bluuebunny/crossref_metadata_2025_split huggingface dataset:
THE PHOTOLYSIS OF TRYPTOPHAN IN THE PRESENCE OF OXYGEN
Authors: PAILTHORPE M. T. , BONJOUR J. P. , NICHOLLS C. H. 
Published: January 2008

Abstract— Quantum yields for the destruction of tryptophan by a single 500 J flash in aqueous solution have been determined over the pH range 1–13 in both air‐equilibrated and nitrogen‐saturated conditions. When these quantum yields are compared with the quantum yields for radical formation and photoejection of electrons, it is found that there is good agreement only for the nitrogen‐saturated case. In air‐equilibrated solutions of tryptophan, there is a large disparity between the measured degradation quantum yields and those for photoejection of electrons and radical formation. Oxygen, therefore, is playing a major role in the photochemical decomposition and it is proposed that the major reaction which occurs, under normal atmospheric conditions, is the reaction of the lowest triplet excited state of tryptophan with oxygen.Preliminary photolysis‐product distributions against pH are discussed, and indicate that a total of nine major products are formed in the presence of oxygen.
EARLY CHANGES IN LIGHT‐IRRADIATED SOLUTIONS OF BILIRUBIN: A SPECTROPHOTOMETRIC ANALYSIS
Authors: DAVIES RONALD E. , KEOHANE SONJA J. 
Published: January 2008

Abstract— Early changes in irradiated solutions of bilirubin were evaluated by spectrophotometric techniques. By absorbance difference (AD) spectroscopy, the photoproducts formed in solutions of bilirubin combined with human serum albumin were found to differ from those formed in naturally or artificially jaundiced rat serum, bovine serum albumin solutions, or chloroform or carbon tetrachloride solutions.With a technique based on variable path‐length compensation for bilirubin loss (compensated absorbance difference or CAD spectroscopy) the approximate shapes of photoproduct absorption spectra could be evaluated. Chloroform and bovine serum albumin solutions produced single‐peaked products absorbing at slightly shorter wavelengths than bilirubin. Human serum albumin solutions produced a twin‐peaked chromophore absorbing most strongly near 490 nm.
SUBSTRATE SPECIFICITY OF A BACTERIAL UV ENDONUCLEASE AND THE OVERLAP WITH IN VITRO PHOTOENZYMATIC REPAIR
Authors: Patrick M. H. , Harm Helga 
Published: January 2008

Abstract— The action of an endonuclease from Micrococcus luteus, that operates on ultraviolet (UV) radiation damage, overlaps greatly with that of the yeast photoreactivating enzyme: homo and hetero cyclobutyl pyrimidine dimers in DNA are substrate for both enzymes, but pyrimidine adducts or the ‘spore photoproduct’ in DNA are not.As expected from this overlap, the action of the two enzymes is mutually interfering: single‐strand nicks introduced by the endonuclease effectively preclude photoreactivation; conversely, formation of a photoreactivating enzyme‐dimer complex can prevent nicking by the UV endonuclease. While complex formation between photoreactivating enzyme and dimers in UV‐endonuclease‐treated DNA is apparently normal, the light‐dependent repair step either fails to occur or proceeds at a very low rate. Hence, besides the requirement of a minimum chain length for the function of the photoreactivating enzyme, there is the additional restriction on the position of the dimer in a polynucleotide strand.Finally, rough approximations of the rate constants, k1 and k2, for the UV endonuclease indicate that the in vitro UV‐endonuclease‐dimer complex is relatively unstable, with dissociation of the complex being more probable than hydrolysis of the phosphodiester bond.
LUMINESCENCE AND PHOTOCHEMISTRY OF 4‐THIOURIDINE IN AQUEOUS SOLUTION
Authors: Favre Alain 
Published: January 2008

Abstract— In bidistilled water, 4‐thiouridine (4TU) exhibits a weak unusual luminescence, the quantum yield of which is 3 × 10‐4 at 25°C. The excitation spectrum corresponds well to the 4TU absorption spectrum. The emission lies at longer wavelengths (Λmax 550 nm) than the 4TU phosphorescence observed at 77 K (Λmax, 470–480 nm). From the emission signal obtained after an excitation flash of 3 ns half‐width, an “apparent” rate constant for the radiative deactivation process, shorter than 5 × 106 s, can be inferred. The 300 K emission is efficiently quenched by halides and by oxygen: quenching involves a long‐lived intermediate (⋍ 200 ns).Clearly the emissive state X is populated through the S0‐S1 electronic transition π→π* of 4TU. The nature of X cannot be unambiguously determined: it cannot be an excimer but can be either the 4TU triplet state or another chemical state distinct from the 4TU excited singlet or triplet states.An interesting finding is that the 300 K emission and the ability of 4TU to photoreact are related: they are quenched with the same efficiency by halide anions. This indicates that quenching occurs at the same long‐lived intermediate species, which is either a precursor of the emitter or the emitter itself.
LIGHT‐INDUCED FREE RADICALS IN ORIENTED DNA‐PROFLAVINE COMPLEXES
Authors: Gräslund A. , Rupprecht A. , Ström G. 
Published: January 2008

Abstract— Oriented wet DNA‐proflavine complexes were illuminated with visible light, Λ > 395 nm, at 77 K, in the presence or absence of oxygen. The electron paramagnetic resonance spectra at 77 K and low microwave power (3 μ W) indicated formation of anionic free radicals in thymine and cationic free radicals, probably in guanine, identical to those induced by y rays at 77 K in similar samples of pure DNA.The free‐radical formation rate showed a quadratic dependence on light intensity, indicating a biphotonic mechanism. The proflavine triplet spectrum was observed during illumination. If the exciting light includes wavelengths below 390 nm, significant amounts of hydrogen addition radicals in thymine are found.
INDICATION OF FAST TRIPLET FORMATION IN BIMOLECULAR QUENCHING OF EXCITED SINGLET STATES STUDIED BY CONVENTIONAL FLASH PHOTOLYSIS
Authors: Vogelmann Ekehardt , Kramer Horst E. A. 
Published: January 2008

SummaryThe bimolecular quenching of the first excited singlet state of oxonine by allylthiourea leads to the formation of the triplet state of the dye. This has been proved by comparison with the triplet‐triplet absorption spectrum of oxonine obtained by triplet‐triplet energy transfer. The conventional flash experiments suggest that the dye triplet state is produced directly rather than by radical recombination.
EXTRAOCULAR PHOTORECEPTION IN AMPHIBIANS
Authors: Adler Kraig 
Published: January 2008

Abstract— Amphibians possess extraocular photoreceptors (EOPs) which exclusively or together with the lateral eyes perceive light for various physiological and behavioral activities. Several kinds of EOPs are discussed but emphasis is given to the pineal complex: the dermal frontal organ (or stirnorgan) found only in frogs and toads among amphibians and the intracranial pineal body (or epiphysis cerebri) found in all Amphibia. Both structures are derived as dorsal evaginations of the diencephalon and have a retina‐like fine structure. Both are sensitive to visible and UV light but not to IR, mechanical or chemical stimuli. The frontal organ gives chromatic and achromatic responses but in most species only achromatic ones are recorded from the pineal. Photopigments have been identified for some of these responses.Pineal EOPs are involved in several activities: (i) neurosecretory activity by the subcommissural organ in the brain; (ii) body‐lightening reaction in larval amphibians, involving the light‐inhibited release by the pineal of a hormone, presumably melatonin, which contracts melanophores in the skin; (iii) cuing of circadian locomotor rhythms, including phase shifts and synchronization with environmental light cycles; (iv) perception of celestial cues for use in time‐compensated compass orientation; and (v) possibly perception of linearly‐polarized light.Non‐pineal EOPs have been implicated in (i) tail‐darkening reaction of frog larvae where light has a direct effect on melanophores; and (ii) in phototaxis where unknown EOPs in various parts of the body and tail mediate withdrawal from light. Evidence for use of pineal and non‐pineal EOPs and location of specific receptors is reviewed drawn from biochemical, ultrastructural, neurophysiological and behavioral studies. The possible use of EOPs for other biological functions and their possible adaptive value are briefly discussed.
GENERATION AND PARTICIPATION OF O‐2 IN 2‐NITROPROPANE DIOXYGENASE REACTION
Authors: Kido Toshiko , Hashizume Katsumi , Soda Kenji , Asada Kozi 
Published: January 2008

Abstract— 2‐Nitropropane dioxygenase (EC 1. 13. 11) of the yeast Hansenula mrakii catalyzes the oxygenative denitrification of 2‐nitropropane as follows:
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The enzyme is significantly inhibited by superoxide dismutase and various scavengers for superoxide such as cytochrome c, epinephrine, thiols and polyhydric phenols. The scavengers added to the reaction mixture were oxidized or reduced. The addition of superoxide dismutase and the omission of 2‐nitropropane or oxygen prevented the oxidation and the reduction of the scavengers. The enzyme catalyzes the formation of nitrite from 2‐nitropropane by KO2 added anaerobically.One mole of NADH is bound per mole of the enzyme and predominantly the pro‐R hydrogen of bound NADH is transferred to superoxide formed enzymatically or provided externally. The enzyme shows incomplete stereospecificity for hydrogen transfer from NADH.
THE ROLE OF CYTOKININS IN THE PHYTOCHROME‐MEDIATED GERMINATION OF DORMANT IMBIBED CELERY (APIUM GRAVEOLENS) SEEDS
Authors: Thomas T. H. , Biddington N. L. , Palevitch D. 
Published: January 2008

AbstractThe dormancy of celery seeds was broken by red light treatment given during imbibition and this effect was reversed by far‐red light. The exact quantitative relationship between the timing and duration of red light treatment and dormancy‐break has not been elucidated. However, the accumulated effect of daily 5 min exposures was greater than a single 5 min exposure on the second day of imbibition. The effects of red light treatment were simulated by treatment with a mixture of the gibberellins A4 and A7 and N6‐‐benzyladenine. A correlation between the requirement for red light and the requirement for exogenous cytokinins in the presence of GA4/7 was demonstrated by using six cultivars with different dormancy characteristics. In order to investigate the role of natural cytokinins in dormancy‐break, quantitative and qualitative changes in cytokinins were measured in celery seeds immediately after red‐light treatments. Rapid increases in n‐butanol‐soluble cytokinins following irradiation were associated with concomitant decreases in water‐soluble cytokinins, suggesting a red light induced cytokinin conversion. Three of the cytokinins present in the n‐butanol fraction of celery seed extracts were chromatographically similar to zeatin, zeatin riboside and N6‐‐A2‐‐isopentenyladenosine (i6Ado). The elution profiles from a PVP column of two others were similar to BA and its riboside. The possibility that these two cytokinins act as specific dormancy‐breaking cytokinins in celery seeds is discussed. There was little evidence of reversal of the cytokinin conversion mechanism by far‐red light exposure.
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

AbstractThe 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.
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.
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.
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.
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.
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.