bluuebunny/crossref_metadata_2025_split huggingface dataset:
BLUE LIGHT EFFECT ON CHLOROPHYLL FORMATION IN CHLORELLA PROTOTHECOIDES
Authors: Oh‐Hama Tamko , Hase EIJI 
Published: January 2008

AbstractThe effectiveness of monochromatic light on chlorophyll formation over a range of 420–80 nm was examined in the regreening cells of Chlorella protothecoides in the presence of chloro‐phenyl dimethylurea (CMU). An action spectrum showed two maxima with a minimum near 450 nm. At the most effective wavelength examined (444 nm), 0.2 W. m ‐2 was sufficient for half saturation. The activity of 5‐aminolevulinic acid (ALA) production was examined in the greening cells under irradiation with white, blue and red light. The activity was always limited by availability of substrate, especially in the case where the greening cells were incubated with cycloheximide or transferred to darkness. Decay of the activity in these cases was delayed by provision of organic compounds such as glycine, pyruvate or glucose. The effectiveness of blue light on ALA* production observed in the presence of CMU was inferred to be brought about by the increased availability of endogenous substrates.
EVIDENCE FOR PHYTOCHROME CONTROLLED ENDOMITOSIS AND CELL ELONGATION IN PISUM SATIVUM EPICOTYLS
Authors: Oostveldt P. Van , Boeken G. , Parus R. Van 
Published: January 2008

AbstractElongation and endomitosis were studied in the epicotyl cortex cells of germinating seeds of Pisum sativum cv. Rondo.One min of red light per 24 h is sufficient to fully inhibit endomitosis. Terminal far‐red irradiation can reverse the red effect to the level established by far‐red light alone. This justifies the conclusion that phytochrome is involved in the regulation of endomitotic DNA replication. Since far‐red light alone inhibits endomitosis to about 50%, we conclude that very low levels of Pfr are required to influence the endomitotic cycle.
MULTISITE TOPOGRAPHIC MICROFLUOROMETRY OF INTRACELLULAR AND EXOGENOUS FLUOROCHROMES*
Authors: Kohen E. , Kohen C. , Hirschberg J. G. , Wouters A. , Thorell B. 
Published: January 2008

Abstract. Microspectro fluorometry combined with microinjection of metabolites allows the monitoring of pathways regulating the energy metabolism, biosynthetic or metabolizing activity of the intact living cell. The topographic scan of ˜ 100–150 adjacent regions within a cell or the spectral scan of fluorescence from a single cell region is completed within 60 ms. The in situ activity of intracellular enzymes and substrate concentration vs rate relationships are derived from the kinetic analysis of transients (e.g. NAD(P) ⇄ NAD(P)H) elicited by sequential injections with increasing doses of substrate (e.g. glucose‐6‐P, 6‐phosphogluconate). A method of approximation is used to predict the non‐linear behavior of whole biochemical systems (e.g. the sum of reactions involved in NAD(P) reduction‐reoxidation transients). Approximation to power law kinetics is validated by prediction of system behavior over a 10–100 fold variation in the input concentration of substrate.The NAD‐dependent glycolytic chain (faster rise kinetics) and NADPH‐dependent shunt pathway (slower rise kinetics) are triggered optionally, by enhanced demand for degradation, synthesis or metabo‐lization of exogenous compounds (hydrocarbons, aflatoxins). Compartmentation of NAD(P) pathways is suggested by differences in the reoxidation of cytoplasmic vs nuclear NAD(P)H. The intercellular transfer of molecules can be evaluated by microinjection of fluorescent tracers.The difference spectra ΔIF due to microinjection of substrate are resolved in terms of bound vs free NAD(P)H (with differentiation of other endogenous and exogenous fluorochromes).On the basis of the above, a tentative scheme of intra‐ and intercellular dynamics can be developed.
APPLICATION OF PHOTOSENSITIVE DEVICES TO BIOLUMINESCENCE STUDIES
Authors: Reynolds George T. 
Published: January 2008

Abstract—A brief review is given of some results obtained by the application of image intensification to studies of bioluminescence. The system consists of an image intensifier placed at the output of a suitable microscope., so that the image from the microscope falls on the intensifier cathode. The photon gain of the intensifier can be varied from a few thousand to one million. The output of the intensifier is recorded either on film or, in most applications to date, by means of a TV vidicon. The TV system permits display on a monitor in real time and simultaneous recording on magnetic tape for subsequent playback and analysis. It also provides time resolution for dynamic studies. Results are summarized for in vivo observations on Noctiluca miliaris, Obelia, Renilla, and Mnemiopsis leidyi. Utilization of the luminescence of aequorin in the presence of Ca2+ has been directed to observations on amoebae and the egg of the Medaka fish.Studies at the molecular level have been made by means of the spectral distribution of the output light. In these, the output of a fast input lens grating spectrometer is focused on the image intensifier cathode. Thus the entire visible spectrum of an in vivo bioluminescent flash can be intensified and recorded on film by photographing the output. The film is then analyzed by means of a digitized densitometer, and a computer program corrects the observed spectrum for system non‐linearities and non‐uniformities. In this way, the in vivo spectra of 15 bioluminescent species have been recorded.
PROFLAVINE PHOTOSENSITIZATION OF DOUBLE AND SINGLE STRANDED DNA: EPR STUDY OF THE EFFECT OF VARIOUS SULPHUR‐CONTAINING SUBSTANCES
Authors: Piette Jacques , Calberg‐Bacq Claire‐M. , Vorst Albert Van de 
Published: January 2008

Abstract—The proflavine‐mediated photosensitization of both double‐stranded calf thymus and single‐stranded DNA from bacteriophage φ× 174 was followed in terms of the induction of free radicals in frozen solutions by EPR measurements in the presence of oxygen. The effect of the addition of various sulphur‐containing substances to the proflavine DNA mixtures was studied and quantitatively expressed for definite amounts of proflavine bound to both DNAs.Upon irradiation with visible light, RS radicals were observed in the presence of these sulphur‐containing substances. Some of them caused a decrease in the amount of peroxide radicals normally induced in the photosensitized DNA. This decrease appeared to be linked to the property of the compounds to interact with DNA in such a way that they modify the binding of proflavine to DNA.Cysteine, cysteamine, cystamine and cystine, protect calf thymus DNA against the “proflavine and light” free radical induction by 55, 58, 64 ahd 62% respectively. φ× 174 single‐stranded DNA is also protected by the addition of cysteamine and cystamine, although to a lesser extent than calf thymus DNA (35%). These protection factors were measured under conditions where strong binding of the dye to the DNA was predominant.
FLUORESCENCE KINETICS OF SPINACH CHLOROPLASTS MEASURED WITH A PICOSECOND OPTICAL KERR GATE
Authors: Pellegrino F. , YU W. , Alfano R. R. 
Published: January 2008

Abstract. An overview of the reported chlorophyll a fluorescence lifetimes from green plant photosystems is presented and the problems encountered in the measurement of fluorescence lifetime using two currently available picosecond techniques are discussed.The fluorescence intensity of spinach chloroplasts exposed to 10 ps flashes was measured as a function of time after the flash and wavelength of observation by the ultrafast Kerr shutter technique. Using a train of 100 pulses separated by 6ns and with an average photon flux per pulse of ˜2 times 1014 photons/cm2, the fluorescence intensity at 685 nm (room temperature) was found to decay with two components, a fast one with a 56 ps lifetime, and a slow one with a 220 ps lifetime. The 730 nm fluorescence intensity at room temperature decays as a single exponential with a 100 ps lifetime. The 730 nm fluorescence lifetime was found to increase by a factor of 6 when the temperature was lowered from room temperature to 90 K while the lifetime of 685 and 695 nm fluorescence were unchanged. At room temperature, the fast and slow components at 685 nm are attributed to the emission from pigment system I (PS I) and PS II, respectively. It is likely that the absolute values of lifetimes, reported here, may increase if single ps low intensity flashes are used for these measurements.
PICOSECOND FLUORESCENCE AND ELECTRON TRANSFER IN PRIMARY PHOTOSYNTHETIC PROCESSES
Authors: Rubin Andrew B. 
Published: January 2008

Abstract. Under conditions that drive the reaction centers (RC's) into the “closed” state, the lifetime (T) of the fluorescence emitted by antenna molecules increases from 80 to 200 ps in PS I, from 300 to 600 ps in PS II, and from 200 to 500 ps in bacterial chromatophores. In Rhodopseudomonas sphaeroides strain 1760‐1, the decay curve for fluorescence from the RC's has a component with T2= 15 ps due to the bacteriochlorophyll of the RC, and a second component with T2= 250 ps due to bacteriopheophytin.Data on electron transfer at low temperatures and under different redox conditions are analyzed. along with the ps fluorescence kinetics. The hypothesis is discussed that electron transfer in RC's is coupled to conformation changes in the interacting molecules.
DNA TURNOVER IN BUFFER‐HELD ESCHERICHIA COLI AND ITS EFFECT ON REPAIR OF UV DAMAGE
Authors: Tang Moon‐Shong , Wang Tzu‐chien V. , Patrick Michael H. 
Published: January 2008

Abstract— Continuous DNA degradation and resynthesis, without a net change in cellular DNA content, were observed in buffer‐held, non‐irradiated E. coli B/r. This constant DNA turnover probably involves most of the genome and reflects random sites of DNA repair due to the polA‐dependent excision‐resynthesis repair pathway. Under these non‐growth conditions, it appears that at any given time there is a minimum of one repair site per 6.5 × 106 daltons DNA, each of which is at least 160 nucleotides long.While the amount of DNA degradation is not influenced by prior exposure to UV radiation, the synthetic activity decreases with increasing UV fluence. We suggest that when sites of DNA turnover occur opposite to cyclobutyl dipyrimidines in UV‐irradiated cells, repair of the latter damage can be prevented. This implies that both beneficial and deleterious processes take place in irradiated buffer‐held cells, and that cell survival depends on the delicate balance between DNA turnover and repair of UV‐damage. Based on these findings, we propose a model to explain the limited repair observed during post‐irradiation liquid‐holding and to account for the large difference in cell survival between irradiation at low fluence rates (fluence‐rate dependent recovery) and at high fluence rates followed by liquid‐holding (liquid‐holding recovery).
PHYSIOLOGICAL STUDIES ON PEA TENDRILS—X. CHARACTERIZATION OF THE LIGHT ACTIVATION EFFECT ON CONTACT COILING AS A BLUE LIGHT TRIGGER*
Authors: Shotwell M. , Jaffe M. J. 
Published: January 2008

Abstract— Tendrils of the Alaska pea lose their capacity to coil in response to a mechanical stimulus between 24 and 48 h after being placed in the dark. Light is thereafter necessary for the motor response to proceed once the mechanical stimulus has becn sensed by dark‐adapted tendrils. An action spectrum for this light activation effect showed that the most effective region of the visible spectrum was a narrow band in the blue region.Tendrils excised from their petiole and leaflets coiled more than any other preparation used. A linear relationship was found between the duration of post‐stimulated white light treatment and the amount of coiling.
AN EPR STUDY OF π‐CATION RADICALS IN DINUCLEOSIDE PHOSPHATES AND DNA PRODUCED BY PHOTOIONIZATION
Authors: Sevilla M. D. , D'Arcy J. B. , Morehouse K. M. , Engelhardt M. L. 
Published: January 2008

Abstract—In this work we have produced the π‐cation radicals of a number of nucleotides, dinucleoside phosphates, and DNA in aqueous glasses (8M NaCIO4) by photoionization and investigated these species by EPR spectroscopy. Results found for nucleotides and dinucleoside phosphates containing one type of DNA base, e.g. TpT, GpG, or dApdA, were used in the analysis of spectra found for mixed dinucleoside phosphates, e.g. TpdG. For TpdG and TpdA in neutral glasses photoionization takes place from the purine base and no transfer of charge to the pyrimidine base is found. In basic conditions both the adenine and thymine π‐cations are observed in TpdA. In both neutral and basic conditions the results found for mixed dinucleoside phosphates containing guanine show that the guanine cation is formed preferentially by photolysis. This result was found to extend to DNA. Photolysis of DNA in 8M NaC1O4 produced principally the guanine cation. Computer simulations using parameters determined by other workers from a study of γ‐irradiated oriented DNA closely match the spectrum found in this work attributed to the guanine cation in dinucleoside phosphates and DNA. This work thus confirms the presence of the guanine cation in γ‐irradiated DNA.
EFFECT OF RECEIVER ORIENTATION ON ERYTHEMA DOSE1,2
Authors: Burt James E. , Luther Frederick M. 
Published: January 2008

Abstract—‐The analysis of solar erythema dose under changing ozone amount, previously confined to the study of horizontal surfaces, is extended to include the effects of receiver orientation. A semi‐empirical model is used to calculate erythema (sunburn) dose for non‐horizontal plane areas under cloudless conditions as a function of latitude, season, and ozone amount. According to the model, in middle and high latitudes, surfaces with inclination angles (α) up to 45° receive at least 80% of the daily erythema dose received by a horizontal surface. Much larger reductions in daily erythema dose occur for α > 45°. which can result in a significant reduction in the latitudinal gradient of erythema dose. The amplification factor for erythema dose (Δdose/ΔO3) varies significantly with latitude, but it is only weakly dependent upon receiver orientation. Additional calculations indicate that the amplification factor may be significantly larger for skin cancer than for erythema.
PHOTOELECTRIC EFFECTS IN DYE‐SENSITIZED ARTIFICIAL LIPID MEMBRANES
Authors: Mountz James M. , Tien H. TI 
Published: January 2008

Abstract—Using dyes of known redox potentials the specific mechanisms of dark and light potential generation is analyzed in pigmented lipid membranes. The role of the ionic and electronic conductance, as well as the redox potential gradient is specifically related to the observed open circuit voltage developed across the membrane. The results can be most easily explained by the redox electrode model.
INTERMOLECULAR INTERACTIONS IN VISUAL PIGMENTS. THE HYDROGEN BOND IN VISLON
Authors: Favrot J. , Leclercq J. M. , Roberge R. , Sandorfy C. , Vocelle D. 
Published: January 2008

Abstract—Model studies including quantum chemical calculations and the measurement of infrared and ultraviolet spectra are presented as contributions to the elucidation of the nature of the photochemical step of vision. The importance of the hydrogen bond in which the protonated nitrogen of the retinal Schiff base is involved is stressed as well as that of the perturbation of the β‐ionone ring by negative groups. It is suggested that by combining these two perturbations the low excitation energy of rhodopsin can be obtained without actual protonation of the Schiff‐base prior to photon absorption. The variation of rhodopsin's color from one species to another could also be related to this. Protonation could be a consequence of photonabsorption and the higher basicity of the excited state. This, in turn, leads to the suggestion that the protonated species is actually bathorhodopsin, not rhodopsin. Comments are made on the identity of the (ππ*) state which is involved.
LASER PHOTOLYSIS STUDIES OF QUINONE REDUCTION BY CHLOROPHYLL a IN ALCOHOL SOLUTION
Authors: Tollin Gordon , Castelli Francesco , Cheddar Glen , Rizzuto Frank 
Published: January 2008

Abstract—Upon laser photolysis of chlorophyll‐quinone solutions in ethanol, transients due to the chlorophyll triplet state (Ct), the chlorophyll cation radical (C+) and the semiquinone radical (Q‐) can be observed. The rise of Q‐ parallels the decay of Ct. demonstrating the precursor role of the triplet. The decay of C+ is second order, consistent with reverse electron transfer, and has a rate constant which is independent of quinone potential, and an activation energy of 14kJ/mol due mainly to the temperature dependence of solvent viscosity. Triplet quenching and C+ yield are found to decrease with decreasing quinone potential.
SPONTANEOUS ORGANIZATION OF TWO XANTHOPHYLL COMPOUNDS IN WATER‐ALCOHOL SOLUTIONS AS SHOWN BY CIRCULAR DICHROISM
Authors: Lematre J. , Maudinas B. , Ernst C. 
Published: January 2008

Abstract— Alcoholic solutions of lutein, violeoxanthin and acetylated lutein containing more than 50% water exhibited strong CD signals in the main absorption region of the polyene chromophore.The CD spectra obtained depended on the water content of the medium and were affected by temperature and detergents.The spectroscopic changes in absorption and circular dichroism reveal a spontaneous ability of such pigment molecules for a stereospecific multimolecular organization in a hydrophilic environment. The biological significance of these spectroscopic phenomena is also discussed.
THE REGENERATION OF VISUAL PIGMENTS AND THE CHANGE OF ROD HYPERSENSITIVITY AFTER IRRADIATION BY BLEACHING LIGHT IN FROG RETINA
Authors: Azuma Katsu , Azuma Masami 
Published: January 2008

Abstract— The regeneration processes of visual pigments and the dark adaptation processes of rod photoreceptor after irradiation by bleaching light were studied by spectrophotometric, electroretinographic(ERG) methods and the measurement of early receptor potentials (ERPs) in bullfrog retina. After irradiation by bleaching light, rhodopsin in the isolated retina regenerated to an extent depending on the wavelength and intensity of the bleaching light as well as pH. Intense blue light and a weak alkaline environment (pH 7.5–9.5) favoured the regeneration. The regeneration of pigment in the green rods could not be detected in these experiments on the isolated retina. The regeneration of cone pigment was studied by measuring ERPs from both isolated retinas and retinas with pigment epithelium‐choroid complex separated from scleras, which are called PEC‐retinas. In the PEC‐retinas, cone pigment regenerated more rapidly and with better efficiency than in the isolated retinas.Rod photoreceptors desensitized permanently by bleaching light did not demonstrate hypersensitivity at 0.1 mM [Ca2+]out, which induced hypersensitivity in non‐desensitized photoreceptor, but showed the hypersensitivity when the [Ca2+]out, was lowered further by the addition of EGTA.
INTERMEDIATE PROCESSES IN PHOTOTRANSDUCTION: A STUDY IN DROSOPHILA MUTANTS
Authors: Minke Baruch , Armon Eli 
Published: January 2008

Abstract— A variety of procedures were used to modify the light response of Drosophila photoreceptors in order to find out if these manipulations produce effects that mimic some aspects of light adaptation. The ultimate goal of our approach is to use these experimental manipulations to dissect the different stages of the phototransduction process.The means which were used to modify the light response were as follows: (a) light adaptation of normal photoreceptors, (b) exposure of normal photoreceptors to various levels of CO2 (c) light adaptation of the trp Drosophila mutant in which the receptor potential decays to baseline during illumination, (d) exposure of the temperature sensitive norpAH52 mutant of Drosophila to elevated temperatures. Intensity‐response functions were obtained using intracellular and extracellular recordings. The maximal response amplitude (Vmax) was then plotted as a function of the light intensity (s̀) which evoked a response of half maximal amplitude. This plot was used to compare the effects of the procedures described above. Qualitatively all the manipulations had similar effects, they reduced Vmax and shifted s̀ to higher levels of light intensity, however, quantitatively the various effects were different.The finding that each experimental manipulation gave a different Vmax versus s̀ plot suggests that they affect different stages in phototransduction. We suggest that the slope of the Vmax versus a function can be interpreted in terms of an ordered cascade of events in phototransduction. This interpretation might give us a tool to distinguish between early and late stages in phototransduction.
ABSORPTION, LUMINESCENCE, SOLVENT‐INDUCED CIRCULAR DICHROISM AND1H NMR STUDY OF BILIRUBIN DIMETHYL ESTER: OBSERVATION OF DIFFERENT FORMS IN SOLUTION*
Authors: Holzwarth Alfred R. , Langer Elisabeth , Lehner Harald , Schaffner Kurt 
Published: January 2008

Abstract—Bilirubin dimethyl ester (I) has been studied by absorption, fluorescence and fluorescence excitation, solvent‐induced circular dichroism, and 1H NMR techniques. The existence of two forms of the solute involving either or both syn‐anti dipyrromethenone and lactam‐lactim equilibria was established, and the occurrence of even more forms remains possible. The relative population is strongly influenced by the nature of the solvent and by temperature. Thus, the population of one species predominates in ethanol. What is presumed to be the same species increases on cooling in all solvents, while the population of another species is strongly preferred in dichloromethane. In other solvents appreciable populations of both forms persist over the temperature range 77–300 K.
CHLOROPHYLL PHOTOCHEMISTRY IN CONDENSED MEDIA—II. TRIPLET STATE QUENCHING AND ELECTRON TRANSFER TO QUINONE IN LIPOSOMES*
Authors: Hurley John K. , Castelli Francesco , Tollin Gordon 
Published: January 2008

Abstract—The fate of excitation energy and electron transfer to quinones within Chl‐a‐containing phosphatidyl choline liposomes has been investigated. The bilayer membrane of the liposome stabilizes the Chl triplet state, as evidenced by a three‐fold increase in the lifetime over that observed in ethanol solution. The relative triplet yield follows the relative fluorescence yield, indicative of quenching at the singlet level. Triplet state lifetimes are markedly shortened as the Chl concentration is increased, demonstrating that quenching occurs at the triplet level as well. This process is shown to be due to a collisional de‐excitation. In the presence of quinones, the Chl triplet reduces the quinone resulting in production of long‐lived electron transfer products. The percent conversion of Chl triplet to cation radical when benzoquinone is employed as acceptor is approximately 60 ± 10%, which is slightly less than in ethanol solution (70 ± 10%). The lifetime of the radical, however, can be as much as 1900 times longer. With respect to potentially useful photochemical energy conversion, the magnitude of this increased lifetime is far more significant than is the decreased radical yield.
EXTERNAL HEAVY ATOM EFFECT IN THE ENERGY TRANSFER FROM TETRAMETHYL‐1,2‐DIOXETANE CHEMI‐EXCITED ACETONE TO ANTHRACENE
Authors: Adam Waldemar , Cilento Giuseppe , Zinner Klaus 
Published: January 2008

Abstract—Generation of the fluorescent state of anthracene by energy transfer from chemi‐excited acetone is remarkably more efficient in bromobenzene than in benzene. Triplet‐triplet energy transfer populates the second triplet of the acceptor and is followed by intersystem crossing (ISC) to the fluorescent state. It is only on the latter ISC step that the external heavy atom perturbation operates. However, with 9,10‐dibromoanthracene as acceptor, spin‐orbital coupling also increases the transfer step and more in bromobenzene than in benzene. A possible inference from this work is that 9,10‐diphenyl‐anthracene, which is commonly used to count singlets, may to some extent also count triplets.