bluuebunny/crossref_metadata_2025 huggingface dataset:
THE PHOTOPHYSICAL PROPERTIES OF PORPHYCENES: POTENTIAL PHOTODYNAMIC THERAPY AGENTS*
Authors: Aramendia Pedro F. , Redmond Robert W. , Nonell Santiago , Schuster Wolfang , Braslavsky Silvia E. , Schaffner Kurt , Vogel Emanuel
Published: January 2008

Porphycene and a tetra‐n‐propyl derivative remained unaltered on irradiation in toluene at room temperature. Quantum yields of fluorescence, S T intersystem crossing, and singlet molecular oxygen sensitization, as well as lifetimes of the singlet and triplet excited states were measured. In view of their structural relationship to porphyrin, their high absorption above 620 nm, their stability towards photooxidation, and their high quantum yields of fluorescence and singlet oxygen sensitization, these compounds qualify as potential agents for tumor marking and photodynamic therapy.
PHOTODYNAMIC GENERATION OF HYDROXYL RADICALS BY HEMATOPORPHYRIN DERIVATIVE AND LIGHT
Authors: Steveninck J. Van , Tijssen K. , Boegheim J. P. J. , Der Zee J. Van , Dubbelman T. M. A. R.
Published: January 2008

In a reaction mixture containing hematoporphyrin derivative, deoxyribose, Fe3+‐EDTA and either methionine or tryptophan, hydroxyl radicals were formed during illumination with visible light. When either hematoporphyrin derivative, Fe3+‐EDTA or the amino acid was omitted from the reaction mixture, the generation of hydroxyl radicals ceased. These observations suggest an iron‐catalyzed Haber‐Weiss reaction, involving superoxide and hydrogen peroxide in the generation of hydroxyl radicals. It could be shown that with methionine H2O2 was indeed an essential intermediate in the reaction sequence. With tryptophan, however, H2O2, was not generated. Apparently a photooxidation product of tryptophan could replace H2O2 in the OH‐generating reaction with Fe2+‐EDTA. Although superoxide was generated in the reaction mixture, it was not an indispensable intermediate. Apparently a porphyrin radical, formed via photoexcitation of hematoporphyrin derivative, could replace superoxide in the Haber‐Weiss reaction.
SUBUNIT SEPARATION (α, αprime;, β) OF CRYPTOMONAD BILIPROTEINS *
Authors: Guard‐Friar Deborah , MacColl Robert
Published: January 2008

Abstract— Phycocyanin 645, phycocyanin 612 and phycoerythrin 545 are biliproteins isolated from the cryptomonad algae, Chroornonas species, Hemiselmis virescens and Rhodomonas lens, respectively. The protein has α and β subunits. which are separated on an ion exchange column by using a urea gradient and omitting 2‐mercaptoethanol from the solvent. This separation establishes that the α and β subunits are not joined by disulfide bonds. In addition it has recently been shown that mercaptoethanol can produce spurious results in the calculation of the chromophore contents of these biliproteins (Guard‐Friar and MacColl, 1984). The mercaptoethanol‐free experiments allow analysis of the chromophore content in a rapid and artifact‐free manner. When the ion exchange chromatography of phycocyanin 645 is manipulated by changing the type of urea gradient, two distinct a subunit fractions are obtained. These two fractions have identical visible absorption spectra but different amino acid compositions. At least two different gene products are, thus. responsible for the a subunits. The sole chromophore on the two a subunits of phycocyanin 645 is the unique 697‐nm bilin as seen in acidic urea. Its reactivity with mercaptoethanol is determined. The α subunits of phycoerythrin 545 have two different bilins: cryptoviolin and phycoerythrobilin. Phycocyanobilin is the chromophore on the α subunit of phycocyanin 612.
CAROTENOIDS QUENCH EVOLUTION OF EXCITED SPECIES IN EPIDERMIS EXPOSED TO UV‐B (290‐320 nm) LIGHT
Authors: Mathews‐Roth Micheline M.
Published: January 2008

Abstract— Reactions involving singlet oxygen and other free radicals have been identified in epidermis containing either exogenous or endogenous photosensitizers. soaked in a singlet oxygen/free radical trap, and then exposed to visible or UV‐A (320‐400 nm) light. Such reactions can be quenched by the presence of the carotenoid pigments β‐carotene and canthaxanthin which accumulate in epidermis after oral administration. We report here that the carotenoid pigments β‐carotene. canthaxanthin and phytoene accumulating in epidermis can also quench to some degree those photochemical reactions involving singlet oxygen and free radicals that occur when epidermis is exposed to the sunburn spectrum of light (UV‐B. 290–320 nm).
PHOTOCHEMICAL SENSITIZATION BY AZATHIOPRINE AND ITS METABOLITES—II. AZATHIOPRINE AND NITROIMIDAZOLE METABOLITES
Authors: Hemmens Violet J. , Moore Douglas E.
Published: January 2008

Abstract— The photochemical reactivity of the immunosuppressant drug, azathioprine (AZT) and two representative metabolites of the nitroimidazole moiety, 1‐methyl‐4‐nitroimidazole (MNI) and lmethyl‐4‐nitro‐5‐thioimidazole (MNTI) has been examined. No transient species of AZT were observed by laser flash photolysis, inferring a low triplet yield or its rapid deactivation. Consequently AZT, MNI and MNTI displayed little or no photodynamic sensitization via photooxidation reactions. However, AZT and MNI are highly reactive radical scavengers when photoexcited, as determined by reaction with polyacrylamide radicals. The photoreactivity of the metabolites of AZT is greater than that of the parent drug. an observation which may be relevant to the photocarcinogenicity of AZT.
LOW TEMPERATURE SPECTROPHOTOMETRIC STUDY OF CATTLE BATHORHODOPSINS PRODUCED FROM RHODOPSIN AND ISORHODOPSIN IN TRANSPARENT MEDIUM WITHOUT CRACKS
Authors: Ono Toshirou , Shichida Yoshinori , Yoshizawa Tǒru
Published: January 2008

Abstract— Cattle rhodopsin (11‐cis‐Rh) and isorhodopsin (9‐cis‐Rh) were prepared from the same extract of cattle opsin by incubation in the dark with 114– and 9‐cis‐retinals, respectively. The preparations obtained were mixed with glycerol (67% in the final concentration) and then cooled to 77 K by a rapid cooling method for freezing the samples as a clear glass, without any cracks. The spectral changes during their photochemical reactions were measured. A computer analysis of the spectra obtained verified that bathorhodopsin from 11‐cis‐Rh was identical in spectrum with that from 9‐cis‐Rh not only in photosteady state but also under a short time irradiation.
INVESTIGATION INTO THE SPECTROSCOPY AND PHOTOISOMERIZATION OF A SERIES OF POLY (ETHYLENE GLYCOL) PEPTIDE SCHIFF BASES OF 11‐cis RETINAL
Authors: Freedman Kenn , Becker Ralph S. , Hannak Dieter , Bayer Ernst
Published: January 2008

Abstract— The 11‐cis and all‐trans isomers of a series of poly(ethylene glycol)‐oligopeptide ‐ Schiff bases as models for rhodopsin were synthesized and studied. Absorption data for certain of the PEG‐peptide Schiff bases demonstrated that no intramolecular hydrogen‐bonding (or protonation) occurs between the Schiff base and an acidic amino acid residue, as was previously thought. Photoisomerization of the 11‐cis protonated and unprotonated Schiff bases were examined using both steady state and laser flash techniques. Also with 355 nm excitation (and additionally 532 nm in one case), an approximate 40% increase in quantum yield of isomerization (φ) occurred for all protonated PEG‐peptide Schiff bases compared to the H+‐n‐butylamine counterparts (in methanol). In one case, a > 100% increase in φ was found in dichloromethane. These data show that PEG‐oligopeptide Schiff bases are still further improved models for rhodopsin compared to their n‐butylamine analogs.
PHOTODYNAMIC ACTION IN Stentor coeruleus SENSITIZED BY ENDOGENOUS PIGMENT STENTORIN
Authors: Yang Ki‐Chun , Prusti Rabi K. , Walker Edward B. , Song Pill‐Soon , Watanabe Masakatsu , Furuya Masaki
Published: January 2008

Abstract— Stentorin acts as the photoreceptor for the step‐up photophobic and negative phototactic responses in Stentor coeruleus. The chromophore of stentorin appears to be hypericin which is linked to apoprotein. In addition to the photomovement responses of the organism, S. coeruleus was found to be photodynamically sensitive to light absorbed by the hypericin chromophore, as the apparent action spectrum for the photodynamic killing matches the absorption spectrum of stentorin. The protective effect of β‐carotene and crocetin on the photodynamic killing of S. coeruleus suggests that singlet oxygen generated by the stentorin‐sensitization plays an important role, according to the so‐called Type II mechanism of photosensitization. The generation of singlet oxygen via hypericin triplet was confirmed by in vitro photooxidation of tryptophan as a substrate. The photodynamic killing was more effective in deuterium oxide than in H2O in both the photosensitization by stentorin (endogenous) and added hypericin (exogenous). These results are consistent with the involvement of singlet oxygen in the photodynamic killing of S. coeruleus.
9, 10‐DICYANOANTHRACENE‐SENSITIZED PHOTOOXYGENATION OF α,α′‐DIMETHYLSTILBENES. MECHANISM AND KINETICS OF THE COMPETING SINGLET OXYGEN AND ELECTRON TRANSFER PHOTOOXYGENATION REACTIONS
Authors: Gollnick Klaus , Schnatterer Albert
Published: January 2008

Abstract— The 9, lodicyanoanthracene‐sensitized photooxygenation of 2‐methyl‐2‐butene and (+)‐limonene proceeds via the singlet oxygen pathway in carbon tetrachloride as well as in acetonitrile, although the fluorescence of the sensitizer in acetonitrile is quenched by these olefins in an electron transfer quenching mechanism. The 9, 10‐dicyanoanthracene‐sensitized photooxygenation of cis‐ and trans‐ä, ä′‐dimethylstilbenes occurs exclusively via the singlet oxygen pathway in carbon tetrachloride; in acetonitrile, however, singlet oxygen and electron transfer photooxygenation reactions compete with one another. Addition of tetra‐n‐butyl ammonium bromide and increasing oxygen concentrations favor the formation of the singlet oxygen product, whereas addition of anisole, increasing substrate concentrations and decreasing oxygen concentrations favor the electron transfer photooxygenation products. In carbon tetrachloride, exciplexes of the sensitizer and the dimethylstilbenes are formed which give rise to cidrrans‐isomerization of the substrates. In acetonitrile, neither exciplex formation nor cisltrans‐isomerization are observed. A mechanism is proposed which allows us to calculate product distributions of the competing singlet oxygen/electron transfer photooxygenation reactions and thus to determine the efficiencies with which encounters between the singlet excited sensitizer and the substrates finally result in electron transfer photooxygenation products. Using (I) these efficiencies, (2) the β‐value obtained from singlet oxygen photooxygenation sensitized by rose bengal, and (3) the appropriate k‐values determined from fluorescence quenching of 9, 10‐dicyanoanthracene in MeCN by oxygen and the stilbene, allows the calculation of the quantum yield of oxygen consumption by this stilbene. The quantum yield thus calculated is strictly proportional to the rate of oxygen consumption experimentally obtained; this result is considered as convincing evidence for the mechanism proposed.
CELLULAR UPTAKE OF HYDROXYETHYLVINYLDEUTEROPORPHYRIN(HVD) AND PHOTOINACTIVATION OF CULTIVATED HUMAN LEUKEMIA (REH6) CELLS
Authors: Dellinger M. , Vever‐Bizet C. , Brault D. , Delgado O. , Rosenfeld C.
Published: January 2008

Abstract—Thein vitroincorporation of purified hydroxyethylvinyldeuteroporphyrin (HVD) into cells (Reh6) derived from an acute lymphocytic human leukemia is investigated using quantitative extraction techniques and fluorescence spectroscopy. A fast incorporation step (< 2 min) is characterized by its dependence on the porphyrin concentration in the incubation medium which suggests a saturation process. It is followed by a slower uptake, the rate of which linearly depends on the porphyrin concentration. No preferential uptake of aggregated form of HVD, which is shown to dimerize with an equilibrium constant of 9.7 × 105M−1, can be evidenced. As inferred from fluorescence spectra of cell suspensions and those of HVD dissolved in aqueous and micellar solutions as references, the porphyrin is mainly located in membrane structures and to a lower extent in cytoplasm. Cell photoinactivation does not depend on the incubation time but is only related to the intracellular porphyrin concentration.
EVIDENCE THAT CHARGE MOTION WITHIN BACTERIORHODOPSIN DEPENDS ON SOLVENT VISCOSITY
Authors: Rayfield G. W.
Published: January 2008

Abstract— It is shown that glycerol in the bathing solutions of a bacteriorhodopsin model membrane slows the photoresponse. The early stage of the photoresponse is only slightly affected while the later stage is appreciably retarded. These results are in agreement with previous measurements by other investigators on the temporal behavior of the photoreaction cycle in viscous bathing solutions. Data is fit to an equation of the form τ=A ηm exp(Δ/kT) where t is a time constant characterizing the photoresponse, τ is the viscosity of the bathing solution and Δ is the activation energy for the thermally driven process.
THE ROLE OF SOLAR UV‐B IN GROWTH REGULATION OF CRESS (Lepidium sativum L.) SEEDLINGS
Authors: Steinmetz Volker , Wellmann Eckard
Published: January 2008

Abstract— Action spectra for growth reduction within the 260 nm to 305 nm waveband were measured for hypocotyls and roots of young etiolated cress (Lepidium sativum) seedlings. The action spectra show increasing photon effectiveness with decreasing wavelength and resemble those due to DNA damage. Using short term irradiations, photoreceptors absorbing in the visible range were found to be without influence. As no photoreactivation could be found and the seedlings showed no outward signs of damage, this growth effect may be due to a UV photoreceptor. A modeling calculation was carried out to estimate the effectiveness of solar UV‐B on this response both under present conditions and under reduced ozone levels. Even under present conditions, solar UV‐B could be involved in regulating growth during the period immediately after germination.
ARE THERE SEVERAL PHOTORECEPTORS INVOLVED IN PHOTOTROPISM OF Phycomyces blakesleeunus? KINETIC STUDIES OF DICHROMATIC IRRADIATION*
Authors: Löser Georg , Schäfer Eberhard
Published: January 2008

Abstract— Photogeotropic equilibrium angles were measured for Phycomyces blakesleeanus wild type firstly by means of dichromatic fluence rate response curves using simultaneous irradiation with near threshold 450 nm reference light (constant at 1.2 × 10−8 W m−2) and variable fluence rates of test light (498–630 nm) from the same side. These curves showed minima for test light fluence rates that were close to the photogeotropic threshold for these wavelengths. Secondly, the time course of this inhibitory effect was studied with both the inductive reference 450 nm light (2 × 10−‐7 W m−2) and the test light (606 or 450 nm) given as light pulses of 2 s duration (2 s light/48 s dark periods for 6 h). The dark period between the onset of the inductive reference light and test light pulses was varied between 0 and 48 s. No inhibitory effects were observed for simultaneous pulses; however, inhibitory effects were demonstrated for delay times of 2 s and 20 s for 606 nm as well as 450 nm test light. If the test light pulses were given immediately before the inductive reference light, only 606 nm test light was effective in producing a significant inhibitory effect.

The results are discussed with regard to a multichromophoric photoreceptor system and to the wavelength dependence of the effects observed. The data and conclusions favor a photoreceptor system with at least two separate chromophoric absorptions of the blue light receptor type, one acting positively, the other acting inhibitorily, and at least one other photoreceptor of presumably minor influence.
COMPARATIVE PHOTOCHEMICAL ANALYSIS OF HIGHLY PURIFIED 124 KILODALTON OAT and RYE PHYTOCHROMES in vitro
Authors: Lagarias J. Clark , Kelly John M. , Cyr Karen L. , Smith William O.
Published: January 2008

Abstract A direct comparison of the photochemical interconversions between red (Pr‐) and far‐red (Pfr‐) absorbing forms of highly‐purified 124 kDa oat and rye phytochromes under identical experimental conditions was performed. In two different buffer systems at 5°C, the quantum yields for the Pr to Ptr and Pfr to Pr phototransformations under constant red and far‐red illumination, φr and φfr respectively, were determined to be 0.152‐0.154 and 0.060‐0.065 for oat preparations and 0.172‐0.174 and 0.074‐0.078 for rye preparations. These values as well as the wavelength dependence of the photoequilibrium produced under continuous illumination throughout the visible and near‐ultraviolet spectrum were based on the absorption spectra of the two phytochrome preparations and revised molar absorption coefficients. The molar absorption coefficients were estimated by quantitative amino acid analysis and shown to be identical for the two monocot phytochromes (i.e. 132 mM−1 cm−1 at the red absorption maximum for the Pr form). Because these measurements were performed under identical experimental conditions, including buffer, temperature, light fluence rate, and instrumentation, the differences observed must reflect structural features inherent to the two different monocotyledonous phytochromes.
POTENTIALLY USEFUL ANTIMICROBIAL and ANTIVIRAL PHOTOTOXINS FROM PLANTS*
Authors: Towers G. H. N. , Hudson J. B.
Published: January 2008

AbstractThe wide range of naturally occurring compounds from microorganisms and plants which are phototoxic in UV‐A light (320‐400 nm) includes cinnamyl esters, coumarins and furanocoumarins, furanochromones, benzofurans, alkaloids, based on tryptophan or phenylalanine, extended naptho‐and anthraquinones, polyacetylenes and their thiophene derivatives. The cellular targets are cell membranes, e.g. acetylenes, or the nucleus, e.g. furanocoumarins. Compounds reacting with cell membranes in light either generate singlet oxygen, e.g. a‐terthienyl, or react by a free radical mechanism, e.g. phenylheptatriyne, or do both. Those that react with nucleic acids intercalate with these macromolecules forming photoadducts, e.g. furanocoumarins, furanochromones and furan‐oquinolines. With others, such as the β‐carbolines, the explanation for their photogenotoxicity is unknown.

A number of these natural photosensitizers have been examined with bacteria, yeasts, and viruses and the mechanisms of phototoxicity have been elucidated. Some of the sulfur‐containing acetylenes may be useful in photochemotherapy.
PHOTOSENSITIZERS IN DERMATOLOGY*
Authors: McCullough Jerry L. , Weinstein Gerald D. , Douglas Janet L. , Berns Michael W.
Published: January 2008

Abstract Systemic injection of hematoporphyrin derivative (HpD) in combination with visible light (red or blue‐green) delivered by laser was used to treat a patient with psoriasis. The psoriatic lesions responded vigorously to laser treatments, forming eschars by 1 week post irradiation. In contrast, only minimal erythema was observed in the noninvolved, clinically normal appearing skin. Two approaches for localized HpD administration were investigated in the guinea‐pig and minipig models as a means of achieving local photodynamic effects. Intracutaneous injection of HpD produced localized cutaneous photosensitization with either UVA or red light. Azone increased percutaneous penetration of HpD in human skin in vitro. Topical application of HpD and irradiation with UVA produced localized cutaneous photosensitivity and inhibition of epidermal DNA synthesis.
PHOTOMODIFICATION OF BIOLOGICAL MEMBRANES WITH EMPHASIS ON SINGLET OXYGEN MECHANISMS
Authors: Valenzeno Dennis Paul
Published: January 2008

AbstractThis review discusses photomodification of biological membranes and model membrane systems. Current concepts of membrane structure are first reviewed briefly. The role of preillumination association of sensitizer with membranes as it relates to photomodification rate is discussed, as well as the role of singlet oxygen in membrane photomodification. Finally the characteristics of singlet oxygen generation in membranes are considered. The evidence clearly indicates that membrane photomodification cannot be understood based only on the properties of sensitizers and singlet oxygen in aqueous solution. Rather the properties of sensitizers in association with membranes are the determinants of membrane photomodification. These properties differ significantly in aqueous solution and in membranes.
MENADIONE SENSITIZED PHOTOOXIDATION OF NUCLEIC ACID and PROTEIN CONSTITUENTS. AN ESR and SPIN‐TRAPPING STUDY
Authors: Krishna C. Murali , Decarroz C. , Wagner J. R. , Cadet J. , Riesz P.
Published: January 2008

The menadione photosensitized reactions of nucleic acid and protein constituents were studied by ESR and spin trapping. Thymine, thymidine, cytosine, 2′‐deoxycytidine,5′‐dCMP, uracil and several N‐acetyl amino acids and dipeptides were investigated. Photolysis at 335 nm was carried out in air‐saturated or Ar saturated DMSO : H2O (1 : 1, vol/vol) containing 10 3M menadione and 10‐2M 2‐methyl‐2‐nitrosopropane as the spin trap. The observed spin adducts were explained in terms of electron transfer from the substrate to the excited triplet state of menadione to form the radical cation of the substrate and the anion radical of menadione which was also detected by ESR.
PHOTOSENSITIZATION BY PORPHYRINS DELIVERED TO L CELL FIBROBLASTS BY HUMAN SERUM LOW DENSITY LIPOPROTEINS. A MICROSPECTROFLUOROMETRIC STUDY
Authors: MORLIERE P. , KOHEN E. , REYFTMANN J. P. , Santus R. , KOHEN C. , Maziere J. C. , Goldstein S. , Mangel W. F. , Dubertret L.
Published: January 2008

Human serum LDL were used as vehicles to deliver protoporphyrin and hematoporphyrin dimer to L cell mouse fibroblasts. Topographic analysis by microspectrofluorometry on single living cells shows that after digestion of LDL, protoporphyrin is localized in cytoplasmic areas. Protoporphyrin and hematoporphyrin dimer are readily bleached by 420 ± 60 nm radiations at the high fluence rate used. Complex bleaching kinetics are observed. Spectral studies using the same technique demonstrate that an intense fluorescent emission (λmax= 450 nm) is produced immediately after the onset of irradiation with 365 ± 2 nm or 420 ± 60 nm radiations using LDL loaded with protoporphyrin or Photofrin II. These fluorescent products have been previously identified as lipofuscin‐like pigments formed by reaction of lipid photoperoxides with amino groups. The permeation of lysosomal membranes is also induced after delivery of the porphyrins by LDL. This permeation can be strongly inhibited not only by the lysosomal inhibitors chloroquine and monensin but also by a‐tocopherol. On the other hand, neither α‐tocopherol nor chloroquine or monensin inhibit the lipofuscin‐like pigment formation.
Monodelphis domestica: A NEW ANIMAL MODEL FOR STUDIES IN PHOTODERMATOLOGY*
Authors: Ley Ronald D.
Published: January 2008

The ability to photoreverse pyrimidine dimers in DNA of the South American opossum Monodelphis domestica provides a powerful tool with which to probe the role of pyrimidine dimers in ultraviolet radiation (UVR)‐induced histopathologic changes of the skin of this mammal. We have observed that post‐UVR exposure to photoreactivation light not only reversed pyrimidine dimers in epidermal DNA, but also suppressed the capacity of UVR to induce macroscopic and microscopic changes in the skin of M. domestica.
PHOTOCHEMISTRY and PHOTOBIOLOGY OF MELANOGENIC METABOLITES: FORMATION OF FREE RADICALS*
Authors: Koch Walter H. , Chedekel Miles R.
Published: January 2008

Normal melanocytes produce specialized subcellular organelles called melanosomes within which the biochemical processes of melanogenesis occurs. During sunlight‐induced melanogenesis, the melanocyte‐specific enzyme tyrosinase catalyzes the oxidative polymerization of 3,4‐dihydroxyphenyl‐alanine (DOPA) to melanin. Nucleophilic addition of cysteine to tyrosinase‐generated dopaquinone leads to the formation of cysteinyldopas, precursors of pheomelanin and excreted by‐products of eumelanogenesis. Under conditions of low sulfhydryl content, dopaquinone undergoes a 1,4 intramolecular cycloaddition to yield, after further oxidation, 5,6‐dihydroxyindoles and/or 5,6‐dihydroxy‐2‐carboxyindoles. These indolic melanogenic intermediates and their O‐methylated metabolites, like cysteinyldopas, are excreted by actively pigmenting as well as dormant melanocytes. Indeed, it has been determined that in humans, the serum and urine concentrations of these melanogenic metabolites increase dramatically following exposure to sunlight, UVA (315‐400 nm), UVB (290‐315 nm) exposure, as well as during PUVA therapy and in melanoma patients, and thus have proved to be excellent biochemical markers of normal and pathological melanocyte function. While controlled light exposure or PUVA therapy generally lead to 100‐300% increases in 5‐S‐cysteinyldopa (5SCD) and 5‐methoxy‐6‐hydroxyindole‐2‐carboxylic acid (6HMICA) serum levels (normal concentration about 4–16 nmol l‐1), the local concentrations in the skin and especially in the actively pigmenting melanocyte may be as high as 200 μM.

Evidence is presented to document that a number of catecholic melanin precursors, including cysteinyldopas and dihydroxyindoles, are photochemically unstable in the presence of biologically relevant ultraviolet radiation (i.e. wavelengths ± 300 nm). Initial photochemical processes involve free radical production; continued photolysis yields polymeric photoproducts. Radicals produced during melanogenic metabolite photolysis have been identified by ESR spin trapping, laser flash photolysis and pulse radiolysis techniques and include hydrated electrons (eaq), hydrogen atoms (H'), hydroxyl radicals (OH), semiquinones, aryl thiyl (ArS), and alanyl carbon‐based radicals. In vitro investigations of the potential photobiological significance of these reactions have demonstrated photolysis of cysteinyldopas may lead to photoinitiated DNA binding and single strand break induction. The above mentioned radical species may also damage proteins and initiate lipid peroxidation. Definitive evidence for the occurrence of these phototoxic reactions in vivo is currently unavailable, however our in vitro studies suggest a possible role for melanogenic metabolite photolysis in acute and chronic solar responses of human skin.
ANALYSIS OF FLASH PHOTOLYSIS DATA BY A GLOBAL FIT WITH MULTI‐EXPONENTIALS–I. DETERMINATION OF THE MINIMAL NUMBER OF INTERMEDIATES IN THE PHOTOCYCLE OF BACTERIORHODOPSIN BY THE ‘STABILITY CRITERION’
Authors: Maurer R. , Vogel J. , Schneider S.
Published: January 2008

A major problem in establishing a kinetic scheme for photo‐induced reaction sequences is the determination of the unknown number of important intermediates. It is shown that in addition to the χ2‐value and the distribution of the residuals obtained from a least‐squares fit of the experimental curves by a sum of exponentials, the stability of the apparent rates towards an increase of the number of exponentials with arbitrary test values can be used as an additional criterion. Experimental data describing the photocycle of bacteriorhodopsin after the appearance of intermediate K (t > 1 μs) are analysed with the described algorithm. It is found that 5 exponentials are necessary and sufficient for the fit.
ISOLATION and CHARACTERIZATION OF THE PHOTOADDUCTS OF 5,7‐DIMETHOXYCOUMARIN and ADENOSINE
Authors: Cho Tae Heung , Shim Hyun Kwan , Shim Sang Chul
Published: January 2008

The isolation and structural characterization of the photoadducts of 5,7‐dimethoxycoumarin and adenosine are described. Two of the major photoadducts were isolated by preparative column chromatography and reverse‐phase high performance liquid chromatography. Structure of the products was determined by UV, FT‐IR, mass spectrometry, 1H NMR and 13C NMR studies, including the homonuclear decoupling, COSY method and DEPT experiments. The photoadducts were not C4‐cycloadducts but simple addition products in contrast to pyrimidine base adducts. Covalent bonds were formed between the carbon‐3 or carbon‐4 of the pyrone ring of 5,7‐dimethoxycoumarin and the carbon‐5’of ribose ring in adenosine.
PURE SINGLET OXYGEN CYTOTOXICITY FOR BACTERIA
Authors: Dahl ThomasA. , RobertMiddenand W. , Hartman PhilipE.
Published: January 2008

We have modified the separated‐surface‐sensitizer singlet oxygen generating system previously described (Midden and Wang, 1983) for the efficient exposure to pure singlet oxygen of bacteria collected on membrane filters. Physical separation of the photosensitizer and the bacteria eliminates the possibility of direct interaction between bacteria and photoexcited sensitizers that could lead to Type I (non‐singlet oxygen) photooxidation processes. This system was used to examine the bacterial cytotoxicity of singlet oxygen. The role of singlet oxygen was confirmed by measuring the decrease in cytotoxicity as the distance between the singlet oxygen source and the bacteria was increased. The gas phase half‐life of the intermediate responsible for cell killing, determined from this distance dependence analysis (24 ± 6 ms), is the same as that calculated from literature data for the gas phase half‐life of singlet oxygen (53 ± 37 ms). Killing of various strains of Salmonella lyphimurium and Escherichia coli was compared at the same dose of singlet oxygen. Bacteria were killed by singlet oxygen at levels several orders of magnitude lower than those effective in killing by H2O2. Altered DNA repair capacities (uvrB, recA, xth, nth, pKM101) did not affect survival. Incomplete cell wall lipopolysaccharide formation decreased survival following singlet oxygen exposure. Overproduction of the singlet oxygen quencher histidine increased survival, as did accumulation of the dipeptide carnosine (β‐alanyl‐L‐histidine). No evidence for mutagenicity of exogenous singlet oxygen exposure was obtained in a variety of S. typhimurium strains killed to 35% survival.
STUDIES ON THE in vitro O2‐DEPENDENT INACTIVATION OF NADH‐GLUTAMATE SYNTHASE FROM Chlamydomonas reinhardii STIMULATED BY FLAVINS
Authors: Gotor Cecilia , Márquez AntonioJ. , Vega JoséM.
Published: January 2008

The NADH‐glutamate synthase (EC 1.4.1.14) complex fromChlamydomonas reinhardiimay experiencein vitrotwo kinds of 02‐dependent inactivation stimulated by flavins.

A peroxide‐mediated inactivation of enzyme, which affects the NADH‐ and MVt‐glutamate synthase activities of the complex, but not the NADH‐dehydrogenase activity, can be obtained by aerobic incubation of the enzyme with NAD(P)H plus flavin. This inactivation of enzyme seems to be due to a permanent modification of sulfhydryl groups near the active site for L‐glutamine or 2‐oxoglutarate. The addition of 10 mM dithioerythritol to inactive NADH‐glutamate synthase produces a significant, but not complete, reactivation of the enzyme.

On the other hand, the NADH‐glutamate synthase is highly susceptible to a photodynamic inactivation caused by singlet02.Aerobic incubation of the active enzyme with flavin under illumination leads to the irreversible inactivation of all the activities associated with the enzymatic complex.
SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS–XII. SPIN TRAPPING STUDY OF THE FREE RADICALS GENERATED DURING THE PHOTOLYSIS OF PHOTO ALLERGENS BITHIONOL and FENTICHLOR
Authors: Li Anson S. W. , Chignell Colin F.
Published: January 2008

Free radicals were trapped and observed by ESR when photoallergens bithionol and fentichlor were irradiated in the presence of spin traps N‐t‐butyl‐α‐phenylnitrone (PBN) and 5,5‐dimethyl‐pyrroline‐N‐oxide (DMPO). In the absence of air, both PBN and DMPO trapped a carbon‐centered radical. The carbon‐centered radical, which was capable of abstracting a hydrogen atom from cysteine, glutathione, ethanol and formate, was identified as an aryl radical derived from the homolytic cleavage of the carbon‐chlorine bond. In the presence of air, both carbon‐centered radicals and hydroxyl radicals were trapped by DMPO. Under similar conditions, the yield of the hydroxyl radicals was greater from bithionol than from fentichlor. The presence of the hydroxyl radical was confirmed by kinetic experiments employing hydroxyl radical scavengers (ethanol, formate). Superoxide and H2O2were not involved. Experiments with oxygen‐17O indicated that the hydroxyl radicals came exclusively from dissolved oxygen. The precursor of the hydroxyl radical is postulated to be a peroxy intermediate (ArOO*) derived from the reaction of an aryl radical (Ar*) with molecular oxygen. Both bithionol and fentichlor photoionized only when excited in the UVC (<270 nm) region. Free radicals have long been postulated in the photodechlorination of bithionol and fentichlor and the present study provides supporting evidence for such a mechanism. Aryl and hydroxyl radicals are reactive chemical species which may trigger a series of events that culminate in photoallergy.
INDUCTION OF SISTER CHROMATID EXCHANGES IN Allium cepa MERISTEMATIC CELLS EXPOSED TO meso‐ TETRA(4‐PYRIDYL) PORPHINE and HEMATOPORPHYRIN PHOTORADIATION
Authors: HAZEN M. J. , VILLANUEVA A. , STOCKERT J. C.
Published: January 2008

The photodynamic effect of two porphyrin derivatives,meso‐tetra(4‐pyridyl)porphine (T4PyP) and hematoporphyrin (HP), and activating red light (647.1 nm) was tested, measuring the number of sister chromatid exchanges induced by this treatment inAllium cepachromosomes. A significant increase in the frequencies of sister chromatid exchanges was observed when chromosomes substituted with 5‐bromo‐2′‐deoxyuridine were treated for 4 h (G1of the second cycle of division) with T4PyP or HP followed by an irradiation with red light for 5 min.
QUANTITATION OF PHOTOSYSTEM II ACTIVITY IN SPINACH CHLOROPLASTS. EFFECT OF ARTIFICIAL QUINONE ACCEPTORS
Authors: McCauley Steven , Melis Anastasios
Published: January 2008

Quantitation of photosystem II (PSII) activity in spinach chloroplasts is presented. Rates of PSII electron‐transport were estimated from the concentration of PSII reaction‐centers (Chl/PSII = 380:1 when measured spectrophotometrically in the ultraviolet [ΔA320] and green [ΔA540–550] regions of the spectrum) and from the rate of light utilization by PSII under limiting excitation conditions. Rates of PSII electron‐transport were measured under the same light‐limiting conditions using 2,5‐dimethylbenzoquinone or 2,5‐dichlorobenzoquinone as the PSII artificial electron acceptors. Evaluation is presented on the limitations imposed in the measurement of PSII electron flow to artificial quinones in chloroplasts. Limitations include the static quenching of excitation energy in the pigment bed by added quinones, the fraction of PSII centers (PSIIβ) with low affinity to native and added quinones, and the loss of reducing equivalents to molecular oxygen. Such artifacts lowered the yield of steady‐state electron transport in isolated chloroplasts and caused underestimation of PSII electron‐transport capacity. The limitations described could explain the low PSII concentration estimates in higher plant chloroplasts (Chl/PSII = 600 ± 50) resulting from proton flash yield and/or oxygen flash‐yield measurements. It is implied that quantitation of PSII by repetitive flash‐yield methods requires assessment of the slow turnover of electrons by PSIIβand, in the presence of added quinones, assessment of the PSII quantum yield.
NOVEL RED ABSORBING BENZO[a]PHENOXAZINIUM and BENZO[a]PHENOTHIAZINIUM PHOTOSENSITIZERS: in vitro EVALUATION
Authors: Cincotta L. , Foley J. W. , Cincotta A. H.
Published: January 2008

Abstract Taking advantage of the‘heavy atom’effect, we have recently prepared a series of nine novel halogenated and sulfur‐substituted benzophenoxazines which have enhanced intersystem crossing to the triplet state as measured by singlet oxygen photobleaching of 1,3‐diphenylisobenzofuran. The dyes were evaluated for their dark and light‐induced toxicities towards several carcinomata and normal primary cell lines. One of these days, 5‐amino‐6‐iodo‐9‐diethylaminobenzol[a]phenoxazinium chloride, was found to be a potent photosensitizer for a murine sarcoma 180 and four human carcinomata cell lines (larynx Hep2, cervical HeLa, rectal tumor cell HRT, and transitional‐cell bladder BTC). Several dyes caused marked light dependent killing of two tumor cell lines (Hep2 and HRT) but were minimally toxic to a normal bovine fetal kidney (BFK) line. Sulfur substitutuion into the benzophenoxazine nucleus results, under the conditions studied, in the largest enhancement of phototoxicity both to normal and cancer cells. Comparisons between appropriate dyes show a correlation between the efficiency of singlet oxygen generation and phototoxicity. These results suggest that the photosensitizing efficacy of certain cationic benzophenoxazinium chromophores, such as Nile Blue A, can be greatly increased by appropriate structural modification. The demonstrated selectivity for carcinoma cells by some of these new photosensitizers may be useful therapeutically.
PHOTODYNAMIC THERAPY IN THE TREATMENT OF PANCREATIC CARCINOMA: DIHEMATOPORPHYRIN ETHER UPTAKE and PHOTOBLEACHING KINETICS
Authors: Mang Thomas S. , Wieman Thomas J.
Published: January 2008

Abstract Results of dihematoporphryin ether (DHE) uptake and fluorescence kinetics show that the concentration in the pancreas is on the order of 40‐60 μg DHE g−1 of tissue at an injected dose of 40 mg kg−1. Previously concentrations on this order have primarily been found in organs of the reticuloendothelial system. Two intra‐pancreatic carcinoma models, one of acinar origin (rat) and one of ductal origin (hamster), were studied. Both showed equal or higher concentrations of DHE as compared with normal pancreas when fluorescence measurements and chemical extraction procedures were performed. Photodynamic therapy (PDT) treatment of the normal pancreas and pancreatic tumors yielded atypical results. When the normal pancreas with DHE present is exposed to 630‐nm light from a dye laser (75 mW cm−2, 30 min), the normal photobleaching measurable by fluorescence decay does not occur. Yet the pancreatic tumor responds with a relatively normal fluorescence decay pattern, with hemorrhaging and a resultant loss of measurable DHE concentration.
PHOTODYNAMIC THERAPY OF MALIGNANT BRAIN TUMORS: CLINICAL and NEUROPATHOLOGICAL RESULTS
Authors: Kostron H. , Weiser G. , Fritsch E. , Grunert V.
Published: January 2008

Abstract Fourteen patients with malignant brain tumors were treated 17 times with photodynamic treatment following either intravenous, selective intraarterial or direct intratumoral injection of Photofrin II. In eight patients the photodynamic treatment was followed immediately by single dose radiation of 4 Gy of ionizing radiation. The three injection modalities resulted in 2.5 μ.g. 3.2 μ.g and 9.8 μ,g g−1 tumor tissue respectively after 3 days. The histological examination immediately after light irradiation after intravenous and intra‐arterial injection demonstrated a predominantly vascular and cellular effect whereas the direct injection resulted in a direct cellular effect with little effect on vascular structures.

The median survival time for the three patients with multiple recurrences of the glioblastoma was 5 months, five patients with the first recurrence have a survival time of 2 to 7 months following PDT and six patients with the primary manifestation are surviving now up to 12 months. The intraarterial and direct intratumoral injection was tolerated well by the patients without increased skin phototoxicity.

These results indicate that the direct intratumoral and selective intraarterial injection of HPD are a feasible route for PDT however they are too preliminary to allow a final conclusion of the value of this modified PDT in the treatment of malignant brain tumors.
HIGH DOSE PHOTOIRRADIATION THERAPY OF HUMAN TUMORS USING THE GOLD METAL VAPOR LASER
Authors: Morstyn G. , Kaye A. H. , Thomas R. , Macrae F. , Abbott M.
Published: January 2008

Abstract The gold metal vapor laser (GMVL; Quentron, Adelaide, South Australia) produces up to 6.0 W of power and this has allowed the study of high dose and high dose rate photoirradiation therapy. We have undertaken 35 treatments in 31 patients with tumors in the rectum (4), esophagus (8), brain (17) and malignant ascites (2). All patients were carefully monitored for complications and, where possible, assessed for response. Dose rates of 1.2‐2.2 W were used and doses were estimated to be between 72 and 245 J cm−2. The major complications noted were in the patients with esophageal cancer and included fever 1‐10 days following therapy in 5/8. There was one early death at 10 days and 3/8 patients developed mediastinitis. Of the 4 anorectal tumors treated (8 treatments) there was one bleed 10 days after treatment and no other local complications. One of 2 patients with malignant ascites developed a bowel obstruction immediately after treatment. Of the 17 patients with glioma there was 1 early death at day 10 and no local complications. We conclude that phototherapy of the gastrointestinal tract with the GMVL is tolerable using high dose rates and doses but significant complications occur. Therapy of intra‐cranial tumors with similar doses and dose rates is not associated with local complications. The basis for this may be the different anatomy, the content of HpD in different sites, and use of steroids in cerebral tumors, or the better control of hyperthermia in the brain.
SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS—IX. A SPIN TRAPPING STUDY OF THE PHOTOLYSIS OF AMIODARONE AND DESETHYLAMIODARONE
Authors: Li Anson S. W. , Chignell Colin F.
Published: January 2008

The photolysis of amiodarone (AM) and its major metabolite mono‐N‐desethylamiodarone (DEA), has been studied by absorption spectroscopy, electron spin resonance spectroscopy (spin trapping) and oxygraph measurements. Changes in the absorption spectrum of both AM and DEA upon UV irradiation indicate that both drugs undergo deiodination. Spin trapping experiments with 2‐methyl‐2‐nitrosopropane (MNP), α‐phenyl‐N‐tert‐butyl‐nitrone (PBN) and 5.5‐dimethyl‐1‐pyrroline‐N‐oxide (DMPO) suggest the formation of an aryl radical from AM during UV irradiation. Amiodarone also undergoes photoionization. Under aerobic conditions the photoelectron is scavenged by oxygen to give superoxide, which is trapped by DMPO. Oxygraph measurements further confirmed the consumption of oxygen and the generation of superoxide during the irradiation of aqueous solutions of AM. Deiodination, photoionization and superoxide formation were all observed at wavelengths as low as 335 nm, suggesting that some or all of these processes may be involved in AM‐induced photosensitivity. The aryl radical derived from AM during UV irradiation abstracted a hydrogen atom from suitable donors (ethanol, glutathione, cysteine, linoleic acid). Reaction of the dienyl radical derived from linoleic acid would yield the corresponding peroxy radical thereby initiating lipid peroxidation. This would explain the deposition of lipofuscin, a pigment formed from the products of lipid peroxidation, in the skin of patients receiving AM.
GENETIC TOXICOLOGY OF THE PHOTOSENSITIZATION OF CHINESE HAMSTER CELLS BY PHTHALOCYANINES
Authors: Ben‐Hur E. , Fujihara T. , Suzuki F. , Elkind M. M.
Published: January 2008

Chloroaluminum phthalocyanine (CAPC) was recently shown to photosensitize cell killing in culture and tumor destruction in vivo. Because this compound is potentially useful in the photodynamic therapy of cancer, its properties as a genotoxic agent were evaluated. Applying the technique of alkaline elution to study DNA integrity, it was found that CAPC could produce single‐strand breaks in the DNA of Chinese hamster cells after exposure to white fluorescent light. At equicytotoxic doses, the number of DNA strand breaks produced by CAPC photosensitization was about three times lower than that induced by X‐irradiation. During incubation in growth medium after exposure to CAPC‐plus‐fluorescent light, cells rejoined DNA strand breaks at a rate similar to that observed after X‐irradiation. Resistance to 6‐thioguanine (6‐TG') or to ouabain (OUA') were used as end points of mutagenic potential. Following a treatment that caused ‐90% cell killing, there was a slight mutagenic effect, i.e. the frequencies were increased by ‐40% above the background or spontaneous mutations. However, this enhancement was not statistically significant. Taken together, the foregoing, plus an earlier observation that there is no variation in the sensitivity of cells to CAPC + light through the cell cycle, lead to the inferences that DNA damage does not play a major role in cell killing and that the mutagenic potential of this treatment is small.
INDUCTION OF DIRECT AND INDIRECT SINGLE‐STRAND BREAKS IN HUMAN CELL DNA BY FAR‐ AND NEAR‐ULTRAVIOLET RADIATIONS: ACTION SPECTRUM AND MECHANISMS
Authors: Peak Meyrick J. , Peak Jennifer G. , Carnes Bruce A.
Published: January 2008

Abstract— An action spectrum for the immediate induction in DNA of single‐strand breaks (SSBs, frank breaks plus alkali‐labile sites) in human P3 teratoma cells in culture by monochromatic 254‐, 270‐, 290‐, 313‐, 334‐, 365‐, and 405‐nm radiation is described. The cells were held at +0.5d̀C during irradiation and were Iysed immediately for alkaline sedimentation analysis following the irradiation treatments. Linear fluence responses were observed over the fluence ranges studied for all energies. Irradiation of the cells in a D2O environment (compared with the normal H2O environment) did not alter the rate of induction of SSBs by 290‐nm radiation, whereas the D2O environment enhanced the induction of SSBs by 365‐ and 405‐nm irradiation. Analysis of the relative efficiencies for the induction of SSBs, corrected for quantum efficiency and cellular shielding, revealed a spectrum that coincided closely with nucleic acid absorption below 313 nm. At longer wavelengths, the plot of relative efficiency vs. wavelength contained a minor shoulder in the same wavelength region as that observed in a previously obtained action spectrum for stationary phase Bacillus subtilis cells. Far‐UV radiation induced few breaks relative to pyrimidine dimers, whereas in the near‐UV region of radiation, SSBs account for a significant proportion of the lesions relative to dimers, with a maximum number of SSBs per lethal event occurring at 365‐nm radiation.
DETECTION OF CHARGE‐PERTURBATION OF TRYPTOPHAN RESIDUES BY FOURTH‐DERIVATIVE SPECTROPHOTOMETRY
Authors: Sabés Manuel , Padrós Esteve
Published: January 2008

Abstract—Fourth‐derivative spectrophotometry has been applied to the analysis of the1LaO‐O band of the indole chromophore. Using several tryptophan models, it is shown that when this band is the most red‐shifted, it produces a minimum at about 300 nm in the fourth‐derivative spectrum. In proteins this red shift and the 300‐nm minimum results from a charge‐perturbation effect acting through space on the indole group of tryptophan residues. It is concluded that fourth‐derivative spectrophotometry can be used for monitoring the effect of charges on tryptophan residues
AN IMPROVED HPLC METHOD FOR THE SEPARATION OF RETINALDEHYDE ISOMERS FROM VISUAL PIGMENTS
Authors: Pepe I. M. , Schwemer J.
Published: January 2008

Abstract— A method for the analytical separation of retinal isomers such as 13‐cis, 11‐cis, 9‐cis and all‐trans retinal, dissolved in aqueous solutions of detergents, is described. The retinals are extracted by means of a non‐isomerizing procedure and separated by HPLC on an octadecyl silane column used in normal phase. This column retains detergents without deteriorating and gives a satisfactory separation of retinal isomers with a resolution comparable with that obtained with silica gel column. The reliability of the method is verified by analysing the chromophore of visual pigment rhodopsin in digitonin solution, before and after irradiation with white light.