bluuebunny/crossref_metadata_2025_split huggingface dataset:
SPECTRAL PROPERTIES OF THE RHODOPSIN‐SYSTEM OF THE CRAYFISH Astacus leptodactylus
Authors: HAMACHER K. , STIEVE H. 
Published: January 2008

Abstract— The absorption spectra of the membrane‐bound and of the digitonin‐solubilized visual pigment of crayfish Astacus leptodactylus were investigated by conventional spectrophotometry. A method was developed to isolate purified rhabdoms almost entirely free from screening pigments from a single retina. The quantity of isolated and purified rhabdoms from a single retina was sufficient to measure the absorption spectra of the visual pigment.The absorption spectra of the chromoprotein system (R and M) show that both the membrane‐bound and the digitonin‐solubilized visual pigment isomers are stable at 0°C and pH 7.0. Rhodopsin and metarhodopsin are photoreversible under these conditions without any light‐induced denaturation. The difference spectra for the chromoprotein isomers and those of different photostationary states yield maximal values for ΔE at 570 and 485 nm.At neutral pH, 0°C, Λmax of rhodopsin is 530 nm. Irradiation with light of Λ= 630 to 640 nm isomerizes rhodopsin nearly quantitatively to metarhodopsin with Λmax, of 500 nm. The molar extinction coefficient of metarhodopsin is greater than that of rhodopsin by a factor of ˜ 1.41. each measured at its respective Λmax Metarhodopsin can be isomerized to rhodopsin by irradiating at Λ > 630 nm. As the absorption spectra of the two chromoprotein isomers overlap, only part of the metarhodopsin can be reversed to rhodopsin. The maximal photoreversion can be achieved by irradiating at 460 nm. The stability of the digitonin‐solubilized chromoprotein is remarkably dependent on temperature. Warming the digitonin extract of rhabdoms from 0 to 20 or 30°C caused a shift of the rhodopsin spectrum to shorter wavelengths (Λmax= 485 nm) accompanied by a decrease of EΛmax by about 30%.
PHOTOCHEMISTRY OF PORPHYRINS: A MODEL FOR THE ORIGIN OF PHOTOSYNTHESIS*
Authors: MERCER‐SMITH JANET A. , MAUZERALL DAVID C. 
Published: January 2008

Abstract— A series of porphyrins and catalysts has been prepared as a model for the origin of photosynthesis on the primordial earth. These compounds have been used to test the hypotheses that (1) the biosynthetic pathway to chlorophyll recapitulates the evolutionary history of photosynthesis, and (2) the proto‐photosynthetic function of biogenetic porphyrins (biosynthetic chlorophyll precursors) was the oxidation of organic molecules by photoexcited porphyrins with the attendant emission of molecular hydrogen.This paper describes experiments in which photoexcited biogenetic porphyrins oxidize ethylenediamine tetraacetic acid (EDTA). The concomitant reduction of protons to hydrogen gas occurs in the presence of a colloidal platinum catalyst. The addition of methyl viologen, a one‐electron shuttle, increases the amount of molecular hydrogen generated during long irradiations and the quantum yield of hydrogen production. When the porphyrin and catalyst are held in association by molecular complexes, the increased efficiency of electron transfer produces higher yields of hydrogen gas.
TRIPLET FORMATION AND TRIPLET DECAY IN REACTION CENTERS FROM THE PHOTOSYNTHETIC BACTERIUM Rhodopseudomonas sphaeroides
Authors: SCHENCK C. C. , MATHIS P. , LUTZ M. 
Published: January 2008

Abstract— In the reaction center of photosynthetic bacteria, with the primary ubiquinone reduced, the triplet state PR of the primary electron donor (a pair of bacteriochlorophylls named P) is PO ulated with a takes place in a few ns. We measured by flash absorption spectroscopy the influence of temperature on formation and decay kinetics of PR and 3Car in the reaction center of several strains of R. sphaeroides. The rate of triplet energy transfer, measured as the decay of PR after a flash, decreases when the temperature is lowered. Between 60 and 30 K the half‐time of energy transfer becomes longer than the 3Car half‐time decay (about 6 μs) and below 20 K the transfer is slower than the internal decay of PR (about 100 μs). In several cases it is clear that PR and 3Car decay independently and are not in thermal equilibrium. The singlet energy transfer from carotenoid to P occurs with a high efficiency at all temperatures.The data can be accounted for on the basis of estimated energy levels of PR and 3Car, in the context of the equilibrium 3P ←3D where 3P is the localized triplet state of P‐870 and 3D is another triplet state. A reasonable kinetic scheme leads us to estimate that 3D is 0.0025 ± 0.005 eV above 3P. 3D may thus be the state observed by Shuvalov and Parson (1981). We propose that both triplet and singlet energy transfer between P and the carotenoid occur via a bacteriochlorophyll, to which the carotenoid should be tightly coupled via exchange interaction.
FURTHER CHARACTERIZATION OF MONOCLONAL ANTIBODY INDICATES SPECIFICITY FOR (6–4)‐DIPYRIMIDINE PHOTOPRODUCTS
Authors: Strickland P. T. , Nikaioo O. , Matsunaga T. , Boyle J. M. 
Published: January 2008

AbstractMonoclonal antibody aUVssDNA‐1 is produced by hybridoma cell line 25JF.C3B6 originally selected from cell fusions using spleen cells from mice immunized with UV‐irradiated polydeoxynucleotides (Strickland and Boyle, Photochem. Photobiol.34, 595–601, 1981). Original and subsequent studies of the binding characteristics of aUVssDNA‐1 indicated that it was specific for cyclobuta‐dithymidine photoproducts. Those investigations examined action spectrum, short‐wavelength photo‐reversal, nucleotide sequence effects, and photoreactivation using E. coli photolyase and incandescent tight. However, the more recent studies reported here examined acetophenone‐UV‐B photosensitization, UV‐B photoisomerization, and photoreactivation using cloned E. coli photolyase and filtered incandescent light. The results indicate that aUVssDNA‐1 recognizes photoproducts with characteristics of (6–4)‐dipyrimidines. Thus, previous studies in which relatively rapid repair of cyclobuta‐dithymidine photoproducts was inferred using this antibody, require re‐interpretation in light of these new findings.
QUENCHING OF CHEMIEXCITED TRIPLET ACETONE BY BIOLOGICALLY IMPORTANT COMPOUNDS IN AQUEOUS MEDIUM
Authors: Catalani Luiz H. , Bechara Etelvino J. H. 
Published: January 2008

Abstract— Thermolysis of tetramethyl‐l,2‐dioxetane is a convenient source of triplet acetone, which can be monitored in aerated solutions by the sensitized fluorescence of 9,10‐dibromoanthracene. We have investigated the quenching of chemiexcited triplet acetone in air‐equilibrated aqueous solutions containing the 9,10‐dibromoanthracene‐2‐sulfonate ion by five classes of compounds: indoles, tyrosine derivatives, quinones, riboflavin, and xanthene dyes. Quenching rates for indoles, tyrosine and its 3,5‐dihalogenoderivatives, and xanthene dyes (kq= 108‐109M‐1 s‐1) are considerably smaller than the diffusion controlled rate, whereas those for quenchers with high electroaffinities, such as quinones (IP = 10–11 eV), approach the diffusion controlled rate (kq= 1010 M‐1 s‐1). Energy transfer for riboflavin probably occurs by a triplet‐singlet Förster type process.A comparison of the present data with previous studies of quenching of enzymically generated triplet acetone (isobutanal/O2/horseradish peroxidase) by the same classes of quenchers (except riboflavin) reveals that, independent of the nature of the quencher and the deactivation mechanism, the Stern‐Volmer quenching constants (kq t0) are systematically about one order of magnitude higher in the enzymatic system. The difference is attributed to a longer lifetime of triplet acetone in the latter case, “protected” in an enzyme cavity against collisions with dissolved oxygen.
PHOTOGENERATION OF SUPEROXIDE and DECARBOXYLATED PEPTIDE RADICALS BY CARBOQUONE, MITOMYCIN C and STREPTONIGRIN. AN ELECTRON SPIN RESONANCE and SPIN TRAPPING STUDY
Authors: Carmichael Alasdair J. , Samuni Amram , Riesz Peter 
Published: January 2008

Abstract—Visible light (405–615 nm) excitation of carboquone, mitomycin C, and streptonigrin dissolved in dimethylsulfoxide in the presence of oxygen generates superoxide anion radicals (O2−). The quantum yields for these reactions range from 4.2 times 10−2 (carboquone, λ= 615 ± 10 nm) to 7.3 times 10−6 (streptonigrin, λ=545 ± 10 nm). O2− radicals were spin trapped with 5,5‐dimethyl‐1‐pyrroline‐1‐oxide (DMPO) and identified by electron spin resonance (ESR). The efficiency of DMPO to spin trap O2− in dimethylsulfoxide was determined and indicated that 91% of the O2− present in dimethylsulfoxide is trapped by DMPO. The oxidation of the photoexcited drug molecules occurs via a direct electron transfer to dissolved oxygen in solution. Ultraviolet irradiation (λ= 313 ± 10 nm) of the aminoquinone drug solutions (80% H2O, 20% dimethylsulfoxide) in the presence of peptides results in the decarboxylation of the peptides. In this case the photoexcited drugs are reduced, abstracting an electron from the C‐terminal carboxyl group of the peptides. The reaction is specific to the C‐terminal amino acid of the peptide. The decarboxylated peptide radicals were spin trapped with 2‐methyl‐2‐nitrosopropane (MNP) and identified by ESR.
RESULTS OF STUDIES OF POTENTIAL LIGHT SPECTRUM EFFECTS ON HUMAN PERFORMANCE
Authors: Irvine A. Blair , Zauner Christian W. , Allen Robert 
Published: January 2008

Abstract—Recent findings suggest that the spectrum of light from fluorescent lamps may influence human behavior and physiology. To evaluate possible light effects on exercising humans, physical performance was measured under two widely different light spectra: the spectrum from one bulb‐type (General Electric Croma‐50) approximated that of sunlight, while the other (General Electric Delux Warm White) was heavy in the red end of the spectrum. Twenty eight moderately active subjects (14 males:14 females; ages 20–32 yrs) were acclimated to light conditions for 30 min before being tested to maximal effort with a modified Balke treadmill protocol (Balke et al., 1954). The interval between tests under each light condition averaged 6.9 days. Heart rate and respiratory parameters were measured at rest, submaximum exercise (5% treadmill grade), maximum, and 3 min after test termination. Data analysis (2‐way ANOVA) indicated expected differences between genders only, with no effects attributable to light spectrum. The mean V02 max was 44.8 ml/kg min for males vs 38.6 ml/kg min for females. Mean maximum heart rate was 197 bpm for males and 194 bpm for females. Mean maximum treadmill grade averaged 24.3% for men and 22.0% for women. A significant difference in submaximum heart rate was found to be due to presentation order. These results fail to indicate that fluorescent light type influences physical performance.
MULTIPLICATIVE ACTION OF A UV‐B PHOTORECEPTOR and PHYTOCHROME IN ANTHOCYANIN SYNTHESIS
Authors: Yatsuhashi Hiroko , Hashimoto Tohru 
Published: January 2008

Abstract—Using 290‐nm light, which excites only a UV‐B photoreceptor, and 385‐ and 660‐nm light, which activate only phytochrome, the fluence rate‐response curves of monochromatic irradiations for anthocyanin synthesis in the first internodes of broom sorghum (Sorghum bicolor Moench, cv. Acme Broomcorn) were analyzed. Although the two photoreceptors absorbed light independently, they multiplicatively increased the action of each other. Accordingly, when the fluence rates of both wavelengths were changed together, the resulting slopes of the fluence rate‐response curves of double‐log plots were steep compared with the slopes obtained with the respective monochromatic irradiations. The slopes of fluence rate‐response curves for monochromatic irradiations at 325 to 345 nm were steeper than those at other wavelengths. This difference was shown to be due to the multiplicative actions of both photoreceptors.
MUTAGENIC EFFECTS PHOTOINDUCED IN MAMMALIAN CELLS IN VITRO BY TWO MONOFUNCTIONAL PYRIDOPSORALENS
Authors: Papadopoulo D. , Averbeck D. , Moustacchi E. 
Published: January 2008

Abstract— The photobiological activity of the two monofunctional pyridopsoralens pyrido (3,4‐c) psoralen (PyPs) and 7‐methyl pyrido (3,4‐c) psoralen (MePyPs) was studied in mammalian cells in vitro taking 8‐methoxypsoralen (8‐MOP) as a reference compound.In the presence of 365‐nm irradiation (UVA) MePyPs was found to be more effective than 8‐MOP in terms of DNA photobinding capacity and inhibition of cell cloning ability in Chinese hamsterV–79 cells. As a function of UVA dose and of the number of total photoadducts induced MePyPs produced a higher frequency of 6‐thioguanine resistant mutants than 8‐MOP. PyPs showed an intermediate response for cell killing and mutation induction. At equal cytotoxic levels both monofunctional pyridopsoralens exhibited the same mutagenic activity as the Afunctional furocoumarin 8‐MOP.The antiproliferative effect being taken as indicative for an efficient photochemotherapeutic activity against psoriasis, the inhibition of cloning capacity induced by MePyPs plus UVA was studied in parallel on human skin fibroblasts. Such cells were more sensitive to 8‐MOP photoadditions thanV–79 cells and even more so to MePyPs photoadditions. Data obtained on the rate of DNA semi conservative synthesis on both cell lines following treatments with the two compounds are in line with these observations.
QUANTITATION OF DNA DAMAGE IN NON‐RADIOACTIVE DNA
Authors: Sutherland Betsy M. , Ciarrocchi Giovanni , Ciomei Marina , Sutherland John C. 
Published: January 2008

AbstractThree principal methods have been developed for measuring femtomoles of damage in nanogram quantities of non‐radioactive DNA. Lesions which can be quantified include single and double strand breaks, alkali labile sites including apurinic and apyrimidinic sites, and pyrimidine dimers. The first in vitro method measures the conversion of supercoiled DNA to relaxed or linear molecules, and can detect up to four lesions per molecule. The second in vitro method (supercoil depletion) assesses the fraction of intact linear molecules of homogeneous length, and allows detection of 8 lesions/molecule. The third method, measurement of molecular length distributions of DNAs of heterogeneous length, reveals the extent of DNA damage and repair in vivo or in vitro.
SOFT X‐RAY SCANNING MICROSCOPY: ITS PRACTICAL USE FOR ELEMENTAL MAPPING AT THE NSLS U15 BEAMLINE
Authors: Jacobsen C. , Kenney J. M. , Kirz J. , McNulty I. , Rosser R. J. , Cinotti F. , Rarback H. , Shu D. 
Published: January 2008

AbstractScanning soft X‐ray microscopy offers several advantages over other forms of X‐ray microscopy. It subjects the specimen to the lower doses of radiation and by digitally recording the image, gives direct quantitative information on the absorption of the specimen as a function of position. Elemental maps can be produced easily by comparing images taken at different wavelengths, chosen to exploit X‐ray absorption edges or resonances. This technique was used to explore the distribution of calcium in 0.2 μm‐thick bone specimens, detecting concentrations of 5% by weight, with a spatial resolution of 0.2 μm. Progress in X‐ray sources in the form of undulators and in X‐ray optics indicates that soon the range of elements that can be mapped will be extended and the spatial resolution and elemental sensitivity will be improved by an order of magnitude.
MECHANISM OF CONCENTRATION QUENCHING OF A XANTHENE DYE ENCAPSULATED IN PHOSPHOLIPID VESICLES
Authors: Plant Anne L. 
Published: January 2008

AbstractEncapsulating a xanthene dye in phospholipid vesicles produces vesicle solutions that contain dye at very high microscopic concentrations, but have a low overall optical density, thereby eliminating reabsorption. Using this system, we have studied the effects of concentration on the fluorescence lifetime of one such dye, sulforhodamine 101. We have observed that the lifetime decreases as a function of encapsulated dye concentration, which is indicative of collisional quenching. The lifetime decreases from 4.5 nsec for sulforhodamine in dilute aqueous solution to 0.69 ns at an encapsulated concentration of 33 mM. The bimolecular rate constant for this event is 2.6 1010M‐1 s‐1, consistent with a diffusion controlled event. However, the quenching constant calculated from changes in intensity is 2.2 1011M‐1 s‐1. Thus, collisional quenching is not the predominant mechanism of quenching. The absorption spectra of dye in vesicles indicate an important contribution from static complex formation. Förster distance calculations indicate that energy transfer can also occur to a significant extent, with a predicted efficiency of transfer of 34% at a dye concentration of only 1 mM
STUDIES ON ENERGY DISSIPATION IN PHYCOBILISOMES USING THE KENNARD‐STEPANOV RELATION BETWEEN ABSORPTION AND FLUORESCENCE EMISSION SPECTRA
Authors: Bjourn L. O. , Bjourn G. S. 
Published: January 2008

AbstractAbsorption and fluorescence emission spectra were measured at room temperature (ca. 22°C) for solutions of phycocyanin‐1, phycocyanin‐2 and allophycocyanin from Phormidium luridum, and also for phycobilisome preparations from various blue‐green algae (Anabaena variabilis, Nostoc muscorum strain A, Nostoc sp. strain Mac, Phormidium luridum). Kennard‐Stepanov (KS) temperatures (T) were computed using the Kennard‐Stepanov relationship F() = b A() ‐5 exp(‐h/kT), where F() stands for fluorescence (energy per wavelength interval) as a function of wavelength (), A() is absorbance as a function of wavelength, b a proportionality factor, and h, c and k are Planck's constant, the velocity of light and Boltzmann's constant, respectively.In most cases experimenta/ data followed the expected relationship, but at low ionic strength allophycocyanin gave a clearly biphasic KS plot, i.e. In 5F()/A() vs 1/. This could be due to the presence of both monomers and trimers in the sample at low ionic strength.For purified allophycocyanin and phycocyanins (PC‐1 and PC‐2) as well as phycobilisomes from Phormidium luridum, the KS temperatures were only slightly (insignificantly) elevated above the sample temperature. Thus, after absorption of a photon, vibrational and configurational equilibration is essentially completed before emission of the fluorescence photon takes place.For phycobilisomes from Anabaena variabilis and the two Nostoc species the KS temperatures were moderately elevated. Since there was no correlation between radiation temperature and excitation wavelength, the elevation is not due to excess (undissipated) vibrational energy, but rather to incomplete configurational equilibration.
INTERACTIONS BETWEEN DNA AND PSORALENAMINES STUDIED WITH DICHROISM TECHNIQUES
Authors: Nordean Bengt , Wirth Michael , Ygge Birgitta , Buchardt Ole , Nielsen Peter E. 
Published: January 2008

AbstractThe interaction of a series of water‐soluble mono‐ and bis‐psoralenamines with calf thymus DNA has been studied with flow UV linear dichroism (LD), circular dichroism (CD) and equilibrium techniques. The positive charge of a protonated amino group strongly enhances the DNA affinity compared to that of the parent compound, 8‐methoxypsoralen. The orientation of the psoralen when bound to DNA, depends on the position of the amino substituent. With amino substituents in the 5‐position (on the‘hydrophobic edge’of psoralen) psoralenamines tend to bind with a considerable tilt relative to the average orientation of the DNA base‐pairs. The tilt generally increases with an increased psoralen: base‐pair ratio, indicating a more random, nonintercalated binding. With the amino substituents in the 8‐position the psoralen binds with its plane parallel to that of the DNA bases as expected for intercalation. The DNA CD supports that these psoralenamines induce a considerable perturbation of the DNA structure, and the CD induced in the psoralen chromophore is in qualitative agreement with intercalation. The study also includes a theoretical and an experimental determination of the UV transition moments of the psoralen chromophore.
THE EFFECT OF THE ANTIPSORIATIC DRUG METABOLITE ETRETIN (Ro 10‐1670) ON UVB IRRADIATION INDUCED CHANGES IN THE METABOLISM OF ARACHIDONIC ACID IN HUMAN KERATINOCYTES IN CULTURE
Authors: Punnonen Kari , Puustinen Tapio , Jansean Christer T. 
Published: January 2008

Abstract[14C]Arachidonic acid was avidly incorporated into human keratinocytes in culture and following exposure to UVB irradiation of 9 mJ/cm2 (erythemally effective, EE) substantial amounts of 14C‐radiolabel were released from the cells. The release of radiolabel was accompanied by a decrease in the labelling of phosphatidylethanolamine whereas the labelling of triacylglycerols and cholesteryl esters was increased. Keratinocytes produced significant amounts of prostaglandin E2 (PGE2) and following UVB irradiation of 9 mJ/cm2 (EE) the formation of prostaglandin E2 was increased.Etretin (Ro 10‐1670), the active metabolite of the antipsoriatic drug etretinate (Ro 10‐9359), affected significantly neither the total release of radiolabel induced by UVB nor the formation of prostaglandin E2. However, in the presence of etretin the UVB irradiation induced transfer of [l4C]arachidonic acid into triacylglycerols and cholesteryl esters was not increased as much as in the corresponding experiments without etretin. On the basis of the present study it appears that etretin does not interfere with the release of arachidonic acid in amounts which could be related to the therapeutic effects of the combination of retinoids with UVB irradiation (Re‐UVB) in the treatment of psoriasis.
NON‐INVASIVE TECHNIQUE FOR OBTAINING FLUORESCENCE EXCITATION AND EMISSION SPECTRA IN VIVO
Authors: Pottier R. H. , Chow Y. F. A. , LaPlante J.‐P. , Truscott T. G. , Kennedy J. C. , Beiner L. A. 
Published: January 2008

AbstractAn intensified photodiode array forms the heart of a sensitive spectrophotofluorometry system that permits the rapid and non‐invasive determination of fluorescence emission spectra in the skin of living, non‐anesthetized animals. Using this system, we found it possible to obtain good emission and excitation spectra of the material responsible for the weak red fluorescence that characterizes normal mouse skin, and to follow the biosynthesis and subsequent clearance of protoporphyrin IX in the skin of non‐anesthetized mice that had been given various doses of the porphyrin precursor 5‐aminolevulinic acid.
PHOTOOXYGENATION OF METHYL LINOLEATE SENSITIZED BY PORPHYRINS AND DYES IN ACETONITRILE SOLUTION AND AQUEOUS EMULSION SYSTEMS
Authors: Ohtani Bunsho , Nishida Makoto , Nishimoto Sei‐ichi , Kagiya Tsutomu 
Published: January 2008

AbstractPhotooxygenation reaction of an unsaturated fatty acid ester, methyl linoleate (methyl 9‐cis.12‐cis‐octadecadienoate, ML‐H), sensitized by porphyrins and several types of dyes has been studied in aqueous emulsion and acetonitrile solution under air at 40°C. The oxygen (O2) uptake proceeded slowly in the absence of sensitizers upon irradiation of an aqueous emulsion and an acetonitrile solution of ML‐H (20 mM) at ?ex > 290 nm (11.4 and 6.1 μmol h‐1, respectively). The rate of O2 uptake was enhanced by a catalytic amount (0.1 mM) of porphyrins and dyes; hematoporphyrin (HP), zinc tetrakis(N‐methyl‐4‐pyridiniumyi)porphyrin (ZnTMPyP), methylene blue (MB), rose bengal (RB), acridine orange (AO), and acriflavine (AF). In both systems, the sensitized photooxidation of ML‐H by O2 proceeded equimolarly to produce isomeric mixture of C9 and C13 hydroperoxides having the trans,cis and trans,trans conjugated diene configurations, independent of the types of the sensitizers used. The yield ratio of trans,trans/ trans,cis products in the MB‐sensitized photooxygenation in acetonitrile and aqueous emulsion were almost equal (0.32 and 0.35. respectively). The sensitizing activity of the sensitizers, as measured by the quantum yield of O2 uptake, increased in the order: MB (≃ 0) < ZnTMPyP < RB < HP < AF < AO in the aqueous emulsion and AO < AF < HP < RB = MB in the acetonitrile solution. The order in homogeneous acetonitrile solution was interpreted by the sensitizing ability of the dyes to produce singlet oxygen, while that in heterogeneous aqueous emulsion was correlated to the lipophilicity of dyes as well as the singlet‐oxygen‐producing ability.