bluuebunny/crossref_metadata_2025_split huggingface dataset:
VARIATION IN THE PHOTOCHEMICAL REACTIVITY OF THYMINE IN THE DNA OF B. SUBTILIS SPORES, VEGETATIVE CELLS AND SPORES GERMINATED IN CHLORAMPHENICOL*,†
Authors: Smith Kendric C. , Yoshikawa Hiroshi 
Published: January 2008

Abstract— The chief photoproduct of thymine produced in u.v. irradiated (2537Å) vegetative cells of B. subtilis is the cyclobutane‐type dimer while in spores very little of this dimer is produced (maximum yield 2·6 per cent of thymine) but a new photoproduct is produced in high yield (maximum of 28·4 per cent of thymine). This difference in photochemical response appears to be due, at least in part, to a difference in uydration of the DNA. The photochemistry of thymine in isolated DNA irradiated in solution is similar to that of DNA in irradiated vegetative cells, but differs markedly from that of isolated DNA irradiated dry. The yield of cyclobutane‐type thymine dimer is much reduced in isolated DNA irradiated dry but a new photoproduct of thymine. is produced which is chromatographically similar to the spore photoproduct. The yield of this photoproduct, however, is never as great as that obtained in irradiated spores.The photochemistry of the DNA thymine of spores germinated in the presence of chloramphenicol is very similar to that of normal vegetative cells. Except for hydration, the physical state of the DNA is probably not otherwise altered by germination in the presence of chloramphenicol since DNA replication is prevented by the presence of chloramphenicol. These results are also consistent with the hypothesis that the unique photochemistry of spores is due, at least in part, to the hydration state of the DNA.The acid stability of the spore photoproduct is indicated by the fact that it is isolated from irradiated spores after hydrolysis in trifluoroacetic acid at 155°C for 60 min. It still contains the methyl group of thymine as judged by the fact that for a given dose of u.v. the same yield of photoproduct was obtained whether the spores were labeled with thymine‐2–C‐14 or ‐methyl‐C‐14. This photoproduct is stable to reirradiation (2537Å) in solution under condiditions where thymine dimers of the cyclobutane‐type are completely converted back to monomeric thymine. On a column of molecular sieve material (Sephadex‐G10), the spore photoproduct elutes in a region intermediate between the cyclobutanetype thymine dimers and monomeric thymine. Of the numerous compounds tested by paper chromatography, the spore photoproduct is most similar (but not identical) in several solvents to 5–hydroxyuracil and 5–hydroxymethyluracil. Our data do not allow us to decide if the product is a monomer or a dimer.Although the photochemistry of thymine in the DNA of spores differs markedly from that for vegetative cells, several lines of evidence make it seem doubtful that the enhanced resistance of spores to u.v. relative to that of vegetative cells can be explained solely on the basis of this difference in the photochemistry of DNA thymine.
EMISSION SPECTRA FROM SYNTHETIC POLYNUCLEOTIDES AND DEOXYRIBONUCLEIC ACID IN AQUEOUS SOLUTIONS†
Authors: KLEINWÄCHTER V. , DROBNIK J. , AUGENSTEIN L. 
Published: January 2008

AbstractA study has been made of the emission spectra at 77°K from poly A, poly U, poly C, their complexes, and from native and heat‐denatured DNA in buffered aqueous solutions containing 0·25 per cent glucose: no emission was observed from these polynucleotides at room temperature. The spectra differed from those obtained in the polyalcoholic glasses used by other workers. The principal differences between the emission spectra of poly A and adenosine at pH 7 in a water‐glucose mixture were: (a) a decrease in both P/F and the overall intensity in poly A; (b) absence of the structure normally found in adenosine phosphorescence; and (c) appearance of a new short‐lived component in the phosphorescence decay. Further changes in the emission characteristics (e.g. the increase of P/F, the proportional increase of the short‐lived component in the phosphorescence decay) from poly A were observed at pH 5. These can not be explained solely by protonization of adenosine residues, but rather appear to depend upon exciton interactions of the most intense π–π* transition in double‐stranded poly A. and perturbation of the lowest‐lying emitting band. When poly A or poly C is complexed with poly U or poly I the luminescence intensity decreases in two‐strand complexes and is completely quenched in poly (A + 2U), poly (A+2I) and poly (C++I); no emission was observed from either, single‐strand poly I or poly U. Identical emission patterns were obtained from native and heat‐denatured samples of DNA. The comparison of polynucleotide emission spectra in the water‐glucose medium with those obtained from polyalcoholic glasses leads to the conclusion that the emission spectra depend most critically upon the relative proportions of base‐solvent and base‐base interactions in each environment: the possible importance of proton tunneling and/or triplet‐triplet transfer mechanisms is briefly discussed.
CHLOROPHYLL a AND CAROTENOID AGGREGATES AND ENERGY MIGRATION IN MONOLAYERS AND THIN FILMS
Authors: SINESHCHEKOV V. A. , LITVIN F. F. , DAS M. 
Published: January 2008

Abstract— The spectra of absorption, fluorescence and excitation of monolayers and thin films containing chlorophyll a together with a carotenoid (cis‐β‐carotene, trans‐β‐carotene, fucoxanthin, or zeaxanthin), were measured at — 196°C. The concentration ratios used, (Chl)/(Car), were 6:1, 4:1, 3:1, 2:1, 1:1 and 1:3, and the area densities, 3·70, 2·55, 1·76, 0·71, 0·37 and 0·17 nm2/pigment molecule.In dilute monolayers, (3·70 nm2/molecule), with a constant concentration ratio (Chl)/(Car) = 3:1, evidence of three β‐carotene forms, with absorption bands at 460, 500 and 520 nm (C460, C500 and C520), and of a chlorophyll a form with an absorption band at 669–672 (Chl669–672) was found. On increasing the density to 0·2–0·3 nm2/molecule, a conversion of C460 and C520 into C500, was observed, and several more additional (probably more strongly aggregated) chlorophyll a forms appeared, with absorption bands at 672–733 nm. With excess carotene [(Chi)/(Car) = 1:3] the forms C460, C500, C520 and Chl669–672 were present even in the most dense films (0·2–0·3 nm2/molecule). The same was found with other carotenoids: if one of the pigments was in excess, aggregated forms of the other tended to disappear.In the transfer of energy from carotenoids to chlorophyll a, C500 was found to be the main donor. In layers with a concentration ratio (Chl)/(Car) = 3:1, the efficiency of transfer was less than 10 per cent at the lowest density used (3·70 nm2/molecule); it increased to 50 per cent, as the density was increased to 0·20 nm2/molecule. When the relative concentration of the carotenoid was increased to (Chl)/(Car) = 1:1, the efficiency of energy transfer dropped to 25 per cent even at 0·20 nm2/molecule. It seems that the efficiency of energy transfer between carotene molecules (prior to its transfer to chlorophyll a) is low, and effective transfer occurs only between β‐carotene and immediately adjacent chlorophyll a molecules.
ENERGY TRANSFER BETWEEN NUCLEIC ACID BASES AND TRYPTOPHAN IN AGGREGATES AND IN OLIGOPEPTIDE‐NUCLEIC ACID COMPLEXES
Authors: Helene Claude 
Published: January 2008

Abstract— Interactions and energy transfer processes between nucleic acid bases and tryptophan have been investigated in several Systems: mixed aggregates of nucleosides and tryptophan in frozen aqueous solutions; and poly‐rA and DNA complexes with oligopeptides containing lysyl and tryptophyl residues. Previous studies (Montenay‐Garestier, Th. and C. Hélène, 1971, Biochemistry10, 300–306) had shown that electron donor‐acceptor interactions in stacked complexes of tryptophan and nucleic acid bases led to the appearance of a new fluorescence at longer wavelengths with a low quantum yield. It is shown here that triplet‐triplet energy transfer can take place from bases to tryptophan in mixed aggregates at low [tryptophan]/[base] ratios and in oligopeptide‐poly‐rA (or DNA) complexes at low [oligopeptide]/[phosphate] ratios. Also the singlet excitation energy of bases can be transferred to base – tryptophan complexes. These results are discussed with respect to the structure of the complexes and to the involvement of energy transfer in nucleic acid – protein photochemistry.RésuméLes transferts de l'énergie d'excitation résultant des interactions des bases des acides nucléiques avec le tryptophane ont étéétudiés dans divers systèmes: agrégats mixtes formés dans les solutions aqueuses congelées de nucléosides et de tryptophane; complexes du poly‐rA et du DNA avec des oligopeptides contenant des résidus lysine et tryptophane.Des études antérieures (Montenay‐Garestier, Th. et C. Hélène, 1971, Biochemistry10, 300–306) ont montré que le tryptophane et les bases des acides nucléiques forment des complexes donneur‐accepteur d'électron, caractérisés par un spectre de fluorescence à plus grandes longueurs d'onde que les spectres des deux composants. L'énergie d'excitation des bases au niveau singulet peut être transférée vers ces complexes.Dans les agrégats, quand le rapport des concentrations en tryptophane et en adénosine est faible (inférieur à 0.2) un transfert d'.énergie est observé au niveau triplet de l'adénosine vers le tryptophane. L'énergie d'excitation est délocalisée au niveau triplet dans les agrégats d'dénosine sur environ 200 molécules. Un transfert d'énergie du même type est observé dans les complexes du poly‐rA (ou du DNA) avec des oligopeptides contenant le tryptophane.L'énsemble des résultats obtenus est en accord avec la structure des complexes formés, déterminée par résonance magnétique nucléaire. Le rôle éventuel des transferts d'énergie des bases vers le tryptophane dans la photochimie des complexes protéines–acides nucléiques est discuté.
A NEW FACET IN RHODOPSIN PHOTOCHEMISTRY
Authors: Meer K. van der , Mulder J. J. C. , Lugtenburg J. 
Published: January 2008

Abstract— A structure is proposed for the prosthetic group of the visual pigments rhodopsin, prelumirhodopsin (bathorhodopsin) and lumirhodopsin. The intrinsic photochemical step in this model is tautomerization of the prosthetic group of rhodopsin to a hexaeneamine retrotautomer with an exomethylene group for prelumirhodopsin. Based on the proposed structures, molecular orbital calculations were carried out; the absorption maxima calculated snowed the same trends as the Λmax values observed. An exact fit was not obtained because many interactions had to be neglected. Essential information of the laser Raman resonance spectrum of prelumirhodopsin can be interpreted based on the structures proposed by our model.The model elucidates why some retinal derivates can and others cannot form visual pigments with opsin and visual pigments having vastly differing absorption maxima yet employ the same mechanism for their photoreaction.
INTERACTION OF RESTORATION PROCESSES IN UV IRRADIATEDESCHERICHIA COLZCELLS
Authors: Sedliakova M. , Brozmanova J. , Masek F. , Slezarikova V. 
Published: January 2008

Abstract—An attempt was performed to estimate survival and course of DNA synthesis inEscherichia coliB/rhcr'andhcr‐cells in relation to the amount of unexcised dimers.In exponential growinghcr+cells irradiated with 30 Jm‐2, dimers were almost completely excised and survival of cells was equal to about 3%. In thehcr+cells prestarved for amino acid and thymine and irradiated by the same fluence, survival of cells was almost equal while two thirds of dimers remained unexcised and could be detected in the hybrid DNA consisting of parental and daughter chains. In exponentially growinghcr+‐cells irradiated with 20Jm‐, the same amount of dimers was produced which remained unexcised in the prestarvedhcr+cells. However, their survival was equal to about 0.02%.Despite the great differences in dimer contents, about one third of DNA was replicated after UV in both exponentially growing and prestarvedhcr+cells producing well defined HL‐hybrid peak, and the newly synthesized DNA was normal‐sized. Inhcr+cells which contained approximately the same amount of dimers as inhcr+prestarved cells, the amount of replicated DNA was too low to form a detectable density labelled hybrid peak, and the newly synthesized DNA was in short pieces.Thus, whenhcr+andhcr+‐cells contain the same number of residual dimers, they have different levels of tolerance to these dimers.
PHOTOALLERGIC RESPONSES TO CHEMICALS
Authors: Kochevar Irene E. 
Published: January 2008

Abstract— –Photochemical and immunologic knowledge about photoallergy to chemicals is briefly summarized. Studies in in vitro systems have demonstrated that photoallergic compounds can covalently bond to proteins through a photochemical reaction. The immunologic nature of the photoallergic response is based mainly on clinical observations, induction of photoallergy in man and in guinea‐pigs and on results of in vitro immunologic tests.Studies of the photoreactions of the photoallergic compound, 3,3′,4′,5‐tetrachlorosalicylanilide (TCSA), with proteins are discussed. TCSA noncovalently bonds to human serum albumin prior to irradiation. Prior interaction is essential for formation of a photoaddition product indicating that a short‐lived reactive species derived from TCSA is involved in the photoaddition and limiting the number of skin proteins which can participate in antigen formation. By fragmentation of the TCSA‐albumin photoadduct with CNBr, it was determined that TCSA can bond to at least three sites on the albumin molecule. TCSA also can sensitize the photooxidation of histidine in albumin.
REVISED SPECTRA FOR THE INACTIVATION OF HAEMOPHILUS INFLUENZAE TRANSFORMING DNA BY MONOCHROMATIC ULTRAVIOLET LIGHT: EFFECT OF HISTIDINE
Authors: Peak M. J. , Tuveson R. W. 
Published: January 2008

Abstract—It was reported previously that histidine sensitizes the genetic activity of Haemophilus influenzae transforming DNA to pure 334 nm ultraviolet light, Further measurements show that this apparent 334 nm sensitization was probably erroneous and that in fact, histidine protects DNA against inactivation by 334 nm light. This is now consistent with all previous observations that transforming DNA is protected by histidine against all near‐UV wavelengths (above 320 nm) investigated.A modified spectrum for the protection of H. influenza transforming DNA by histidine against ultraviolet light is described.
ON THE PHOTOIONIZATION ENERGY THRESHOLD OF TRYPTOPHAN IN AQUEOUS SOLUTIONS
Authors: Amouyal E. , Bernas A. , Grand D. 
Published: January 2008

Abstract— To investigate the existence and energy position of a photoionization threshold. tryptophan (Trp) has been photoionized in desecrated neutral aqueous or alcoholic solution under monochromatic light of variable frequency, in presence of N2O to scavenge the photoelectron.Present findings and some literature data converge to show the existence of a threshold for the one photon ionization process. This threshold is located at 4.5 ± 0.1 eV and 4.85 ± 0.1 cV for Trp in aqueous and ethanol solutions. respectively, which corresponds to a lowering with respect to the gas phase ionization potential of 3.4 and 3.0 eV.The photoionization quantum yields for Trp is found about 4 times greater at 250 nm than at Λcx= 265 nm, where ϕe‐4M=0.080±0.025. In such spectral range. at most one photoelectron out of 4–5 escaping geminate recombination would lead to Trp photodegradation in acrated solutions.These results also point out that the neutral radical Trp. which has been previously observed for Λcx > 275 nm, i.e. below the ionization threshold energy—would not necessarily derive from Trp + deprotonation or cation‐electron dissociative recombination. Similarly, the opening of the indole ring with formylkynurenine (FK) formation which is observed under aerobic conditions and Λcx >, 280 nm would not imply an electron attachment on O2 but reactions such as Trp +3O2 or Trp*+3O2 or else
HETEROEXCIMER SYSTEMS IN AQUEOUS MICELLAR SOLUTIONS
Authors: Waka Yasuhiro , Hamamoto Kimihiko , Mataga Noboru 
Published: January 2008

Abstract—Fluorescence quenching due to charge transfer interactions in the excited state has been studied in aqueous micellar solutions. Fluorescers used were pyrene, various pyrene derivatives and several other conjugated π‐electronic systems, and quenchers were N, N‐dimethylaniline, N. N‐dimethylaniline sulfonate, dicyanobenzenes and cyanopyridine. Strong quenching of the aromatic hydrocarbon fluorescence with dimethylanilines as well as dicyanobenzenes was observed, while no heteroexcimer emission was detected. The dependences of relative fluorescence yield and fluorescence decay curve upon the quencher concentration have been explained with equations derived on the basis of a simple model. Based on the obtained results, some discussions were given on the nature of micelle ‘interior’ and micelle ‘surface’.
ACTINIC EFFECTS OF LIGHT AND BIOLOGICAL IMPLICATIONS*
Authors: Thorington Luke 
Published: January 2008

Abstract—Illumination is not the only, nor even the most important, benefit of the earth's complement of solar optical radiation; life itself is physically and chemically balanced between effects of too much and too little of it. Chemically, the effects range from the synthesis of ozone in the stratosphere and biochemicals in the biosphere, to the influence or control of complete living organisms, including humans. This actinism depends upon the spectrum, irradiancc and modulation, or SIAM. of the natural optical radiation environment. By manipulating the SIAM of artificially produced actinic optical radiation, profound effects are now routinely induced in people, animals and plants. The next logical application for this SIAM technology is in the environments where people themselves live and work. Meanwhile, it should be recognized that artificial illumination, as presently prescribed for these environments, is actinic.
TEMPERATURE‐SENSITIVITY OF LIGHT‐INDUCED PHASE SHIFTING OF THE CIRCADIAN CLOCK OF NEUROSPORA
Authors: Nakashima Hideaki , Feldman Jerry F. 
Published: January 2008

Abstract—Two new mutants of Neurospora craasa, designated hth‐1 and hth‐2, have been isolated which allow clear expression of the circadian conidiation rhythm at high temperature (36°C). Both strains showed single‐gene segregation and produced similar phenotypes but mapped to different genetic loci. These mutants allowed an analysis of the effect of temperature on (1) light‐induced phase‐shifting of the circadian rhythm, (2) period length of rhythm, and (3) growth rate. The amplitude of the phase response curve to light was drastically reduced as the temperature was increased from 25°C to 34°C. Phase advances were decreased more than phase delays. As previously reported (Sargent et al., 1966), the period length of the rhythm is temperature‐compensated below 30°C (Q10˜ 1) but not well‐compensated above 30°C (Q10 1.3–1.7). The decrease in amplitude of the light phase response curve occurred in both temperature ranges. Furthermore, the Q10 value was lowered by addition of yeast extract in the high temperature range but not in the low range. Q10 values for growth rate also differed in these strains both in the low temperature range (25–30°C) and the high temperature range (30–34°C).
ON THE STATE OF CHROMOPHORE PROTONATION IN RHODOPSIN: IMPLICATION FOR PRIMARY PHOTOCHEMISTRY IN VISUAL PIGMENTS
Authors: Narva D. , Callender R. H. 
Published: January 2008

Abstract—Resonance Raman multicomponent spectra of bovine rhodopsin, isorhodopsin, and bathorhodopsin are obtained at low temperature. Application of the double beam, ‘pump‐probe’ technique allows an extraction of the rhodopsin and bathorhodopsin spectra in both protonated and deuterated media. Our results show that the Schiff bases of both rhodopsin and bathorhodopsin are fully protonated and the degree of protonation is unaffected by the rhodopsin‐bathorhodopsin transformation. Further, the data support the concept or cis‐trans isomerization as occurring in this transition. The effect of these results on various models for the primary photochemical event in vision is discussed.
DNA DAMAGE IN RAT 9L CELLS TREATED WITH 8‐METHOXYPSORALEN AND NEAR‐UV LIGHT ASSAYED BY VISCOELASTOMETRY AND S1 NUCLEASE
Authors: Shafer Richard H. , Chase Eric S. , Wun Kai‐Lam W. 
Published: January 2008

Abstract–The techniques of viscoelastometry and S1 nuclease digestion were applied to the analysis of DNA damage in rat 9L cells treated with the combination of 8‐MOP (8‐methoxysporalen) and near‐UV light. Treatment of cells with near‐UV light alone resulted in a decrease in the viscoelastic retardation time under both denaturing and nondenaturing conditons. Exposure of cells to 8‐MOP alone yielded a maximum in the plot of retardation time vs dose under nondenaturing conditions, similar to that found with ionizing radition. This observation suggests that treatment with 8‐MOP alone leads to DNA strand breaks. Viscoelastic analysis of cell lysates under denaturing conditions demonstrated that treatment of cells with 8‐MOP and UV radiation led to substantial increases in both the viscoelastic retardation time and recoil, consistent with formation of DNA interstrand cross‐links. Viscoelastic analysis of cell lysates under nondenaturing conditions showed that exposure to long wavelength UV light in the presence of 8‐MOP produced a decrease in retardation time. This decrease reflects the combined effect of strand breaks and interstrand cross‐links. Results from the S1 nuclease assay confirmed these observations and permitted quantitation of DNA damage arising from single‐strand breaks and DNA interstrand crosslinks. The importance of including the effect of strand breaks in the quantitation of cross‐link formation is discussed.
SPONTANEOUS AGGREGATION OF BACTERIORHODOPSIN IN BROWN MEMBRANE
Authors: Hwang S.‐B. , Tseng Y.‐W. , Stoeckenius W. 
Published: January 2008

Abstract— Halobacterium halobium cells grown in nicotine‐containing medium synthesize bacterio‐opsin (bO) but little bacteriorhod‐opsin (bR) because nicotine inhibits retinal synthesis. In nicotine‐grown cells, bacterio‐opsin is found in a specific cell membrane fraction, the brown membrane (b.m.), which consists mainly of small round sheets. Freeze‐fracture of isolated brown membrane reveals a dense particle population on its cytoplasmic fracture face, with few particles on the external face. There is no apparent order in the particle distribution and the fracture faces are practically indistinguishable from those of red membrane (r.m.). The absorbance spectrum of b.m. shows peaks at 550 and 410nm, the circular dichroism (CD) spectrum a positive band around 540nm and positive and negative bands around 410nm with a cross‐over at 412nm. The photoreaction cycle of bR in b.m. has the same intermediates found in purple membrane (p.m.), but the apparent kinetics resemble those of bR monomers.Addition of 13‐cis‐, or all‐trans‐retinal to b.m. induces a rapid 5‐ to 10‐fold increase in the visible absorbance band, and the absorbance maximum shifts to 560nm in the dark. Kinetic analysis of the absorbance increase shows three first order kinetic constants with t½= 0.5 min, 6 min and 100 min, with most of the increase contributed by the fastest component. The CD bilobal pattern typical for purple membrane appears together with the strong negative band at 320nm. Ellipticity change at 590nm is nearly as rapid as the absorbance increase; within 5 min, 85% of the negative band is formed. Electron microscopy after addition of retinal reveals structurally distinct domains in the b.m. sheets which have the characteristic appearance of p.m. However, X‐ray reflections are more diffuse compared to p.m. Flash spectroscopy of reconstituted b.m. detects the same photocycle intermediates as in b.m. or p.m., but with apparent kinetics closer to those of purple membrane than before reconstitution. These results show that bO in the b.m. binds retinal to form bR which spontaneously aggregates into a lattice. However, the reconstituted bR lattice is not as well‐ordered as in p.m. and some bR is still present in the form of monomers and/or small aggregates.