liposomes containing cholesterol and zinc phthalocyanine (ZnPC). The effects of liposome size, the hydrophobic (O2(1δg)) quencher, β‐carotene, and hydrophilic O2(1δg) quenchers upon the amount of 6β‐CHP formed were determined and interpreted in terms of a one dimensional model of 2(1δg) quenching and diffusion. The model correctly predicted (1) that the amount of 6β‐CHP was increased with increasing liposome size, (2) that P‐carotene was more effective at reducing 6β‐CHP formation in 400 nm diameter liposomes than 100 nm diameter liposomes and (3) that the hydrophilic quencher, water, was also more effective in large liposomes than in small liposomes.

The hydrophobic quencher, β‐carotene, was more effective at reducing the formation of 6β‐CHP than at reducing the 1270 nm O2(1δg) emission. This difference was found to be due to the size distribution present in the liposome preparations because the difference between the 6β‐CHP data and the 1270 nm emission data was much smaller in liposome preparations with a narrow size distribution. When a significant size distribution was present, the 6β‐CHP data were weighted more heavily with large‐diameter liposomes, while the 1270 nm emission data were weighted more heavily with small‐diameter liposomes.
The Angular Distribution of Solar Ultraviolet, Visible and Near‐Infrared Radiation from Cloudless Skies
Authors: Ireland W. , Sacher R.
Published: January 2008

Abstract— The amount of solar radiation intercepted by an object depends on the orientation of the object with respect to the sun and the angular distribution of the diffuse component of solar radiation, which is commonly considered to be approximately isotropic. The angular distribution of the diffuse UV, visible and near‐infrared insolation was measured at several solar zenith angles between 32° and 68° under cloudless skies at Lauder, New Zealand (45S), and shown to be anisotropic. The diffuse solar UV radiation increases markedly with solar elevation and is a large proportion of the total UV irradiance. The diffuse visible light and infrared radiation are small components of the total irradiance and almost independent of solar elevation. The angular distribution of erythemal UV radiation was tabulated and is available on request.
Optics of a Bifacial Leaf: 1. A Novel Combined Procedure for Deriving the Optical Parameters
Authors: Richter T. , Fukshansky L.
Published: January 2008

Abstract— A novel experimental‐theoretical procedure, deriving optical parameters of a bifacial leaf, is presented and analyzed. Its theoretical basis is the four‐flux approximation of the radiative transfer theory. Its experimental basis is three‐dimensional measurements of internal radiances at different depths and in different directions within a leaf by using optical microprobes. The intrinsic instrumental error of the microprobe measurements is accounted for by a special correcting theory. The treatment yields the spectral curves for attenuation, scattering and absorption coefficients as well as for the asymmetry of scattering in both palisade and spongy tissue layers. The values of obtained optical parameters were verified by comparing calculated transmission and remission of a leaf with those measured with the integrating sphere. It is concluded that the treatment provides a sound basis for the analysis of the light microenvironment as a function of leaf structure and the nature of incident light.
Optics of a Bifacial Leaf: 2. Light Regime as Affected by the Leaf Structure and the Light Source
Authors: Richter T. , Fukshansky L.
Published: January 2008

Abstract— This paper presents a theoretical analysis of the light regime in a bifacial leaf performed on the basis of optical parameters estimated from the measurements of internal light fluxes with optical microprobes. Pathlength distributions, absorptances and gradients of absorption rates are calculated as affected by different aspects of leaf optics and morphology: scattering of tissue layers, overall scattering, surface reflection, thickness and absorption to attenuation ratio in single tissue layers. The in vivo measured transmission spectrum of a leaf is correlated with the in vitro chlorophyll spectrum by accounting for two main disturbing factors: multiple scattering (pathlength statistics) and distributional error (absorption statistics).
Quantifying Light and Ultraviolet Radiation in Plant Biology
Authors: Björn Lars Olof , Vogelmann Thomas C.
Published: January 2008

Abstract— Fluence rate and irradiance, two parameters used to quantify light and ultraviolet radiation, do not have a constant relation under natural light conditions. A method is described for measuring fluence rate, the preferred parameter, using meters intended for irradiance measurements. Values measured under natural light conditions are compared to a daylight model.
Spectral Modeling of UV Inhibition of In Situ Antarctic Primary Production Using A Field‐Derived Biological Weighting Function
Authors: Boucher Nicolas P. , Prézelin Barbara B.
Published: January 2008

Abstract— Our major aim is to illustrate an approach for hindcasting or forecasting UV radiation (UVR, 280–400 nm) effects on in situ rates of aquatic primary production when field measurements do not include estimates of UVR effects. A composite of spectral field measurements is employed to model UVR‐dependent rates of photosynthesis in diatomdominated waters in a coastal region of the Southern Ocean. Assumptions, caveats and limitations of the modeling are discussed. Calculations begin with the 1991 Palmer Long Term Ecological Research (LTER) primary production and optical databases, from which daily integrated rates of carbon fixation in the absence of UVR are calculated as a function of depth for a 140 km transect line sampled between dawn and dusk of a single day (14 November 1991). The UVR measurements from the nearby NSF/OPP Polar Network at Palmer Station are used to determine ozone (O3) concentration on the day of the transect, which is then employed in Madronich's (In UV‐B Radiation and Ozone Depletion (Edited by M. Tevini), pp. 17–68. Lewis, Boca Raton, FL, 1993) spectral code to model daytime variations in surface spectral irradiances under clear sky conditions. These data are corrected for cloudiness and then combined with estimates of in‐water UVR spectral attenuation coefficients, derived from Icecolors 90 data, to estimate in situ light exposure for phytoplankton collected at different depths and locations. An absolute chlorophyllspecific biological weighting function (BWF), determined under natural solar light fields for Antarctic diatom communities and shown to be reproducible while differing from a laboratory diatom BWF and other in situ BWF determined for other phytoplankton assemblages, is combined with estimates of in situ UVR exposure to derive in situ estimates of chlorophyllspecific losses of carbon fixation due to UVR inhibittion. By repeating calculations for every sampling site along the transect, we derive a spatial map of estimated UVR effects on primary production across the region. We repeat calculations for different O, concentrations expected during the austral spring over Antarctica and illustrate the O, dependency of UVB (280–320 nm) inhibition effects in near surface waters. We estimate ambient UVR reduced carbon fixation rates up to 65% in surface waters, depending upon location, down to undetectable levels at 36 m. Reducing stratospheric O3 concentrations by 50% further inhibits near surface primary production by 8% and integrated primary production by 5%. Primary production was forced to subsurface maxima across the entire transect line in the presence of UVR.
Photoionization of Indole, N‐Methylindole and Tryptophan In Aqueous Solution upon Excitation at 193 nm
Authors: McGimpsey W. Grant , Görner Helmut
Published: January 2008

Abstract—The 193 nm photoionization of aqueous indole, A'‐meth‐ylindole and tryptophan–as a function of pH and under several saturating gas conditions–has been studied by laser photolysis using optical and conductometric detection methods. Monophotonic ionization leads to production of the cation radicals and hydrated electrons, the quantum yield of electron ejection is 0.3–0.4. The cation radicals have pKavalues of 4.5, <5 and 4.5 for indole,N‐methylindole and tryptophan, respectively. Above these pH values, the cation radical deprotonate rapidly, having lifetimes of 1.0, ≅6 and 1.1 μs, respectively. Under N2O, neutral indolyl radical production is accompanied by formation of an OH adduct radical (<1 μs). The conductivity results in Ar‐ and N2O‐saturated solution support the deprotonation mechanism and indicate that in the acidic pH range, the cation radical decays by release of protons with kinetics on the millisecond time scale.
Combined Application of Picosecond Transient Absorption and Emission Measurements in Studies of Radical‐Ion Pair Dynamics
Authors: Arnold Bradley R. , Atherton Stephen J. , Farid Samir , Goodman Joshua L. , Gould Ian R.
Published: January 2008

Abstract— Much of the emphasis in the development of methods for time‐resolved measurements is on increasing experimental time resolution. Equally important, however, is the establishment of methods to apply existing techniques to problems of increasing complexity. Here we describe the application of a combination of picosecond absorption and emission measurements to solve a complex kinetic problem in organic photophysics, namely, the dynamics of interconverting radical‐ion pairs. Although fairly routine, the emission measurements require higher time resolution and the absorption measurements require higher signal‐to‐noise ratios than are often achieved. In the first part of this paper we describe the ways in which these experimental requirements have been met. Next, the radical‐ion pair kinetic problem and its solution are described. Finally, we discuss some future directions for the techniques as they relate to studies of radical‐ion pair dynamics.
Induction of Cell Killing, Mutation and umu Gene Expression by 6‐Mercaptopurine or 2‐Thiouracil with UVA Irradiation
Authors: Komeda Kazuko , Iwamoto Sakae , Kominami Seiji , Ohnishi Takeo
Published: January 2008

Abstract— When Escherichia coli cells were irradiated by UVA in the presence of 6‐mercaptopurine (6‐MP) or 2‐thiouracil (S2Ura), two kinds of repair‐deficient strains of recA− and uvrA− were killed more efficiently than the parental wild‐type strain having normal repair capacities. In addition, these agents with UVA exposure greatly induced the incidence of mutations in the uvrA− strain as compared with the wild‐type strain but not the uvrA− strain. Furthermore, the induction of expression of umuDC genes was investigated in two Salmonella typhimurium strains, TA1S35 and TA1538, carrying a pSK1002 plasmid. In these systems, it is easy to measure β‐galactosidase activities for the induced activities of SOS responses. These agents with UVA exposure also induced expression of the umuDC genes. These results suggest that 6‐MP and S2Ura with UVA induce DNA damage which is repairable by the excision repair mechanism.
Changes in Bacteriochlorophyll c Organization during Acid Treatment of Chlorosomes from Chlorobium tepidum
Authors: Steensgaard Dorte B. , Matsuura Katsumi , Cox Raymond P. , Miller Mette
Published: January 2008

Abstract— We have investigated changes in the organization of bacteriochlorophyll c (BChl c) in chlorosomes isolated from the green sulfur bacterium Chlorobium tepidum during the formation of bacteriopheophytin and bacteriopheo‐phorbide in acidic media. The reaction was much slower than that observed with BChl dissolved in methanol, suggesting that the aggregation of BChl or the presence of the chlorosome envelope constitutes a barrier to the reaction with protons in the aqueous phase. In most cases the first two‐thirds of the reaction showed time courses that were close to linear. Simultaneously with the pheo‐phytinization process we observed a red‐shift of the Qy band of the remaining aggregated BChl c reaching a maximum extent of 9 nm. Analysis of the spectral changes provided evidence at least for two spectrally distinct pools of aggregated BChl c with different rates of reaction with acid. An HPLC analysis showed that there were no changes in the distribution of the four major homologs of BChl c remaining in chlorosomes during the course of acid treatment, at least up to the time when two‐thirds had been converted to pheophytin. This suggests that the homologs of BChl c are uniformly distributed within the chlorosome.
The Mechanism of Photofrin Photobleaching and Its Consequences for Photodynamic Dosimetry
Authors: Georgakoudi Irene , Nichols Michael G. , Foster Thomas H.
Published: January 2008

Abstract— We report experimental results that support a theory of self‐sensitized singlet oxygen‐mediated bleaching of the porphyrin photosensitizer Photofrin. Microelectrode measurements of photodynamic oxygen consumption were made near the surface of individual, Photofrin‐sensitized EMT6 spheroids during laser irradiation. The progressive decrease in photochemical oxygen consumption with sustained irradiation is consistent with a theory in which bleaching occurs via self‐sensitized singlet oxygen reaction with the photosensitizer ground state. A bleaching model based solely on absorbed optical energy density is inconsistent with the data. Photobleaching has a significant effect on calculated photodynamic dose distributions in 500 pin diameter spheriods. Dose distributions corrected for the effects of bleaching produce a new estimate (12.1 ± 1.2 mM) for the threshold dose of reacting singlet oxygen in this system.
Identification of Two Palmitoyl Groups in Octopus Rhodopsin
Authors: Nakagawa Masashi , Iwasa Tatsuo , Kikkawa Satoshi , Takao Toshifumi , Shimonishi Yasutsugu , Tsuda Motoyuki
Published: January 2008

Abstract— We determined the structure and site of fatty acid incorporated in octopus rhodopsin using a combination of fluorescence label and enzymatic cleavage methods in conjunction with fast‐atom bombardment (FAB) mass spectrometry. A single peptide containing two adjacent cysteines, Cys337 and Cys338, was successfully isolated using the fluorescence from a dye conjugated to Cys345. The FAB mass spectrometric analysis of the peptide (323phe‐340phe) revealed that two palmitoyl groups are linked to Cys337 and Cys338 via thioester bonds in octopus rhodopsin as in bovine rhodopsin.
The Effect of Charge on Cellular Uptake and Phototoxicity of Polylysine Chlorine6Conjugates
Authors: Soukos Nikolaos S. , Hamblin Michael R. , Hasan Tayyaba
Published: January 2008

Abstract— The effect of charge on the cellular uptake, localization and phototoxicity of conjugates between chlorine6 (ce6) and poly‐L‐lysine was studiedin vitro. These conjugates (average MW35–55 kDa) were synthesized to have polycationic, polyanionic or neutral charges. Two human cell lines (A431 epidermoid carcinoma cells and EA.hy926 hybrid endothelial cells) were studied and the cellular uptake of ce6 delivered by the conjugates of varying charge and free ce6 was measured at conjugate ce6 equivalent concentrations up to 0.4 μM. Uptake was time and concentration dependent and temperature dependent in the case of neutral and anionic conjugates. Relative uptake at 6 h for A431 cells was 73:15:4:1 and for EA. hy926 cells was 63:11:3:1 for cationic, anionic, neutral and free ce6, respectively, but EA. hy926 cells took up 1.5‐2 times as much ce6 from all the conjugates as A431 cells. Localization as studied by fluorescence microscopy indicated that the cationic conjugate was in aggregates bound to the plasma membrane, while the other forms were internalized in organelles and membranes. Phototoxicity was measured by 3‐(4,5‐dimethylthiazol‐2‐yl)‐diphenyltetra‐zolium bromide (MTT) assay after irradiation with5–20 J cm−2of 666 nm light. In contrast to the uptake, the order of phototoxicity for both cell types per mole of ce6 uptake per cell was neutral ≫ anionic > cationic > free ce6. Polymeric ce6 conjugates bearing positive, negative and neutral charges may have different tissue‐localizing properties and could play a role in photodynamic therapy.
Purification and Characterization of Recombinant Affinity Peptide‐Tagged Oat Phytochrome A
Authors: Murphy John T. , Lagarias J. Clark
Published: January 2008

Abstract— Full‐length Avena sativa (oat) phytochrome A (ASPHYA) was expressed in the yeast Saccharomyces cerevisiae and purified to apparent homogeneity. Expression of an ASPHYA cDNA that encoded the full‐length photoreceptor with a 15 amino acid'strep‐tag'peptide at its C‐terminus produced a single polypeptide with a molecular mass of 124 kDa. This strep‐tagged polypeptide (ASPHYA‐ST) bound tightly to streptavidin agarose and was selectively eluted using diaminobiotin, with a chromatographic efficiency of 45%. Incubation of ASPHYA‐ST with phytochromobilin (PφB) and the unnatural chromophore precursors, phycocyanobilin (PCB) and phycoerythrobilin (PEB), produced covalent adducts that were similarly affinity purified. Both PφB and PCB adducts of ASPHYA‐ST were photoactive‐the PφB adduct displaying spectrophotometric properties nearly indistinguishable from those of the native photoreceptor, and the PCB adduct exhibiting blue‐shifted absorption maxima. Although the PEB adduct of ASPHYA‐ST was photochem‐ically inactive, it was intensely fluorescent with an excitation maximum at 576 nm and emission maxima at 586 nm. The superimposability of its absorption and fluorescence excitation spectra established that a single bilipro‐tein species was responsible for fluorescence from the adduct produced when ASPHYA‐ST was incubated with PEB. Steric exclusion HPLC also confirmed that ASPHYA‐ST and its three bilin adducts were homodimers, as has been established for phytochrome A isolated from natural sources. The ability to express and purify recombinant phytochromes with biochemical properties very similar to those of the native molecule should facilitate detailed structural analysis of this important class of photoreceptors.
Photoreactivation of UV‐lnactivated Spores of Trichoderma harzianum
Authors: Sametz‐Baron Liat , T. Gloria M. Berrocal , Amit Rivka , Herrera‐Estrella Alfredo , Horwitz Benjamin A.
Published: January 2008

Abstract— Photoreactivation in the filamentous soil fungus Trichoderma harzianum is of interest because its blue, UVA photoreceptors (cryptochromes) may share homology with DNA photolyases. Furthermore, this organism antagonizes, by mycoparasitism, a number of soil‐borne pathogens. Photoreactivation is thus important as one of the factors that may contribute to survival in the field. Exposure of asexually produced spores (conidia) to UVC inhibits germination. Nongerminating spores either do not swell or are inhibited later in germination, swelling but failing to put out a germ tube. Both types of inhibition can be reversed by photoreactivation with visible and UVA (320‐400 nm) light, restoring high germination percentages. Conidia of mutants lacking the normal greenish pigmentation are more sensitive to UVC (200‐280 nm) than wild‐type conidia but photoreactivation still occurs. The action spectrum for photoreactivation indicates that T. harzianum has a DNA photolyase with a pterin as second chromophore. The most effective wavelengths for photoreactivation correspond to valleys, rather than peaks, in the action spectrum for photoinduction of sporulation. Furthermore, mutants with defects in photoinduction of sporulation (dimY) are not defective in photoreactivation. Induction of sporulation and DNA photorepair, while sharing parts of the blue/UVA spectrum, are different, by spectroscopic, kinetic and genetic criteria.