bluuebunny/crossref_metadata_2025_split huggingface dataset:
EVENTS SURROUNDING THE EARLY DEVELOPMENT OF EUGLENA CHLOROPLASTS—XI PROTOCHLOROPHYLL(IDE) AND ITS PHOTOCONVERSION*
Authors: Cohen Charles E. , Schiff Jerome A. 
Published: January 2008

Abstract— The small amounts of chlorophyll precursors in dark‐grown cells of Euglena gracilis Klebs var. bacillaris Pringsheim and the presence of contaminants which interfere with their purification have made their isolation and characterization difficult. We now extract cells with acetone: 0.1 M NH4OH (9:1 v/v). Protochlorophyll is obtained by extracting this solution with petroleum ether (30–50° b.p.) and extracting this petroleum ether fraction with 80% acetone to remove substances which interfere with subsequent chromatography. Protochlorophyllide remaining in the original acetone: NH4OH fraction is extractable into diethyl ether after adjusting the pH to approximately 5.5. Both pigments are verified and further purified by chromatography on Whatmann 3 MM paper using benzene:petroleum ether:acetone (30:10:1) or cellulose MN 300 thin layers with methanol:methylene chloride:water (100:18:20). These pigments resemble their well‐described barley counterparts in solubility properties, spectral absorption maxima in ether (432, 530, 571 and 623 nm) and chromatographic behavior. Substantial amounts of protopheophytin and protopheophoribide are also found along with the Mg2+— containing pigments in cell extracts even when precautions are taken to avoid loss of Mg2+ during extractions and purification.Using heated cells before and chilled solvents after illumination to preclude enzymatic modification of pigments, chlorophyll and very small amounts of chlorophyllide are found as products of the photo‐conversion of the protopigments suggesting that both protochlorophyll and, to a much smaller extent, protochlorophyllide are photoconvertible in these organisms. These properties join several others which suggest that the Euglena chorophyll‐forming system more closely resembles that found in young bean leaves rather than the chlorophyll‐forming system of the older leaf material usually studied.
EFFECTS OF PIGMENT HETEROGENEITY ON FLUORESCENCE IN PHOTOSYNTHETIC UNITS
Authors: Swenberg C. E. , Dominijanni R. , Geacintov N. E. 
Published: January 2008

SummaryA computer solution of the Pauli Master Equation is used to study the fluorescence quantum yield of a two‐dimensional random host‐trap‐anti‐trap system. Calculations predict that both the quantum yield and prompt fluorescence lifetime from photosynthetic units increase as pigment heterogeneity increases. From the temperature dependent action spectrum of fluorescence the pairwise Forster transfer rate is predicted to decrease with decreasing temperature.
A SINGLE PULSE PICOSECOND LASER STUDY OF EXCITON DYNAMICS IN CHLOROPLASTS
Authors: Geacintov Nicholas E. , Breton Jacques , Swenberg Charles E. , Paillotin Guy 
Published: January 2008

Abstract. Using single picosecond laser pulses at 610 nm, the fluorescence yield (φ) of spinach chloroplasts as a function of intensity (I) (1012‐1016 photons/pulse/cm2) was studied in the range of 21–300 K. The quantum yield decreases with increasing intensity and the φ vs I curves are identical at the emission maxima of 685 and 735 nm. This result is interpreted in terms of singlet exciton‐exciton annihilation on the level of the light‐harvesting pigments which occurs before energy is transferred to the Photosystem I pigments which emit at 735 nm.The yield φ is decreased by factors of 12 and 43 at 300 and 21 K, respectively. The shapes of the φ vs I curves are not well accounted for in terms of a model which is based on a Poisson distribution of photon hits in separate photosynthetic units, but can be satisfactorily described using a one‐parameter fit and an exciton‐exciton annihilation model. The bimolecular annihilation rate constant is found to be γ= (5–15) times 10‐9cm3s‐1 and to exhibit only a minor temperature dependence. Lower bound values of the singlet exciton diffusion coefficient (≥ 10‐3cm2s‐1), diffusion length (≥ 2 times 10‐6cm) and Förster energy transfer rates (≥ 3 ≥ 1010s‐1) are estimated from γ using the appropriate theoretical relationships.
FERRIC ION AS PHOTORECEPTOR OF PHOTO‐ PHOBOTAXIS IN NON‐PIGMENTED RHODOSPIRILLUM RUBRUM
Authors: Harayama Shigeaki , Iino Tmsuo 
Published: January 2008

Abstract— Rhodospirillum rubrum cultivated aerobically and containing no detectable bacteriochloro‐phyll assembled in their phobotactic response into a spot of blue and near UV light. The shape of the action spectrum for the phenomenon was similar to that of the absorption spectrum of ferric ion in aqueous solution. The photophobotactic response was not observed in media containing no ferric ion. Increasing concentration of the ion in the media resulted in an increasing degree of their photophobotactic response. Ferrous ion could not be substituted for ferric ion unless its autooxidation in medium was allowed.In addition to ferric ion, existence of appropriate anion, by which photoreduction of ferric ion took place efficiently, was necessary to induce an appreciable photophobotactic response. This suggested that the apparent photophobotaxis was, strictly speaking, chemophobotaxis induced by a photochemical product of ferric complex in medium.
THE EFFECT OF 8α‐SUBSTITUTION ON FLAVIN TRIPLET STATE AND SEMIQUINONE PROPERTIES AS INVESTIGATED BY FLASH PHOTOLYSIS*
Authors: Edmondson Dale E. , Rizzuto Frank , Tollin Gordon 
Published: January 2008

Abstract— Flash photolysis techniques have been used to study the effect of 8α‐substitution on flavin triplet state formation and decay and on the properties of neutral and anionic serniquinones. Compared with riboflavin, the N(1) and N(3) isomers of 8α‐histidylriboflavin show a lower triplet yield (˜10%) and a faster rate of decay (˜ 4‐Cfold). Acetylation of the histidyl a‐amino groups and of the flavin ribityl side chain results in a 2‐fold increase in triplet yield and a 2‐fold slower rate of decay.The yield of neutral 8α‐substituted flavin semiquinones upon flash photolysis in the presence of EDTA was approximately 50% that given by riboflavin. These substituted flavin neutral semiquinones dismutated at a rate 2–3 times slower than the corresponding unsubstituted form, although the anionic semiquinones dismutated at approximately the same rate.In the presence of oxygen, the kinetics of semiquinone decay changed from second order to pseudo‐first order upon raising the pH, thus showing anionic semiquinone oxidation as seen previously with unsnbstituted flavins. The pK values for the ionization of the neutral 8α‐substituted Aavin semiquinones are 1–1.5 units lower than the unsubstituted form. The anionic 8α‐substituted flavin semiquinones react with oxygen at a rate 2–10 times more slowly than does the riboflavin form. Such alterations in properties probably reflect the electron‐withdrawing effect of the 8α‐substituents on the flavin ring system.
CHEMIENERGIZED SPECIES IN PEROXIDASE SYSTEMS
Authors: Cilento Giuseppe , Durán Nelson , Zinner Klaus , Vidigal Carmen C. C. , Oliveira Olga M. M. Faria , Haun Marcela , Fauoni Adelaide , Augusto Ohara , Baptista Roberto Casadei de , Bechara Etelvino J. H. 
Published: January 2008

Abstract— Several hemeprotein‐catalyzed reactions generate products of the type expected from the cleavage of a high energy intermediate. For some systems, the formation, in high yield, of a carbonyl compound in its excited triplet state has been firmly established on the basis of (i) equivalence of the chemiluminescence and phosphorescence spectra of the expected products; (ii) energy transfer to sensitizers containing heavy atoms and (iii) occurrence of photoproducts. The excited species appears to be generated within the enzyme and shielded from quenching by oxygen. It may be quenched, however, via long‐range triplet‐singlet energy transfer.This work strongly supports our hypothesis that excited electronic states are also formed in biological systems which are not necessarily bioluminescent. One of the functions which peroxidases may thus fulfill might be the utilization of the potential of photochemistry in the absence of light.
COMPARATIVE STUDY OF OXIDATION OF NUCLEIC ACID COMPONENTS BY HYDROXYL RADICALS, SINGLET OXYGEN AND SUPEROXIDE ANION RADICALS
Authors: Cadet Jean , Teoule Robert 
Published: January 2008

Abstract— Superoxide radicals, singlet oxygen and hydroxyl radicals are individually or in combination involved in radiation or photochemical processes and in various enzymatic reactions. The reactivity and the mechanism of reaction of these oxygen species with some biologically significant DNA components were investigated through the characterization of the final oxidation products.Superoxide radicals appear to be unreactive with purine and pyrimidine 2'‐deoxyribonucleosides. However, the autoxidation reaction of 6‐hydroxydopamine leads to extensive degradation of thymine through the intermediary of hydroxyl radicals. Chemically and microwave‐discharge generated singlet oxygen oxidation is specific to 2'‐deoxyguanosine. The main oxidized products of these reactions were also characterized as well as an as yet unidentified nucleoside in the methylene‐blue photooxydation of 2‐deoxyguanosine. These results, in addition to specific deuterium effect experiments, lend support to the involvment of singlet oxygen (type II mechanism) in the methylene‐blue photosentization. No singlet oxygen effect was observed in aqueous irradiated system.
AN OSCILLATING SYSTEM REGULATING DEVELOPMENT OF PLANTS
Authors: Gregory Anne , Klein Attila O. 
Published: January 2008

AbstractPhytochrome conversion shifts the developmental pattern of dark‐grown bean (Phaseolus vulgaris) seedlings. Red light was found to initiate rapid oscillations in a system that links illumination with subsequent growth. A single 8 s flash of red light increased the average leaf weight measured 24 h later by 8%. When total illumination was kept constant but the interval between two 4 s flashes was varied, the resulting leaf weight increase was not uniform but depended on the length of the interval between flashes and showed a series of deep minima followed by sharp maxima. Weight increase at the maximum was 60% greater than at the minimum. The minimum‐maximum transitions recurred every 45 s for at least 22 min. Four s of far red light interposed between the two red flashes abolished the oscillation. Temperature between 15 and 30°C had no significant influence on the period of the oscillation but the period varied directly with the duration of the initial red flash. A 2 s initial flash resulted in a 35 s period, while 40 s of red light caused a 2 min period. Oat (Avena sativa) and radish (Raphanus sativus) seedlings were found to possess similar oscillating mechanisms of growth regulation. The lack of pronounced temperature effects as well as our other findings, suggest that this oscillating system may participate in the time measuring as well as growth regulating mechanisms by which phytochrome controls circadian periodicity and development.
EVENTS SURROUNDING THE EARLY DEVELOPMENT OF EUGLENA CHLOROPLASTS. 12. SPECTROSCOPIC EXAMINATION OF THE PROTOCHLOROPHYLL(IDE) PHOTOTRANSFORMATION IN INTACT CELLS*
Authors: Kindman L. Allen , Cohen Charles E. , Zeldin Michael H. , Ben‐Shaul Yehuda , Schiff Jerome A. 
Published: January 2008

Abstract— Absorption measurements in the 600–720 nm region of dark‐grown cells of Euglena gracilis Klebs var. bacillaris Cori were made in vivo at room temperature using computer‐assisted spectrophotometry. Dark‐grown wild‐type cells have a prominent absorption maximum at 634 nm due to protochlorophyll(ide) absorption. Upon illumination, the absorption at 634nm decreases and a peak appears at 674nm, representing the phototransformation of protochlorophyll(ide) to chlorophyll(ide). Using difference spectroscopy, the resynthesis in the dark of protochlorophyll(ide) by previously‐illuminated wild‐type dark‐grown cells was found to begin at about 10min after illumination and reached completion by about 25 min, the amount of protochlorophyll(ide) resynthesized being equivalent to that of dark‐grown cells. Resynthesis of protochlorophyll(ide) following a second illumination follows the same kinetics, indicating that protochlorophyll(ide) resynthesis is under tight regulation, possibly via feedback control. Cells of dark‐grown wild‐type and W3BUL, a mutant lacking protochlorophyll(ide) contain a component absorbing at 658 nm which does not undergo phototransformation when examined by difference spectroscopy at room and liquid N2 temperatures.Following the phototransformation of protochlorophyll(ide) 634 to chlorophyll(ide) 674, the chlorophyll(ide) 674 shifts to shorter wavelengths, ultimately to 671 nm. Possible relationships among the various spectroscopic forms of protochlorophyll(ide) and chlorophyll(ide) at room temperature and liquid N2 temperature in Euglena and higher plants are presented. It is concluded that Euglena, unlike older, etiolated higher plants, contains only protochlorophyll(ide) 634, making it an excellent system in which to examine the phototransformation of this pigment species in the absence of other forms.
THE REACTION CENTER OF PHOTOSYNTHETIC BACTERIA
Authors: LeslieDutton P. , Prince RogerC. , Tiede DavidM. 
Published: January 2008

Abstract. Investigations on the bacterial photosynthetic reaction center have recently made several important steps forward. Progress has been made in measuring the time course of the light‐driven reactions, and in understanding the thermodynamics of these processes, in determining the chemical‐structural properties of the protein and its constituents, and in elucidating the functional relationship of the reaction center with the chromatophore membrane. Although the well‐characterized Rhodopseudomonas sphaeroides reaction center has been the main exploratory vehicle in many of these studies, we now have an ever increasing body of information from bacteria of other species and genera. This work is providing information from which we can underline features that are common to bacterial reaction centers, but it also reveals differences which may reflect different selection pressures on the separate species.In this report we shall describe the early photochemical events of the reaction center, summarize the comparative biology of the reaction center, and discuss some of the current physical‐chemical problems pertaining to the redox components of the reaction center.
A POSSIBLE MECHANISM FOR THE ROLE OF N‐RETINYLIDENE PHOSPHATIDYL ETHANOLAMINE IN THE REGENERATION OF RHODOPSIN
Authors: Rabinovitch B. 
Published: January 2008

Abstract— A series of molecular orbital calculations on a model Schiff base comparable to protonated N‐retinylidene phosphatidyl ethanolamine isomers has been made. The effect of the charged oxygen atoms of the phosphate moiety on the distribution of positive charge along the polyene chain of these isomers has been calculated. The stabilizing coulombic energy of interaction of these opposite charges and the possibility of free rotation around carbonxarbon double bonds in the electronically excited state has led to the conclusion that an 11‐cis Schiff base isomer is the most probable product of the photoisomerization of an all‐trans Schiff base.The formation of a stable unprotonated all‐trans Schiff base in aqueous detergent dispersion and its subsequent conversion to the protonated form, both with absorption spectra in conformity with the literature, is demonstrated.
PHOTOCHEMICAL DECOMPOSITION OF 1, 4‐BENZODIAZEPINES. NITRAZEPAM*
Authors: Cornelissen P. J. G. , van Henegouwen G. M. J. Beijersbergen 
Published: January 2008

Abstract— The photochemical activity of nitrazepam, a drug of which phototoxic effects are known, is investigated. Nitrazepam decomposes photochemically in an oxygen‐poor medium, while it is relatively stable in the presence of oxygen. It appears that this quenching of excited nitrazepam by molecular oxygen leads to the formation of singlet oxygen. This is demonstrated in three different ways:1. In the presence of 2‐methyl‐2‐pentene as acceptor of singlet oxygen, two characteristic products are formed: 2‐methyl‐1‐penten‐3‐ol and 2‐methyl‐3‐penten‐2‐ol.2. The photosensitized oxidation of L‐dopa in the presence of nitrazepam is increased when D2O, instead of H2O, is added to the solvent system, due to the longer lifetime of singlet oxygen in D2O.3. The β‐value, the ratio of the rate of decay of singlet oxygen to its rate of reaction, is determined with L‐dopa as acceptor of singlet oxygen. The same value is obtained with both nitrazepam and methylene blue, a known singlet oxygen generator.
SENSITIVITY OF MONONUCLEAR CELLS TO UV RADIATION: EFFECT ON SUBSEQUENT STIMULATION WITH PHYTOHEMAGGLUTININ
Authors: Morison Warwick L. , Parrish John A. , McAuliffe Daniel J. , Bloch Kurt J. 
Published: January 2008

Abstract—The ability of peripheral blood mononuclear cells to incorporate 3[H] thymidine into nuclear DNA following stimulation by phytohemagglutinin is reduced by prior exposure to UV radiation in vitro: the reduction is dose and wavelength dependent. The doses required to affect this function of mononuclear cells are higher than the doses required to reduce trypan blue dye exclusion, so that following exposure to radiation populations of cells that are unable to exclude trypan blue dye are still capable of responding to phytohemagglutinin. This finding indicates that trypan blue dye exclusion may not accurately reflect the viability of cells after exposure to UV radiation.
PHOTOMOVEMENT, PIGMENTATION AND UV‐B SENSITIVITY IN PLANARIA
Authors: Barcelo Jeanne A. 
Published: January 2008

Abstract—Four differently pigmented species of planarians were examined for UV‐B (Λ= 320 280 nm) tolerance and ability to delect and avoid UV‐B‐exposed areas. It was found that lighter‐pigmented species are more UV sensitive and that movement out of the UV‐B is directly related to UV sensitivity. Three species showed positioning preference corresponding to their pigmentation; the darker the species, the less avoidance of UV‐B. The white (unpigmented) species showed exceptional and very sensitive behavior.
ULTRAVIOLET LIGHT‐INDUCED INHIBITION OF CELL DIVISION AND DNA SYNTHESIS IN AXENICALLY GROWN REPAIR MUTANTS OF DICTYOSTELIUM DISCOIDEUM
Authors: Kielman J. K. , Deering R. A. 
Published: January 2008

Abstract—Cell division and DNA synthesis were studied during axenic growth following 254 nm ultraviolet light (UV) irradiation of a repair‐proficient parental strain (rad+, D10 colony formation = 195 J/m2) and two repair mutants (radC. D10= 50 J/m2; radB. D10= 5 J/m2) of Dictyostelium discoideum. Isopycnic CsCI gradients were used to distinguish uptake of labeled precursors into nuclear (n) and mitochondrial (m) DNA, using Netropsin to enhance the density resolution. In all strains, m‐DNA synthesis was inhibited to a lesser extent than was n‐DNA synthesis. For radC, which has been shown in other experiments to be slow in incision and dimer removal, the UV‐induced lags in division and n‐DNA synthesis were longer than for rad+. However, radB showed a more complex response. Although brief division lags were observed for < 10 J/m2, little immediate division lag was detected at greater fluences. Instead, a brief period of cell multiplication of up to but not exceeding two‐fold occurred, followed by a cessation of division, and then by lysis. Fluences that yielded extensive lags in n‐DNA synthesis in rad‐ and radC resulted in little detectable immediate postirradiation lag in n‐DNA synthesis in radB. However, later in the postirradiation period, when DNA synthesis had resumed in rad+ and radC. it gradually declined to near zero in radB. We conclude: (1) that the more extended lag in division and n‐DNA synthesis in radC is consistent with its slower rate of excision repair, and (2) that radB contains a defect resulting in less initial blockage of DNA replication by UV lesions.
ULTRAVIOLET ENHANCED REACTIVATION OF HERPES SIMPLEX VIRUS INACTIVATED BY DIFFERENT WAVELENGTHS OF UV RADIATION
Authors: Detsch Richard M. , Bryant F. Dudley , Moore Sharon P. , Coohill Thomas P. 
Published: January 2008

Abstract—The degree of ultraviolet enhanced reactivation (UVR) exhibited by mammalian cells when infected with Herpes simplex virus inactivated by different wavelengths of far ultraviolet (UV) radiation was measured. A wavelength dependence for this effect is presented over the wavelength region 238–297 nm. Within the limits of the deviations obtained, the degree of UVR exhibited is similar at each wavelength. This suggests that virus irradiated with different wavelengths of UV radiation received the same type of damage or that cells repaired the different types of viral damage with the same efficiency.
DNA DAMAGE AND REPAIR IN HUMAN CELLS EXPOSED TO SUNLIGHT
Authors: Parsons P. G. , Goss P. 
Published: January 2008

Abstract—Cultured human cells were treated with direct sunlight under conditions which minimised the hypertonic, hyperthermic and fixative effects of solar radiation. Sunlight produced similar levels of DNA strand breaks as equitoxic 254 nm UV in two fibroblast strains and a melanoma cell line, but DNA repair synthesis and inhibition of semiconservative DNA synthesis and of DNA chain elongation were significantly less for sunlight‐exposed cells. DNA breaks induced by sunlight were removed more rapidly. Thus, the repair of solar damage differs considerably from 254 nm UV repair. Glass‐filtered sunlight (> 320 nm) was not toxic to cells and did not induce repair synthesis but gave a low level of short‐lived DNA breaks and some inhibition of DNA chain elongation; thymidine uptake was enhanced. Filtered sunlight slightly enhanced UV‐induced repair synthesis and UV toxicity; photoreactivation of UV damage was not found. Attempts to transform human fibroblasts using sunlight, with or without phorbol ester, were unsuccessful.
STRUCTURE AND PHOTOBIOLOGICAL ACTIVITY OF 7‐CHLORO‐1,4‐BENZODIAZEPINES. STUDIES ON THE PHOTOTOXIC EFFECTS OF CHLORDIAZEPOXIDE, DESMETHYLCHLORDIAZEPOXIDE AND DEMOXEPAM USING A BACTERIAL INDICATOR SYSTEM
Authors: Cornelissen P. J. G. , Beijersbergen G. M. J. , Henegouwen Van , Mohn G. R. 
Published: January 2008

Abstract—The photobiological activity of chlordiazepoxide, an active ingredient of the drug Librium, which is known to induce phototoxic effects, and two of its metabolites, desmethylchlordiazepoxide and demoxepam, was investigated. Upon irradiation of these biologically active compounds with longwave UV light, the main decomposition product formed is an oxaziridine. Using a strain of Salmonella typhimurium as a test organism for cytotoxicity, it could be demonstrated that not only the drug itself, but also the major mammalian metabolites are phototoxic and, furthermore, that the respective oxaziridines are responsible for the toxic effects found upon irradiation. A close relationship appears to exist between the phototoxicity of the nitrones and the toxicity in the dark of their respective oxaziridines. Investigations of the photobiological activity of a few closely structurally related benzodiazepines could establish that a 4‐oxide moiety in the benzodiazepine nucleus is the structural characteristic responsible for the appearance of phototoxicity; in those compounds which contain a 4‐oxide in the benzodiazepine nucleus, photo‐decomposition to a toxic oxaziridine is observed, while the analogues lacking the 4‐oxide moiety do not show this characteristic and, therefore, no phototoxic effects can be observed. Finally, mutagenicity tests performed with the same bacterial indicator as used for phototoxic studies, and including chlorpromazine as a positive reference compound, indicate that under the present experimental conditions photoproducts formed upon irradiation of chlordiazepoxide and its metabolites with longwave UV light do not exert a mutagenic effect.