bluuebunny/crossref_metadata_2025_split huggingface dataset:
LIGHT INDUCED ISOMERISATION, AT ACIDIC pH, INITIATES HYDROLYSIS OF BACTERIORHODOPSIN TO BACTERIO‐OPSIN AND 9‐CIS‐RETINAL
Authors: Fischer Ulrich Ch. , Towner Paul , Oesterhelt Dieter 
Published: January 2008

Abstract— Bacteriorhodopsin (BR) from the purple membrane of Haiobacterium halobium contains covalently bound retinal in the 13‐cis and all‐trans configurations. Several forms of bacteriorhodopsin are known, with different absorption maxima which are designated as BRλmax (nm). At acidic pH, BR605 is formed from BR560. The following sequence of reactions was found, which is initiated by irradiation of BR605 with red light:An all‐trans/13‐cis to 9‐cis isomerisation occurs in the light induced reaction BR605 ∼ BR500. BR500 seems to contain covalently bound retinal, whereas BR390 contains free retinal. By irradiation with light, BR500, BR450 and BR390 can be reconverted to BR560.
EFFECTS OF FLUENCE FRACTIONATION ON UV‐INDUCED MALIGNANT TRANSFORMATION AND CELL KILLING IN NON‐CYCLING PLATEAU PHASE MOUSE CELLS
Authors: Chan Gerald L. , Little John B. 
Published: January 2008

AbstractPlateau phase C3H 10T 1/2 mouse cells were used to measure the response to split fluence UV light irradiation in the absence of any cell cycle effects. It was found that fluence fractionation with up to 24 h between the fluences resulted in no survival enhancement. The frequency of malignant transformation was potentiated 2.5‐fold when the time interval between the fluences was greater than 4h. This potentiation of transformation was attributed to plateau phase holding rather than to fluence fractionation per se.
INTRAMOLECULAR DONOR‐ACCEPTOR SEPARATIONS IN METHIONINE‐ AND LEUCINE‐ENKEPHALIN ESTIMATED BY LONG‐RANGE RADIATIONLESS TRANSFER OF SINGLET EXCITATION ENERGY*
Authors: Kupryszewska M. , Gryczyński I. , Kawski A. 
Published: January 2008

AbstractThe Förster theory of radiationless electronic excitation energy transfer was used to determine the intramolecular separation between the tyrosine and phenylalanine residues in leucine‐ and methionine‐enkephalin. The spectral overlap integrals and the Förster critical distances were evaluated. Transfer efficiencies were determined by observing sensitized fluorescence of the acceptor and quenching of the donor fluorescence. The results were compared with theoretical estimations, better agreement being obtained with the first method.
INTERMEDIATES IN THE ROOM TEMPERATURE FLASH PHOTOLYSIS OF ADENINE AND SOME OF ITS DERIVATIVES
Authors: Arce R. , Rodriaguez G. , Singmaster K. 
Published: January 2008

Abstract—The transient absorption spectra of aqueous solutions of adenine, 2′‐deoxyadenosine, 2′‐deoxyadenosine‐5′‐phosphate and 2′‐deoxyadenylyl‐(3′‐5′)‐2′‐deoxyadenosine have been determinated at different pH values using conventional flash photolysis. Reactives intermediates produced in the flash photolysis of these adenine derivatives present similar absorption regions: two higher intensity bands in the UV and 560–720 nm wavelength region and a third weaker band at 420–560 nm. On the basis of the effects produced by triplet quenchers and/or electron scavengers the bands have been assigned to hydrated electrons, radical cations, radical anions and/or neutral radicals resulting from neutralization reactions of the charged radicals. The results indicate that the bases photoionize via a triplet state under these conditions.
PHOTOCHEMICAL STUDIES OF ARTIFICIAL BACTERIORHODOPSINS
Authors: Umadevi P. , SHEVES M. , Rosenbach V. , Ottolenghi M. 
Published: January 2008

Abstract— Three artificial bacteriorhodopsins are prepared [from synthetic aromatic and bicyclic analogues of retinal and exposed to spectroscopic and pulsed lader photolysis studies. The spectra of the pigments, all perturbed in the ring region of the molecule, are markedly blue shifted in respect to natural bacteriorhodopsin. The shift is attributed to a decreased effect of a protein charge in the vicinity of the ring, in agreement with the point‐charge model of Nakanishi et al., 1980. The photocycles of the synthetic pigments exhibit a primary red‐shifted (K) intermediate and a blue shifted (M) transient, analogous to those observed for the natural pigment. Such observations impose considerable limitations, both on the possible chromophore conformational changes and on the effects of neighbouring protein charges associated with the photocycle.It is concluded that only the Schiff base counter‐ion, but not the ring charge, may be associated with the generation of the primary red shifted K species. Moreover, the rigidity imposed on the polyene by the additional ring in the bicyclic analogue shows that the photocycle can not be initiated by conformational changes in the retinyl moiety up to the C9 carbon in the polyene chain. It is also observed that the K→L process in the photocycle is considerably slower in the case of the synthetic pigments. The observation is rationalized by attributing the process to a conformational change in the polyene moiety catalyzed by the ring protein charge.
FLUORESCENCE QUENCHING OF 5,10,15,20‐TETRA(p‐TOLYL)PORPHINE and ITS ZINC COMPLEX BY QUINONES. CHARGE‐TRANSFER INTERACTION and TRANSIENT EFFECT
Authors: Yamada Sunao , Sato Toshinori , Kano Koji , Ogawa Teiichiro 
Published: January 2008

AbstractThe fluorescent states of tetratolylporphyrin and its zinc complex in acetone were quenched by various kinds of quinones. The transient effect for the collisional quenching caused the upward deviation of the plots of the inversed fluorescence intensities of the porphyrins vs the quinone concentrations. A charge‐transfer interaction between the porphyrins in the singlet excited states and the quinones was suggested from the dependence of the quenching rate constants on the electron affinities of the quinones.
SPECTRA OF FLUORESCENCE LIFETIME AND INTENSITY OF Rhodopseudomonas sphaeroides AT ROOM AND LOW TEMPERATURE. COMPARISON BETWEEN THE WILD TYPE, THE C 71 REACTION CENTER‐LESS MUTANT AND THE B800–850 PIGMENT‐PROTEIN COMPLEX
Authors: SEBBAN PIERRE , JOLCHINE GENEVIEVE , MOYA ISMAEL 
Published: January 2008

Abstract— Spectra of the fluorescence lifetime and intensity of chromatophores from the wild type Rhodopseudomonas sphaeroides, from the C 71 reaction center‐less mutant and of the B800–850 light harvesting pigment‐protein complex have been studied by phase fluorimetry techniques at different light modulation frequencies at room and low temperature.As already known, closed reaction centers (saturating light) are still quenchers of antenna fluorescence although with a lower efficiency than when they are opened. The fluorescence yields and lifetimes of both the C 71 mutant strain and the B800–850complex are found to increase by about 30% between room and low temperature.The fluorescence lifetimes obtained for the C 71 strain (0.65 ns at 20C; 0.85 ns at 77 K) and for the B850 complex (1 ns at 20C; 1.3 ns at 77 K) indicate that the non‐radiative deactivation pathways, in the antenna, remain important in the absence of the reaction centers even at low temperature. We suggest that these data arise from the presence of special antenna molecules which act as intrinsic quenchers of the B875 antenna fluorescence. Between room and low temperature, the fluorescence yield and lifetime of the wild type are found roughly constant. This result suggests that the energy trapping by the reaction centers is independent of the temperature. The mechanism governing the energy transfer from the antenna to the reaction centers may differ from the mechanism leading to the energy transfer within the antenna. We suggest that a partially irreversible trapping of the excitation energy, on its way to the reaction center, takes place in the vicinity of the reaction center.
PHOTOTOXIC POTENTIALITIES OF TARTRAZINE: SCREENING TESTS
Authors: Merville M. P. , Decuyper J. , Lopez M. , Piette J. , Van De Vorst A. 
Published: January 2008

Abstract Tartrazine (TRT) a cosmetics, food and drug additive, was tested with respect to phototoxic potentialities. Although, using the cholesterol technique, TRT did not appear to produce any 1O2 upon visible light irradiation, the EPR spin trapping experiments with 5,5‐dimethyl‐1‐pyrroline‐N‐oxide, as spin trap, were in favour of activated oxygen species (O2˙, OH˙) and hydrated electron production by photoexcited TRT.Irradiation of TRT with complementary biological systems (nucleic acids, bacteria, biological membranes) showed that few of them can be damaged by this photosensitizer. Tartrazine could induce a weak deoxyribose degradation but did not produce any DNA strand breaks on isolated φXRFI DNA. Tartrazine was detected as mutagen in the Salmonella microsome (Ames) assay, only in conjunction with visible light. In the presence of photoexcited TRT, erythrocyte membranes were damaged by covalently cross‐linking proteins.The tests developed here seem thus to be suitable for detecting any unwanted phototoxic activity associated with potential photosensitizers.
SISTER CHROMATID EXCHANGES AND CHROMOSOME ABERRATIONS IN HUMAN CELLS INDUCED BY H2O2 AND OTHER PHOTOPRODUCTS GENERATED IN FLUORESCENT LIGHT‐EXPOSED MEDIUM
Authors: Estervig David , Wang Richard J. 
Published: January 2008

AbstractExposure of Dulbecco's modified Eagle's tissue culture medium to visible fluorescent light generated photoproducts toxic to human cells in culture. Toxicity manifested at the chromosome level was increased chromosome aberrations and sister chromatid exchanges in cells exposed to the photoproducts. Hydrogen peroxide (H2O2), a major photoproduct, induced SCE but failed to increase chromosome aberrations. Pure H2O2, or the H2O2 generated in light‐exposed medium, was necessary and sufficient for inducing all the increase in SCE. However, H2O2 was necessary but insufficient to cause most of the chromosome aberrations. Only when acting synergistically with other photoproducts did H2O, induce extensive chromosome aberrations. The relatively high cell densities at near confluence levels used in these experiments were less sensitive to light‐induced effects, nevertheless the entire light exposure dosage range effected photoproduct production adequate for inducing SCE and chromosome aberrations. Thus, mammalian tissue and cell culture media can receive sufficient dosage from fluorescent lights illuminating rooms and culture hoods for generation of photoproducts causing gross and insidious SCE and chromosome alterations.
ISOLATION and SPECTROSCOPIC CHARACTERIZATION OF THE B875 ANTENNA COMPLEX OF A MUTANT OF Rhodopseudomonas sphaeroides
Authors: Sebban Pierre , Robert Bruno , Jolchine Geneviève 
Published: January 2008

Abstract— We describe a procedure of purification of the B875 antenna complex isolated from the 3P17 mutant strain of Rhodopseudomonas sphaeroides, enriched in B875. The integrity of this isolated complex, as well as a very low content of residual B800‐850 antenna, was suggested from low temperature absorption and resonance Raman spectra. Time resolved experiments were also carried out. The important result is the identity of the fluorescence lifetime of the B875 isolated complex (0.64 ± 0.03 ns) with that of the B875 antenna in vivo (0.63 ns), in the membrane of the C71 reaction center‐less mutant of Rhodopseudomonas sphaeroides, measured in our previous study.Our data suggest that the interactions between the bacteriochlorophylls of the complex, as well as the constraints imposed by their protein environment are not much changed from the in vivo state.
COMPARISON BETWEEN THE LUMINOL‐DEPENDENT CHEMILUMINESCENCE OF POLYMORPHONUCLEAR LEUKOCYTES AND OF THE MYELOPEROXIDASE‐HOOH SYSTEM: INFLUENCE OF pH, CATIONS AND PROTEIN
Authors: Dahlgren C. , Briheim G. 
Published: January 2008

Abstract— Measurements of luminol‐dependent chemiluminescence (CL) from normal human polymorphonuclear leukocytes (PMNL) were carried out and the results were compared to the CL obtained from a cell‐free myeloperoxidase(MPO)‐HOOH‐system.The chemotactic peptide formylmethionyl‐leucyl‐phenyl‐alanine (fMLP) induced a bimodal luminol‐dependent CL response in PMNL, while phorbol myristate acetate (PMA) induced a one‐peak response. Calcium was found to be required for the fMLP but not for the PMA induced response. The absence of glucose reduced the PMA but not the fMLP induced PMNL CL response. Neither calcium nor glucose had any effect on the light emitted from a cell‐free MPO‐HOOH‐system.The PMNL CL response to both fMLP and PMA was affected by the pH‐value, in that at a low pH (6.3) the response was decreased and at a high pH (8.0) the response was increased. These effects were also obtained in cell‐free MPO‐HOOH‐systems. The presence of human serum albumin (HSA) totally inhibited the CL of a cell‐free MPO‐HOOH‐system while, in PMNL CL, HSA reduced only the first phase of the fMLP induced response.The results are discussed in view of the fact that CL is increasingly used as a clinical instrument to study defects in PMNL function and the effects on PMNL function of various agents such as drugs.
BENZOFUROCOUMARINS: NEW MONOFUNCTIONAL DNA‐PHOTOBINDING AGENTS
Authors: Palumbo M. , Rodighiero P. , Gia O. , Guiotto A. , Magno S. Marciani 
Published: January 2008

Abstract— The tetracyclic furocoumarin 2H‐benzofuro[3,2‐g]‐1‐benzo‐pyran‐2‐one and its 4 and/or II methyl analogues have been investigated in their DN A‐photobinding properties. Spectrophotometric and radioactivity measurements show that these compounds exhibit prominent ability to bind to the polynucleotide double helix by covalent photoaddition of the furocoumarin 3,4 double bond.Denaturation‐renaturation experiments demonstrate that no cross‐link of DNA chains occurs. Benzopsoralens can thus be considered as a new class of monofunctional DNA‐photobinding agents.
VACUUM UV CIRCULAR DICHROISM OF POLYSACCHARIDES
Authors: Stevens Eugene S. 
Published: January 2008

AbstractPolysaccharides are of great commercial and biological importance. At the molecular level they display a richness in structural and conformational variability, and helical structures are commonplace. Of the various experimental techniques applicable to the study of polysaccharide conformation, optical spectroscopy has been limited by the relatively high energy of the electronic excitations, the first excitation in unsubstituted saccharides being in the vacuum ultraviolet region. In the past decade, the development of VUV CD spectrometers, including the use of synchrotron radiation, has allowed the chiroptical properties of polysaccharides to be observed directly. In this brief review the major CD features of polysaccharides are summarized, and several applications are described illustrating the usefulness of VUV CD spectroscopy in the study of the polysaccharide conformation. Examples include the glucans, dextran and acetylated cellulose; the glycosaminoglycan, heparin; and the microbial polysaccharides, gellan and xanthan. A recently proposed quadrant rule which describes the sign of the 175 nm n‐σ* polysaccharide CD band also is discussed. This rule is the first attempt to place the descriptionof polysaccharide VUV CD on a theoretical foundation.
GLOBAL ANALYSIS OF FLUORESCENCE DECAY: APPLICATIONS TO SOME UNUSUAL EXPERIMENTAL AND THEORETICAL STUDIES
Authors: Beechem Joseph M. , Brand Ludwig 
Published: January 2008

AbstractThe methodology for the simultaneous analysis of fluorescence decay curves is shown to create the possibility for some new types of fluorescence decay experiments. These new experiments include the use of the T‐format in anisotropy experiments without the need to match the timing characteristics of photomultiplier tubes. Decay surfaces obtained at multiple timing calibrations can be analyzed simultaneously to resolve widely differing decay rates. Methodologies are described for the discrimination of associative from nonassociative behavior for multiexponential anisotropy decay. A systems theory approach to the analysis of excited state reactions is described.
THE TIME‐RESOLVED PHOTON‐COUNTING FLUOROMETER AT THE NATIONAL SYNCHROTRON LIGHT.SOURCE
Authors: Laws William R. , Sutherland John Clark 
Published: January 2008

AbstractA single‐photon‐counting fluorometer, capable of steady‐state and time‐dependent measure‐ments, is now operational at port U9B of the National Synchrotron Light Source at Brookhaven National Laboratory. Excitation wavelengths are selected by a prism‐grating double monochromator. Emission energies are chosen by filter(s) or by a one‐meter Spex monochromator. Commercial electronics are used for data acquisition, except for special circuitry required by the high (53 MHz) repetition rate of the synchrotron. A large sample chamber allows flexibility in arranging optical components and samples. The standard optical configuration of the sample chamber consists of a focusing mirror, a six position excitation optic wheel, a turntable with four thermostatted cuvette holders, a six position emission optic wheel, and an f/0.7 emission collection lens. Data acquisition and the setting of correct wavelengths and sample chamber optics are controlled by a Tektronix 4052 computer via the IEEE‐488 General Purpose Interface Bus. Time‐dependent fluorescence data are transferred to a VAX 11/730 for analysis; current deconvolution software includes nonlinear least‐squares programs for single curve and global analysis.
A NEW APPROACH TO THE OBSERVATION OF THE RESIST IN X‐RAY CONTACT MICROSCOPY
Authors: Shinohara Kunio , Aoki Sadao , Yanagihara Mihiro , Yagishita Akira , Iguchi Yasuo , Tanaka Akira 
Published: January 2008

AbstractX‐ray microscopy is one of the useful applications of synchrotron radiation researches, and at present, X‐ray contact microscopy is the best developed method in this field. The images on the resist in X‐ray contact microscopy have been observed with a scanning electron microscope, and there have been some attempts to use the transmission electron microscope, but few have used the replica method. We have applied the replica method with plasma polymerization‐film to observe X‐ray images on the resist with a transmission electron microscope and found it to be applicable.A long exposure time is required when we use the monochromatic synchrotron radiation with a grasshopper monochromator. Our preliminary experiments with a new light source, undulator radiation, showed that it is very intense and useful for X‐ray contact microscopy.
THE VASCULAR RESPONSE OF HUMAN SKIN TO ULTRAVIOLET RADIATION
Authors: Farr P. M. , Diffey B. L. 
Published: January 2008

AbstractThe vascular response of human skin to 300 nm (UV‐B) and 254 nm (UV‐C) ultraviolet radiation was assessed using the reflectance measurement of erythema and the technique of laser Doppler velocimetry. For both wavelengths, the increase in measured Doppler blood flux varied with the increase in erythema in a quadratic manner predicted by a simple model based on the principles of fluid mechanics. This suggests that the mean red blood cell velocity increases significantly in areas of UV‐B and UV‐C erythema. No qualitative difference in response to these two wavelengths was demonstrated, suggesting that the same blood vessels are involved in the causation of both UV‐B and UV‐C erythema.
FLUORESCENCE LIFETIMES OF ANGULAR FUROCOUMARINS
Authors: Andreoni A. , Cubeddu R. , Knox C. N. , Truscott T. G. 
Published: January 2008

AbstractProperties of singlet states of a range of non‐substituted and aceto‐substituted angular furocoumarins as investigated by the technique of time‐resolved fluorescence are reported. In the three solvents studied, water, ethanol and benzene, a variety of 1, 2 or 3 fluorescence lifetime components were found and resolved, the importance of which varied in the different media. No correlation or marked variation could be observed for this lifetime data with either solute concentration or excitation wavelength. The results are discussed with respect to triplet quantum yields and to the possible role of the close proximity of various excited singlet states.
PHOTOCHEMICAL COUPLING OF 5‐BROMOURACIL TO TRYPTOPHAN, TYROSINE AND HISTIDINE, PEPTIDE‐LIKE DERIVATIVES IN AQUEOUS FLUID SOLUTION
Authors: Dietz Timothy M. , Koch Tad H. 
Published: January 2008

AbstractDirect irradiation of 5‐bromouracil (BU) in aqueous fluid solution in the presence of tryptophan (trp), tyrosine (tyr) or histidine (his) derivatives using a XeCl excimer laser at 308 nm yielded photocoupling of BU to the aromatic ring of each amino acid. Irradiation of BU at 308 nm most likely results in excitation of the n‐φ* transition, intersystem crossing to the triplet manifold, and coupling via electron transfer from the aromatic amino acid. The coupling observed was regiospecific between the 5‐position of uracil (U) and the 2‐position of the indole and phenol rings and the 5‐position of the imidazole ring of the respective amino acids. Quantum yields of photocoupling to BU ranged from 1 × 10‐3 to 7 × 10‐3 and paralleled known rates of electron transfer and ionization potentials of the aromatic rings. The photocoupling between BU and some of the aromatic amino acid peptide‐like derivatives possibly mimics photocrosslinking of BU‐DNA to associated proteins, a potentially useful photoreaction for studying nucleic acid‐protein interactions. Formation of crosslinks of the type proposed here might be detected by the characteristic fluorescence emission of the uracil amino acid adducts.
CHEMICALLY MODIFIED PHOTOSYNTHETIC BACTERIAL REACTION CENTERS: CIRCULAR DICHROISM, RAMAN RESONANCE, LOW TEMPERATURE ABSORPTION, FLUORESCENCE AND ODMR SPECTRA AND POLYPEPTIDE COMPOSITION OF BOROHYDRIDE TREATED REACTION CENTERS FROM Rhodobacter sphaeroides R26
Authors: Beese D. , Steiner R. , Scheer H. , Angerhofer A. , Robert B. , Lutz M. 
Published: January 2008

Abstract— Reaction centers from Rhodobacter sphaeroides have been modified by treatment with sodium borohydride similar to the original procedure [Ditson et al., Biochim. Biophys. Acta766, 623 (1984)], and investigated spectroscopically and by gel electrophoresis.(1) Low temperature (1.2 K) absorption, fluorescence, absorption‐ and fluorescence‐detected ODMR, and microwave‐induced singlet‐triplet absorption difference spectra (MIA) suggest that the treatment produces a spectroscopically homogeneous preparation with one of the ‘additional’ bacteriochlorophylls being removed. The modification does not alter the zero field splitting parameters of the primary donor triplet (TP870).(2) From the circular dichroism and Raman resonance spectra in the1500–1800 cm‐1 region, the removed pigment is assigned to BchlM, e.g. the “extra” Bchl on the “inactive” M‐branch.(3) A strong coupling among all pigment molecules is deduced from the circular dichroism spectra, because pronounced band‐shifts and/or intensity changes occur in the spectral components assigned to all pigments. This is supported by distinct differences among the MIA spectra of untreated and modified reaction centers, as well as by Raman resonance.(4) The modification is accompanied by partial proteolytic cleavage of the M‐subunit. The preparation is thus spectroscopically homogeneous, but biochemically heterogenous.
UROCANIC ACID AND IMMUNOSUPPRESSION
Authors: Norval M. , Simpson T. J. , Ross J. A. 
Published: January 2008

Abstract—Urocanic acid, a molecule found at high concentration in the stratum corneum, acts as a photoreceptor for UV‐light, isomerizing from the naturally occurring trans‐lorm to the cis‐form. It has been proposed that cis‐urocanic acid may mediate the transient alteration in immune surveillance resulting in immunosuppression induced after UV‐irradiation, by interacting with immune cells locally and/or systemically to generate T cells with suppressor function. The evidence to support this hypothesis is summarized, and possible interactions of urocanic acid with immune cells and their outcome are discussed.