bluuebunny/crossref_metadata_2025_split huggingface dataset:
PHOTOMOVEMENT IN AN “EYELESS” MUTANT OF Chlamydomonas
Authors: Morel‐Laurens N. M. L. , Feinleib M. E. 
Published: January 2008

AbstractThe function of the stigma (“eyespot”) in the green flagellate Chlamydomonas reinhardtii was investigated by comparing the photomovement of the wild‐type alga with that of an “eyeless” mutant (ey 627). Movements of individual cells in response to a blue‐green stimulus light were recorded using a videomicroscope system and were analyzed using vectorial methods. Cells of the “eyeless” mutant were phototactic; at a high stimulus fluence rate, their swimming paths were directed away from the light source. Although the orientation of the mutant was not as strongly directional as that of the wild type, it was statistically significant. However, the swimming paths of the mutant cells were very erratic in the presence of the stimulus beam, undergoing frequent changes of direction. Despite the differences in their phototactic orientation, cells of mutant and wild type all showed a distinct step‐up photophobic response at the onset of stimulation. These results are consistent with the hypothesis that the stigma plays an accessory role in phototaxis, either by shading the photoreceptor or by acting as a quarter‐wave reflector.
THE CHLOROPHYLL‐SENSITIZED REACTION BETWEEN BENZOQUINONE AND ETHANOL*
Authors: Seely G. R. , Rutkoski A. M. , Shaw E. R. 
Published: January 2008

AbstractThe electron‐transfer reaction between triplet excited chlorophyll and quinones has been extensively studied as a model of the primary reaction in photosystem II. There has also been reported a minor reaction in which the chlorophyll cation radical ostensibly oxidizes the alcohol solvent or even water, leading to a gradual net reduction of quinone, but the exact mechanism and even the existence of this reaction has been uncertain. We have examined the consequences of prolonged irradation of ethyl chlorophyllide and benzoquinone in acidulated ethanol, and find a chlorophyllide‐sensitized reaction which is not analogous to the better‐known autosensitized reduction of quinones in blue or UV light. In the chlorophyllide‐sensitized reaction, benzoquinone is apparently converted to ethoxy‐substituted quinones and quinols, and polymeric material. Ethyl chlorophyllide (or chlorophyll) is simultaneously oxidized to more polar products which themselves continue to photosensitize the reaction of quinones. The production of acetaldehyde could not be demonstrated in the sensitized reaction. Chlorophyllide‐sensitized reaction of (l‐hydroxyethyl)benzoquinone, ethoxybenzoquinone and 2.5‐diethoxybenzo‐quinone were examined for additional information. A reaction sequence, tentatively proposed to accommodate the known facts, starts with oxidative attack by quinone on an oxidized chlorophyllide radical formed by loss of a hydroxyl proton from alcohol bound as a ligand to Mg2+. It is not likely that this reaction is closely related to events at the oxidizing side of photosystem II.
OXIDATION‐REDUCTION AND EPR PROPERTIES OF A CYTOCHROME COMPLEX FROM Chromatium vinosum
Authors: Knaff David B. , Kraichoke Saran 
Published: January 2008

AbstractA cytochrome b560‐c553 containing fraction from the photosynthetic purple sulfur bacterium Chromatium vinosum has been shown to contain equimolar amounts of the two cytochromes and also to contain ubiquinone. The oxidation‐reduction midpoints (at pH 7.5) of cytochrome b560 and c553 in this fraction are −5 and +20 mV, respectively, essentially identical to the values found for the cytochromes in chromatophores. The fully oxidized fraction exhibits EPR features at g = 2.93 and 3.35. The former had previously been identified as originating from ferricytochrome c553, while the latter appears to arise from ferricytochrome bS60.
SPECTRAL STUDY OF THE PHOTOCHEMISTRY OF DIPYRROLE MODELS FOR BILIRUBIN BOUND TO HUMAN SERUM ALBUMIN
Authors: Lamola Angelo A. , Braslavsky Silvia E. , Schaffner Kurt , Lightner David A. 
Published: January 2008

Abstract—Dipyrromethenones, which include xanthobilirubinic acid (I), its methyl ester (II) and the endo‐vinyl analog of neoxanthobilirubinic acid methyl ester (“half bilirubin” methyl ester) (III) bind to human serum albumin (HSA) and thereby exhibit greatly increased fluorescence as well as induced circular dichroism in their long wavelength transitions. As determined from fluorescence studies, the “tightness” of the binding to HSA is, inter alia, inversely related to the inherent solubility of the dipyrromethenone in aqueous buffer. Fast (ps) configurational isomerization (Z→E) is the major pathway for decay of the first excited (singlet) states of the HSA‐bound dipyrromethenones. A quantum yield of − 0.4 is associated with the Z→E isomerization. Binding to HSA enhances the lifetimes of the less thermodynamically stable E‐isomers. The results of these studies of “half bilirubins” allow a clear evaluation of the effects of protein binding upon the photophysics and photochemistry of bilirubin.
PHOTOSENSITIZATION OF METHYL LINOLEATE OXIDATION BY TRYPTOPHAN IN PEPTIDES
Authors: Kochevar Irene E. , Yoon Minjoong 
Published: January 2008

AbstractThe ability of tryptophan in peptides to photosensitize the oxidation of methyl linoleate (ML) was evaluated. Purified ML was irradiated (λ > 270 nm) alone or in the presence of a tryptophan‐containing peptide in ethanol solution. Oxidation was monitored by measuring the dienc hydroperoxides formed from ML by high performance liquid chromatography. N‐acetylphenylalanyltryptophan (NAPT) and N‐acetyltryptophan were about 2‐fold more effective as photosensitizers than leucyltryptophan and tryptophylleucine. N‐acetylphenylalanyltryptophan photolyzed in ethanol to form multiple photoproducts including N‐formylkynurenine‐type compounds. However, the NAPT photoproducts did not photosensitize the oxidation of ML and N‐formylkynurenine was about 8% as effective as NAPT. Sodium azide partially quenched the photooxidation sensitized by NAPT.
AN ACTION SPECTRUM FOR ULTRAVIOLET RADIATION‐INDUCED MEMBRANE DAMAGE IN Escherichia coli K‐12
Authors: Kelland L. R. , Moss S. H. , Davies D. J. G. 
Published: January 2008

AbstractA wild‐type Escherichia coli K‐12 strain was irradiated using monochromatic radiation in the range 254 to 405 nm. A measure of the cell membrane damage induced at each wavelength was investigated by comparing cell viability after irradiation on nutrient agar and on minimal medium containing either a low or high inorganic salt concentration. An action spectrum for lethality and for cell membrane damage was then determined. From 254 to 310 nm lethality closely corresponded to the absorption spectrum of DNA, and there was no indication of membrane damage. However, above a wavelength of 310 nm, the direct absorption of radiation by DNA could not account for the sensitivity observed. Moreover, at wavelengths longer than 310 nm, cell membrane damage was induced and by an increasing factor up to a peak at 334 nm. At the longer wavelengths of 365 and 405 nm, there was a gradual decrease from the peak of damage to cell membranes induced by 334 nm radiation. These results indicate that cell membrane damage may contribute significantly to near‐UV radiation‐induced cell lethality in wild‐type E. coli K‐12.
REPAIR OF ULTRAVIOLET‐IRRADIATED TRANSFORMING DNA IN A recA MUTANT OF Haemophilus influenzae
Authors: Stuy Johan H. , Walter Ronald B. 
Published: January 2008

Abstract—Ultraviolet‐irradiated transforming DNA was assayed on a wild‐type strain of Haemophilus influenzae strain Rd, on an excision repair‐deficient (uvr‐2) mutant, on a recombination repair‐deficient (recA4) mutant, and on a strain carrying both mutations. The donor DNA had a point mutation genetic marker (strAl) and a long nonhomologous plasmid‐derived DNA segment inserted in the HP1 prophage. The shape of the inactivation curves suggested that only recombination was responsible for the inverse square root kinetics observed with excision repair‐proficient recipients.
STATE I‐STATE II TRANSITIONS IN THE THERMOPHILIC BLUE‐GREEN ALGA (CYANOBACTERIUM)Synechococcus lividus*
Authors: Fork David C. , Satoh Kazuhiko 
Published: January 2008

AbstractTime courses of state I‐state II transitions were measured in the thermophilic blue‐green alga (Cyanobacterium),Synechococcus lividus, that was grown at 55°C. The rate of the state I–II transition using light II illumination was the same as that in the dark, and the dark state was identified to be state II. Therefore, light regulation attained by state transitions is produced by the state II–I transition induced by system I light. The redox level of plastoquinone did not affect this dark state II.Arrhenius plots of the state transitions showed a break point around 43°C that corresponded to the phase transition temperature of this alga. Since both the state I–II and II–I transitions were very much temperature‐independent, we could keep the alga in either state for a long time at a “low” temperature such as room temperature.Activities of both photosystems I and II in states I and II were also measured. After a state II–I transition, the system II activity increased about 16% and at the same time, svstem I activity decreased about 30%.
FORMATION OF 5‐HYDROXYMETHYLCYTOSINE‐CONTAINING PYRIMIDINE DIMERS IN UV‐IRRADIATED BACTERIOPHAGE T4 DNA
Authors: Childs John D. , Ellison Michael J. , Pilon Raymond 
Published: January 2008

AbstractCyclobutyl pyrimidine dimers composed of 5‐hydroxymethylcytosine and thymine (5HMC><T) have been detected in UV‐irradiated bacteriophage T4 DNA. During sample preparation. 5HMC in such a dimer, but not as a monomer, deaminates to form 5‐hydroxymethyluracil. The yield of 5HMC><T relative to thymine‐thymine dimer (T><T) increased from 0.07 at 254 nm to a maximum of 0.41 at 313 nm and then declined to 0.26 at 320 nm. These relative yields are 3‐10‐fold lower than the corresponding yields of cytosine‐thymine dimer relative to T><T previously determined in Escherichia coli DNA at these wavelengths. The lethality of a 5HMC><T dimer appears to be 4 times higher than that of a T<>T dimer for a mutant of T4 (denV) that is unable to excise pyrimidine dimers from its DNA. The ability of 5HMC to form dimers suggests that other modified pyrimidines such as 5‐methylcytosine can participate in dimer formation, particularly at the UV wavelengths in sunlight likely to be responsible for the induction of skin cancer.
COMPARISON OF THE ERYTHEMOGENIC EFFECTIVENESS OF ULTRA VIOLET‐B (290‐320 nm) and ULTRA VIOLET‐A (320‐400 nm) RADIATION BY SKIN REFLECTANCE
Authors: Wan San , Jaenickeand KurtF. , Parrish JohnA. 
Published: January 2008

Abstract–Based on optical properties of the skin, its constituent layers and the blood, and a previously experimentally verified quantitative model for the optical transfer properties in skin, noninvasive determinations of the amount of cutaneous blood in the superficial plexus are made from skin reflectance. This method is used to determine UVA and UVB fluences that cause cutaneous blood in the superficial plexus to increase to 1.5, 2 and 2.5 times the pre‐radiation volume at various times after irradiation. Our results show that on an equal fluence basis, UVB is two to three thousand times as effective as UVA in inducing erythema, whether erythema is evaluated 8, 24 or 72 h after irradiation. This agrees with the result obtained in terms of minimal erythema dose by visual inspection.
PROTOPORPHYRIN‐INDUCED PHOTODAMAGE: STUDIES USING CULTURED SKIN FIBROBLASTS
Authors: Latham Patricia S. , Bloomer Joseph R. 
Published: January 2008

AbstractA new system is described for the study of protoporphyrin‐induced photodamage of cells. This system differs from those previously described in that fibroblasts are induced to synthesize protoporphyrin from its precursor δ‐aminolevulinic acid.Fibroblasts were cultured from skin biopsies of 6 normal individuals and 6 patients with protoporphyria. All cell lines in both groups accumulated protoporphyrin when incubated with δ‐aminolevulinic acid in the absence of iron. Irradiation for 2 min with long‐wave UV light caused death of cells which had accumulated protoporphyrin, but not of cells which had been incubated without δ‐aminolevulinic acid. Cell damage could be quantitatively assessed by the release of chromium‐51 into the medium.Examination of irradiated protoporphyrin‐rich fibroblasts by electron microscopy revealed no significant differences between lines from patients with protoporphyria and normal individuals. The earliest indications of photodamage were rarifaction of the mitochondrial matrix with dilatation of cristae. dilatation of endoplasmic reticulum, and loss of plasma membrance integrity. Condensation of the cells correlated with cell death. These structural alterations suggest a generalized cellular injury.
PHOTOSENSORY BEHAVIOR OF A BACTERIORHODOPSIN‐DEFICIENT MUTANT, ET‐15, OFHalobacterium halobium
Authors: Hildebrand Eilo , Schimz Angelika 
Published: January 2008

Abstract–Halobacterium halobium, strain ET‐15, which does not contain detectable amounts of bacteriorhodopsin (BR) shows behavioral responses to UV and yellow‐green light. Attractant stimuli. i.e. light‐increases in the yellow‐green range or light‐decreases in the UV, suppress the spontaneous reversals of the swimming direction for a certain time. Repellent stimuli, i.e. light‐decreases in the yellow‐green range or light‐increases in the UV, elicit an additional reversal response after a few seconds. Action spectra of both sensory photosystems, PS 370 and PS 565, were measured with attractant as well as with repellent stimuli. As in BR‐containing cells, maximal sensitivity was always found at 370 nm for the UV‐system and at 565 nm for the long‐wavelength system. Fluence‐response curves at 370 and 565 nm obtained with strain ET‐15 and with a BR‐containing strain show that the sensitivity of both photosystems is not reduced in the absence of BR. It is concluded that BR is required neither for PS 565 nor for PS 370. Instead retinal‐containing pigments different from BR have to be assumed to mediate photosensory behavior.
INFLUENCE OF THE LOCATION OF TRYPTOPHANYL RESIDUES IN PROTEINS ON THEIR PHOTOSENSITIVITY
Authors: Pigault Claire , Gerard Dominique 
Published: January 2008

AbstractThe environmental effect on Trp residues photolysis was investigated on four proteins containing a single Trp residue in environments of various polarities: glucagon (exposed residue), nuclease (partially buried residue), RNase T1 (fully buried residue) and melittin (exposed or partially buried residue depending on the salt concentration). Direct photolysis was performed in neutral N2‐saturated phosphate solution at 20°C using 302 nm monochromatic light. Tryptophan loss was monitored by both absorption and fluorescence spectroscopy and by amino acid analysis. The results suggest that tryptophan photodegradation depends on the location of the residue in the protein, with regard to the exposure to the aqueous medium and to the neighbouring amino acids in the primary amino acid sequence and in the three dimensional structure. Photochemical products were not analysed but fluorescence spectra indicate that they vary with protein.
CHANGES IN TERTIARY STRUCTURE OF CALF‐LENS α‐CRYSTALLIN BY NEAR‐UV IRRADIATION: ROLE OF HYDROGEN PEROXIDE
Authors: Andley Usha P. , Sutherland Philip , Liang Jack N. , Chakrabarti B. 
Published: January 2008

AbstractThe effect of 300 nm irradiation on the three lens crystallins, α‐, β‐, and γ‐, was studied by using fluorescence and circular dichroism techniques. α‐Crystallin showed a pronounced change in tertiary structure as manifested in fluorescence and circular dichroism measurements. This finding is in agreement with our earlier findings that the tryptophan residues of α‐crystallin are more exposed than those of the other two crystallins. The results of studies using inhibitors specific for the different active species of oxygen suggest that H2O2‐mediated damage is involved in the change of tertiary structure of the proteins. Analyses of circular dichroism spectra indicate that, upon irradiation, the secondary structure of α‐crystallin remains virtually unaltered, and that the change in tertiary structure results primarily from photoinduced damage to the tryptophan residues.
FLAVIN‐MEDIATED PRODUCTION OF HYDROGEN PEROXIDE IN PHOTOELECTROCHEMICAL CELLS
Authors: Roncel Mercedes , Navarro José A. , Rosa Francisco F. De la , Rosa Miguel A. De la 
Published: January 2008

AbstractA photoelectrochemical cell for hydrogen peroxide production using flavin photosystems is described. The anodic solution, which is kept free of oxygen by passing an Ar stream through it, contains the photoreceptor (flavin mononucleotide or lumiflavin) and the electron donor (EDTA, semicarbazide or hydroxylamine), while the peroxide is formed at the electrode of the cathodic solution, whose oxygen content is increased by bubbling with pure oxygen. Among several electrode metals that have been tested (Ag, Pt and Hg), Hg is the most efficient. The pH of the anodic and cathodic solutions should be adjusted to 14 and 1, respectively, for optimum results.
THE PHOTOCHEMISTRY OF 5‐METHYLCYTOSINE AND 5‐METHYL‐2′‐DEOXYCYTIDINE IN AQUEOUS SOLUTION
Authors: Celewicz Lech , Sheilar Martin D. 
Published: January 2008

AbstractThe nucleobase 5‐methylcytosine (I) is a minor component of eukaryotic DNA thought to be important in regulation of gene expression. The photochemical reactions of this nucleobase and its 2′‐deoxyribonucleoside, 5‐methyl‐2′‐deoxycytidine (II), in water have been studied. These reactions lead, respectively, to 3‐amino‐2‐methylacrylamidine (Ib) and 3‐(2‐erythro‐d‐pentopyranos‐1‐yl) amino‐2‐methylacrylamidine (IIb) as the main photoproducts. The structure of the photoproducts was established by spectroscopic methods (1H and13C NMR, UV spectroscopy, electron impact and liquid secondary ion mass spectrometry); in the case ofIb, confirmatory evidence was obtained by chemical methods (photolysis of 5‐methyl[2–13C]cytosine, hydrolysis ofN‐carbomethoxy‐3‐amino‐2‐methylacryl‐amidine and reaction ofIbwith 1,1′‐carbonyldiimidazole to giveI). The quantum yield for formation ofIbwas determined to be 1.8 × 10‐3at pH 7.5 while the quantum yield for formation ofIIbhas a lower value of 0.2 × 10‐3at pH 7.5. These quantum yields depend strongly on pH and reach maximum values of 2.0 × 10‐3at pH 7.0 (Ib) and 0.6 × 10‐3at pH 5.0 (IIb). The mechanism of formation ofIb(orIIb) is proposed to involve nucleophilic attack of water on the C‐2 position of photoexcitedI(orII), followed by ring opening and decarboxylation of an intermediate carbamic acid.
PHOTO ACOUSTIC SPECTRA OF PHYCOBILIPROTEINS and CHLOROPHYLLIN IN ISOTROPIC and ANISOTROPIC POLYVINYL ALCOHOL FILMS
Authors: Frackowiak Danuta , Hotchandani Surat , Leblanc Roger M. 
Published: January 2008

Abstract—Photoacoustic spectra (PAS) of biliproteins: R‐phycoerythrin (PE) with R‐phycocyanin (PC) admixture in isotropic and anisotropic polyvinyl‐alcohol (PVA) films were measured. The mixtures of biliproteins and chlorophyllin (Chllin) in PVA were also investigated. In order to establish the influence of PVA anisotropy on PAS amplitude, the stretched and unstretched PVA films colored by Congo red were studied. The films with PE and Chllin mixture when illuminated in the region of PE absorption, show higher PAS signals than the films with PE alone. This is explained by the excitation energy transfer from efficiently fluorescent PE to Chllin that has much lower yield of fluorescence. The stretched films always show a higher PAS signal than isotropic films because of the increase in the thermal conductivity of PVA. But normalized PAS of Congo red and Chllin in stretched PVA are similar to those in unstretched films.Pigment molecules oriented parallel to the direction of film stretching have a lower rate of thermal deactivation compared to that of unoriented molecules as has been found by comparing PAS of differently oriented Congo red molecules using photoselection by polarized light. The same result was obtained for various PE chromophores which are differently oriented in anisotropic films.
SITE‐SELECTION and SHPOLSKII SPECTROSCOPY OF MODEL PHOTOSYNTHETIC SYSTEMS
Authors: Hala J. , Pelant I. , Ambroz M. , Pancoska P. , VACEK K. 
Published: January 2008

Abstract—Low temperature (T= 10 K) site‐selection fluorescence and excitation spectra of both isolated pheophorbide‐a molecules (I PHEO) and pheophorbide covalently bonded to the synthetic l‐lysyl‐l‐alanyl‐l.‐alanine polypeptide (B PHEO) were measured in dimethylformamide (DMF) matrices. The fluorescence spectra display sharp vibronic lines at different wavenumbers for different dye laser excitation wavelengths, superimposed on a broad band background. Spectral analysis provides frequencies of normal vibrations (FNV) and site distribution functions (SDF). The FNV and SDF of I PHEO in DMF have been found to show good agreement with other chlorophyll‐like molecules. A covalent binding between the polypeptide and PHEO molecules produces only slight changes in FNV but significant broadenings and shifts to lower energies in SDF. The fluorescence spectra of I PHEO in a typical Shpolskii matrix (n‐octane) were also measured and found to exhibit sharp non‐shifting vibronic lines for all wavelengths and kinds of excitation. A general model explaining both site‐selection and Shpolskii spectroscopy is presented.
AN EXTENDED SEMI‐EMPIRICAL MOLECULAR ORBITAL STUDY OF THE * EXCITED STATES OF NUCLEIC ACID BASES
Authors: Callis Patrik R. 
Published: January 2008

AbstractSpectroscopic CNDO/S and INDO/S calculations of the * spectra of the nucleic acid bases uracil, cytosine, adenine and guanine were performed. Oscillator strengths, polarizations and transition densities are displayed for transitions to 140 nm using several parameter sets and demonstrating the effect of doubly excited configurations. Inclusion of near‐neighbor off‐diagonal transition density elements greatly assists in making state correlations and assignments. Interesting effects regarding electron repulsion parameterization are noted. The results are compared with recently reported experimental results and several serious points of disagreement are noted.
A MICROSPECTROFLUOROMETRIC STUDY OF PORPHYRIN‐PHOTOSENSITIZED SINGLE LIVING CELLS—II. METABOLIC ALTERATIONS
Authors: Kohen E. , Reyftmann J. P. , Morliere P. , Santus R. , Kohen C. , Mangel W. F. , Dubertret L. , Hirschberg J. G. 
Published: January 2008

AbstractThe transient change in the NAD(P)H NAD(P) equilibrium following microinjection of mitochondrial (malate) or extra‐mitochondrial (6‐phosphogluconate) substrates into single living cells is strongly modified a few seconds after the onset of 365 nm irradiation in the presence of hematoporphyrin. There is no major difference in the time frame for the alterations of the Krebs cycle and pentose pathway. In view of the complex interrelationships between mitochondrial and extramitochondrial pathways, there is a reasonable chance that effects on both pathways are not unrelated‐ However there is no definite evidence for a direct correlation between the photoeffects on these two pathways.