bluuebunny/crossref_metadata_2025 huggingface dataset:
REDUCED PHOTOINACTIVATION OF 10‐DODECYL ACRIDINE ORANGE‐SENSITIZED YEAST CELLS AT HIGH FLUENCE RATES MEASUREMENTS AND COMPUTER SIMULATIONS
Authors: Keij Jan F. , Jansen Jan Th. M. , Schultz Frank W. , Visser Jan W. M.
Published: January 2008

Abstract‐During the development of a photodamage cell sorter several photosensitizers were tested for their ability to photoinactivate more than 90% of the sensitized cells after a brief irradiation with a fluence of 10 kJ/m2. In pilot experiments, yeast cells sensitized with 10‐dodecyl acridine orange (DAO) were effectively photoinactivated after receiving a fluence of 10 kJ/m2 delivered in 8 s. However, when the same fluence was delivered in 3 μs during passage through a focused laser beam in the cell sorter, all cells survived.

Computer simulations of the relevant photophysical and chemical reactions inside the irradiated cell were used to investigate the cause of this phenomenon. The results indicated that the absence of photoinactivation by DAO, after flash irradiations, was caused by the combined effects of (1) limited oxygen diffusion into the cell and (2) a reduced number of collisions between photosensitizer triplet and oxygen molecules during the irradiation due to saturation of the intracellular photosensitizer triplet concentration. The contributions of triplet‐triplet annihilation and triplet quenching by ground state photosensitizer molecules were found to be minimal and not significant. These findings indicate that Type II photosensitizers are incapable of rapid selective photoinactivation in cell sorters.
PHOTOPHYSICS OF THE FLUORESCENT Ca2+ INDICATOR QUIN‐2
Authors: Bergh Viviane Van den , Boens Noël , Schryver Frans C. De , Gallay Jacques , Vincent Michel
Published: January 2008

The photophysics of the complex forming reaction between Quin‐2 and Ca2+ were investigated using steady‐state and time‐resolved fluorescence measurements. The fluorescence decay traces were analyzed with global compartmental analysis yielding the following values for the rate constants at room temperature in aqueous solution with EGTA as Ca2+ buffer: k01= 8.6 times 108 s−1, k21= 1 times 1011M−1 s−1, k02= 8.8 times 107 s−1, k12= 4 times 104 s−1. k01 and k02 denote the respective deactivation rate constants of the Ca2+ free and bound forms of Quin‐2 in the excited state. The constant k21 represents the second‐order rate constant of binding of Ca2+ and Quin‐2 in the excited state while k12 is the first‐order rate constant of dissociation of the excited Ca2+:Quin‐2 complex. From the estimated values of k12 and k21 the dissociation constant Kd* in the excited state was calculated. It was found that pKd* (6.4) is slightly smaller than pKd (7.2). There was no interference of the excited‐state complex forming reaction with the determination of Kd. Intracellular Ca2+ concentrations can thus accurately be determined from fluorometric measurements using Quin‐2 as Ca2+ indicator.
PREFERENTIAL INHIBITION OF NUCLEOSOME ASSEMBLY BY ULTRAVIOLET‐INDUCED (6‐4)PHOTOPRODUCTS
Authors: Matsumoto Hideki , Takakusu Akira , Mori Toshio , Ihara Makoto , Todo Takeshi , Ohnishi Takeo
Published: January 2008

We reconstituted nucleosomes in vitro using two kinds of damaged pBR322 plasmid DNA carrying cyclobutane pyrimidine dimers (CPD) or (6‐4)photoproducts. The results indicate that nucleosome assembly is inhibited preferentially by (6‐4)photoproducts compared with CPD, suggesting that the regions carrying (6‐4)photoproducts retain their nucleosome‐free form, i.e. linker‐like conformation until completion of the repair processes.
INDUCTION OF SLOWLY DEVELOPING ALKALI‐LABILE SITES IN HUMAN P3 CELL DNA BY UVA AND BLUE‐ AND GREEN‐LIGHT PHOTONS: ACTION SPECTRUM
Authors: Peak Jennifer G. , Peak Meyrick. J.
Published: January 2008

Action spectra (365–520nm) for the formation of DNA single‐strand breaks (SSB) and slowly developing alkali‐labile sites (SDALS) in human teratocarcinoma P3 cells in culture were determined. Induction of SDALS results from the absorption of blue‐ and green‐light photons. The spectrum has a broad peak that is maximal between 400 nm to 500 nm and declines sharply above and below these wavelength regions. Negligible yields of SDALS were produced by photons at wavelengths of 365 nm or shorter and at 520 nm or longer, whereas for SSB, the action increases with shorter wavelength throughout the whole spectral range studied. The configuration of the SDALS action spectrum suggests that the primary chromophore, and therefore possibly the photosensitizer, is a mixture of porphyrin and flavin residues.
THE ROLE OF TRANSFERRIN RECEPTOR (CD71) IN PHOTODYNAMIC THERAPY OF ACTIVATED AND MALIGNANT LYMPHOCYTES USING THE HEME PRECURSOR δ‐AMINOLEVULINIC ACID (ALA)
Authors: Rittenhouse‐Diakun K. , Leengoed H. VAN , Morgan J. , Hryhorenko E. , Paszkiewicz G. , Whitaker J. E. , Oseroff A. R.
Published: January 2008

Endogenously generated protoporphyrin IX (PpIX) from exogenous ALA can be an effective photosensitizer. PpIX accumulation is inversely dependent on available intracellular iron, which is required for the conversion of PpIX to heme. Iron also is necessary for cell replication. Since iron can be toxic, intracellular iron levels are tightly controlled. Activated and proliferating cells respond to the demand for intracellular iron by upregulating membrane expression of the transferrin receptor (CD71) which is needed for iron uptake. We predicted that activated lymphocytes (CD71 +) would preferentially accumulate PpIX because of their lower intracellular iron levels and because of competition for iron between ALA‐induced heme production and cellular growth processes. Thus, the CD71+ cells could serve as PDT targets. Stimulation of human peripheral blood lymphocytes (PBL) with the mitogens, phytohemagglutinin A, concanavalin A and pokeweed prior to incubation with ALA results in PpIX accumulation correlating with level of activation. Activated lymphocytes expressing high levels of surface CD71 transferrin receptors generated more PpIX than those with low CD71 expression. Incubating activated cells in transferrin depleted medium (thereby decreasing the iron availability) further increased PpIX levels. Malignant, CD71 + T lymphocytes from a patient with cutaneous T‐cell lymphoma (CTCL)/Sezary syndrome also accumulated increased PpIX levels in comparison to norma] lymphocytes. PDT of activated lymphocytes and Sezary cells after ALA incubation demonstrated preferential killing compared to normal, unstimulated PBL. These findings suggest a possible mechanism for the selectivity of ALA PDT for activated CD71+ cells. They also indicate a clinical use for ALA‐PDT in therapy directed towards the malignant lymphocytes in leukemias and lymphomas, and as animmunomodulatory agent.
CHEMILUMINESCENCE and EPR STUDIES ON THE EXCITATION SITE OF FERRIC‐HEME‐OXO COMPLEXES OF NATURAL and MODEL HEME SYSTEMS
Authors: Liu Yang , Nohl Hans
Published: January 2008

Abstract—

Chemiluminescence was detected both in the reaction system of H2O2 plus heme proteins such as methemo‐ and metmyoglobin and ferric‐protoheme complexes used as a model system. The intensity of chemiluminescence was found to be mediated by ligand binding to the sixth coordination site of the ferric‐protoheme compounds, e.g. chemiluminescence was not observed with the bisimidazole ferric‐protoheme complex. On the other hand the pentacoordinated histidine ferric‐protoheme complex exhibited strong light emission. Comparative studies with various ligand‐heme compounds elucidated that light emission was inversely correlated with the binding strength of the respective ligand at the sixth coordination site.

The basic reaction mechanism causing the establishment of an excited state was studied by monitoring chemiluminescence and EPR signal formation of ligand‐modified heme proteins in the presence of different electron donors. External electron donors such as Trolox C, TMPD and ascorbic acid affected a strong reduction in the development of chemiluminescence suggesting the essential involvement of an inner‐molecular electron transfer process. Our results allow the conclusion that chemiluminescence is generated from the decay of an excited state of oxo‐heme compounds established as a result of a one electron transfer step from a ligand group to heme iron.
EFFECT OF IRON(III) ON CHEMILUMINESCENCE FROM THE NEUTRALIZATION REACTION OF NITRIC ACID and POTASSIUM HYDROXIDE
Authors: Fujiwara Terufumi , Sakai Hiroyuki , Kumamaru Takahiro
Published: January 2008

Abstract—

Low levels (around 90 μM) of iron(III) caused an increase in chemiluminescence (CL) from the neutralization reaction involving nitric acid and potassium hydroxide without use of any luminescent reagent. When oxygen was excluded from the reaction, a significant decrease in the CL emission was observed. This suggests that molecular oxygen present in the solutions may play an important role in the process of the iron‐catalyzed CL induced by the neutralization reaction, which liberates a sufficient energy. Other experimental parameters like the influence of several other metal ions, counteranions and acid media were also examined. The results showed that the observed CL enhancement by iron(III) proved to become most remarkable under sporadical conditions alone, and the presence of small amounts (less than 0.20 mM) of sulfate ion increase the catalytic activity of iron(III). A possible mechanism involving transient formation of iron–radical complexes upon neutralization and subsequent reaction of the complexes with molecular oxygen is considered for the present CL reaction.
THE ACTION SPECTRA FOR UV‐INDUCED SUPPRESSION OF MLR and MECLR SHOW THAT IMMUNOSUPPRESSION IS MEDIATED BY DNA DAMAGE
Authors: Hurks H. M. H. , Out‐Luiting C. , Vermeer B. J. , Claas F. H. J. , Mommaas A. M.
Published: January 2008

Abstract—

‐Ultraviolet‐B (UVB,280–320 nm) radiation can promote the induction of skin cancer by two mechanisms: damage of epidermal DNA and suppression of the immune system, allowing the developing tumor to escape immune surveillance. The mixed lymphocyte reaction (MLR) and the mixed epidermal cell lymphocyte reaction (MECLR) are commonly used methods to study the immunosuppressive effects of UVB radiation. To obtain a better understanding of the mechanism by which UVB radiation decreases the alloactivating capacity of in vitro‐irradiated cells, action spectra for the MLR and MECLR were determined. Suspensions of peripheral blood mononuclear cells or epidermal cells were irradiated with monochromatic light of 254, 297, 302 or 312 nm and used as stimulator cells in the MLR or MECLR. Using dose‐response curves for each wavelength, the action spectra were calculated. Both MLR and MECLR action spectra had a maximum at 254 nm and a relative sensitivity at 312 nm that was a thousand times lower than at 254 nm. Strikingly, the action spectra corresponded very closely to the action spectra that were found by Matsunaga et al. (Photochem. Photobiol. 54,403–410, 1991) for the induction of thymine dimers and (6‐4)photoproducts in irradiated calf thymus DNA solutions, strongly suggesting that the UV‐induced abrogation of the MLR and MECLR responses is mediated by UV‐induced DNA damage. Furthermore, the action spectra for the MLR and MECLR were similar, suggesting that they share a common mechanism for UV‐induced suppression.
In vitro DEMONSTRATION OF A FUNDAMENTAL DIFFERENCE IN THE PROLIFERATION OF MURINE and HUMAN BONE MARROW and LYMPHOCYTES FOLLOWING ULTRAVIOLET IRRADIATION: RELEVANCE TO BONE MARROW TRANSPLANTATION
Authors: Hudson J. G. , Pullens R. , Godwin V. , Preece A. W. , Pamphilon D. H.
Published: January 2008

Abstract—

Exposure of rodent allogeneic donor marrow and splenocyte grafts to ultraviolet radiation (UVR) has been shown to permit durable engraftment at doses that abolish graft‐versus‐host disease (GVHD) and graft rejection. We have compared both murine and human alloreactive and mitogen‐induced lymphoid responses and bone marrow proliferation in mixed lymphocyte culture (MLC), phy‐tohemagglutinin (PHA)‐induced proliferation and colony‐forming unit‐granulocyte/macrophage (CFU‐GM) assays using germicidal UVC (200–290nm), broadband and narrowband UVB (290–320nm) and UVA (320^100 nm) sources. Our data show a wavelength and dose‐dependent reduction in lymphoid proliferation in the mouse with CFU‐GM survival of50–75% of control at doses required to abolish allogeneic lymphocyte responses for all lamps. In contrast, human lymphocyte responses are more resistant to UVC with CFU‐GM proliferation reduced to zero when allostimulation is abolished. Mito‐gen‐induced lymphoid responses show a similar wavelength‐dependent sensitivity. Abolition of response in MLC using UV‐irradiated stimulator cells was less sensitive than proliferation with UV‐irradiated responder cells at all wavelengths in both species. With all sources, murine CFU‐GM proliferation is less susceptible to UVR than human marrow at doses required to abolish lymphoid responses.
INHIBITION OF OXYGEN EVOLUTION IN CHLOROPLAST PHOTOSYSTEM II BY THE PROTEIN‐MODIFYING AGENT TETRANITROMETHANE
Authors: Gingras Yves , Harnois Johanne , Ross Geneviève , Carpentier Robert
Published: January 2008

Abstract— The protein‐modifying agent tetranitromethane (TNM) reacts with tyrosine residues and ‐SH groups. It was found to inhibit photo synthetic electron transport on the water splitting side of photosystem II (P. V. Sane and U. Johanningmeier, Z. Naturforsch. 35c, 293–297, 1979). In the present work the inhibition by TNM is studied in detail using photosystem II submembrane fractions. It is shown that the action of TNM with membrane‐bound proteins could imply the modification of tyrosine residues. At concentrations below 30 μM and with short incubation periods (<2 min), TNM produces the release of the extrinsic polypeptides involved in the stabilization of the water‐splitting complex, this being correlated with inhibition of electron transport at a site prior to H2O2 electron donation even though the inhibition cannot be prevented by the addition of Cl or Ca2+, which are known cofactors for oxygen evolution. As the incubation period or the concentration of TNM is increased, photosynthetic pigments are bleached, starting with aggregates absorbing at relatively long wavelengths. The inhibition by low concentrations of TNM differs from the effect of most of the previously reported inhibitors acting at the oxygen‐evolving complex of photosystem II.
INHIBITION OF LIGHT‐DEPENDENT PHOTOMORPHOGENESIS OF SPORANGIOPHORES FROM Phycomyces blakesleeanus BY APPLICATION OF PTERIDINE BIOSYNTHESIS INHIBITORS*†
Authors: Maier Josef , Ninnemann Helga
Published: January 2008

Abstract— In the zygomycete Phycomyces blakesleeanus the morphogenesis of both macrosporangiophores and microsporangiophores is under separate control of different blue‐light photoreceptors. Blue light represses microphorogenesis and enhances macrophorogenesis. Both, flavins and pterins are discussed as possible components of these blue‐light photoreceptors. 2,4‐Diamino‐6‐hydroxypyrimidine (DAHP) was shown to be an inhibitor of GTP‐cyclohydrolase I, the initial enzyme of pteridine biosynthesis, in vitro and in vivo in Phycomyces. When grown on agar plates containing 5 mM of DAHP, Phycomyces shows a 6.0‐fold reduction of light‐dependent enhancement of macrophorogenesis, and microphorogenesis was 3.1 times less repressed when compared with controls grown without DAHP. This implies a participation of pteridines in blue‐light photoreception in both phenomena, with greater influence on macrophorogenesis enhancement than on microphorogenesis repression.
TEMPERATURE DEPENDENCE OF CHLOROPHYLL FLUORESCENCE FROM THE LIGHT HARVESTING COMPLEX II OF HIGHER PLANTS
Authors: Ruban Alexander V. , Dekker Jan P. , Horton Peter , Grondelle Rienk VAN
Published: January 2008

Abstract— Chlorophyll fluorescence spectra of LCHII, the light harvesting complex of photosystem II, have been recorded in the aggregated and trimeric forms for a range of temperatures from 293 to 4 K. At least five long‐wavelength emitters in the 682–702 nm region with different temperature dependencies were found in the spectra of the aggregates. At 293 K the yield of LCHII trimers was higher than aggregates by a factor of 4, but, upon lowering the temperature, a fluorescence rise was observed which was much stronger for LCHII aggregates than for LCHII trimers, so that at 4 K their yields were comparable. The implications of these data in terms of the function of LCHII are discussed.
UNIQUE DNA REPAIR PROPERTY OF AN ULTRAVIOLET‐SENSITIVE (radC MUTANT OF Dictyostelium discoideum
Authors: Okaichi Kumio , Mori Toshio , Ihara Makoto , Ohnishi Takeo
Published: January 2008

Abstract— Dictyostelium discoideum is an organism that shows higher UV resistance than other organisms, such as Escherichia coli and human cultured cells. We examined the removal of cyclobutane pyrimidine dimers (CPD) and 6–4 photoproducts from DNA in the radC mutant and the wild‐type strain using an enzyme‐linked immunosorbent assay with monoclonal antibodies. Wild‐type cells excised more than 90% of both CPD and 6–4 photoproducts within 4 h. Dictyostelium discoideum appeared to have a special repair system, because 6–4 photoproducts were repaired faster than CPD in E. coli and human cultured cells. In radC mutant cells, although only 50% of CPD were excised from DNA within 8 h, effective removal of 6–4 photoproducts (80% in 8 h) was observed. Excision repair‐deficient mutants generally cannot remove both CPD and 6–4 photoproducts. Though the radC mutant shows deficient excision repair, it can remove 6–4 photoproducts to a moderate degree. These results suggest that D. discoideum has two kinds of repair systems, one mainly for CPD and the other for 6–4 photoproducts, and that the radC mutant has a defect mainly in the repair enzyme for CPD.
UNUSUALLY HIGH AFFINITY OF Zn(II)‐TETRADIBENZOBARRELENOOCTABUTOXY‐ PHTHALOCYANINE FOR LOW‐DENSITY LIPOPROTEINS IN A TUMOR‐BEARING MOUSE
Authors: Soncin M. , POLO L. , REDDI E. , JORI G. , RIHTER B. D. , KENNEY M. E. , RODGERS M. A. J.
Published: January 2008

Abstract— An important factor in determining the efficacy of photosensitizing compounds in photodynamic therapy of tumors is the level to which tumors take up the photosensitizers after systemic injection. This parameter seems to be related to the transport modalities of the photosensitizer in the bloodstream. In this work the photosensitizer Zn(II)‐tetradibenzobarreleno‐octabutoxyphthalocyanine was shown to have an unprecedentedly high association with low‐density lipoproteins (71% of the phthalocyanine in the plasma) when delivered in Cremophor micelles to tumor‐bearing mice. This was accompanied by a particularly high tumor uptake at 24 h post‐injection.
THE DEVELOPMENT OF PERSONAL DOSIMETERS FOR USE IN THE VISIBLE AND ULTRAVIOLET WAVELENGTH REGIONS
Authors: Duncan D. D. , Schneider W. , West K. J. , Kirkpatrick S. J. , West S. K.
Published: January 2008

Abstract—

We have designed, developed, and field evaluated a two‐part personal dosimeter for estimating ocular exposure to visible and ultraviolet radiation. The detector head is compact enough to be mounted on the bow of eyeglass frames, and the recorder is small enough to be carried in a shirt pocket. The detector head consists of a silicon photodiode with filter (Schott glass GG400) and diffuser for visible light measurements and a polysulphone film badge for ultraviolet‐B (UVB, 290–320 nm) measurements. The measurements correspond well to those obtained using ambient monitors and should be useful for studies of ocular UVB exposure.
INCREASED UV EXPOSURE IN FINLAND IN 1993
Authors: Jokela Kari , Leszczynski Kirsti , Visuri Reijo , Ylianttila Lasse
Published: January 2008

Abstract—

Exceptionally low total ozone, up to 40% below the normal level, was measured over Northern Europe during winter and spring in 1992 and 1993. In 1993 the depletion persisted up to the end of May, resulting in a significant increase of biologically effective UV radiation. The increases were significantly smaller in 1992 and 1994 than in 1993. The UV exposure of the Finnish population was evaluated through measurements and theoretical calculations. The increase in measured erythemal (International Lighting Commission) UV falling onto horizontal surfaces on clear days was determined relative to model calculations for an average ozone amount. The increase was on average 10% from April to May 1993, and the maximal measured increase was 34%. Theoretical calculations for both erythemal and carcinogenic (Skin Cancer Utrecht‐Philadelphia) UV indicated that in 1993 the theoretical annual increase to a vertical (cylinder) surface ranged from 8 to 13% in Finland. The reflection of UV from snow considerably increases facial UV doses in Northern Finland.
COMPARISON OF THE SOLID‐MATRIX LUMINESCENCE PROPERTIES OF BENZO(a)PYRENE‐DNA ADDUCTS ON α‐CYCLODEXTRIN/NaCl and TREHALOSE/NaCl MATRICES
Authors: Chu Yu , Hurtubise Robert J.
Published: January 2008

Abstract— The solid‐matrix luminescence properties of (±)‐trans‐7,8‐dihydroxy‐anti‐9,10‐epoxy‐7,8,9,10‐tetrahydrobenzo(a)pyrene‐DNA ([±]‐anti‐BPDE‐DNA) adducts were compared on α‐cyclo‐dextrin (CD)/NaCl and trehalose/NaCl solid matrices. Both the optimum composition for the solid matrices and the best solvent system were obtained experimentally for acquiring the maximum room‐temperature fluorescence (RTF) and room‐temperature phosphorescence (RTP) signals for the (±)‐anti‐BPDE‐DNA. Most of the solid‐matrix RTF and RTP data were obtained at 296 K and 93 K for (±)‐anti‐BPDE‐DNA adducts adsorbed on 1%α‐CD/NaCl and 80% trehalose/NaCl. The RTF signals were strong for (±)‐BPDE‐DNA adducts on both solid matrices, but RTP was only obtained on the trehalose/NaCl solid matrices with the 80% trehalose yielding the strongest RTP signal for (±)‐anti‐BPDE‐DNA. The fluorescence lifetime data for (±)‐anti‐BPDE‐DNA gave two components on 1 %α‐CD/NaCl. For 80% trehalose/NaCl, three components were revealed, but two components were obtained with 80% trehalose/NaCl after ether extraction of the solid matrix. The third component was ascribed to the formation of the tetrols from (±)‐anti‐BPDE‐DNA adducts during the drying step in the sample preparation of 80% trehalose/NaCl. The results give the first reported data on the solid‐matrix luminescence of the (±)‐anti‐BPDE‐DNA adducts. These results should be of considerable interest not only from an analytical viewpoint but as a new means of studying the luminescence characteristics of the adducts.
HETEROGENEITY OF THE QUINONE ELECTRON ACCEPTOR SYSTEM IN BACTERIAL REACTION CENTERS
Authors: Baciou Laura , Sebban Pierre
Published: January 2008

Abstract— In reaction centers from Rhodopseudomonas viridis, biphasicity of the charge recombination kinetics between P+, the primary electron donor, and QA and QB‐, the primary and secondary quinone electron acceptors, respectively, have been analyzed by the flash‐induced absorption change technique. We have studied the effect of quinone environment modifications on the ratio of the two phases for the P+QA‐ ([Afast/Aslow]a) and P+QB‐ ([Afast/Aslow]b) charge recombination processes. In reaction centers from Rps. viridis reconstituted in phosphatidylcholine liposomes a notable influence of the nature of the QB pocket occupancy was observed on (Afast/Aslow)a. This ratio is much affected by the presence of o‐phenanthroline compared to reaction centers with an empty QB pocket or with terbutryn present. Because o‐phenanthroline was proposed to hydrogen bind HisL190, whereas terbutryn does not, we suggest that a HisLI90‐Fe‐HisM217 (the equivalent to HisLI90 in the QA pocket) “wire” may be involved in the existence of the two conformational states associated with the two phases of charge recombination. In chromat‐ophores from the T1 (SerL223→ Ala; ArgL217→ His) and T4 (TyrL222→ Phe) mutants no modification of the (Afast/Aslow)a ratio is detected, whereas the (Afast/Aslow)b ratios are substantially modified compared to the wild type (WT). In the T3 mutant (PheL216→ Ser; ValM263→ Phe [4.1 Å apart from QA]), (Afast/Aslow)a is notably changed compared to the WT. Our data show that any modification in the close protein environment of the quinones and/or of the HisL190 and HisM217 affects the equilibrium between the two reaction center states. This is consistent with the existence of two reaction center states from Rps. viridis, associated with two different conformations of the quinones‐histidines‐iron system. This “wire” allows both quinone protein pockets to interact over quite long distances.
RESEARCH NOTE ON THE CHARGE‐TRANSFER PATHWAY IN THE MEROCYANINE 540 TRIPLET STATE QUENCHING BY NITROXYL RADICAL
Authors: Hoebeke M. , Vorst A. Van De
Published: January 2008

Abstract— Quenching of merocyanine 540 triplet state by nitroxyl radical has been investigated by flash photolysis. An increase of solvent polarity leads to an increase of the quenching rate. This polarity effect shows that merocyanine 540 triplet state is able to react with nitroxyl radical via a charge‐transfer process. The data presented in this work are shown to be consistent with previous results obtained in micelles and liposomes.
HYDROPEROXYNAPHTHALIMIDE DERIVATIVE‐MEDIATED OXIDATION OF LYSOZYME
Authors: Yamamoto Takahiro , Maeda Yasushi , Matsugo Seitchi , Kitano Hiromi
Published: January 2008

Abstract— Lysozyme was photoirradiated in the presence of photo‐Fenton reagents (hydroperoxynaph‐thalimide derivatives) at 366 nm. Enzymatic activities of photoirradiated lysozymes were lower than that of native lysozyme. Taking account of the results of amino acid analysis and of fluorescence spectra, it was probably that Trp residues in the photoirradiated lysozyme were oxidized with hydroxyl radicals. The reagents formed complexes with lysozyme as proved by the inhibitory effects of the reagents on the enzymatic activities (K1= 4.7 ± 1.2 × 104M for HPO II, a hydroperoxide derivative of naphthalimide), which suggested that these reagents were bound to the active site cleft of lysozyme, and the Trp residues located in or near the active site cleft were photooxidized. Fluorescence‐difference spectra of photoirradiated lysozymes showed that Trp 62 was preferentially photooxidized. Furthermore, sodium dodecyl sulfatepolyacrylamide gel electrophoresis and circular dichroism spectra showed that the photooxidation examined here induced no significant change in the molecular size but a slight change in the conformation of lysozyme, which suggests the usefulness of the reagents in the site‐selective oxidation of biopolymers.
A Photophysical Study of Purines and Theophylline by Using Laser‐Induced Optoacoustic Spectroscopy
Authors: Murgida Daniel H. , Bilmes Gabriel M. , Erra‐Balsells Rosa
Published: January 2008

Abstract— The photophysics of purinic compounds (purine, 6‐meth‐ylpurine, 6‐aminopurine [adenine], 6‐chloropurine, 6‐methoxypurine) and theophylline in acetonitrile solution were studied by pulsed laser‐induced optoacoustic spectroscopy (LIOAS) exciting at 266 nm. The effect of O2, Xe and MnCl2 on the photophysical behavior of these compounds was studied; as well, the formation quantum yield of purine and 6‐methylpurine triplet states were determined, with φT= 0.88 ± 0.03 for both compounds. Multiphotonic and depletion processes were observed at high laser fluences. In order to explain this behavior, theoretical UV‐visible absorption electronic spectra from both the S0 and S1 state have been calculated for purines and theophylline by using the semiempirical PM3 and ZINDO/S methods.
Use of Uracil Thin Layer for Measuring Biologically Effective UV Dose
Authors: Gróf Pal , Gáspái Sándor , Rontó Györgyi
Published: January 2008

Abstract— Dimerization of uracil monomers in a polycrystalline state by UV radiation changes the absorption characteristics of a thin layer of the material. The change in optical density, measured by spectrophotometry in the250–400 nm range, as a function of the exposure time is evaluated in terms of the biologically effective UV dose. A statistical evaluation of a great number of uracil dosimeters irradiated with a TL01 lamp from Philips establishes the possibility of evaluating the biologically effective UV dose using a uracil dosimeter. Nonlinear regression procedures were introduced to correct the absorption spectra for contributions due to light scattering and to determine the optical density values required to calculate the UV dose expressed in HUunits. Comparison of cumulative daily doses and long‐term monitoring measured by the uracil thin‐layer dosimeter and a phage T7 dosimeter are given, which allow the determination of conversion factors between various biological dosimeters under different irradiation conditions.
An Azulenic Bacteriorhodopsin Analog Has Photoinduced Activity
Authors: Druzhko Anna B. , Vanderah David J. , Robertson Baldwin , Weetall Howard H.
Published: January 2008

Abstract— The photoinduced changes of absorbance as well as proton release and uptake have been observed for an azulenic analog of wild‐type bacteriorhodopsin. The release and uptake of protons have been measured using a highly sensitive electrochemical technique. Bacteriorhodopsin membrane patches on a tin‐oxide electrode produce a transient photocurrent that is negative for proton release and positive for proton uptake. For azulenic bacteriorhodopsin the photocurrent is approximately 20% of the transient observed with native bacteriorhodopsin. The existence of the photoinduced absorbance changes and the transient photocurrent are important results for gaining further insight into the photoinduced function of bacteriorhodopsin.
Fluorescent Characteristics and Pharmacokinetic Profiles of the Fluorescent Probe BCECF in Various Tissues: The Role of Blood Content
Authors: Devoisselle J. M. , Soulié S. , Mordon S. , Maillols H.
Published: January 2008

Abstract— The purpose of this study was to investigate the in vitro and in vivo spectral characteristics of the fluorescent pH‐sensitive probe Ws‐carboxyethylcarboxyfluorescein (BCECF) in different tissues and its fluorescence kinetics profiles. The in vivo study was performed on anesthetized adult Wistar rats. After intravenous administration (4.8 mg/kg), fluorescence spectra were recorded on the following tissues: skin, an isolated blood vessel and liver. Measurements performed in vitro on blood samples show modifications of the BCECF emission spectrum with a blue‐shift (10 nm) and a low fluorescence emission. Blood content greatly influences the pH measurement by increasing the I(490 exc, 530 em.)/I(470 exc, 530 em.) fluorescence ratio value (ratio of the fluorescence intensities at 530 nm following excitation at 470 nm and 490 nm) when the hematocrit is high. A 0.35 ratio difference is observed between a BCECF‐buffered solution and blood samples of 44% hematocrit. The emission spectra recorded on the skin are quite similar to the emission spectrum of BCECF in aqueous solution and are consistent with an extravascular localization of the dye a few minutes after injection. On the contrary, spectra recorded on the blood vessel and the liver are more similar than those recorded in vitro on high hematocrit solutions. Kinetic profiles in skin, liver and isolated blood vessels compared to the clearance obtained by blood sampling provide information about tissue perfusion. Then the variation of in vivo spectra in different tissues may be taken into account to measure tissue pH with special regard to the blood content of the illuminated area and the time range in which the measurement is performed.
The Effects of the Broadband UVA Radiation on Myeloid Leukemia Cells: The Possible Role of Protein Kinase C in Mediation of UVA‐lnduced Effects
Authors: Leszczynski Dariusz , Fagerholm Susanna , Leszczynski Kirsti
Published: January 2008

Abstract— We examined the effects of broadband UVA radiation (320–400 nm) on a rat myeloid leukemia cell line–chlo‐roma (ChL). A Phillips face tanner model HB 171/A was used as a light source. Chloroma were irradiated through a 5 mm thick glass Alter that cut off all of the UVB contamination. The irradiances were measured, from 250 to 400 nm, with a well‐characterized and calibrated double‐grating spectroradiometer Optronic 742. The overall uncertainty of dose evaluation was estimated to be <15% (2s̀). The cells were irradiated with UVA doses of 4 and 8 J/cm2 and cultured thereafter for 24 h. After this period of time, a marked decline up to 50% was observed in cell proliferation in UVA‐irradiated ChL cultures. The cell proliferation decline was found to be caused by simultaneously occurring G2/M phase cell cycle arrest and apoptosis in part of the UVA‐irradiated ChL population. Concomitantly, with the decline in cell proliferation, an increase was observed in the expression of the major histocompatibility (MHC) class I and II antigens. Because protein kinase C (PKC) is known to regulate cell proliferation, apoptosis and expression of MHC antigens, and because UVA was shown to regulate PKC activity/expression, we therefore examined whether UVA irradiation has any effect on the expression of isozymes of PKC. Western blots revealed that ChL express α, βI, δ, α, γ, and π isozymes of PKC and that expression of all isozymes declined 24 h after UVA irradiation (8 J/cm2). Finally, PKC activation in ChL by exposure to phorbol ester caused cell cycle arrest in G1 phase but did not induce apoptosis. This suggests that the previously shown UVA‐induced PKC activation in ChL might be responsible for the induction of MHC antigens but the simultaneously observed ChL apoptosis is likely to be mediated by PKC down‐regulation. All together, our results suggest that UVA, at irradiance levels that resemble the outdoor exposure, may have profound effects on the immune‐related properties of leukocytes. Thus, we speculate that in vivo the immune functions of leukocytes passing through dermal capillaries might be altered by exposure to solar UVA radiation.
Chronic Low‐Dose UVA Irradiation Induces Local Suppression of Contact Hypersensitivity, Langerhans Cell Depletion and Suppressor Cell Activation in C3H/HeJ Mice
Authors: Bestak Rosa , Halliday Gary M.
Published: January 2008

Abstract— It has previously been demonstrated that chronic low‐dose solar‐simulated UV radiation could induce both local and systemic immunosuppression as well as tolerance to a topically applied hapten. In this study, we have used a chronic low‐dose UV‐irradiation protocol to investigate the effects of UVA on the skin immune system of C3H/HeJ mice. Irradiation with UVA+B significantly suppressed the local and systemic primary contact hypersensitivity (CHS) response to the hapten 2,4,6‐trinitrochlo‐robenzene. Furthermore UVA+B reduced Langerhans cell (LC) and dendritic epidermal T cell (DETC) densities in chronically UV‐irradiated mice. Ultraviolet A irradiation induced local, but not systemic, immunosuppression and reduced LC (32%) but not DETC from the epidermis compared to the shaved control animals. Treatment of mice with both UVA+B and UVA radiation also induced an impaired secondary CHS response, and this tolerance was transferable with spleen cells. These results suggest that depletion of LC, but not DETC, may be involved in UVA‐induced local immunosuppression in our model, and that tolerance was induced in the presence of normal numbers of DETC. Hence exposure of C3H/HeJ mice 5 days per week for 4 weeks with UVA can induce local immunosuppression and tolerance.
Photophysics and Intracellular Distribution of a Boronated Porphyrin Phototherapeutic Agent
Authors: Spizzirri Paul G. , Hill John S. , Kahl Stephen B. , Ghiggino Kenneth P.
Published: January 2008

Abstract— The absorption and emission spectra, fluorescence quantum yields and lifetimes and triplet state properties of a boronated porphyrin, the tetrakiscarborane carboxylate ester of 2,4‐(α,β‐dihydroxyethyl) deuteroporphyrin IX (BOPP), have been determined. This compound is an alternative photodynamic therapy (PDT) agent that exhibits highly selective tumor localization, with the potential to be used in conjunction with boron neutron capture therapy. The photophysical characteristics of BOPP are similar to other porphyrins and it exhibits marked aggregation and acid‐base speciation under typical physiological conditions. In particular, protonation of the porphyrin imino (‐N=) nitrogens occurs in the pH 5–7 region and influences the photophysical properties. Time‐resolved confocal fluorescence imaging of the intracellular distribution of BOPP in C6 glioma cells indicates distinct subcellular localization and heterogeneity of emission. The results are interpreted and discussed in terms of the possible mechanisms for cellular uptake and localization.
Picosecond Fluorescence of Merocyanines Derived from Photochromic Spironaphthoxazines
Authors: Monti Sandra , Malatesta Vincenzo , Bortolus Pietro , Magde Douglas
Published: January 2008

The emission of the merocyanines derived from the photochromic 1, 3, 3‐trimethylspiro[indoline‐2,3′[3H]naphth[2,1‐b][1, 4]oxazine] 1, the 4, 5‐dimethyl‐substituted compound 2 and the 6′‐piperidino‐substituted derivative 3, in solution with acetonitrile or ethanol, was studied by means of a time‐correlated single photon counting system with ca 10 ps time resolution. The signal decays were described by a sum of two or three exponential components with τ1=10–60 ps, τ2= 0.5–1ns, τ3=1–2 ns, corresponding to the contribution of different fluorescing merocyanine isomers. The most intense emission, the shortest lived one, is characterized by extremely low quantum yields (<10−6). The effect of the addition of LiClO4 to acetonitrile solutions of 2 is in agreement with the formation of ground‐state complexes with particular open isomers.
The Use of UV Radiation to Control the Architecture of Salvia splendens Plants. II. Relationships between PAR Levels and UV Radiation in the Photoregulation of Stem Elongation
Authors: Bertram Lise , Lercari Bartolomeo
Published: January 2008

The effects of UV irradiation on stem elongation of Salvia splendens plants preadapted to two and grown under four different irradiances of visible light, were studied using linear voltage differential transducers. The levels of radiant energy during the experimental phase showed a temporary and opposite effect during the day‐time and the night‐time: increasing levels of photosynthetically active radiation (PAR)† reduced stem growth during the day and enhanced elongation growth during the night. It appears, therefore, that similar final stem elongation in plants grown under very different PAR levels is the result of the algebraic sum of different and sometimes opposite effects of PAR on stem growth. Except for the controls, the plants received one UV treatment from Philips TL 12 40 W fluorescent tubes either in the middle of the light period or at the beginning of the dark period. The results show that the preadapting PAR conditions changed the sensitivity of the plants to both UV and to the following PAR conditions. The sensitivity of S. splendens to UV radiation is inversely correlated to the PAR levels before and during the UV treatments. Furthermore the presence of active photosynthetic and photomorphogenic systems, i. e. the presence of visible light during the UV treatment, decreases the sensitivity of the plants to UV radiation. Depending on PAR levels, the UV treatments given during the night induced a temporary inhibition of growth followed by a promotion of stem elongation.
Serine Conjugates of Chlorophyll and Bacteriochlorophyll: Photocytotoxicity in vitro and Tissue Distribution in Mice Bearing Melanoma Tumors
Authors: Rosenbach‐Belkin V. , Chen L. , Fiedor L. , Tregub I. , Pavlotsky F. , Brumfeld V. , Salomon Y. , Scherz A.
Published: January 2008

Chlorophyll (Chl) and bacteriochlorophyll (Bchl) have been made water soluble by transesterfication with serine (Ser) at the propionyl residue and tested as potential reagents for photodynamic therapy (PDT). Photocytotoxicity of the conjugates Chl‐Ser and Bchl‐Ser in M2R mouse melanoma was tested in cell cultures. Tissue uptake and clearance of the photosensitizers in CD1 nude and C57B1 mice implanted with M2R tumors are described. Photocytotoxicity in cell cultures was determined microscopically and by [3H]thymidine incorporation. The LD50 values in vitro were 0.05‐0.1 μM for both sensitizers while that of the commercially available hematoporphyrin derivative (HPD, Photosan) was over 100 times higher for the same light intensity (45 mW/cm2). Pigment concentrations were determined fluorometrically in acetone extracts of the tissues of interest at different times after intraperitoneal injection of 20 mg pigment/kg body weight. The distribution pattern of Chl‐Ser in the different tissues resembled that reported for Photofrin, chlorin and bacteriochlorin derivatives. Clearance from normal tissues was essentially completed within 16 h for Bchl‐Ser and 72 h for Chl‐Ser with mean half‐lives (t1/2) of about 2 and 7 h, respectively. In contrast, the clearance rates of these pigments and their metabolites from melanoma tumor tissue were significantly longer: t1/2= 20 h for Chl‐Ser and 15 h for Bchl‐Ser and metabolites. The clearance rates showed biphasic or single exponential decay patterns in normal tissues and in tumors, respectively. Cumulatively the high phototoxicity, simple mode of delivery and fast tissue clearance rates reported here suggest that polar conjugates of Chl and Bchl promise to be highly effective PDT reagents.
The Origin of Magnetic Field Dependent Recombination in Alkylcobalamin Radical Pairs
Authors: Natarajan Ettaya , Grissom Charles B.
Published: January 2008

Magnetic field effect studies of alkylcobalamin photolysis provide evidence for the formation of a reactive radical pair that is born in the singlet spin state. The radical pair recombination process that is responsible for the magnetic field dependence of the continuous‐wave (CW) quantum yield is limited to the diffusive radical pair. Although the geminate radical pair of adenosylcob(III)alamin also undergoes magnetic field dependent recombination (A. M. Chagovetz and C. B. Grissom, J. Am. Chem. Soc. 115, 12152–12157, 1993), this process does not account for the magnetic field dependence of the CW quantum yield that is only observed in viscous solvents. Glycerol and ethylene glycol increase the microviscosity of the solution and thereby increase the lifetime of the spin‐correlated diffusive radical pair. This enables magnetic field dependent recombination among spin‐correlated diffusive radical pairs in the solvent cage. Magnetic field dependent recombination is not observed in the presence of nonviscosigenic alcohols such as isopropanol, thereby indicating the importance of the increased microviscosity of the medium. Paramagnetic radical scavengers that trap alkyl radicals that escape the solvent cage do not diminish the magnetic field effect on the CW quantum yield, thereby ruling out radical pair recombination among randomly diffusing radical pairs, as well as excluding the involvement of solvent‐derived radicals. Magnetic field dependent recombination among alkylcobalamin radical pairs has been simulated by a semiclassical model of radical pair dynamics and recombination. These calculations support the existence of a singlet radical pair precursor.
Formation of Cyclobutane Thymine Dimers from UVA Photosensitization of Pyridopsoralen Monoadducted DNA
Authors: Guillo Lidia Andreu , Beylot Bénédicte , Vigny Paul , Spassky Annick
Published: January 2008

The present report provides evidence that thymine dimerization can be UVA photosensitized at a tetranucleotide, 5′‐TATT‐3′, by a 7‐methyl‐pyrido(3, 4‐c)psoralen monoadduct in DNA. The efficiency of the photoprocess depends on the tetranucleotide flanking sequences. These results demonstrate that one DNA lesion can originate the contiguous formation of a second type of lesion and emphasize the sequence‐specific response to interaction of drugs with DNA. Results are related to the sensitivity of DNA to 1, 10‐phenanthroline‐cuprous ion complex nucleolytic activity and discussed in terms of the major role of local deformability of DNA in interaction with ligands.
Determination of Fluorescence Polarization and Absorption Anisotropy in Molecular Complexes Having Threefold Rotational Symmetry
Authors: Demidov Andrey A. , Andrews David L.
Published: January 2008

Abstract— The current work concerns investigation of the polarization properties of complex molecular ensembles exhibiting threefold (C3) rotational symmetry, particularly with regard to the interplay between their structure and dynamics of internal energy transfer. We assume that the molecules or chromophores in such complexes possess strongly overlapped spectra both for absorption and fluorescence. Such trimeric structures are widely found in biological preparations, as for example the trimer of C‐phycocyanin (C‐PC). Higher order aggregates, e.g. hex‐amers and three‐hexamer rods, are also investigated and compared with the trimer case. The theory addresses both steady‐state and 8‐pulse excitation and establishes some links between them. Monochromophoric, bichro‐mophoric and trichromophoric molecular complexes are individually examined.

For steady‐state excitation, analytical formulas are reported for the degree of fluorescence polarization and absorption anisotropy. It is shown that the polarization is dependent on the chromophore inclination relative to the symmetry axis, the relative efficiencies of absorption and fluorescence by chromophores of different spectral types, and the rates of energy equilibration. To assess the validity of the theory, it has been applied to C‐PC aggregates. Here it was found that different C‐PC aggregates provide practically identical polarization response. For S‐pulse excitation we give analytical formulas for determination of the fluorescence depolarization, and also the depolarization associated with absorption recovery, both for a monochromophoric trimer and some particular cases of bichromophoric trimer. More complicated systems are analyzed by computer modeling. Thus it transpires that the initial polarization anisotropy r(t = 0) takes the value 0.4 for all considered aggregates; the long‐time limit r(t →∞) has about the same value as is associated with steady‐state excitation. We also show that with steady‐state excitation the degree of fluorescence polarization is practically equal for various C3 aggregates of C‐PC, and that the major factor determining the polarization is the chromophore orientation relative to the symmetry axis.
Role of Fapy Glycosylase and UvrABC Excinuclease in the Repair of UVA (320‐400 nm)‐mediated DNA Damage in Escherichia coli
Authors: Shennan Michael G. , Palmer Claire M. , Schellhorn Herb E.
Published: January 2008

Abstract— In contrast to the damage caused by far‐UV, the damage caused by UVA (320‐400 nm) is largely oxygen dependent, suggesting near‐UV‐mediated DNA damage involves reactive oxygen species. The DNA repair enzymes that recognize oxidized bases may, therefore, be an important part of the cell's near‐UV defense repertoire. To evaluate the relative importance of Fpg (Fapy) glycosylase (an enzyme known to remove oxidized bases) and the DNA damage‐inducible UvrABC excinuclease in recovery from near‐UV‐induced stress, we have constructed,fpg and uvrA derivatives of Escherichia coli and tested the response (survival) of these strains to both UVA and far‐UV radiation. Relative to control strains, the fpg‐ derivatives were found to be consistently more sensitive to the lethal effects of UVA, but not far‐UV radiation. In contrast, uvrA mutants were more sensitive than control strains to both UVA and far‐UV radiation. Thymine dimers, known to be produced by far‐UV and corrected by UvrABC, were not generated by the UVA fluences used in this study, suggesting that some other UVA‐induced lesion(s) is recognized and repaired by this excinuclease.