bluuebunny/crossref_metadata_2025_split huggingface dataset:
FAST AND SLOW PHASES OF LUMINESCENCE IN CHLORELLA
Authors: Lavorel J. 
Published: January 2008

Abstract— The decay of luminescence of Chlorella in repetitive steady‐state flashing light displays two categories of phase, broadly characterized as ‘fast’ and ‘slow’. They are strongly contrasted in amplitude and lifetime; the transition from fast to slow occurs a few milliseconds after the flash.

The slow phases observed in the presence of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) are clearly of the deactivation type. i.e. the luminescence intensity is quantitatively correlated with the rate of relaxation of the System II reaction center to its photoactive state. The significance of the deactivation type is a reverse flow of the light‐produced ⊕ and ⊖ charges through the luminescence‐producing recombination path. This mechanism is probably not limited to the DCMU‐poisoned systems. The light regime (flash duration, flashing period, induction effects) modifies specifically the amplitude of the slow phases; this effect is strikingly not dependent on the presence of DCMU. Although the light‐driven pH gradient is the likely explanation, it is argued that its action bears more directly on the exciton and/or emission yield of luminescence rather than on the rate of recombination itself.
Most of the fast‐phase components are ascribed under normal conditions to stabilization steps involving the donor side of the System II reaction centers. However, when the reaction center turnover is much reduced (DCMU) or completely abolished (DCMU + NH2OH, after preillumination), a fast luminescence phase is still visible. This phase is barely affected by the light regime (notably the flash duration). It must be attributed to an anomalous residual photochemical turnover of the reaction centers. Another type of fast photochemical turnover has been characterized with NH2OH‐pretreated cells.A two‐quantum functioning of some sort seems required to account for the anomalous photochemical turnover. The importance of the luminescence loss during the fast phases and its possible connection with the ‘misses’ of the O2‐evolving system are discussed.
ROLE OF COMPLEX FORMATION IN THE PHOTOSENSITIZED DEGRADATION OF DNA INDUCED BY N‘‐FORMYLKYNURENINE
Authors: Walrant P. , Santos R. , Charlier M. 
Published: January 2008

Abstract— N'‐Formylkynurenine derivatives efficiently bind to DNA or polynucleotides. Homopolynucleotides and DNA display marked differences in the binding process. Association constants are derived which indicate that the oxidized indole ring is more strongly bound to DNA than the unoxidized one. Irradiation of such complexes with wavelengths greater than 320 nm induces pyrimidine dimer formation as well as DNA chain breaks. Complex formation is shown to play an important role in these photosensitized reactions.The photodynamic action of N'‐formylkynurenine on DNA constituents is negligible at neutral pH but guanine and xanthine derivatives are sensitizable at higher pH. Thymine dimer splitting can occur in aggregated frozen aqueous solutions of N'‐formylkynurenine and thymine dimer but this photosensitized splitting is negligible in liquid solutions at room temperature.
PHOTOOXIDATION OF XANTHOBILIRUBIC ACID IN AQUEOUS SOLUTION: PRODUCT AND MECHANISM STUDIES
Authors: Grunewald J. O. , Walker J. C. , Strope E. R. 
Published: January 2008

Abstract— Xanthobilirubic acid, an oxodipyrrylmethene with a chromophore very similar to that of bilirubin, was aerobically irradiated as its sodium salt in borate buffer at pH 8. Two photooxidation products, methylethylmaleimide and 5‐formyl‐2,4‐dimethyl‐1H‐pyrrole‐3‐propanoic acid, were isolated. These products can be rationalized on the basis of either a Type I or a Type II (singlet oxygen) photooxygenation mechanism. The reaction is inhibited by azide, a singlet oxygen quencher, and sensitized by methylene blue. However, both the self‐sensitized and the methylene blue‐sensitized reactions are enhanced, rather than inhibited, by high concentrations of 1,4‐diazabicyclo[2.2.2]octane, another known singlet oxygen quencher. It is therefore proposed that the diazabicyclooctane can also act as an electron donor.The self‐sensitized photooxidation of xanthobilirubic acid is an autocatalytic reaction. This is supported by the fact that addition of a previously irradiated solution to a freshly‐prepared solution significantly increases the rate of photodegradation. A similar catalyst is formed, but much more slowly, from xanthobilirubic acid in the dark in the presence of oxygen.
CHARGE TRANSFER ACROSS PIGMENTED BILAYER LIPID MEMBRANE AND ITS INTERFACES
Authors: Hong Felix T. 
Published: January 2008

Abstract— The technique of forming bilayer lipid membranes (BLM) has made it possible to study photoreactions of pigments in an environment that is much closer to those in photosynthetic and visual membranes. A pigmented BLM system with Mg2+‐porphyrins as membrane‐bound pigments and with ferricyanide and ferrocyanide as the aqueous electron acceptor and donor, respectively, was used to illustrate the photoelectric effects due to coupled interfacial charge transfer reactions.The steady‐state continuous photoresponse was studied by means of the voltage clamp method and a null current method. The independence of the pigment conductance channel and the ionic conductance channel was demonstrated. A tunable voltage clamp method was used to study the transient pulsed photoresponses. Such a measurement permits us to characterize the photosystem in terms of an equivalent circuit model which contains a novel chemical capacitance. Molecular interpretation of this equivalent circuit model was given.A microscopic model based on the Gouy–Chapman theory and chemical kinetics calculation leads to an equivalent circuit which is also equivalent to the previous one. Generalization of this microscopic model further leads to a physical mechanism of the generation of the early receptor potential (ERP) in visual membranes. Relevance of pigmented BLM research to photosynthesis and other disciplines was also discussed.
MEASURING SUBNANOSECOND FLUORESCENT LIFETIMES USING PHOTON COUNTING
Authors: Wong David K. , Halpern Arthur M. 
Published: January 2008

SummaryAn evaluation is made of a typical time‐correlated single photon counting apparatus using a D2‐filled gated flash lamp. The aim is to determine: (1) the valid flash lamp profile, and (2) the reliability and sensitivity of subnanosecond lifetime measurements. As model systems for very short‐lived fluorescence possessing single exponential decay, concentrated JV‐methylpiperidine (NMP) solutions in n‐hexane were used. Stern‐Volmer self‐quenching kinetics were observed over a concentration range of 0.508 M to 1.00 × 10‐4M. Solutions having known subnanosecond lifetimes were accordingly prepared. The flash lamp profile was altered so that the tail‐portion (time > 3.6 ns after maximum) was reduced by a factor of 0.80. This altered profile provided the best convoluted functions as compared with the observed fluorescence decay curves. For lifetimes less than about 1 ns, the full‐width‐tenth‐maximum values of the convoluted and observed decay functions were used as the criterion for best fit. Using highly concentrated NMP solutions, lifetimes of 0.30, 0.50, and 0.70 ns could be clearly distinguished; a lower limit for reliable measurement is placed at ca 0.2 ns for a flash lamp having a FWHM of 2.6 ns and a 1/e value of 0.8 ns.
FLUORESCENCE ANALYSIS ON SOLID SURFACES*
Authors: Guilbault George G. 
Published: January 2008

Abstract— One of the recent uses of fluorescence has been in the assay of substances directly on solid surfaces such as paper chromatograms, thin‐layer chromatography (TLC) plates, potassium bromide disks, electrophoresis strips, and silicone‐rubber pads. Chromatography and electrophoresis are widely used analytical techniques and it is not surprising that fluorometric methods are used in conjunction with them. Advantages are increased sensitivity and rapidity of analysis.In this paper the use of fluorescence in the assay of substances after separation on paper and TLC chromatograms, as well as the direct assay of substances on a solid surface placed directly in a commercial fluorometer, are discussed. Particular emphasis is placed on the direct analysis of enzymatic reactions.
QUENCHING OF OXONINE EXCITED STATES BY EDTA VIA ELECTRON TRANSFER AND DEACTIVATION PROCESSES. A COMPARATIVE STUDY OF EXCITED SINGLET AND TRIPLET STATE REACTIVITY
Authors: Bonneau Roland 
Published: January 2008

SummaryThe quenching of excited singlet oxonine by EDTA in aqueous solution leads mainly to deactivation of the dye to the ground state and, to a lesser extent, to electron abstraction. The rate constants for these processes have been measured and compared to those for the same reactions involving the oxonine triplet state. The rate constant of electron abstraction is about ten times greater via the singlet state than via the triplet state. However, the rate constant of deactivation to the ground state is 103‐104 times greater for the excited singlet state than for the triplet state, so that the efficiency of electron transfer is much smaller for the singlet state.
ULTRAVIOLET MICRO‐IRRADIATION ON LOCALIZED AREAS OF THE CELL NUCLEUS: EFFECTS ON RNA SYNTHESIS
Authors: Moreno G. , Nocentini S. , Salet C. 
Published: January 2008

Abstract— …Ultraviolet (UV) micro‐irradiation of the cell nucleus was used to study RNA synthesis. CV‐1 cells in culture were irradiated in the nucleoplasm in an area of 5 µm in diameter, with UV doses of the order of 10 and 102 Jm‐2 at 254 nm and pulsed with 3H‐uridine (3HU) 1 h and 24h after irradiation. Parallel cultures were irradiated under the same conditions and labeled with 3H‐thymidine (3HTdR) to measure unscheduled DNA synthesis (UDS).For the two incident doses used, 1h after irradiation, RNA synthesis was decreased over the whole nucleus by 50% compared to unirradiated control cells. Moreover, for irradiation with 102 Jm‐2, 3HU uptake was completely inhibited in the irradiated spot; UDS occurred only in the irradiated area. At 24h after irradiation, 3HU uptake occurred over the whole nucleus in the same amount as in non‐irradiated cells. At this time, UDS was undetectable. These studies indicate the occurrence of a repair process leading to a recovery of the function of transcription, and suggest the role of pyrimidine dimers in the inhibition of RNA synthesis.
MAGNESIUM ION EFFECTS ON CHLOROPLAST PHOTOSYSTEM II FLUORESCENCE AND PHOTOCHEMISTRY
Authors: Henkin Bruce M. , Sauer Kenneth 
Published: January 2008

Abstract. –Although there have been several reports that divalent cations, especially Mg2+, can significantly affect chloroplast photoprocesses, the molecular mechanism of cation interaction is not well understood. We have investigated the interaction of Mg2+with Photosystem II photoprocesses by studying cation effects on chloroplast fluorescence and the Hill reaction. Our results are summarized as follows.1. Mg2+stimulation of background fluorescence (20–30%) saturates at about 0.5 mM Mg2+, while Mg2+stimulation of variable fluorescence (250%) saturates at about 2.5 mM Mg2+.2. Addition of Mg2+to chloroplasts treated with 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea or dithionite causes a doubling in the amount of total (background + variable) fluorescence.3. Studies on chloroplasts in the presence of 2,6‐dichlorophenolindophenol indicate that Mg2doubles the relative yield of variable fluorescence under light‐limiting conditions.4. Mg2causes large (70–120%) increases in the light‐limited rate of the DCIP Hill reaction.We interpret these results in terms of a model involving two components of chloroplast emission. Our analysis indicates that Mg2+increases the effective absorption cross section (size) of the pigment array associated with Photosystem II photochemistry.
SYNERGISTIC INTERACTION BETWEEN THE TRYPTOPHAN PHOTOPRODUCTS AND NEAR‐ULTRAVIOLET LIGHT IN AMOEBA
Authors: Bhattacharjee S. K. , Chatterjee S. 
Published: January 2008

Abstract. Both S‐ and G2‐phase cells of amoeba are found to be sensitized by coirradiation of cells with Tryptophan (Trp). At a fluence of 1.5 times 105 Jm‐2 to which G2 phase cells are resistant, they show a drastic (8‐fold) increase in sensitivity when irradiated in 0.5% Trp solution. Freshly irradiated Trp solution is found to be lethal to G2 cells that have received a sublethal fluence of near‐UV light. Irradiated Trp, however, does not kill unirradiated amoeba.Nuclear transplantation experiments have shown that the lethality of cells when coirradiated with Trp is due to damage located predominantly in the cytoplasm. It is suggested that sublethal fluence of near‐UV light makes the cells “leaky” to the toxic photooxidation products of Trp solution.
THE SENSITISING EFFECT OF A SUNSCREENING AGENT, p‐AMINOBENZOIC ACID, ON NEAR UV INDUCED DAMAGE IN A REPAIR DEFICIENT STRAIN OF ESCHERICHIA COLI*
Authors: Hodges N. D. M. , Moss S. H. , Davies D. J. G. 
Published: January 2008

Abstract. The use of repair deficient strains of bacteria for detecting mutagenic properties of chemical species is now an established technique. In this paper we present inactivation results obtained with Escherichia coli K12 AB2480 (uvr A rec A) which indicate that p‐aminobenzoic acid, a common component of sunscreening formulations, may increase the frequency of lethal damage induced in DNA when cell populations are exposed to near ultraviolet radiation.Preliminary experiments, utilising the selective action of photoenzymatic repair, indicated that the sensitisation to near ultraviolet radiation is partially but not wholly due to increased formation of pyrimidine dimers.
PHOTODESTRUCTION OF PHAEOMELANIN
Authors: Chedekel M. R. , Post P. W. , Deibel R. M. , Kalus M. 
Published: January 2008

Abstract. Phaeomelanin readily decomposes by the action of UV light and oxygen. This finding may explain many of the abnormal reactions of the skin of redheads and blondes to sunlight, including their high susceptibility to skin cancer. In aqueous solution, phaeomelanin displays an EPR signal rich in hyperfine splitting, consistent with structural information.SUMMARYPhaeomelanin readily, decomposes by the action of UV light and oxygen. This finding may explain many of the abnormal reactions of the skin of redheads and blondes to sunlight, including their high susceptibility to skin cancer. We have yet to identify any of the fragmentation products. Chromatographic analysis of the photolysate indicates at least 17 different compounds. Work on the reactions of phaeomelanin with superoxide, and the identification, synthesis, and physiological evaluation of these photoproducts as etiological factors in sunburn and carcinogenesis is in progress. In aqueous solutions, phaeomelanin displays an air stable EPR signal rich in hyperfine splitting. Complete analysis of this signal will provide a better understanding of the structure of the pigment.
THE SUBUNIT STRUCTURE OF YEAST DNA PHOTOLYASE AND THE PURIFICATION OF A FLUORESCENT ACTIVATOR OF THE ENZYME
Authors: Werbin Harold , Madden John J. 
Published: January 2008

Abstract— Yeast DNA photolyase purified twice by affinity chromatography was analyzed by electrophoresis on polyacrylamide gradient gels or by sedimentation velocity through 5–200/, sucrose gradients containing 0.4MKC1. Its molecular weight estimated by both these methods was130,000 and136,000, respectively. However, the enzyme dissociated into two bands having molecular weights of60,000 and85,000 when it was examined by electrophoresis on SDS polyacrylamide gradient gels. The subunit structure of the enzyme was confirmed when two absorption maxima corresponding to polypeptides of54,000 and82,500 daltons were observed in sucrose gradients run in 1.0 M KCI. Upon mixing these two fractions, a time‐dependent increase in activity occurred, demonstrating that active enzyme could be reconstituted from these subunits.The activity of photolyase purified by affinity chromatography is enhanced by a compound (activator III) obtained from yeast by acidification, neutralization, ion exchange chromatography and gel filtration. Activator III emits at 350 and 440 nm when excited at 290 nm, and emits at 440 nm when excited at 358 nm. After acid hydrolysis, emission at 440 nm is produced only by excitation at 358 nm, indicating that it contains two separate chromophoric moieties. The chromophore excited by 358 nm light has a pK of 9–11, while the other has a pK of 4–5. Enhancement of photolyase activity by activator III at a concentration equimolar with that of the enzyme and the similarity of the fluorescent spectra of the activator and heat‐denatured photolyase suggest that the activator may be the chromophore associated with the enzyme.
CHANGES IN ULTRAVIOLET RESISTANCE AND PHOTOPRODUCT FORMATION AS EARLY EVENTS IN SPORE GERMINATION OF BACILLUS CEREUS T
Authors: Irie R. 
Published: January 2008

Abstract— In order to determine the timing of the change in the state of DNA in bacterial spores during the course of germination, L‐alanine‐induced germination of Bacillus cereus spores was interrupted by 0.3 M CaCl2 as an inhibitor, and the resulting semi‐refractile spores (spores at the end of the first phase of germination) were examined on the UV‐resistance and the photoproduct formation.Upon UV‐irradiation, these spores, still having a semi‐refractile core as observed under a phase‐contrast microscope, gave rise to mainly the cyclobutane‐type thymine dimer. It was concluded that change in the state of the spore DNA occurs early in the process of germination, i.e. before the refractility of the core was lost.It was also found that CaCl2 markedly prolonged the duration of the transient UV‐resistant stage.
SINGLET OXYGEN: A MAJOR REACTIVE SPECIES IN THE FUROCOUMARIN PHOTOSENSITIZED INACTIVATION OF E. COLI RIBOSOMES
Authors: Singh Harwant , Vadasz Joseph A. 
Published: January 2008

Abstract— The skin photosensitizing furocoumarins, 8‐methoxypsoralen (MOP) and 4,5′,8‐trimethylpsoralen (TMP), inactivate E. coli ribosomes in vitro, on UV irradiation at 313 nm. Purging the solutions with N2 protects the ribosomes considerably against photoinactivation (75% with MOP and 80% with TMP). In air, the ribosome photoinactivation is mainly due to singlet oxygen (1O2), since the presence of NaN3 and other 1O2 quenchers protects the system and the inactivation is enhanced in D2O. Although 1O2 dominates as the inactivating species, the possibility of additional (∼15%) minor mechanisms involving free radicals exists. However, O‐2 does not appear to be the damaging species, since superoxide dismutase does not provide any protection.Photosensitization of the partially purified enzyme, phe‐tRNA‐synthetase with MOP or TMP shows inactivation and protection curves similar to those seen with the ribosomes. On the other hand, unfrac‐tionated tRNAphc is not photosensitized under similar conditions, although it shows self‐photosensitization. It is likely that in the furocoumarin‐sensitized ribosomes, the primary events of photoinactivation are associated with the proteins.
GAMMA AND PULSE RADIOLYSIS STUDIES OF THE REACTION BETWEEN SUPEROXIDE IONS AND OXYHEMOGLOBIN‐METHEMOGLOBIN SYSTEM
Authors: Ferradini Christiane , Foos Jacques , Gilles Lucien , Haristoy Didier , Pucheault Jacques 
Published: January 2008

Abstract— The radiolytic studies of oxyhemoglobin or methemoglobin in neutral aerated aqueous solutions with formate ions, lead to three conclusions:The oxidation of oxyhemoglobin by O‐2 is not important. The observed low oxidation yield is probably due to the slow reaction with hydrogen peroxide produced by O‐2 disproportionation.The reduction of methemoglobin in γ radiolysis reaches a plateau which could be explained by structural considerations.The reduction of methemoglobin by O‐2 ions, if it occurs, is relatively slow: k= 1.4 × 103M‐1 s‐1. But a problem remains concerning the spectral characteristics of the product.
IN SlTU ESTIMATION OF SPATIAL DISTRIBUTION OF PHYTOCHROME ALONG THE AXIS OF THE ACTINIC BEAM
Authors: Fukshansky Leonid 
Published: January 2008

AbstractNon‐stationary photoconversions of the two forms of the photochromic sensory plant pigment phytochrome are theoretically analyzed. It is shown that from actual in situ measurements of changes of absorbances caused by these photoconversions in a sequence of exposures to actinic light, one can calculate the spatial distribution of phytochrome along the path of the actinic beam.The necessary condition of such a calculation is the existence of a screen with a known spatial distribution, which must be obtained in an independent experiment. Thus, the possibility is proved to measure, instead of phytochrome spatial distribution, that of the screen which is a much larger chemical and optical body inside the object.Expressions to calculate the spatial distribution of phytochrome and to estimate the errors involved are presented in the present paper.
DIFFERENTIAL EFFECT OF CALCIUM ON CHLOROPLAST MOVEMENT IN MOUGEOTIA
Authors: Wagner Gottfred , Klein Karin 
Published: January 2008

AbstractThe flat, ribbon‐shaped chloroplast in the filamentous green alga Mougeotia sp. undergoes light‐induced orientational movement controlled by an intracellular tetrapolar gradient of the active form of phytochrome, Pfr. Some substructural and physiological aspects of this reaction were studied. An intracellular pattern of microfilaments (diameter: 5–10nm), presumably related to chloroplast movement, was identified in situ. In addition, it could be shown that chloroplast movement decreases parallel to a nitric acid soluble fraction of intracellular calcium. These results might indicate that phytochrome governs chloroplast movement in Mougeotia via control of the binding state of calcium.
SPECTRAL DEPENDENCE OF A SINGLE AND A SUBSEQUENT SECOND LIGHT PULSE INDUCING BARLEY LEAF UNFOLDING
Authors: Deutch Bente , Deutch Bernhard I. 
Published: January 2008

AbstractThe unfolding of etiolated barley leaves was induced by two short pulses of light separated by a dark interval. For certain wavelengths of light the effect of the “second light pulse was enhanced when the pulse was given after a 300–2000 s dark interval as compared with its effect when the two light pulses were given simultaneously. We investigated the spectral dependence of the effect of the first, inducing light flash and of the effect of the second Light flash given after a 500 s dark interval. The spectral actinity for the effect of the first flash showed phytochrome involvement. The spectral actinity for the effect of the second light flash, however, was shifted towards shorter wavelengths and the inductive action of red and far red light was attenuated.
LIGHT REQUIREMENTS FOR THE ENHANCED SYNTHESIS OF A PLASTID mRNA DURING SPIRODELA GREENING
Authors: Gressel Jonathan 
Published: January 2008

AbstractA plastid mRNA (5 × 105 mol wt) appears as a burst 3 h after white light greening of steady state dark grown plants of Spirodela oligorrhiza. In this species, chlorophyll synthesis begins after 12 h. The light requirement is different from the pulse of far‐red reversible red light required to abolish the lag of chlorophyll synthesis in many species, including Spirodela. Continuous high energy far‐red is not stimulatory. When the illumination is not continued throughout the time of incorporation, the stimulation is minimal. Low energy blue and red light are stimulatory, and green and far‐red light are ineffectual. Blue light was > 5 times as effective as red light at many dose levels. Illumination with 3 × 1017 quanta/m2/s (50pEm/cm2/s) blue light at 476 nm gave about half maximum stimulation.