bluuebunny/crossref_metadata_2025_split huggingface dataset:
GLOW CURVES FROM PHOTOSYNTHETIC BACTERIA*
Authors: FLEISCHMAN DARRELL E. 
Published: January 2008

Abstract— Cells and chromatophores of the photosynthetic bacterium Rhodopseudomonas viridis were frozen in the dark and illuminated while frozen or were illuminated during freezing. Upon being heated they emitted light. The conditions under which glow curves could be produced and the kinetics of the light emission indicate that the glows resulted from the thermal release of electrons from secondary electron acceptors and their recombination with oxidized reaction center bacteriochlorophyll b.Glow curves could not be obtained with Rhodospirillum rubrum.
THE PHOTOCHEMISTRY OF 14 C‐5‐BROMO‐2‘‐DEOXYURIDYLYL‐(3’→5‘)‐THYMIDINE DETERMINATION OF QUANTUM YIELDS AS A FUNCTION OF pH
Authors: PETER HEINRICH H. , DREWER ROBERT J. 
Published: January 2008

Abstract— Quantum yields for the formation of the major photoproduct of 2‐14C‐5‐bromo‐2′‐deoxyuridylyl‐(3‘→5’)‐thymidine (BrdUpT) have been determined by irradiation of the 2‐14C‐BrU‐labeled dinucleotide at pH 2.3, 5.9, 7.05, 8.0 and 10.25 with U.V. light at 280nm. At acidic and neutral pH the quantum yield was 0.0063; the value decreased markedly above pH 8.0 to 0.0025 at pH 10.25. Some evidence of the formation of additional photoproducts at high and low pH was found. Some aspects of the mechanism of the reaction are discussed.Consideration of pKa values calculated for singlet and triplet excited states indicates that the decrease in the quantum yield of main photoproduct at high pH is due to dissociation of the excited bromodeoxyuridine moiety. It is suggested that the formation of BrdUpT photoproduct and the debromination of bromouracil‐labeled DN A occur via different excited states.
ABSORPTION CHANGES IN THE REACTION CENTER OF PHOTOSYNTHETIC BACTERIA AND n‐ELECTRON CALCULATIONS ON BACTERIOCHLOROPHYLL, ITS MONO CATION AND ANION
Authors: OTTEN H. A. 
Published: January 2008

Abstract— π‐Electron calculations of the MO‐SCF‐CI type in the PPP approximations are carried out for the tetra pyrrole ring of the bacteriochlorophyll molecule, its mono cation and anion.According to the calculations the formation of the positive ion will be accompanied by the disappearance of the longest wavelength absorption band of the neutral system and the appearance of a new band near 1200 nm. Absorption changes of the same kind are found in the reaction center of photosynthetic bacteria upon illumination, supporting the hypothesis that the primary reaction is an expulsion of an electron from the π‐electron system of the reaction center bacteriochlorophyll.
SENSITIZED PHOTOOXYGENATION ACCORDING TO TYPE I MECHANISM (RADICAL MECHANISM) — PART III. EXPERIMENTS WITH CONTINUOUS ILLUMINATION
Authors: ZÜGEL M. , FÖRSTER TH. , KRAMER H. E. A. 
Published: January 2008

Abstract— The photochemical reaction in the system thionine (sensitizer), allylthiourea (ATU, acceptor), and oxygen was studied with continuous illumination. In oxygen‐free aqueous solution thionine is photoreduced to leucothionine. With oxygen, however, a photooxygenation of the acceptor takes place. At the same time the quantum yield of the bleaching reaction of thionine decreases markedly in comparison with that of the oxygen‐free solution. At about 100 sec after the beginning of illumination, the overall quantum yield of the bleaching reaction diminishes further because the leucothionine formed during the reaction now becomes transformed into thionine. The quantum yields do not change significantly over the range of oxygen concentrations studied (initial concentration 1 × 10‐5 to 5 × 10‐5M). In addition they are independent of the light intensity. The influence of the pH and the acceptor concentration were also investigated.The sensitizer is not only bleached reductively, but is also partly destroyed by oxidation. The results are in agreement with the reaction scheme elucidated by flash photolysis measurements.In accordance with this reaction scheme, the primary reaction (a) of the reductive bleaching of the sensitizer, (b) of the photooxygenation of the acceptor and (c) of the oxidative destruction of the sensitizer, is identical in all cases. This process is the redox reaction between the sensitizer triplet and the acceptor, where a semithionine and an ATU‐radical are formed. The reaction represents an example of a Type I photooxygenation according to the notation of Gollnick.
POST‐LUMINESCENCE DES CHLOROPLASTES INTACTS ET ALTERES PAR DENATURATION PARTIELLE: ETUDE EXPERIMENTALE, INTERPRETATION THEORIQUE ET CALCUL D'ENERGIES D'ACTIVATION
Authors: LAINE‐BÖSZÖRMENYI M. , PAILLOTIN G. , ROUX P. FALLOT et E. 
Published: January 2008

Abstract— The authors have studied the temperature effect on the luminescence of spinach chloroplast suspension after illumination at 675 nm.The decay of the luminescence has been followed at constant temperature (from 0°C to 40°C) or after sudden temperature jumps (0°C ≤ΔT≤ 47°C).They have compared the results obtained with intact chloroplasts and those after mild thermal denaturation.From these experimentally found values they have calculated the activation energies related to the radiative and non‐radiative ways of disappearence of the entity which is at the origin of the luminescence.On the basis of the values found for these energies (0·9 eV and 0·43 eV respectively), the authors evolve the hypothesis that this entity may be an electron self‐trapped in the chloroplast structure (small polaron).
THE FLAVIN‐SENSITIZED PHOTOOXIDATION OF NUCLEOTIDES — III. THE PARTICIPATION OF OXYGEN
Authors: KNOWLES A. , MAUTNER GILLIAN N. 
Published: January 2008

Abstract— Quantum yields for the lumiflavin‐sensitized oxidation of guanosine monophosphate and adenosine monophosphate in solution have been measured as functions of oxygen and nucleotide concentration. The quantum yield increases with oxygen concentration at low oxygen concentrations, but quenching of the excited flavin molecule by oxygen results in a fall in quantum yield at higher concentrations. It has also been established that the reciprocal of the quantum yield is linearly related to the reciprocal of the nucleotide concentration. A mechanism in which molecular oxygen reacts with an excited complex formed between triplet lumiflavin and the nucleotide is consistent with these observations.A value for the second‐order rate constant for the quenching of triplet lumifiavin by oxygen of 2·65 × 109M‐1 sec‐1 has been obtained.
PHOTOREACTIVATION IN THE YEAST SCHIZOSACCHAROMYCES POMBE
Authors: FABRE F. 
Published: January 2008

Abstract— Visible light (VL) illumination of u.v.‐irradiated cells of the fission yeast Schizosaccharomyces pombe does not increase the survival of wild‐type cells, but does increase the survival of some specific UVS strains. This photoreactivation has been studied in the U VS 1,1 mutant in the stationary growth phase.

It is not dependent on temperature during VL illumination.
The effect of pre‐u.v. or post‐u.v. illumination on survival is the same.
There is an overlap of photoreactivation and liquid holding recovery.
VL does increase the growth delay after irradiation.It is concluded from these results that the photoreactivation is not due to a photoreactivating enzyme, but to an indirect process.The existence in this yeast of two different repair pathways of u.v. lesions has been demonstrated previously. The study of indirect photoreactivation in different strains, blocked in one or the other repair pathway by mutation or by a repair inhibitor (caffeine), leads to the conclusion that the VL treatment favours only one of these two repair mechanisms, which is presumably the excision‐repair pathway. The strain UVS A, which would repair u.v. lesions by a recombinational mechanism, does not show any photoreactivation.
NANOSECOND IRRADIATION STUDIES OF BIOLOGICAL MOLECULES‐I. COENZYME Q 6 (UBIQUINONE‐30)
Authors: BENSASSON R. , CHACHATY C. , LAND E. J. , SALET C. 
Published: January 2008

Abstract— The coenzyme ubiquinone, an isoprenoid benzoquinone present in the electron‐transport chain of mitochondria, has been studied using nanosecond laser flash photolysis and pulse radiolysis. The hitherto undetected triplet excited state of the coenzyme has been identified and some of the physico‐chemical properties determined. These measurements may assist the understanding in molecular terms of the degradative action of light upon biological materials, photophosphorylation and the possible initiation of biological electron transport via quinone light absorption.Laser photolysis of ubiquinone in cyclohexane and pulse radiolysis of ubiquinone in benzene results in the formation of a transient absorption with maximum around 440 nm and a half‐life of 650 nsec in cyclohexane and 450 nsec in benzene. Energy transfer sensitisation of the β‐carotene triplet absorption by ubiquinone in cyclohexane at a rate consistent with the life‐time of the 440 nm transient absorption, yields strong evidence that this transient species is triplet ubiquinone. The triplet reacts with oxygen with a rate constant of 2 × 10‐‐9 mole‐1 sec‐1.Photolysis studies of ubiquinone in ethanol and isopropanol and addition of ethanol to ubiquinone in cyclohexane show that little ubisemiquinone is formed by reaction of the triplet with alcohols. Electron spin resonance studies support this conclusion, and also show that some ubisemiquinone is however formed on photolysis of solutions of ubiquinone in methylcyclohexane.Energy transfer experiments in the presence of various triplet energy donors and acceptors suggest that the triplet energy of ubiquinone lies between 176 and 123 W mole‐1, and that the triplet extinction coefficient at 440 nrn is 19,000 mole‐1 cm‐1 in cyclohexane and 13,000 mole‐1 cm‐1 in benzene (at 430 nm).The singlet to triplet crossover efficiency for ubiquinone in cyclohexane was estimated to be 0.04. The low triplet energy level, crossover efficiency and abnormal type of reaction with alcohols are reflections of the profound influence of the isoprenoid chain upon excited states of this quinone.
PHOTOCHEMIE ANOMALER NUCLEINSÄUREBAUSTEINE‐VIII. ZUR PHOTOCHEMIE DES 6–AZACYTOSINS UND 6–AZACYTIDINS
Authors: KITTLER L. 
Published: January 2008

Abstract— The photochemical behavior of 6–azacytosine and 6–azacytidine has been investigated by spectrophotometric, polarographic, and chromatographic methods. Both compounds form photohydration products, similar to cytosine and cytidine, but their photosensitivity is about ten fold higher. The greatest stability against u.v. light was found in strong acid and alkaline medium, indicating that under these conditions the electronic density at the reaction center is decreased.For estimation of the photochemically active excited state triplet‐triplet‐transfer, experiments and measurements in the presence of paramagnetic metal ions were done. The results show that the photohydration reaction involves the first excited singlet state and the corresponding triplet state probably as well.The photoproducts of both substances can be reactivated by heat. This reaction in acidic medium is strongly overlapped by a deamination reaction which yields 6–azauracil as a final product. In alkaline solution the ring system of the photohydration product is disrupted in the dark. The kinetic parameters of the heat‐reversible reaction of 6–azacytosine and 6–azacytidine are completely identical. This is in contrast to the published results with cytosine and cytidine where the back reaction is lowered for the latter. The differences in the behavior of the normal bases and their azaanalogues can be explained by means of an intramolecular hydrogen bond stabilization of the cytidine photoproduct. An analogous stabilization effect in the case of the 6–azacytidine photoproduct seems to be improbable for sterical reasons.
MECHANISM OF THE REACTION BETWEEN LUMINOL AND MOLECULAR OXYGEN
Authors: BECK MI. T. , JOÓ F. 
Published: January 2008

Abstract— The oxidation of luminol by molecular oxygen in dimethylsulfoxide was studied by following the intensity of emitted light. The results indicate that the reaction takes place through reversible formation of an oxygen‐containing intermediate. The stability constant of this compound has been determined in IDMSO: ethanol (4:1) mixed solvent. The effects of different parameters were investigated and a quantitative relationship established between the intensity of emitted light and the concentrations of the reactants.New methods for determining (oxygen concentrations in gases and for demonstrating cold light emission are suggested.
ULTRAVIOLET‐LIGHT‐INDUCED CONFORMATIONAL CHANGES IN DNA
Authors: LANG H. , LUCK G. 
Published: January 2008

Abstract— Irradiation of DNA at 254 nm produces alterations in the secondary structure leading to changes in the circular‐dichroism (CD) spectrum. A new Cotton effect around 320 nm, and a change in the rotatory strength of the CD maximum at 275 nm, was observed. Whereas the new negative maximum at 320 nm generally increases with increasing radiation dose, the maximum at 275 nm is enhanced at lower UV doses but is diminished at higher doses. Thus we suppose that there are two different DNA conformations, the transition between which occurs at 15times104 ergs/mm2. Below this dose, the DNA is in a partially closed and twisted state, but above it the DNA has a C‐like conformation.It is possible that those regions of the DNA containing altered conformation may act as recognition sites for repair.ZusammenfassungUV‐Bestrahlung von DNS mit 254 nm UV‐Licht führt zu Strukturänder‐ungen in der DNS, die sich in einem veränderten CD‐Spektrum manifestieren. So kann erstens ein neuer Cotton‐Effekt bei 320 nm und zweitens eine Veränderung der Rotatorstärke des positiven Maximums bei 275 beobachtet werden. Während der neue Übergang bei 320 nm sukzessive mit steigender Bestrahlungsdosis zunimmt, wird das Maximum bei 275 nm erst vergrößert um bei höheren UV‐Dosen wieder abzufallen. Es wird angenommen, daß die DNS somit in zwei verschiedenen Konformationen vorliegt, deren Übergang bei einer Bestrahlungsdosis von etwa 15times104 erg/mm2 erfolgt. Während bei niedrigen UV‐Dosen die DNS in einem teilweise ringförmigen, verdrillten Zustand vorliegen soll, müßte bei höheren Bestrahlungsdosen vorwiegend ein C‐konformationsähnlicher Zustand existieren. Es wäre denkbar, daß die konformativ veränderten Bereiche im DNS‐Molekül als Erkennungsorte für die Reparaturenzyme fungieren und somit die Reparatur initiieren.
PHOTOREGULATION OF α‐CHYMOTRYPSIN ACTIVITY BY ISOMERIZABLE INHIBITORS. STUDY OF THE ACTION MECHANISM*
Authors: Fournier M. , Bourdon J. 
Published: January 2008

Abstract— The N‐p‐phenylazophenyl‐N‐phenylcarbamyl chloride (PAPC) in its cis form is five times more active as inhibitor of α‐chymotrypsin than in the trans form. In the present work, derivatives of PAPC have been synthesized. Each of these new compounds is photoisomerizable and is an inhibitor (in the cis and in the trans form) of α‐chymotrypsin. The cis isomer is always more active than the trans. The m‐methyl derivative is 17.5 times more active in the cis form than in the trans, whereas, for the para‐substituted compound, this ratio is only 3.5.Several hypotheses can explain this difference of activity between the cis and trans isomers: (1) steric hindrance towards the trans isomer, (2) lower affinity of the enzyme for the trans isomer, (3) higher reactivity of the complex formed between the enzyme and the cis form of the inhibitor. These hypotheses are discussed.
PRIMARY PHOTOCHEMICAL PRODUCTS OF DITHIOGLYCOLIC ACID IN AQUEOUS SOLUTION
Authors: Feitelson Jehuda , Shafferman Avigdor , Stein Gabriel 
Published: January 2008

Abstract— The photochemistry of dithioglycolic acid at 254 nm was investigated in deaerated aqueous solutions in the pH range 1.4–7.3. Initial yields of the primary photochemical products H2S,–SH and aldehyde‐(probably glyoxylic acid) were determined. The complex pH dependence of these simultaneously formed first stable products is interpreted in terms of the ground‐state ionic equilibria, and in addition pH‐dependent processes occurring in the excited state and labile intermediate sequence.It is suggested that the photochemical mechanism involves two parallel pathways: one a hydrolytic splitting of S ‐ S leading to H2S formation (unaffected by the presence of O2 or isopropanol), the other a free radical mechanism via C–S breakage, which is affected by the presence of O2 or isopropanol.
ULTRAVIOLET AND γ‐RAY‐INDUCED REACTIONS OF NUCLEIC ACID CONSTITUENTS. REACTIONS OF PURINES WITH AMINES
Authors: Salomon J. , Elad D. 
Published: January 2008

Abstract— Photochemical and γ‐ray‐induced reactions of purines with amines are described. These lead to the appropriate 8‐substituted purines. The photoproducts were obtained in yields of up to 100% by the use of a variety of photosensitizers, including peroxides. A free radical mechanism is proposed for these reactions.Such reactions may be relevant to the problem of the nature of DNA‐protein cross‐links induced by ultraviolet radiation.
PHOTOSYNTHETIC ACTIVITY AND CHLOROPHYLL ABSORPTION SPECTRA OF FRACTIONS FROM THE ALGA, DUNALIELLA*
Authors: Brown J. S. , Gasanov R. 
Published: January 2008

Abstract— Dunaliella chloroplasts were fractionated according to C. Arntzen et al, Biochim. Biophys. Acta256, 85–107, 1972. The initial French‐press treatment and differential centrifugation produced Fraction 1 (Fr 1) enriched in photosystem I activity and a heavier Fraction 2 (Fr 2). When Fr 2 was treated with digitonin followed by either gradient or differential centrifugation, two more fractions were recovered: Fr 1 g with a photosystem 1 activity similar to that of Fr 1, and Fr 2 g with very low photosystem II activity.Photosystem II activity was considerably lower in these Dunaliella chloroplasts and fractions than in spinach particles measured under the same conditions, but the relative activities between the fractions were similar to those for spinach. Fr 2 always had greater photosystem II activity than Fr 1, but the digitonin fractions were low and similar in photosystem II activity.Photosystem II activity was measured as the reduction of 2, 6–dichlorophenol indophenol (DCIP) with H2O, diphenylcarbazide (DPC) or Mn2+ as electron donor. The results indicated that exogenous manganous ion competed with H2O as an electron donor to photosystem II in broken chloroplasts initially, but after 10–15 s of illumination, the Mn3+ formed began to reoxidize DCIP and a cyclic reaction ensued. DPC and Mn2+ appeared to react at different sites.Computer‐assisted curve analysis of the absorption spectrum of each fraction revealed four major component curves representing the absorbing forms of chlorophyll a at 663, 670, 679 and 684 nm seen in numerous other in vivo chlorophyll spectra (C. S. French et al., Plant Physiol.49, 421–429, 1972). However, Fr 2g had approx. 20 percent more of Ca663 and Ca670 and 10% more absorption by chl b than Fr 1 which correlated with the difference in photosystem II activity. On the long wavelength side, Fr 2 g had no Ca694 and almost no photosystem I activity.The results are not sufficient to answer the question of whether the photosystem I particle obtained from the original homogenate is significantly similar to or different from the corresponding fraction obtained from Fr 2 with digitonin.
NEAR‐ULTRAVIOLET MODIFICATION OF ESCHERICHIA COLI B UBIQUINONE IN VIVO AND IN VITRO*
Authors: Werbin Harold , Lakchaura Bala D. , Jagger John 
Published: January 2008

Abstract— Ubiquinone Q‐8 in Escherichia coli B was labeled by growing the bacteria in a synthetic growth medium containing p‐hydroxybenzoic acid‐ 14C(U). The cells were then irradiated with light of wavelengths 313, 334, 366, and 405 nm, and Q‐8‐ 14C was extracted and assayed. Q‐8‐ 14C was also isolated from unirradiated bacteria, partially purified, and then irradiated similarly in hexane and assayed. Ubiquinone in the cells was four to eight times as resistant to radiation as ubiquinone in hexane. From 313 to 366 nm, the in vivo and in vitro action spectra were similar to each other and to the absorption spectra of synthetic Q‐8 dissolved in hexane or ethanol, but at 405 nm the action spectra deviated from the absorption spectra. Quantum yields for the modification (loss) of ubiquinone in hexane decreased from 0·021. at 313 nm to 0·005 at 405 nm.The chromenol of Q‐8 was not detected in labeled cells irradiated at 334 nm, but several more‐polar photoproducts were separated by thin‐layer chromatography.
N‐FORMYL‐KYNURENINE, A TRYPTOPHAN PHOTOOXIDATION PRODUCT, AS A PHOTODYNAMIC SENSITIZER
Authors: Walrant P. , Santus R. 
Published: January 2008

Abstract— Photodynamic properties of a tryptophan ultraviolet‐photooxidation product, N‐formylkynurenine, were investigated with amino acids and nucleotides as substrates. Steady‐state kinetic studies are presented as a function of sensitizer, substrate, oxygen concentration and pH. Involvement of singlet oxygen has been suggested for the sensitized oxidation of histidine and tryptophan. For the latter, 02‐ is suggested as a supplementary oxidizing species. Lifetime computations from kinetic and quenching experiments suggest that sensitization occurs via the N‐formyl‐kynurenine triplet state. The importance of the photodynamic properties of N‐formyl‐kynurenine in protein and DNA photochemistry is discussed.RésuméLes propriétés photodynamiques d'un produit de photooxydation ultraviolette du tryptophane, la N‐formyl‐cynurénine, ont étéétudiées vis‐à‐vis d'acides aminés et de nucléotides tenant lieu de substrats. La cinétique de l'action photodynamique a étéétudiée en fonction des concentrations en sensibilisateur, en substrat et en oxygène, et en fonction du pH. La participation de l'oxygène singulet a été mise en évidence dans l'oxydation sensibilisée de l'histidine et du tryptophane. Pour ce dernier, nous suggérons l'intervention de O2‐ comme agent oxydant supplémentaire. A partir d'expériences cinétiques et d'extinction, le calcul du temps de vie de l'état excite du sensibilisateur initiant la réaction suggère que ce dernier est l'état triplet. L'importance des proprifétés photodynamiques de la N‐formyl‐cynurénine dans la photochimie des protéines et de l'ADN est discutée.
THE EFFECT OF AROMATIC AMINO ACIDS ON THE PHOTOCHEMISTRY OF A DISULFIDE: ENERGY TRANSFER AND REACTION WITH HYDRATED ELECTRONS
Authors: Shafferman Avigdor , Stein Gabriel 
Published: January 2008

Abstract—The decomposition of dithioglycolic acid in oxygen‐free solutions illuminated by low‐intensity 254 nm light at pH 1.5‐4.7 is enhanced by light absorbed in tyrosine. This occurs through an interaction with excited tyrosine, leading to the formation of excited dithioglycolic acid. At pH 6‐1 an additional pathway appears, through the formation of a hydrated electron from excited tyrosine.In the presence of tryptophan at pH 1 ‐2–6‐1 the pathway involving sensitized formation of excited dithioglycolic acid is much less important, and that due to hydrated‐electron (or H) formation from excited tryptophan of greater importance.
INDUCTION OF SKIN TUMORS IN HAIRLESS MICE BY A SINGLE EXPOSURE TO UV RADIATION*
Authors: Hsu J. , Forbes P. D. , Harber L. C. , Lakow E. 
Published: January 2008

Abstract— Skin tumors were induced in hairless mutant mice following a single exposure to ultraviolet radiation (UV). Tumors were first noted as early as 7 weeks following irradiation. The UV, emitted by FS20/40T12 fluorescent lamps, was principally in the 280–320 nm spectral region with a peak at 313 nm. Single (skin surface) doses of 3 times 104 J/m2 to 24 times 104 J/m2 were delivered in 3 h or less. The higher doses resulted in more severe acute damage as well as greater tumor yield.Most of the tumors were benign hyperplastic epithelial papillomas; 4 out of 96 tumors examined histologically proved to be squamous cell carcinomas. This appears to be the first report of experimental carcinogenesis due to a single UV exposure, not requiring exogenous chemical promotion.