bluuebunny/crossref_metadata_2025 huggingface dataset:
GENETIC AND PHYSIOLOGICAL STUDIES OF THE EFFECT OF LIGHT ON THE DEVELOPMENT OF THE MOSS, PHYSCOMITRELLA PATENS
Authors: Cove D. J. , Schild A. , Ashton N. W. , Hartmann E.
Published: January 2008

The germination of Physcomitrella patens spores only occurs when wet spores are exposed to light. Depending on their ripeness, spores require from 44 to 64 h illumination to bring about maximum germination. There is a lag period of about 15 h between the reception of sufficient light to elicit germination before germination can be observed. Wavelengths in the range 640–64080 nm are much more effective in inducing germination than longer or shorter wavelengths, but far‐red reversal of red light induction of germination has not been demonstrated. Light also has very marked effects on protonemal and gametophore development. In darkness, only caulonemata are produced, and these grow negatively geotropically. No new gametophores develop but existing gametophores grow negatively geotropically, etiolate and bear only scale leaves. In light, chloronemata, as well as caulonemata are produced, the former grow positively phototropically, while the latter grow at right angles to the direction of light, and neither cell type is sensitive to gravity. In the light, gametophores grow positively phototropically, are indifferent to gravity, produce large leaves and do not etiolate. All these responses to light by protonemata and gametophores are shown by cultures growing in a 23 h dark/l h red light cycle, but if this red light treatment is followed by 15min far‐red light, the effect of the red light is reversed, indicating an involvement of phytochrome in the mediation of these responses. Mutants showing abnormal growth in the dark have been isolated, as well as mutants having abnormal phototropic responses. The latter type has lost the phototropic response of both the protonemal cell types, as well as of gametophores, indicating that these different responses may share a common component.
LIGHT‐DEPENDENT AND LIGHT‐INDEPENDENT PRODUCTION OF HYDROGEN GAS BY PHOTOSYNTHESIZING RHODOSPIRILLUM RUBRUM MUTANT C
Authors: Gorrell T. E. , Uffen R. L.
Published: January 2008

Abstract. Rhodospirillum rubrum mutant C grew photosynthetically in the light and produced copious amounts of H2. During light‐growth mutant C produced 7.9mmol of H2 in medium with 9mmol of Na‐pyruvate per mg protein. When parent strain R. rubrum S1 was grown similarly, these cells only produced a trace amount of H2. Light‐grown mutant C evolved H2 by H2‐nitrogenase and formic hydrogenlyase. Although both hydrogenases were previously detected in R. rubrum S1, the activities of the reactions in light‐grown mutant C were higher and they operated under different conditions. In the parent strain S1, the production of nitrogenase was strongly repressed during growth in medium enriched with organic nitrogen and the cells only reduced 0.06 pmol of acetylene per mg protein after 30 min in the light. Under similar conditions, nitrogenase activity measured by the acetylene reduction test in mutant C was 10‐fold greater. In addition to nitrogenase, mutant C also produced large amounts of H2 with formate as an intermediate when the cells were grown with Na‐pyruvate. Formic hydrogenlyase in mutant C operated equally well in anaerobic light or dark conditions. The analogous formate oxidation reaction in parent strain S1 only functioned in the dark. These data, compared with results with R. rubrum S1 suggested that C was a regulatory mutant. Additional observations suggested that formic hydrogenlyase occurred constitutively in R. rubrum. Pyruvate formate‐lyase, however, which produced formate for formic hydrogenlyase, was only detected in the cells after growth in media with Na‐pyruvate. The reaction was not formed when R. rubrum was grown in the light in media with dl‐malate as the sole carbon substrate.
265 NM LASER FLASH PHOTOLYSIS OF SOME ORTHO‐SUBSTITUTED ANILIDES AND RELATED N‐FORMYLKYNURENINE DERIVATIVES
Authors: Pileni M. P. , Santus R. , LAND E. J.
Published: January 2008

Abstract— The physical and chemical properties of the triplet state of eight ortho‐substituted anilides including N‐formylkynurenine (FK), the major trp UV‐photooxidation product and a remarkable photodynamic agent, have been investigated using both pulse radiolysis and 265 nm laser flash photolysis techniques. The molar extinction coefficient, the intersystem‐crossing quantum yield and the oscillator strength of the T1→Tn absorption band (Λmax˜ 450 nm) have been determined. It is shown that anilides having n,π* triplets readily react with most solvents whereas those having π,π* triplets slowly react with alcohols. In both cases, the semi‐reduced species are formed. In water, the formation of the semi‐reduced. species most probably involves the first excited singlet state. The triplet state properties of the FK derivatives (i.e. ortho‐substituted anilides having a side chain bearing charged groups such as carboxylic or amino groups) are strongly modified by the ionization state of the charged side chain. In the case of the FK derivatives possessing an uncharged amino group, quenching of the triplet state occurs via a fast reversible electron transfer reaction from the NH2 to the triplet anilide.
FLASH PHOTOLYSIS OF 3‐IODOTYROSINE IN AQUEOUS SOLUTION AT pH 5
Authors: Arvis M. , Kraljić I. , Girma J. P. , Morgat J. L.
Published: January 2008

Abstract— The 3‐tyrosinyl free radicals (3‐Tyr) and iodine atom are formed by flash photolysis of 3‐iodotyrosine (3‐Tyr‐I) in aqueous solutions at pH 5. The presence of iodine atoms in the medium is characterized by the absorption spectrum and the decay kinetics of I formed when KI is added to the system. In the absence of radical scavengers, the 3‐Tyr adds to or reacts with the parent molecule to produce a transient species, probably a radical dimer, which has an absorption maximum at 405 nm. The decay of this transient follows second order kinetics whose rate constant increases with decreasing 3‐iodotyrosine concentration. Measurements of the dependence of the transient yield on the concentration of added ethanol indicate that the 3‐Tyr radical reacts with ethanol by hydrogen abstraction. The rate constants of reaction of the 3‐Tyr radical with 3‐iodotyrosine and ethanol are deduced from results.
NEAR ULTRAVIOLET INDUCTION OF GROWTH DELAY STUDIED IN A MENAQUINONE‐DEFICIENT MUTANT OF BACILLUS SUBTILIS
Authors: Taber H. , Pomerantz B. J. , Halfenger G. M.
Published: January 2008

Abstract— The induction by near UV light of growth delay in Bacillus subtilis was studied utilizing a menaquinone‐deficient (men–) strain. Menaquinone appears to be a target molecule in this bacterial species, in view of the following: (i) the men– strain requires menaquinone precursors to terminate growth delay; (ii) the menaquinone synthesis inhibitor diphenylamine prolongs growth delay; (iii) the men– strain must be phenotypically Men* at the time of near UV irradiation to induce growth delay. These findings suggest that growth delay in B. subtilis may be associated with a prerequisite removal of photochemically altered menaquinone from the cytoplasmic membrane, rather than simply the time required for resynthesis of menaquinone. Alternatively, the altered menaquinone may inhibit some critical reaction(s) of intermediary metabolism or macromolecular synthesis.
ELECTRICAL RESISTANCE OF THE YELLOW STRIPS OF SOCIAL WASPS UNDER ILLUMINATION
Authors: Croitoru Nathan , Ishay Jacob S. , Arcan Lelia , Perna Bice
Published: January 2008

Abstract— The yellow strips usually present on the frons and the gaster of Vespinae and Polistinae have photoconductive properties. When the yellow strips of living as well as of dead wasps are initially illuminated their resistance increases until it reaches a saturation value after which photoconduction occurs.

Measurements of photoconductivity were carried out on the following hornet and wasp species: Vespa orientalis, V. crabro, V. mongolica, V. mandarinia, V. analis, V. sulphured, Vespula atropilosa, Vespula maculato (Vespinae) and Apoica pallida (Polistinae).

Qualitative and quantitative differences in photoconduction were detected between wasps (or hornets) of the same species but from different castes, wasps of the same caste but at different ages, and between wasps of diurnal and nocturnal species. The photoconductive yellow strips and the non‐photoconductive brown strips of the cuticle of the same segment were morphologically compared. To obtain information on the energy of incident light necessary to produce the increased resistance and the consequent photoconduction, the spectral distribution of the photoconduction was also measured.
AN INFRARED STUDY OF THE BASICITY OF NON‐AROMATIC IMINES: RELATION TO VISUAL PIGMENTS
Authors: Favrot J. , Sandorfy C. , Vocelle D.
Published: January 2008

Abstract— The knowledge of the basicity of non‐aromatic Schiff‐bases is important for the interpretation of the photochemical primary step of vision. In order to obtain an estimate of it, the infrared spectra in chloroform d solution of a number of aliphatic amines, pyridine derivatives and non‐aromatic Schiff‐ bases have been measured. From the known pKa values of the aliphatic and pyridine bases and the free‐associated frequency shift (Av) of the C—D. N hydrogen bonds, the pKa values for the Schiff‐bases were inferred. They range from 6 to 8. 5, less basic than aliphatic amines but somewhat more basic than pyridine bases.
FLUORESCENCE PROPERTIES OF HUMAN ADULT APOHEMOGLOBIN AND ITS SUBUNITS
Authors: Lindqvist L. , Lopez‐Campillo A. , Alpert B.
Published: January 2008

Abstract. Fluorescence excitation, emission and quantum yields for human A apohemoglobin and its subunits have been examined and compared to those of horse heart apomyoglobin, a single subunit protein.
ANALYSIS OF MICROSECOND FLUORESCENCE YIELD AND DELAYED LIGHT EMISSION CHANGES AFTER A SINGLE FLASH IN PEA CHLOROPLASTS: EFFECTS OF MONO‐ AND DIVALENT CATIONS
Authors: Wong D. , Jursinic P.
Published: January 2008

Abstract. New results are presented on the effects of mono‐ and divalent cations on concurrent changes in the microsecond yields and kinetics of chlorophyll a fluorescence and delayed light emission, and the light saturation curve for the latter at 100 μs, following a 10 ns flash at 337 nm. (1) The fluorescence yield increases exponentially from 3 to 30 μs (lifetime, τ, 6.4 ± 0.6/μs), and decays biphasically between 50 and 800μs. (2) The delayed light emission decays biphasically with two exponential phases: fast phase, T= 7–10μs, and slow phase, T= 33–40μs. (3) The light saturation curve for 100μs delayed light emission is satisfactorily represented by a one‐hit Poisson saturation curve. (4) Addition of 5 mM NaCl to salt‐depleted chloroplasts decreases (by as much as 40%) the yields of μs fluorescence and delayed light emission, and the subsequent addition of 5mM MgCl2 increases the yields (≤2 × over samples with only NaCl). (5) The fluorescence yield rise and delayed light emission decay kinetics are independent of low concentrations of cations. The lifetime of the fast phase of fluorescence decay changes from ˜90μs to ˜160μs, when Na+ or Na++ Mg2+ are added.

Based on a detailed analysis presented in this paper, the following conclusions regarding the effects of low concentrations (few mM) of mono‐and divalent cations in sucrose‐washed chloroplasts at room temperature are made: (a) Na+ decreases (˜6%) and Mg2+ increases (˜ 20% compared with the Na+ sample) the sensitization of photosystem II photochemistry: this effect is small, but significant. (b) Na+ increases and Mg2+ decreases the efficiency for radiationless transitions in singlet excited Chl a in the antenna and closed reaction center of PS II; this includes non‐radiative energy transfer to PS I, intramolecular intersystem crossing and internal conversion. The ratio of the sum of the rate constants for radiationless transitions to that for fluorescence increases by ˜ 2‐fold upon the addition of Na+, and is completely reversed by the addition of Mg2+. (c) The rate constant for the re‐oxidation of Q‐ decreases (about 50%) in the presence of Na+ or Na++ Mg2+. These conclusions imply that cations produce multiple changes in the primary photoprocesses of PS II at physiological temperatures. It is proposed that these changes are mutually independent and can co‐exist.
PHOTOCHEMICAL INTERACTION BETWEEN XANTHYLETINE AND DNA
Authors: Dall'acqua F. , Bordin F. , Vedaldi D. , Recher M. , Rodighiero G.
Published: January 2008

Abstract— Xanthyletine, a dimethyl‐pyranocoumarin having a structural relationship to psoralen, has been studied in connection with its interaction with DNA. In the dark, it forms a weak molecular complex with DNA, which is not of the intercalated type. Under irradiation at 365nm, it is able to bind covalently to DNA, with, however, a much lower rate relative to psoralen. In this photobinding, it behaves as a pure monofunctional reagent, involving only its3,4‐double bond of the α‐pyronic ring.

3‐(α,α‐dimethyl‐allyl)‐xanthyletine, studied for a comparison, showed only a very low photoreactivity with DNA for covalent addition; this is attributed to the presence of a bulky group at position3, which prevents almost completely the photoreaction of the3,4‐double bond.

Because of the low capacity of photobinding with DNA and the inability to form cross‐links, the photobiological effects of xanthyletine are accordingly reduced: Inhibition of DNA and RNA synthesis in Ehrlich ascites tumor cells, killing of E. coli bacterial cells, inactivation of T2 bacteriophage have been observed. By contrast, it was inactive in producing erythema on guinea pig skin.
EFFECT OF NEAR‐ULTRAVIOLET IRRADIATION ON PLANARIA*
Authors: Spencer H. Todd , Klelnt Richard M.
Published: January 2008

Abstract— Near‐UV radiation in the UV‐B range prevented regeneration of segments of the turbellarian worm, Planaria. and reduced survival of intact animals as a direct function of the fluence supplied. Survival was photoperiod dependent suggesting dark‐repair capacity. Near‐UV radiation induced melanogenesis
PHOTOCHEMICAL DECOMPOSITION OF CATECHOLAMINES—II.* THE EXTENT OF AMINOCHROME FORMATION FROM ADRENALINE, ISOPRENALINE AND NORADRENALINE INDUCED BY ULTRAVIOLET LIGHT
Authors: Mol N. J. de , Henegouwen G. M. J. Beijersbergen van , Gerritsma K. W.
Published: January 2008

Abstract— During photochemical decomposition (Λ= 254 nm) adrenaline, isoprenaline and noradrenaline in aqueous solution are converted to the corresponding aminochrome for 65, 56 and 35%,. respectively. In determining this conversion, photochemical instability of the aminochromes is taken into account. Irradiations are performed in such dilute solutions that the neglect of the inner filter effect is permissible. Furthermore. quantum yields for the decomposition of the aminochromes in aqueous solution are given.
STUDIES ON AMINODIOXETANES AS A MODEL OF BIOLUMINESCENCE INTERMEDIATES. 1‐(1‐METHYL‐3‐INDOLYL)‐6‐PHENYL‐2,5,7,8‐TETRAOXABICYCLO[4,2,0]OCTANE, AN AMINODIOXETANE RESULTING IN EFFICIENT ULTRAVIOLET AND EXCIPLEX CHEMILUMINESCENCE*
Authors: Nakamura Hideshi , GOTOT Toshio
Published: January 2008

Abstract— The title aminodioxetane prepared by photooxygenation of 2–(l‐methyl‐3‐indolyl‐3‐phenyl‐1,4‐dioxene is fairly stable at −46°C and gives on warming to room temperature an ultraviolet light at Λmax 320 nm, which corresponds to 377kJ/mol; the highest energy ever observed among the efficient chemiluminescent compounds. The efficiency of chemiluminescence and excited singlet molecule formation in n‐hexane were 3.6% and at least 50%, respectively. Substitution and solvent effects suggest polar nature of the transition state as expected from the ‘CIEEL’ mechanism. In polar solvents, the dioxetane gives visible light (Λmax 400 nm in dichloromethane) as well as the UV light; the former being quenched by methanol. This is interpreted in terms of an intramolecular exciplex formation between the indole and phenyl groups. This is the first example of an intramolecular exciplex produced by the dioxetane decomposition.
THE OXIDATION OF CHOLESTEROL BY HYDROXYL RADICAL
Authors: Ansari G. A. S. , Smith Leland L.
Published: January 2008

Abstract— The oxidation of chblesterol by hydroxyl radical generated by 60Co y‐radiolysis of aqueous cholesterol dispersions or of dispersions saturated with N2O ave in low yields the products 38‐hydroxy‐cholest‐5‐en‐7‐one. the epimeric cholest‐5‐ene‐3β,7‐diols, 5,6α‐epoxy‐5α‐cholestan‐3β‐ol, 5.6β‐epoxy‐5β‐cholestan‐3,β‐ol, and 5α‐cholestane‐38,5,6β‐triol. Sterol hydroperoxides were not detected except in the radiolysis of dispersions saturated with oxygen.
THE WAVELENGTH DEPENDENCE OF 8‐METHOXYPSORALEN PHOTOSENSITIZATION OF HOST CAPACITY INACTIVATION IN A MAMMALIAN CELL‐VIRUS SYSTEM
Authors: Coohill Thomas P. , James Leslie C.
Published: January 2008

Abstract— The addition of 8‐methoxypsoralen to cultures of African green monkey cells (CV‐I) sensitized the inactivation by near UV radiation (302–370 nm) of the ability of the cells to host herpes simplex virus. No sensitizing effect by drug addition was noted for far UV radiation (232–297 nm). An action spectrum for the photosensitized inactivation of this cellular parameter was obtained. This action spectrum is consistent with the absorption spectrum of 8‐methoxypsoralen.
PHOTODYNAMIC CYTOTOXICITY OF MAMMALIAN CELLS EXPOSED TO SUNLIGHT‐SIMULATING NEAR ULTRAVIOLET LIGHT IN THE PRESENCE OF THE CARCINOGEN 7,12‐DIMETHYLBENZ(a)ANTHRACENE
Authors: Utsumi H. , Elkind M. M.
Published: January 2008

Abstract— The coal‐derived carcinogen 7,12‐dimethylbenz(a)anthracene (DMBA), added to cultures of V79 Chinese hamster, C3H mouse 10T1/2, and human HeLa cells, enhances photolethality induced by the sunlight‐simulating emission from Westinghouse Sun Lamps (‐ 29˜100 nm) but only in the presence of O2. Treatment of cells with DMBA after irradiation is without lethal effect; the endoperoxide of DMBA is ineffective both before as well as after irradiation, and DMBA incubation before far‐UV exposure (254 nm) is protective. Cells rendered photosensitive by incubation with DMBA rapidly lose their sensitivity (in < 10 min, 37°C) if incubated in a DMBA‐free solution containing serum, but maintain their sensitivity at least for several hours if a serum‐free solution is used. Although DMBA enhances light‐induced killing of cells in all phases of the cycle, those undergoing DNA syntheses are preferentially sensitized. The data support photodynamic lethality due to one or both of the following: (1) the reaction with DNA of either DMBA radicals followed by oxidation, or DMBA‐produced singlet oxygen; or (2) the peroxidation of lysosomal membranes followed by the release of hydrolases including DNAses. As a model system of the combined effects of a fossil‐fuel derived polycyclic aromatic hydrocarbon and sunlight, the results with DMBA + near‐UV are discussed in the context of altered cell properties (e.g. neoplastic transformation) in sublethally affected cells.
PHYSICOCHEMICAL DETERMINANTS OF THE SENSITIZING EFFECTIVENESS FOR PHOTOOXIDATION OF NERVE MEMBRANES BY FLUORESCEIN DERIVATIVES
Authors: Pooler John P. , Valenzeno Dennis P.
Published: January 2008

Abstract— Fluorescein and 8 of its halogenated derivatives were employed as sensitizers for the photochemical block of sodium channels on giant nerve axons from lobsters. Axons were voltage clamped using a double sucrose gap technique and illuminated by filtered light from a Xe arc following exposure to sensitizer at concentrations of 5 µM or less dissolved in the external bath. An assay for the magnitude of sensitizing effectiveness was developed consisting of the rate constant for block of channels during illumination scaled to the rate of photon capture in a thin layer of bathing solution. The kinetics for development of effectiveness during pre‐illumination periods of up to 16‐min duration varied widely for different derivatives despite similarities in molecular structure. At a standard 8‐min pre‐illumination exposure, the relative effectiveness extended over a 30,000‐fold range. A model system consisting of octanol and the artificial sea‐water (ASW) bathing solution was compared with the axon membrane and its environment. Octanol/ASW partition coefficients were measured for each sensitizer as well as the relative absorption in the 2 solvents at equal concentrations. Predicted values of relative sensitizing effectiveness based on the product of partition coefficient, relative absorption in octanol and mol wt of the substituents on the fluorescein skeleton were found to correlate highly with measured values. The diffusion kinetics prior to illumination correlated inversely with partition coefficients, suggesting that the more permeable sensitizers may penetrate into diffusion sinks, thus slowing the rise in concentration at sites for modification. It is concluded that sensitizers must penetrate into the membrane in order to sensitize and that the photochemistry appropriate for a low polarity environment controls the degree of membrane modification following photon capture.
APPARENT INCREASE IN PHOTODETECTABLE PHYTOCHROME IN THE PRESENCE OF CALCIUM CARBONATE*
Authors: Boisard Jean , Cordonier Marie‐Michéle , Gabriac Brigitte , Marmé Dieter , Pratt Lee
Published: January 2008

Abstract— –Using squash seedling extracts (Cucurbita pepo L.), we describe an apparent increase in photodetectable phytochrome content that is depended upon the use of either CaCO3 or starch as a scattering agent and is also a function of preirradiation with red light of either intact tissue or crude extracts prior to sample preparation for spectrophotometric assay. This apparent increase in photodetectable phytochrome content requires about 1 h for full expression after addition of the scattering agent. If irradiations are given in vitro, the increase is partially reversed by far red light when using squash extracts, and is fully reversed with Aoena and Zea extracts. For squash extracts the magnitude of this increase. which is typically between 20 and 40%. is quantitatively correlated with both the amount of Pfr produced by a brief red irradiation and with the proportion of the total phytochrome pool that is pelletable upon centrifugation at 20,000 g. The correlation with pelletable phytochrome does not hold for Auena and Zea, at least when irradiations are gwen in uitro. The increase in photodetectable phytochrome may result from changed phytochrome extinction, changed phototransformation quantum yields, and/or specific trapping of phytochrome by the scattering agent as it settles. An important consequence of these data is that they indicate a need for caution when using a scattering agent during spectrophotometric assay of phytochrome.
TWO NEW METHODS OF ACTINOMETRY FOR EPR‐MEASUREMENTS
Authors: Moan J. , Høvik B. , Wold E.
Published: January 2008

Abstract— Two methods to perform actinometry in an EPR‐cavity are described. One method is based on the observation that photoproduced anion radicals of hematoporphyrin react with the stable free radical 2,2,6,6‐tetramethyl‐4‐piperidone‐N‐oxyl to eliminate the spin. The other method is based on the dye sensitized photoproduction of nitroxyl radicals resulting from the reaction of singlet oxygen with sterically hindered amines.
ULTRAVIOLET ACTION SPECTRUM (238–405 nm) FOR INHIBITION OF GLYCINE UPTAKE IN E. COLI*
Authors: Ascenzi Joseph M. , Jagger John
Published: January 2008

Abstract— Initial rate of uptake of 3H‐glycine by Escherichia coli B/r was measured immediately after irradiation with monochromatic light. Uptake was proportional to time for at least 2 min in both control and irradiated samples. Inhibition of uptake is an exponential function of fluence to about 20% remaining activity, beyond which it is much more resistant to irradiation, suggesting two different uptake systems. The principal (sensitive) system shows an F37 of 2.2 kJ/m2 at 280 nm and 110 kJ/m2 at 334 nm. The response is independent of cell killing and of presence of the rel gene. The chromophore remains unidentified, although an action spectrum suggests a protein chromophore in the far‐UV (below 300 nm) region and a menaquinone chromophore in the near‐ultraviolet (above 300 nm).

A 10–20%, stimulation of uptake rate, which we cannot account for, is observed at low fluences (generally below 100 kJ/m2) at 313, 366 and 405 nm, but not at 334 nm.
SOME FURTHER CONSIDERATIONS ON THE USE OF REPAIR‐DEFECTIVE ORGANISMS AS BIOLOGICAL DOSIMETERS FOR BROAD‐BAND ULTRAVIOLET RADIATION SOURCES
Authors: Calkins John , Barcelo Jeanne A.
Published: January 2008

Abstract— The extreme variation in biological effectiveness of the various components of solar ultraviolet radiation (solar UV) which reaches the earth's surface, especially photons of wavelengths between 295 and 330 nm, makes the dosimetry of solar UV a complex and, as yet, unresolved problem. A proper weighting of the various components of solar UV would permit expression of expsoure as a single parameter (dose). Weighting could compensate for the variations in composition of solar UV which might occur during exposure or the differences in sources of UV radiations; weighting would permit comparison of exposures at various locations on the earth and extrapolation of laboratory observations to field situations where wavelength composition might be rather different. Various radiation‐sensitive microorganisms have been proposed as biological dosimeters. Biological dosimeters automatically weight the subcomponents of solar UV differently than a purely physical irradiance meter. We have examined the available evidence regarding the weighting which repair‐defective mutants provide in comparison with response of a number of wild‐type organisms and would caution investigators that, for broad‐band UV sources, especially those with significant biological actions through the range of 300–330 nm, repair‐sensitive mutants may improperly weight the components, leading to errors of dosimetry and thus to possible errors of interpretation of results of solar UV exposure of wild‐type organisms
TRIPLET EXCITED STATES OF PYRIMIDINE NUCLEOSIDES AND NUCLEOTIDES
Authors: Salet C. , Bensasson R. , Becker R. S.
Published: January 2008

Abstract— The triplet absorption spectra, lifetimes, extinction coefficients, eTT, and intersystem crossing quantum yields to the lowest triplet T1, øT1, of thymidine, thymidine monophosphate, uridine and uridine monophosphate, have been determined in various solvents at 300 K.

The effect of H‐bonding on øT1, of these nucleosides and nucleotides and also of uracil has been determined and discussed. This effect allows, an ordering of l,3n, π* and 1,3π, π* states in protic and aprotic solvents.
CHLOROPHYLL a FLUORESCENCE OF GONYAULAX POLYEDRA GROWN ON A LIGHT‐DARK CYCLE AND AFTER TRANSFER TO CONSTANT LIGHT
Authors: Govindjee  , Wong D. , Prézelin Barbara B. , Sweeney Beatrice M.
Published: January 2008

Abstract— The chlorophyll a fluorescence properties of Gonyaulax polyedra cells before and after transfer from a lightdark cycle (LD) to constant dim light (LL) were investigated. The latter display a faster fluorescence transient from the level ‘I’ (intermediary peak) to ‘D’ (dip) to ‘P’ (peak) than the former (3 s as compared to 10 s), and a different pattern of decline in fluorescence from ‘I’ to ‘D’ and from ‘P’ to the steady state level with no clearly separable second wave of slow fluorescence change, referred to as ‘s' (quasi steady state)→‘M’ (maximum) →‘T’ (terminal steady state). The above differences are constant features of cells in LD and LL, and are not dependent on the time of day. They are interpreted as evidence for a greater ratio of photosystem II/photosystem I activity in cells in LL.

After an initial photoadaptive response following transfer from LD to LL, the cell absorbance at room temperature and fluorescence emission spectra at 77 K for cells in LL and LD are comparable. The major emission peak is at 685–688 nm (from an antenna Chl a 680, perhaps Chl a‐c complex), but, unlike higher plants and other algae, the emission bands at 696–698 nm (from Chl aII complex, Chl a 685, close to reaction center II) and 710–720 nm (from Chl a1, complexes, Chl a 695, close to reaction center I) are very minor and could be observed only in the fluorescence emission difference spectra of LL minus LD cells and in the ratio spectra of DCMU‐treated to non‐treated cells.

Comparison of emission spectra of cells in LL and LD suggested that, in LL, there is a slightly greater net excitation energy transfer from the light‐harvesting peridinin‐Chl a (Chl a 670) complex, fluorescing at 675 nm, to the other antenna chlorophyll a complex fluorescing at 685–688 nm, and from the Chl a., complex to the reaction center II. Comparison of excitation spectra of fluorescence of LL and LD cells, in the presence of DCMU, confirmed that cells in LL transfer energy more extensively from the peridinin‐Chl a complex to other Chl a complexes than do cells in LD.
REPAIR OF PSORALEN PLUS NEAR ULTRAVIOLET LIGHT DAMAGE IN BACTERIOPHAGE T4
Authors: Zerler Bradley R. , Wallace Susan S.
Published: January 2008

Abstract— The sensitivity of bacteriophage T4 to psoralen plus NUV was investigated using a series of T4 repair defective mutants. The recombinational repair deficient mutants T4x, T4y and T4w were more sensitive than wild‐type; while T4v, an endonuclease V mutant, exhibited the same sensitivity as wild‐type. However, endonuclease V appears to initiate abortive repair in the absence of the x and presumably y gene products. Host repair gene products were shown not to be involved in the repair of psoralen plus NUV damages in T4.
ASSIGNING THE RESONANCE RAMAN SPECTRAL FEATURES OF RHODOPSIN, ISORHODOPSIN AND BATHORHODOPSIN IN BOVINE PHOTOSTATIONARY STATE SPECTRA‡
Authors: Marcus Michael A. , Lewis Aaron
Published: January 2008

Abstract—High resolution resonance Raman spectra of rhodopsin. isorhodopsin and photostationary state mixtures containing a high percentage of bathorhodopsin arc presented. New spectral features are detected which were not obsei‐ved in lower resolution studies by other workers. All of the hands in the photostationary state spcctra arc assigned based on pure rhodopsin and isorhodopsin resonance Raman results and alterations in the photostationary state mixture. The spectral features in these spectra are invariant from 20 to 150K indicating that retinal and protein structural alteration, consistent with a model of excitation proposed by Lewis, occurs in steady‐state spectra even at 20 K. In addition, the relative intensity of certain features in the photostationary state spectra are altered upon D2O suspension. One explanation for these alterations is that the contributions of various intcrmediates to the photostationary state mixture are changed when membrane fragments are suspended in D2O.
EXCITATION WAVELENGTH DEPENDENCE OF PROTOTROPIC DISSOCIATION AND TAUTOMERISM OF SALICYLAMIDE IN THE LOWEST EXCITED SINGLET STATE
Authors: Schulman Stephen G. , Underberg Willy J. M.
Published: January 2008

Abstract—The fluorescence spectra of salicylamide in cyclohexane, ethanol and at different pH in water were studied. The short and long wavelength fluorescences observed in the organic solvents originate from emissions of a weakly or non‐intramolecularly hydrogen bonded conformer and from phototautomerization of a strongly intramolecularly hydrogen bonded conformer, respectively. Evidence for at least 2 conformers in the ground state exists in the excitation wavelength dependence of the ratio of short wavelength to long wavelength emission. In water, prototropic dissociation of the phenolic group of salicylamide in the lowest excited singlet state also shows an excitation wavelength dependence, indicating that the weakly or non‐intramolecularly hydrogen bonded conformer in water is predominately responsible for photodissociation.
EFFECT OF INTENSITY AND WAVELENGTH OF FLUORESCENT LIGHT ON CHROMOSOME DAMAGE IN CULTURED MOUSE CELLS
Authors: Parshad Ram , Sanford Katherine K. , Taylor William G. , Tarone Robert E. , Jones Gary M. , Baeck Anne E.
Published: January 2008

Abstract—A single 3‐ to 20‐hr exposure of line NCTC 9266 mouse cells to cool‐white fluorescent light (4.6 W/m2) produces chromatid breaks and exchanges. The effective wavelength is in the visible range and coincides with the mercury emission peak at 405 nm. Increasing light intensity from 4.6 W to 15.3 W/m2 for 20 h causes a concomitant increase both in production of chromosome damage and formation of hydrogen peroxide (H2O2) in the serum‐free medium. Cells washed free of medium and illuminated in saline for 3 h show chromosome damage to the same extent as cells illuminated in culture medium. Addition of catalase during the exposure period of 3 h eliminates the light‐induced damage. We conclude that the light‐induced chromatid breaks and exchanges result from H2O2 production within the cell and that exogenous catalase can enter the cell and prevent the damage.
FLUORESCENCE OF COMPLEXES OF QUINACRINE MUSTARD WITH DNA. I. INFLUENCE OF THE DNA BASE COMPOSITION ON THE DECAY TIME IN BACTERIA
Authors: Bottiroli G. , Prenna G. , Andreoni A. , Sacchi C. A. , Svelto O.
Published: January 2008

Abstract—

The fluorescence of several bacterial DNAs stained with quinacrine mustard have been investigated using a laser microfluorometer with a spatial resolution of ‐ 0.3 μm and a temporal resolution of ˜0.3 ns connected to a digital signal averager.

Experiments performed on Micrococcus lysodeikticus samples show that both cytological preparations and the corresponding purified DNAs give coincident fluorescence curves, thus indicating that the fluorescence observed in the former case is to be attributed to the bacterial DNA only. Experiments thereafter performed on smears of several bacteria with known AT percentages show that each fluorescence decay curve, after a fast transient, can be fitted by an exponential decay law with a single time constant. This time constant has been found to depend linearly on the square of the AT percentage.

We explain this result on the basis of an energy transfer mechanism between dye molecules intercalating AT:AT sequences (donors) and dye molecules bound to either GC:GC or GC:AT sequences (acceptors). The agreement with the experimental data requires that all the bacteria considered present a common value for both the number of base pairs contained in a Förster sphere and for the maximum saturation of the strong binding process.
TRIPLET‐TRIPLET ENERGY TRANSFER IN P‐TRYPSIN 1 THE ROLE OF THE INDOLE TRIPLET IN THE ULTRAVIOLET‐INDUCED PHOTOLYSIS OF β‐TRYPSIN
Authors: Ramachandran N. , Ghiron C. A.
Published: January 2008

Abstract—

Detection of triplet‐triplet energy transfer in an aqueous solution of P‐trypsin is reported. This conclusion is based on the observation that a light excited phenolate side chain can sensitize the destruction of an adjacent indole side chain. The role that the indole triplet might play in the UV‐induced photolysis of /l‐trypsin is also investi‐gated. The results suggest that the UV (309 nm)‐induced inactivation of P‐trypsin is not caused by indole ring destruction but by the disruption of disulfide bonds without thiol formation.
FACTORS INFLUENCING THE NEAR‐UV EFFECT ON DNA IN THE PRESENCE OF 8‐METHOXYPSORALEN: RENATURABILITY OF DNA.
Authors: Fujita Hitoshi , Sano Miyaharu , Suzuki Kenshi
Published: January 2008

Abstract—

Factors affecting the near‐UV induced reaction of calf thymus DNA in the presence of 8‐methoxypsoralen were examined. DNA became more renaturable with increasing concentration of 8‐methoxypsoralen and fluence. Existence of paramagnetic ions, Mn2+, Co2+, or Ni2+, largely repressed the photoreaction. It was ascertained that the highest renaturability was attained by the illumination with light between 310 and 345 nm.
SEASONAL PHOTOSENSITIVITY OF BLEPHARISMA: THE ROLE OF TEMPERATURE
Authors: Glese Arthur C.
Published: January 2008

Abstract—

Red blepharismas (B. japonicum) in Pyrex test tubes exposed near noon to clear summer daylight are killed. If similarly exposed at dawn, they turn blue as the red pigment blepharismin is oxidized to oxyblepharismin. and they resist further exposure to daylight. Red blepharismas similarly exposed to sunlight at dawn in winter are killed. The experiments reported seek the reasons for the seasonal difference in photosensitivity and the way in which blepherismas survive winter.

Red blepharismas (B. japonicum) exposed to visible and near ultraviolet (UV) radiation from two 4W coolwhite fluorescent lamps (5 Wm‐2; 2151ux) resist an 8h exposure between 15° and 34°C. turning blue. Blue and colorless blepharismas also resist 8h exposures to the light at 15° and 34°C. At 8°C both red and blue populations are killed, death appearing to result from deranged water regulation; colorless ones are not affected.

Red blepharismas are killed by fluorescent light at 8° C even when the near‐UV radiation is largely excluded by a Corning glass filter; blue and colorless ones are not. The reds are also killed at all temperatures by sunlight filtered through Pyrex glass if exposed near noon on a sunny day. At temperatures above 8° C they are not killed by direct sunlight passed through glass if exposed at dawn, but they turn blue. Blepharismas in fluorescent light divide at the same rate as controls in the dark, but they get smaller.

When exposed to sunlight at dawn, at temperatures above 8°C. blepharismas in Pyrex test tubes containing stones or fruiting spikes of grass, hid in the shade of these objects, apparently by random movements. If exposed under similar conditions near noontime, the majority failed to find cover and were killed. Blepharismas survive in summer by avoiding sunlight, in winter by encystment.

Colorless protozoans Paraineciurn multimicronucleatum, Colpidium colpoda and Spirostomum teres resisted killing in summer sunlight and with fluorescent light at all temperatures tested.
THE DETERMINATION OF PERIODICITIES IN SHORT‐TERM TIME‐SERIES DATA IN THE PRESENCE OF HIGH FREQUENCY NOISE AND LONG‐TERM TREND
Authors: Hopkins D. W. , Deitzer G. F. , Wagner E.
Published: January 2008

Abstract—

The presence of periodicities in biological data may often be obscured by superposition of a background trend or high frequency oscillations. A method of least squares curve fitting was utilized to remove the trend in signal level. Subsequent removal of higher frequency noise utilizing smoothing convolution functions allows the determination of rhythmic components. A new “noise” convolution function gives a measure of the noise in data containing both signal and noise and allows the estimation of a limit above which an observed oscillation is considered significant. The effects of treating data with these convolution functions are discussed with reference to amplitude‐frequency response curves. The results of data analysis utilizing convolution functions are compared with results obtained utilizing a moving interval Fourier technique (Blume, 1965). The convolution analysis have the advantages that they are easily programmed and rapidly calculated by programmable calculators, give results relatively insensitive to the length of convolution interval, and allow estimation of the variation in period and amplitude of the rhythm investigated.
PHOTOCHEMICAL GENERATION OF REDUCED QUINONE CATALYSTS OF PHOTOSYSTEM I CYCLIC PHOTOPHOSPHORYLATION ACTIVITY
Authors: Robinson Howard H. , Yocum Charles F.
Published: January 2008

Abstract—

When reaction mixtures containing 9,10‐anthraquinone‐2‐sulfonate and chloroplasts poisoned with 3–(3,4‐dichlorophenyl)‐l, l′‐dimethylurea were illuminated with white light, photosystem I‐catalyzed cyclic photophosphorylation was observed. Illumination of identical reaction mixtures with red light produced no ATP synthesis. This phenomenon is due to photoreduction of the anthraquinone which is supported by the electron donor activity of Tricine buffer. The photoreduction reaction was used to generate reduced catalysts (anthraquinone sulfonate, menadione bisulfite) of photosystem I cyclic photophosphorylation activity. The rates of ATP synthesis obtained by this method (250–300 μmol/h‐mg chlorophyll) indicate that sulfonated quinones are efficient mediators of cyclic electron transport around photosystem I. Although the activity catalyzed by these compounds is highly sensitive to dibromothymoquinone, very little decrease in activity is observed with antimycin A.
SPECTRAL CHARACTERIZATION OF MONOMERIC C‐PHYCOERYTHRIN FROM PSEUDANABAENA W 1173 AND ITS α AND β SUBUNITS: ENERGY TRANSFER IN ISOLATED SUBUNITS AND C‐PHYCOERYTHRIN
Authors: Zickendraht‐Wendelstadt Barbara , Friedrich Josef , Rüdiger Wolfhart
Published: January 2008

Abstract— Molecular weight determination by gel chromatography and analytical ultracentrifugation revealed that C‐phycoerythrin from Pseudanabaena W 1173 exists as the monomer ∝βat a concentration up to 7μM and as the dimer (∝β)2 at 40 μM. The purified subunits were monomeric species ∝ or β, respectively at 20 μM. Native monomeric C‐phycoerythrin was compared with the renatured subunits in a number of spectral properties: absorption spectroscopy including determination of molar extinction coefficients, fluorescence emission and excitation at 293 and 4 K, and fluorescence polarization. Whereas spectra of denatured subunits and denatured C‐phycoesythrin are identical, substantial changes occurred upon renaturation. Linear superposition of the absorption spectra of renatured subunits results in a curve identical with the absorption of native monomeric C‐phycoerythrin.

The following conclusions were drawn: (a) Chromophore conformation is identical in renatured subunits and in native αβ monomer of C‐phycoerythrin. (b) In C‐phycoerythrin there are two fluorescing chromophores, degenerate in energy, one in the α‐ and the other in the β‐subunit and three sensitizing chromophores which differ in their energies and spectral shapes, (c) The energy transfer in C‐phycoerythrin occurs not only within but also between the subunits. (d) A weak fluorescence from sensitizing chromophores observed at low temperature (4 K) in the α‐subunit and in C‐phycoerythrin shows the limitations of the concept of sensitizing chromophores.

C‐PE, C‐phycoerythrin; P, degree of polarization; R, degree of anisotropy; SDS, sodium dode‐cyl sulfate; s20, sedimentation coefficient
TRIPLET EXCITED STATE OF THE 4'5' PHOTOADDUCT OF PSORALEN AND THYMINE
Authors: Bensasson R. V. , Salet C. , Land E. J. , Rushton F. A. P.
Published: January 2008

Abstract— The triplet‐triplet absorption spectrum of the 4'5' psoralen‐thymine mono‐adduct has been determined in water and methanol using the technique of laser flash photolysis. The extinction coefficient of the triplet was measured by the energy‐transfer method with retinol triplet as standard, and used to determine the singlet → triplet intersystem crossing quantum yield for 353 nm excitation. Reaction rate constants for mono‐adduct triplet with thymine and tryptophan were measured in water. Long‐lived transient absorptions detected after quenching the mono‐adduct triplet with thymine and tryptophan are assigned mainly to the corresponding mono‐adduct radical anion, whose spectrum was established in separate pulse radiolysis studies of the mono‐adduct in aqueous formate.

The significant singlet → triplet quantum yields found for the mono‐adduct might be consistent with the involvement of triplet excited mono‐adduct in DNA cross‐link formation, as also may be the high reactivity obtained for the triplet with thymine. The initial quenching products observed resulted from a charge‐transfer reaction.
STEREOELECTRONIC PROPERTIES OF PHOTOSYNTHETIC AND RELATED SYSTEMS—VII. AB INITIO QUANTUM MECHANICAL CHARACTERIZATION OF THE ELECTRONIC STRUCTURE AND SPECTRA OF CHLOROPHYLLIDE a AND BACTERIOCHLOROPHYLLIDE a CATION RADICALS
Authors: Petke J. D. , Maggiora Gerald M. , Shipman Lester L. , Christoffersen Ralph E.
Published: January 2008

Abstract— Ab initio configuration interaction wavefunctions and energies are reported for 29 doublet states and three quartet states of the cation radicals of ethyl chlorophyllide a (Et‐Chl a+) and ethyl bacteriochlorophyllide a (Et‐BChl a+).

In Et‐Chl a.+ I the lowest excited doublet state D1 is estimated to lie 5220 cm‐1 above the ground state D0, with a negligibly small D1← D0 transition probability. The lowest quartet state, Q1, is estimated to lie 7980 cm‐1 above D1. The absorption spectrum up to 20,000cm‐1 is shown to consist primarily of numerous low‐intensity ‘background’ transitions, with transitions to D5 and D11 accounting for the observed peaks at 12,200cm‐1 and 17,500cm‐1, respectively. The large intense band at 25,000cm‐1 is due primarily to transitions to D22 and D23, with numerous lower‐intensity transitions to neighboring states.

In Et‐BChl a.+ D1 is estimated to lie 7112 cm‐1 above D0, and Q, is approximately 5725 cm‐1 above D. A pair of states, D3 and D5, account for the absorption at 11,000 cm‐1, while another pair of states, D13 and D14, are associated with the broad, weak absorption near 20,000 cm‐1. The two prominent intense peaks at 23,700 cm‐1 and 27,700 cm‐1 are assigned to D23 and D28, respectively, while the shoulder located at 25,500cm‐1 is attributed to transitions to D24 and D26. As in Et‐Chl at, numerous background transitions are found throughout the spectrum.

The π spin density distribution in D0 of both molecules is similar, with spin density found predominantly on the α‐carbon atoms. In both systems, approximately 65% of the π spin density in D1 is found on the methine carbon atoms, with the remainder found largely on the nitrogen atoms.
FLUORESCENCE LIFETIMES OF OCULAR LENS CHROMOPHORES
Authors: Borkman R. F. , Tassin J. D. , Lerman S.
Published: January 2008

Abstract— Fluorescence lifetimes are reported for intact human lenses in vitro. Two spectral regions were investigated: The first was excited at 296nm and detected at 332 or 370nm and corresponds to emission from tryptophan residues in the lens proteins. The second spectral region was excited at 359 nm and detected at 435 nm and corresponds to non‐tryptophan ‘fluorogen’ fluorescence. The latter displayed a constant lifetime, 3.8 ns, independent of the anatomical part of the lens excited. This value was compared with measured lifetimes for some model fluorogens. The tryptophan fluorescence lifetime (332 nm detection) was found to vary from 1.8 to 2.8 ns depending on the anatomical part of the lens excited.
OXYGEN QUENCHING IN MICELLAR SOLUTION AND ITS EFFECT ON THE PHOTOCYCLIZATION OF N‐METHYLDIPHENYLAMINE
Authors: Roessler Norbert , Wolff Thomas
Published: January 2008

Abstract— Oxygen effects on the photocyclization of N‐methyldiphenylamine to N‐methylcarbazole were investigated in n‐hexane, water, and aqueous surfactant solutions by steady state irradiations and flash photolysis measurements. The reaction sequence in micelles was found to involve the same intermediate steps as in homogeneous solutions. In aerated micellar solutions, the quantum yield of N‐methylcarbazole is significantly higher than in n‐hexane, while the rate constants of the unimolecular reaction steps show no solvent dependence. The bimolecular dehydrogenation of the intermediate 4a, 4b‐dihydro‐N‐methylcarbazole by oxygen is enhanced in aqueous and micellar solutions, whereas the quenching rate of triplet intermediates by oxygen was not affected. The lesuhs are interpreted using a dispersed phase model of micellar solutions. Special ‘micellar effects’ need not be invoked since the dependence of the quantum yield on the solvent is shown to be due to the difference in the overall oxygen concentration.