bluuebunny/crossref_metadata_2025 huggingface dataset:
PHOTOFRAGMENTATION OF HYDROXYACETONE, 1.3‐DIHYDROXYACETONE, AND 1.3‐DICARBOXYACETONE IN AQUEOUS SOLUTION. AN EPR STUDY
Authors: Steenken S. , Jaenicke‐Zauner W. , Schulte‐Frohlinde D.
Published: January 2008

Abstract—On photoexcitation, hydroxyacetone undergoes a Norrish‐type‐1 fragmentation to yield CH3CO and CH2OH. CH2OH is identified by its EPR spectrum. The existence of CH3CO is inferred from the presence of diacetyl and acetaldehyde in irradiated solutions. Above pH 5, in addition to CH2OH, the cis and trans forms of the hydroxyacetone enediol radical anion, CH3C(O‐)=C(O***)H, are detected. 1.3‐Dihydroxyacetone is photodecomposed to HOCH2C̀O and C̀H2OH. The former radical decarbonylates to yield CH2OH and CO. At 254 nm the overall quantum yield of CO production is 0.75. Above pH 5, in addition to CH2OH, the cis and trans forms of the 1.3‐dihydroxyacetone enediol radical anion, HOCH2C(O‐)C(O***)H, are observed.

Electronically excited hydroxyacetone and 1.3‐dihydroxyacetone react exclusively by C‐C fragmentation, and no H‐abstraction from H‐donors is observed. In contrast, electronically excited 1.3‐dicarboxyacetone shows H‐abstraction from H‐donors in competition with C‐C fragmentation. In the absence of H‐donors, fragmentation resulting in CH2CO2‐ and ‐O2CCH2C̀O occurs followed by decarbonylation of ‐O2H2C̀O. At 254 nm the quantum yield of CO production is 0.02. In the presence of H‐donors, H‐abstraction, yielding HO2CCH2C(OH)CH2CO2, predominates.
INFLUENCE OF LIGHT ON THE EPR‐DETECTABLE, ELECTRON TRANSPORT COMPONENTS IN WHOLE CELL RHODOSPIRILLUM RUBRUM
Authors: Corker G. A. , Sharpe S. A.
Published: January 2008

Abstract—The influence of light upon the electron paramagnetic resonance (EPR)‐active components of R. rubrum, both in whole cells and in subcellular particle preparations, is presented. In the whole cells, 16 EPR signals can be detected, 11 of which are influenced by illumination of the bacteria. Four of these are also affected by illumination at 77 K. The effects of K3Fe(CN)6, Na2S2O4 and heating upon the signals observed in the whole cells are also presented. The whole cells contain several photoinfluenced, EPR‐active components that are missing in the subcellular particle preparations. The kinetics of most of the signals in the whole cells are complex, whereas in the subcellular particles the kinetics are generally monotonic. For comparison, some of the EPR signals detected in whole‐cell Chromatium D are also presented. The signals observed in these two strains of bacteria differ considerably. A discussion of the possible identities of the R. rubrum signals and speculation as to the role of some of them in the photosynthetic electron transport system are also included.
DETERMINATION OF THE pk VALUES OF THE LUMIFLAVIN TRIPLET STATE BY FLASH PHOTOLYSIS
Authors: Schreiner S. , Steiner U. , Kramer H. E. A.
Published: January 2008

Abstract— The triplet‐triplet absorption spectra in aqueous solution of the acid (3LfH2+), the neutral (3LfH) and the basic (3Lf‐) forms of lumifiavin (6,7,9‐trimethylisoalloxazine) were measured by flash photolysis. The pKa values of the corresponding protolytic equilibria of the lumifiavin triplet were found to be 4.45±0.1 and 9.8±0.15.
KINETIC ANALYSIS OF A VERY RAPIDLY REVERTING POPULATION OF HIGH‐MOLECULAR‐WEIGHT PHYTOCHROME*
Authors: Pratt Lee H.
Published: January 2008

Abstract— Purified high‐mol‐wt phytochrome preparations in the absence of ethylenediaminetetraacetic acid or 2‐mercaptoethanol may exhibit lower far‐red extinction in the far‐red‐absorbing form (Pfr) than has previously been reported. Kinetic analyses suggest that such preparations of phytochrome in the Pfr form consist either of two populations of Pfr, one with normal extinction and one with greatly reduced far‐red extinction, or of one population of Pfr in which each molecule possesses both one or more high far‐red extinction chromophores and one or more low far‐red extinction chromophores. The low‐extinction form of Pfr undergoes reversion to the red‐absorbing form of phytochrome with a half‐life of approximately 2 min at 3°C and may represent as much as 35 per cent of the total Pfr present.
REDOX DYES AS ARTIFICIAL PHOTORECEPTORS IN LIGHT‐DEPENDENT CAROTENOID SYNTHESIS*
Authors: Lang‐Feulner J. , Rau W.
Published: January 2008

Abstract— The photodynamically active dyes methylene blue, toluidine blue, and neutral red act as artificial photoreceptors in light‐dependent carotenoid synthesis in Fusarium aquaeductuum. Normally, carotenoid production is only induced by light of wavelengths shorter than 520 nm, but when mycelia are incubated with neutral red, methylene blue, and toluidine blue, red light is also effective in inducing carotenogenesis. Experiments with methylene blue and red light showed that pigments induced under these conditions are qualitatively the same as those induced with white light, and also that, in accord with the results found for photoinduction with white light, the amount of pigment synthesized was proportional to the logarithm of illumination time. In addition to their role in photoinduction, the dyes were also shown to interfere with the biosynthesis of carotenoids, whereas addition after irradiation caused an increase in pigment production that involves a quantitative change in the more unsaturated components.
PHOTOSENSITIZED DEAMINATION OF SULFUR‐AMINO ACIDS BY FLAVIN MONONUCLEOTIDE*
Authors: Bowen John R. , Yang S. F.
Published: January 2008

Abstract— S‐Methylcysteine, methionine and cystine were found to be photochemically deaminated at a much higher rate than methionine sulfoxide, homomethionine and other non‐sulfur amino acids in the presence of flavin mononucleotide. These data strongly support the view that the initial oxidation of those sulfur‐amino acids by the photoactivated flavin is a one‐electron abstraction from the sulfur atom followed by an intramolecular electron transfer from the carboxyl anion of the amino acid to the sulfinium radical, resulting in the decarboxylation‐deamination.
EXCITED‐STATE REACTIONS OF OXIDIZED FLAVIN DERIVATIVES
Authors: Lasser Nehama , Feitelson Jehuda
Published: January 2008

Abstract— The reactivity of flavin mononucleotide and of lumiflavin triplets was studied by flash and laser photolysis. The rate constants of the triplets with oxygen, with flavin ground‐state molecules, and with Br‐ ions were determined. Although in solution at room temperature, the protonated flavin triplet, 3F1H+, is not formed directly from its very short lived singlet state, a transient, which we think is this triplet, results from protonation of the neutral triplet. This conclusion is based on a comparison between the neutral and the protonated triplet spectra in a low‐temperature glass. It is proposed that the protonated triplet can also be formed by sensitization via the phenanthrene triplet.
THE ‘HIGH‐IRRADIANCE RESPONSE’ IN ANTHOCYANIN FORMATION AS RELATED TO THE PHYTOCHROME LEVEL
Authors: Drumm H. , Wildermann A. , Mohr H.
Published: January 2008

Abstract— The involvement of phytochrome in light‐mediated anthocyanin synthesis in the mustard seedling (Sinapis alba L.) under inductive conditions (law of reciprocity valid) was shown previously (Drumm and Mohr, 1974). In the present paper the hypothesis (Hartmann, 1966) is checked that light‐mediated anthocyanin synthesis in continuous high‐irradiance far‐red light (‘high‐irradiance response’) is also due exclusively to phytochrome. The data indicate that the effectiveness of the far‐red light is indeed a function of total phytochrome [Ptotal]* and therewith [Pfr]*. The data are not consistent with the suggestion (Schneider and Stimson, 1972) that photosynthesis (in particular, photosystem I) is involved in the ‘high‐irradiance response’ of photomorphogenesis.
THERMOLUMINESCENCE STUDIES ON SPINACH LEAVES AND EUGLENA
Authors: Desai T. S. , Sane P. V. , Tatake V. G.
Published: January 2008

Abstract— Spinach leaves and Euglena cells when frozen in light to 77 K emit light during slow warming in the dark to give 6 peaks. The peak appearing at 118 K is observed even after DCMU or heat treatment and also in aged chloroplasts that are inactive in electron transport.

The data indicate that peaks appearing at 261 and 321 K are due to back reactions of primary acceptors of PS II and PS I respectively with oxidized chlorophylls. The DCMU sensitivity of Tl peaks at 283 and 298 K suggests that they are associated with the flow of electrons between PS II and PS I. Evidence has been presented to show that the PS 1 chlorophylls are involved in part of the luminescence observed during the temperature rise.

A mechanism involving the return of the thermally detrapped electrons to the ground state of chlorophylls through their excited states has been proposed to explain some of the Tl peaks.
ULTRAVIOLET IRRADIATION OF SUSPENSIONS OF MICRO‐ORGANISMS: POSSIBLE ERRORS INVOLVED IN THE ESTIMATION OF AVERAGE FLUENCE PER CELL*
Authors: Jagger John , Fossum Tore , Mccaul Scott
Published: January 2008

Abstract— Experiments on cell survival in concentrated suspensions of Escherichia coli B/r show that application of the well known “Morowitz correction” (H. J. Morowitz, (1950) Science111, 229–230) can lead to large errors in estimation of the average fluence per cell if light scattering is not taken into account. The magnitude of the effect is illustrated for this organism, but it is pointed out that experimenters should determine the correction for each organism and set of experimental conditions used.
PHOTOFRAGMENTATION OF α‐OXOCARBOXYLIC ACIDS IN AQUEOUS SOLUTION. AN EPR STUDY. FORMATION OF SEMIDIONE RADICALS BY DECARBOXYLATIVE SUBSTITUTION OF α‐OXOCARBOXYLIC ACIDS BY ACYL RADICALS‐I: GLYOXYLIC, PYRUVIC, α‐OXOBUTYRIC, α‐OXOGLUTARIC AND α‐OXOISOCAPROlC ACIDS
Authors: Steenken S. , Sprague E. D. , Schulte‐Frohlinde D.
Published: January 2008

Abstract—By means ofin situphotolysis EPR of aqueous solutions of α‐oxocarboxylic acids (RCO‐CO2H) at pH values above 5, semidione radical anions [RC(O‐)=C(O‘)R] and α‐hydroxy‐α‐carboxy alkyl radicals [RC(OH)CO2‐] were detected. C02was identified as a reaction product. On photolysis of mixtures of α‐oxocarboxylic acids (RCOCO2H and R'COCC2H), “mixed” semidione radical anions [RC(O‐>=C(O)R’] were observed in addition to RC(O‐)=C(O‘)R, R'C(O‐)=C(O’)R‘, RC(OH)CO2‐and R'C(OH)CO2‐. The experimental results are explained in terms of photodecarboxylation (α‐clea‐vage) of electronically excited RCOCOJ to yield RCO and CO2. The radicals RC(OH)CO2‐are formed by reduction of RCOCO2‐by CO2‐. The semidione radicals are produced by addition of RCO to RCOCO2‐followed by decarboxylation of the intermediate adduct. This mechanism was confirmed by generating acyl radicals independently and reacting them with α‐oxocarboxylic acids. Selected product studies support the mechanism suggested.
ADENOSINE 5‐TRIPHOSPHATE CONTENT AND ENERGY CHARGE DURING PHOTOMORPHOGENESIS OF THE MUSTARD SEEDLING SIN APIS ALBA L.
Authors: Freederich K. E. , Mohr H.
Published: January 2008

Abstract— The contents of ATP, ADP and AMP (enzymatic assay) and the rate of respiration (output of CO2 per h, continuously measured with an infrared CO2 analyzer) were determined in long‐term experiments with intact dark‐grown and far‐red‐light‐grown mustard (Sinapis alba L.) seedlings. While there is a strong effect of far‐red light treatment on the respiratory rate (inhibition as well as promotion, depending on the onset of light), an effect on the contents of adenosine nucleotides, and therewith on energy charge, is hardly detectable. At most, there is a tendency that long‐term far‐red light slightly lowers ATP levels and energy charge. The results suggest that the adenylate system (and therewith the energy charge) in the mustard seedling is controlled by endogenous homoeostasis even under intense phytochrome‐mediated photomorphogenesis. It is unlikely that the levels of adenosine nucleotides or the energy charge are links in any causal chain originating from Pfr and leading to phenomena of photomorphogenesis.
KINETIC STUDIES OF THE TRYPTOPHAN TRIPLET STATE IN SOLID FILM AND IN WOOL KERATIN
Authors: Ghiggino K. P. , Nicholls C. H. , Pailthorpe M. T.
Published: January 2008

Abstract— The triplet state of tryptophan in the solid environments of a polyvinyl alcohol) (PVA) film and the protein wool keratin has been studied by emission and absorption spectroscopy at room temperature. The decay kinetics of the triplet state vary depending on the conditions under which the study is made. The observation of second order kinetics suggests triplet‐triplet interactions play a major role in the deactivation of the tryptophan triplet state in PVA films plasticised by the presence of water vapour. For wool keratin in the presence of air the major mechanism appears to be a first order reaction between tryptophan residues and oxygen. The actual effects of moisture and oxygen on the tryptophan triplet state are discussed.
INTER‐ AND INTRAMOLECULAR EFFECTS OF TYROSYL RESIDUES ON FLAVIN TRIPLETS AND RADICALS AS INVESTIGATED BY FLASH PHOTOLYSIS*
Authors: McCormick Donald B. , Falk Michael C. , Rizzuto Frank , Tollin Gordon
Published: January 2008

Abstract— Addition of tyrosine or derivatives to aqueous solutions of flavins does not significantly impede either formation of the flavin triplet or the rate of O2 oxidation of the flavin radical generated by reaction of triplet with the phenol. However, the rate of radical decay is decreased.

There is only a modest effect that results from altering the nature of the group on alkyl side chains of the flavin when the substituent, e.g. phenylalanine, does not complex avidly with the isoalloxazine system. However, when a tyrosyl or O‐methyltyrosyl residue is covalently attached to an alkyl side chain at the N10‐position of the flavin, the considerable intramolecular complexing that results markedly decreases the formation of flavin triplet and, therefore, the radical yield. The rate of triplet decay is not much different than for noninternally complexed flavins, but extensive intramolecular radical decay occurs, and the rate of 02 oxidation of radical is decreased. A shorter alkyl chain is more effective than a longer one for decreasing triplet production, but the greater proximity of a photooxidiz‐able tyrosyl residue to the flavin nucleus within the former allows a slightly higher intramolecular radical yield. Attachment of a tyrosyl residue by a short chain from the N3‐position of the flavin has only a modest effect on the production of flavin triplet and its decay. There is less radical production from internal than from external tyrosyl residues, and the rate of O2 oxidation of the flavin radical generated by such intermolecular photoreductants as N‐acetyl tyrosine ethyl ester or EDTA is somewhat decreased.

The tyrosyl residue within the active‐site peptide of mitochondrial monoamine oxidase is not so susceptible to photooxidation by the 8α‐(S‐L‐cysteinyl)flavin involved, since the thioether linkage at this position severely reduces triplet production. Upon oxidation of the thioether to sulfone, however, the triplet yield is partially restored. Some flavin radical can then be generated from either the intra‐ or an intermolecular tyrosyl residue.

Taken together, these results demonstrate that tyrosyl residues near the flavin‐binding sites of flavo‐proteins can become oxidized by the flavin triplet that is light‐generated unless the proximity and steric disposition of the interactants is such as to allow dissipation of much of the energy as radiationless decay within a tight complex or unless an 8α‐thioether linkage to the flavin coenzyme is involved. Also, flavin radicals, whether generated photochemically or by biochemical oxidation of substrate, are readily oxidized by O2 in the presence of tyrosyl functions unless tight complexing occurs. More remarkable, though, is the decreased rate of radical decay conferred by the association with a tyrosyl residue. This stabilization of reactive flavin radicals may have considerable consequence in the catalytic mechanism of such enzymes.
INFLUENCE OF THE ENVIRONMENT ON THE EXCITATION WAVELENGTH DEPENDENCE OF THE FLUORESCENCE QUANTUM YIELD OF INDOLE
Authors: Tatischeff I. , Klein R.
Published: January 2008

Abstract— The influence of excitation wavelength, pH, oxygen and solvents, upon fluorescence quantum yields, were measured for insole Indole in neutral aqueous solution exhibits the same wavelength dependence as tryptophan, which indicates that COO‐ absorption is not responsible for the effect. Parameters such as pH and oxygen influence only the absolute fluorescence quantum yields but not their relative variation with wavelength, indicating competition with fluorescence emission for S1 deactivation. without any influence upon deactivation of higher excited states. In contrast, solvents exhibit a specific influence upon the wavelength dependence; for indole, the decrease of fluorescence yield excited around 215 nm, compared with the yield in the first absorption band is about 40% in water, 10% in acetonitrile, 70% in n‐hexane and cyclohexane, whereas no appreciable decrease occurs in methanol, ethanol or n‐butanol. These observations, together with the Stokes shifts of the emission spectra, may be well correlated with Kosower's Z‐values, expressing microscopic solvent‐solute interactions.
INTRINSIC FLUORESCENCE OF S4 AND S7 E. COLI RIBOSOMAL PROTEINS*
Authors: Gerard Dominique , Lemieux Gerald , Laustriat Gilbert
Published: January 2008

Abstract— Fluorescence properties of S4 and S7 ribosomal proteins, excited at 280 and 295 nm, have been studied; emission spectra, fluorescence quantum yields and lifetimes, effects of external quenchers (I‐ and Cs' ions) and of temperature. I t has been shown that the emissions are due to tyrosine and tryptophan for S4 and to tryptophan only for S7. The discussion of results showed that the emitfiny residues are not exposed in S4 and of two kinds, exposed (class a) or partially buried (class b), in S7. Above 35T, the single tryptophan of S4 is released into the aqueous medium, following thermal conformation changes of this protein. The spectral characteristics and the high values of quantum yields of S4 and S7 class b tryptophan emissions are consistent with the location of these residues in helical regions of the proteins. The absence of tyr‐ trp energy transfer in S4 may be due to a stretched conformation of this protein. The possibility of a further fluorescence study of the complexes between RNA and S4 and S7 proteins has been pointed out.
THE ACTION SPECTRUM AND DOSE RESPONSE STUDIES OF UNSCHEDULED DNA SYNTHESIS IN NORMAL HUMAN FIBROBLASTS
Authors: Ichihashi M. , Ramsay C. A.
Published: January 2008

Abstract— Excision repair of DNA damage by UV has been assessed in normal human fibroblasts in culture by measuring unscheduled DNA synthesis. Dose response experiments indicated that the same chromophore was involved in UV‐induced damage and excision repair at three different wavelengths between 260 and 300 nm. Action spectra for unscheduled DNA synthesis were determined at wavelengths between 260 and 320 nm 30 min after irradiation using 2 doses of UV, 100 J m‐2and 10Jm‐2. Experiments at the lower dose were carried out because it appeared that repair was saturated with the higher dose at 260 and 280 nm. To explore this part of the spectrum further, experiments were performed with different doses at 260 and 280 nm and unscheduled DNA synthesis assessed 30 min and 24 h after irradiation. At 24 hr after irradiation a significantly greater amount of unscheduled DNA synthesis occurred at 280 nm. It is suggested, therefore, that both DNA and protein are concerned in the absorption of UV which leads to DNA damage and excision repair.
FLASH PHOTOLYSIS OF N‐ACETYL‐L‐TRYPTOPHANAMIDE: ANALYSIS OF TRANSIENTS EMPLOYING VIDICON TUBE DETECTION*
Authors: Evans R. F. , Volkert W. A. , Kuntz R. R. , Ghiron C. A.
Published: January 2008

Abstract— An improved method for recording transient absorption spectra obtained by flash photolysis is described. The detection system, comprising a vidicon tube coupled to a multichannel analyzer, is shown to permit the rapid acquisition of accurate and precise spectra spanning any 360 nm interval within the 200 to 1100 nm wavelength range. The successful dissection of the complex spectrum obtained when N‐acetyl‐L‐tryptophanamide is flashed under nitrogen‐saturated conditions is utilized to highlight the capabilities of the detection system. This analysis suggests that the observed radicals must originate, in part, from an oxygen sensitive long‐lived precursor which is not the triplet state.
DYE‐MEMBRANE INTERACTION AND ITS CHANGES DURING NERVE EXCITATION
Authors: Tasaki Ichiji , Warashina Akira
Published: January 2008

Abstract— With a view toward elucidating the physiocochemical properties of the nerve membrane, the behavior of various dye molecules incorporated into the membrane was investigated. By measuring the difference between the absorption spectra of dyes in the membrane at rest and those during nerve excitation, the nature of the conformation changes of the membrane macromolecules were examined. Mathematical expressions were developed describing the absorbance changes of dye molecules during nerve excitation. Experimental evidence was presented indicating that there is, during nerve excitation, rotation of dye molecules in the membrane. The physicochemical bases of the process of production of fluorescence changes during nerve excitation are discussed. Based on the results of measurements of the polarization of the fluorescent light, the existence of a highly ordered macromolecular structure at or near the inner surface of the membrane was inferred.
KINETIC FORMALDEHYDE ANALYSIS OF DNA ULTRAVIOLET IRRADIATED IN THE PRESENCE OF SILVER IONS*
Authors: Rahn R. O. , Stafford R. S.
Published: January 2008

Abstract— DNA from Escherichia coli was irradiated at 254 nm in the presence of silver in order to preferentially enhance the rate of formation of pyrimidine‐dimer damage over nondimer damage. The irradiated DNA was treated with formaldehyde in order to measure the unwinding velocity of the defects associated with the pyrimidine dimers. This velocity was found to be 0.18 base pairs/min per pyrimidine dimer, which is nearly 8 times less than that found for a double‐strand break (1.37 base pairs/min) obtained by use of sheared DNA whose size was determined by electron microscopy. The rate of reaction of the DNA with formaldehyde varied linearly with the pyrimidine dimer concentration and showed no inflection due to clustering. Treatment of irradiated DNA with UV endonuclease enhanced the formaldehyde reaction by ˜ 7‐fold, consistent with the conversion of a dimer into the faster‐reacting defect associated with a single‐strand break. These results indicate that the distribution of dimers in DNA is random and not clustered, and that previous interpretations of clustering were based on the false assumption that dimer and chain break defects unwind with similar velocities when treated with formaldehyde.
THE PHOTOREACTIONS AND FREE RADICAL INDUCED REACTIONS OF 1,3‐DIMETHYLURACIL IN METHANOL AND OTHER ALCOHOLS
Authors: Shetlar Martin D.
Published: January 2008

Abstract— Photoexcited 1,3‐dimethyluracil (DMU) reacts with methanol to give 1,3‐dimethyl‐6‐hydroxymethyl‐5‐hydrouracil (1a) in addition to cyclobutane type dimers and 1,3‐dimethyl‐6‐methoxy‐5‐hydrouracil (2a). Free radical induced reaction, initiated by photodecomposition of di‐t‐butyl peroxide with light of wavelength greater than 290nm, leads to 1a, 5,6‐dihydroxymethyl‐5,6‐dihydro‐1,3‐dimethyl‐uracil (1d) and 6‐hydroxymethyl‐1,3‐dimethyluracil as the products.
MODEL CONSIDERATIONS OF THE LIGHT CONDITIONS IN NONCYLINDRICAL PLANT CELLS
Authors: Gabryś‐Mizera Halina
Published: January 2008

Abstract— A geometric model of a noncylindrical plant cell has been constructed using optical and geometrical parameters obtained for the cells of Funaria hygrometrica and Lemna trisulca leaves. The distribution of the incident light intensity and the absorption profile in the monomolecular photoreceptor layer on the walls of the model cell irradiated with the parallel beam have been calculated. Calculations were performed for two surrounding media with refractive indices of 1.33 (water) and 1.00 (air). Various chloroplast arrangements were considered. The course and kinetics of the phototactic movements of Funaria and Lemna chloroplasts have been discussed on the basis of the results obtained. The best agreement between the theoretical and experimental data is obtained by assuming that the transition moments at 450 nm of the dichroic photoreceptor molecules are oriented parallel to the surface of the cell wall.
ISOTHERMAL LUMINESCENCE AND THERMO‐LUMINESCENCE OF NUCLEIC ACID BASES FOLLOWING γ‐IRRADIATION
Authors: Tatake V. G. , Desai T. S. , Sane P. V.
Published: January 2008

Abstract— The emission spectra of radiation induced isothermal luminescence (ITL) and the thermolu‐minescence (TL) of purines and pyrimidines of nucleic acids and analogue 6‐azauracil in the form of pellets of dry polycrystalline powders have been studied at 77 K, and compared with their low temperature fluorescence and phosphorescence spectra. The qualitative and quantitative measurements of isothermal luminescence and thermoluminescence show that the two result from the same radiative transitions. The thermoluminescence emission was observed to coincide with the phosphorescence emission of the compounds in all the cases. The thermoluminescence of the pyrimidines and their analogue, however, have shown an additional component corresponding to their fluorescence in the ultraviolet region. An extension of the Weissbluth model based on the location of the electron traps in relation to the excited states of the compounds is proposed to explain their thermoluminescence emission.
INDEPENDENCE OF PHOTOPRODUCT FORMATION ON DNA CONFORMATION*
Authors: Patrick Michael H. , Gray Donald M.
Published: January 2008

Abstract— In an ethanolic solution native T7 DNA can undergo conformational transitions from the B conformation (0% ethanol) to the C‐like (60% w/w ethanol) and the A (80% w/w ethanol) conformations. We have investigated the formation of three classes of thymine‐derived photoproducts in T7 DNA irradiated (280 nm) in the B, C‐like, and A conformations, which were monitored by circular dichroism measurements. We find that the predominant class of thymine‐derived photoproducts in any conformational state is cyclobutyl dipyrimidines. While the ‘spore product,’ 5‐thyminyl‐5,6‐dihydrothymine, which belongs to another class of photoproductsf does form in native DNA in the A conformation, its yield in denatured DNA at 80% ethanol is the same as that in native DNA. The yield of pyrimidine adduct, a third photoproduct class, is a maximum at 50–60% ethanol. This effect of ethanol is probably not due to the ethanol‐induced C‐like conformation, however, since pyrimidine adduct formation is not enhanced when T7 DNA is irradiated in the C conformation in 6 M CsCl or in intact phage. We conclude from these and other data in the literature that the degree of hydration rather than the conformational state is the critical factor in determining which of the photoproducts will form in native DNA.
THE EFFECT OF ENVIRONMENTAL LIGHT EXPOSURE ON DRUG‐INDUCED PORPHYRIA IN THE RAT
Authors: Bickers David R. , Keogh Louise , Harber Leonard C. , Kappas Attallah
Published: January 2008

Abstract— The porphyrinogenic drug, 3,5‐diethoxycarbonyl 1,4‐dihydrocollidine (DDC) when administered orally to rats evoked large increases in hepatic δ‐aminolevulinic acid synthetase (ALAS) activity and hepatic protoporphyrin levels. These increases varied markedly according to light exposure patterns of the animals. DDC‐treated animals continuously exposed for one week to fluorescent Blacklight lamps (Westinghouse FS‐40) demonstrated a greater than two‐fold increase in hepatic ALAS and a greater than threefold increase in liver protoporphyrin levels as compared to DDC‐treated animals exposed to ambient light‐dark cycling. Furthermore, the skin of porphyric animals continuously exposed to light showed larger increases in porphyrin content as compared to rats exposed to ambient light. These studies indicate that light exposure patterns can profoundly alter the activity of the hepatic heme pathway in the rat and suggest that light exposure could play a role in the production of drug‐induced porphyria in man.
EXTRARETINAL PHOTORECEPTION IN LIZARDS
Authors: Underwood Herbert , Menaker Michael
Published: January 2008

Abstract— In lizards both photoperiodic photoreception and entrainment (synchronization) of the biological clock by environmental light cycles can be accomplished by extraretinal photoreceptors. Testicular size and spermatogenic activity in the green anole, Anolis carolinensis, is maintained under long (14 h) photoperiods in the summer in both sighted and blinded lizards whereas short days (6h) cause testicular regression. In the fall, long photoperiods cause testicular recrudescence and maturation in blinded and blinded‐parietalectomized anoles as well as in sighted anoles.

Extraretinal photoreceptors can mediate entrainment of the circadian locomotor rhythm in every lizard species examined to date (8 species). The photosensory pineal complex in lizards (pineal organ and parietal eye) may not be involved in entrainment; in any case, its removal does not prevent entrainment of blinded lizards. Localization experiments have shown that the brain is the site of the extraretinal receptors mediating entrainment. The lateral eyes can also contribute to entrainment. In some species, but not all, blinding alters the pattern of the entrained activity rhythm. The free‐running activity rhythms of two species of lizards exposed to continuous illumination respond very differently to blinding; these experiments yield insight into the mechanisms of entrainment in the two species as well as showing that caution must be observed when generalizing about the role of retinal and extraretinal receptors not only among different vertebrate classes but also among species of the same class.
EXTRARETINAL PHOTORECEPTION IN BIRDS
Authors: Menaker Michael , Underwood Herbert
Published: January 2008

Abstract— It is clearly established that in birds, as in the other lower vertebrates, brain photoreception is a critically important perceptual mode. In this review, the variety of extraretinally‐mediated responses has been described, and the physiological properties and anatomical location of extraretinal photoreceptors have been briefly discussed. In order to deepen our understanding of its place in the sensory armamentarium, several unresolved problems have been pointed out.
PHOTOCHEMICAL CROSSLINKING OF ATP TO HISTONE H4
Authors: Sperling Joseph
Published: January 2008

Abstract— A covalent crosslink occurs between histone H4 and the adenine moiety of ATP, when the complex they form is irradiated with UV light of Λ > 290 nm in the presence of acetone. Within 1 h of irradiation a 48% yield of crosslinked product is thus obtained. It is also shown that in the photosensitized reaction, 80% of the crosslinked product is monomeric, whereas protein precipitation and aggregation occur as a result of direct irradiation with 254 nm light.
ACTION SPECTRUM AND QUANTUM YIELD FOR THE PHOTOINACTIVATION OF MNEMIOPSIN, A BIOLUMINESCENT PHOTOPROTEIN FROM THE CTENOPHORE MNEMIOPSIS SP.*
Authors: Ward William W. , Seliger Howard H.
Published: January 2008

Abstract— Ctenophores are bioluminescent marine invertebrates closely related to the coelenterates. The isolated bioluminescent systems of the ctenophores Mnemiopsis and Beroë and the hydrozoan jellyfish Aequorea are protein‐luciferin complexes (photoproteins) which flash upon the addition of Ca2+ ions. The photoprotein mnemiopsin has an oxygen‐independent quantum yield for photoinactivation of bioluminescence as high as 0.5, placing it among the most light‐sensitive proteins known. We have measured the action spectrum for this photoinactivation at 107 narrow (3.4 nm) wavelength bands between 230 nm and 570 nm, covering a range of four decade units in the action. The action spectrum in the visible region is identical with the absorption spectrum of native photoprotein, implicating bound luciferin. The UV action spectrum implies that absorption by aromatic amino acid residues also leads to extremely efficient photoinactivation. Although photoinactivation is a rapid first‐order reaction, destruction of the luciferin is a slower, multiple‐order process. Therefore, protein‐bound luciferin is not the ultimate target of the photoinactivation. Absorption of light results in the dissociation of “active oxygen” from the photoprotein. Therefore, the ctenophore photoprotein is a precharged enzyme already containing bound luciferin and oxygen.
PHOTOCHEMICAL INVESTIGATIONS OF OXAZINE, THIAZINE AND SELENAZINE DYES. THE REACTIVITY OF PROTOLYTIC TRIPLET FORMS IN ELECTRON TRANSFER REACTIONS
Authors: Vogelmann Ekehardt , Kramer Horst E. A.
Published: January 2008

Abstract—The photoreduction of oxonine, thionine and selenine with the reducing agent allylthiourea was investigated by flash photolysis. The oxonine triplet state was produced by triplet‐triplet energy transfer with 9,10‐dibromoanthracene as donor. For all three dyes the rate constant of the electron transfer is considerably higher for the acid triplet form than that of the corresponding reaction of the basic triplet form. It is shown that the higher reactivity of the acid triplet can be related to its higher reduction potential which is available from the difference of the pK values of triplet and semiquinone of the dye.
THE PHOTOPHYSICS OF 5‐METHOXYINDOLE. A NON‐EXCIPLEX FORMING INDOLE: ADDITIONAL EVIDENCE FOR TWO CLASSES OF EXCIPLEXES*
Authors: Hershberger Martin V. , Lumry Rufus W.
Published: January 2008

Abstract—5‐Methoxyindole is a non‐exciplex forming indole, and its excited state behavior is qualitatively different from that of indole and its methyl substituted derivatives. This fact supports the idea that there are two limiting classes of exciplexes, charge‐transfer and dipole‐dipole stabilized. The fluorescence quantum yield in water is 0.29 with a lifetime of 4.0 ns at 25d̀C. The activation energy for fluorescence quenching in water is 15.9 pM 0.5 kJ/mol, which is smaller than for indole and the methyl substituted indoles which have been measured. In cyclohexane at 25d̀C, the fluorescence quantum yield is 0.63 with a lifetime of 6.7 ns. The fluorescence is efficiently quenched by electron scavengers, as is the case for other indoles. Some electron ejection to solvent probably occurs in both solvents.
STUDIES ON THYMINE‐DERIVED UV PHOTOPRODUCTS IN DNA—I. FORMATION AND BIOLOGICAL ROLE OF PYRIMIDINE ADDUCTS IN DNA
Authors: Patrick Michael H.
Published: January 2008

Abstract— Pyrimidine (Pyr) adducts constitute a significant fraction of the photoproducts formed in DNA exposed to far UV light. The primary and secondary DNA structure affects the rate of Pyr adduct formation; for example, it increases with decreasing (Ade + Thy)/(Gua + Cyt) of the DNA and with increasing dehydration, and it is greater in double‐stranded than in single‐stranded DNA. Pyrimidine adducts do not appear to be involved in inter‐strand cross‐links, and 313 nm‐induced photolysis of Pyr adducts does not cause strand breakage. The action spectrum for Pyr adduct formation is qualitatively similar to that for Pyr < > Pyr formation; the calculated quantum yields for its formation is essentially wavelength independent over the range 254 nm to 280 nm, but decreased somewhat at shorter wavelengths (240 nm). The biological role of Pyr adducts is still not clear. The data suggest that either Pyr adducts and their photolysis products are not lethal, or that both are lethal but can be repaired under certain conditions.
DNA SYNTHESIS‐KINETICS, CELL DIVISION DELAY, AND POST‐REPLICATION REPAIR AFTER UV IRRADIATION OF FROZEN CELLS OF E. COLI B/r
Authors: Smith Kendric C. , Hamelin Claude
Published: January 2008

Abstract— Previous studies have shown that the relative yields of photoproducts produced in the DNA of Escherichia coli cells UV irradiated at ‐79°C differ from those produced at +21°C; the yield of DNA‐protein cross‐links was markedly enhanced at ‐79°C while the yield of thymine dimers was reduced. In the present studies, cells of E. coli B/r thy were frozen at ‐79°C, and then UV irradiated (254nm) while frozen(4.7 J m‐2), or after thawing (22 Jm‐2). Essentially the same survival, cell division delay, and DNA synthesis kinetics were observed for these two samples after irradiation, even though the UV fluence differed by a factor of ˜5. This supports previous observations that a correlation exists between the magnitude of the effects of UV radiation upon DNA synthesis kinetics and on cell survival. The weight average molecular weight of the pulse labeled DNA in the sample irradiated at +21°C was one‐half that of the sample irradiated at ‐79°C, and complete repair of daughter‐strand gaps was observed in both cases. Thus, UV‐induced lesions produced in cells at ‐79°C (i.e. DNA‐protein cross‐links) appear to be amenable to post‐replicational repair. While the overall DNA synthesis kinetics were the same for the two irradiation procedures, the apparent number of lesions produced per unit length of DNA was not. This suggests that each of the lesions produced in frozen cells, although apparently fewer in number, must cause a longer local delay in DNA synthesis than those lesions produced at +21°C.
UBIQUINONE AND PHOTOCHEMICAL ACTIVITY IN RHODOSPIRILLUM RUBRUM*
Authors: Morrison Larry , Runquist Jennifer , Loach Paul
Published: January 2008

Abstract— An analytical procedure was developed for quantitatively determining the ubiquinone content of bacterial photosynthetic material. High sensitivity was obtained by supplementing growth media with14C‐labelled p‐hydroxybenzoic acid which was specifically incorporated into the benzoquinones, ubiquinone and rhodoquinone. Sufficiently radioactive p‐hydroxybenzoic acid was used so that 10 picomoles of ubiquinone could be quantitatively measured. High accuracy was obtained by using a carrier technique which was employed during the extraction and isolation of quinones for analyses. Purification of quinones was achieved by selective solvent extraction and thin layer chromatography in two different solvent systems. This analytical procedure was employed to determine the ubiquinone content of R. rubrum chromatophores following hydrocarbon solvent extraction to remove ubiquinone from the chromatophores. Ubiquinone was found to exist in at least two pools: a loosely bound pool which easily extracted with hydrocarbon solvents, and a tightly bound pool which required addition of some polar solvent for its removal. It was demonstrated that ubiquinone would not exchange readily between these two pools. Careful analyses of all protein fractions showed that less than 0.06 ubiquinone per primary electron donor unit (P865) could be covalently bound to these components. From the average of a number of measurements, the tightly bound ubiquinone was determined as very nearly one‐half ubiquinone per phototrap (0.48 ± 0.05 S.D.). Removal of the tightly bound ubiquinone was linearly related to the loss of primary photochemical capacity. These results are consistent with the ‘duplex model’ for primary photochemical events but would seem to rule out an iron‐ubiquinone complex where the ubiquinone can function only between the semiquinone and the fully oxidized oxidation state.
PHOTOTRANSFORMATIONS OF PHYTOCHROME: THE CHARACTERIZATION OF LUMI‐F AND META‐Fa
Authors: Spruit C. J. P. , Kendrick R. E.
Published: January 2008

Abstract— …Phototransformations of the red/far red reversible plant pigment phytochrome involve several intermediates. At 77K, lumi‐F, the initial product of phototransformation of the far red absorbing form Pfr and some of its relaxation products are shown to undergo further phototransformations. Lumi‐F has an absorption maximum in the region 690–730nm. The product, giving rise to a maximum in the difference spectra at 650nm, formerly thought to be lumi‐F, is now believed to represent one of its relaxation products. The nature of the reactions connecting these various intermediates are discussed.
PHOTOCHEMISTRY OF POLYURIDYLATE‐TERBIUM(III) COMPLEX
Authors: Formoso Carl
Published: January 2008

Upon irradiation with 240–300nm light a photochemical reaction occurs in Tb3+ complexes of polyuridylate and oligouridylate. The reaction is monitored by the appearance of a fluorescence excitation band which does not exist in non‐irradiated samples. The photochemical reaction is not observed in uridine nucleotides, dinucleoside phosphates, or when polyuridylate forms a double stranded helix with polyadenylate.
KINETIC INVESTIGATION OF THE PHOTOLYSIS OF 2‐OXO‐2,5‐DIHYDRO‐1,3,4‐OXADIAZOLES
Authors: Daniil Dimitra , Gauglitz Günther , Meier Herbert
Published: January 2008

Abstract. –A reaction scheme for the photolysis of 2‐oxo‐2,5‐dihydro‐1,3,4‐oxadiazoles is given by kinetic analysis, quantum yield measurement and product determination. The different reaction pathways in acetonitrile and ether are discussed.
ULTRAVIOLET INACTIVATION OF THE MIDI VARIANT OF Qβ‐RNA. DETERMINATION OF QUANTUM YIELD AND LESIONS PRODUCED
Authors: Ryan F. J. , Huang C.‐W. , Gordon M. P.
Published: January 2008

Abstract. –MDV‐1 RNA is a sequenced variant of Q/β RNA. This study analyzed the ultraviolet photosensitivity of the RNA with respect to its activity as template for the Q/β replicase reaction. An assay to measure the template activity is described and the quantum yield for inactivation of the template activity is shown to be 1.1 × 10‐3. Both uridine hydrates and pyrimidine dimers were found in the irradiated RNA. 1.4 hydrates were produced per lethal hit while less than 0.2 dimers were present per lethal hit. The production of uridine hydrates paralleled ultraviolet inactivation. It was concluded that hydrates were the significant lesion in irradiated MDV‐1 RNA.
ACTION OF DETERGENTS AND ELECTROPHORESIS ON SPINACH CHLOROPLASTS UNDER HIGH ALKALINE CONDITIONS
Authors: Gupta Anupam Das , Hales Brian J.
Published: January 2008

Abstract. The alkaline solubilization treatment (AUT) procedure followed by column electrophoresis is an easy and effective method for the preparation and isolation of PS I complexes. The subchloroplast particles prepared by the action of the detergents Triton or Triton/SDS differ in that, in the latter case, only low molecular weight polypeptides are observed. Similarly, the liquid He EPR spectra are almost identical except for the absence of a g˜ 2.03 line in the case of the Triton/SDS treated sample and the significant absence of 1.86 and 1.89 inflections in either spectra.
NEAR UV LIGHT AND CATARACTS*
Authors: Zigman Seymour
Published: January 2008

Abstract. Sunlight and many types of artificial lighting contain near‐UV light (300–400 nm). These wavelengths can enter the eye and are maximally absorbed in the lens due to its chemical composition. The lenses of certain animals develop cataracts from exposure to this light, and changes similar to those that occur in human lenses with certain types of cataracts and with aging are inducible in isolated human lenses. These changes seem to be associated with chemical alterations in the essential amino acid tryptophan either as a part of proteins or in free form. Such changes in tryptophan would result in lens cell toxicity, in increased pigmentation of the lens, and in large aggregates of proteins. The latter two changes would result in losses in the ability of the lens to transmit visible light needed for vision, and the abnormal state called cataract would result. Much more work is needed to prove that near‐UV light can accelerate cataractous changes in the lenses of living humans. Studies at the basic chemical level are needed, but population studies would be most essential for the final proof. Many preventive measures could become available, including the use of special types of spectacles and dietary additives.
ON THE ORIGIN OF LOW TEMPERATURE THERMOLUMINESCENCE IN NUCLEIC ACID BASES: EXCITATION AND EMISSION SPECTRAL STUDIES
Authors: Desai T. S. , Sane P. V. , Tatake V. G.
Published: January 2008

Abstract. Thermoluminescence excitation spectra of adenine, guanine, thymine and 1,3‐dimethyluracil were observed to be similar to their phosphorescence excitation spectra. Intensity dependence studies of thermoluminescence induced by ultraviolet light suggest that thermoluminescence could not be due to biphotonic ionisation of the molecule by UV. Evidence is presented which demonstrates that the fluorescence component observed in thermoluminescence of some compounds may not be due to triplet‐triplet fusion. Further, phosphorescence and thermoluminescence measurements following excitation with monochromatic light at very low intensities and short durations have shown for both a linear dependence on excitation intensity. It thus appears that direct entry of the electrons from the traps into the singlet manifold is necessary for explaining the fluorescence component of thermoluminescence.
NEW EMISSION BAND OF TYROSINE INDUCED BY INTERACTION WITH PHOSPHATE ION
Authors: Shimizu Okiyasu , Imakubo Keiichi
Published: January 2008

Abstract. Excitation of tyrosine solutions (pH 7.5) containing dipotassium phosphate was found to be accompanied by an appearance of a new emission band around 345 nm, with a specific quenching of tyrosine fluorescence. From the features of UV absorption and fluorescence excitation spectra, it is concluded that the new emission is due to the interaction between phosphate and tyrosine in the ground state.
FLUORESCENCE LIFETIME STUDY OF THE DENATURATION OF RIBONUCLEASE‐A
Authors: Barboy Natalia , Feitelson J.
Published: January 2008

Abstract. Fluorescence quantum yield and lifetime measurements of the tyrosine residues in ribonuclease‐A (RNase) were used to study the conformational changes involved in the denaturation of the enzyme. Measurements were done on RNase and on selectively acetylated RNase in the native, the partly denatured (reductive cleavage of S‐S bridges or treatment with 8 M urea) and in the fully denatured state. The data were interpreted to mean that the opening of the S‐S bridges causes large parts of the enzyme chain to unfold while leaving a hydrophobic region; including one of the tyrosine residues, intact. The biological activity of RNase is destroyed by this unfolding. Urea apparently does penetrate the protein coil but does not greatly affect the RNase structure since some of its biological activity is still retained. The opening of the S‐S bridges in the presence of urea destroys the native conformation (and biological activity) completely leaving the protein in the form of an uncoiled polypeptide chain. It is suggested which parts of the protein structure might be affected by partial denaturation.
PHOTODYNAMIC EFFECTS OF PROFLAVINE ON BACTERIOPHAGE φ times 174 AND ITS ISOLATED DNA
Authors: Calberg‐Bacq C. M. , SiquetDescans F. , Piette J.
Published: January 2008

Abstract. Proflavine‐mediated photoinactivation of φ times 174 phage and its isolated DNA was studied under identical irradiation conditions. The inactivations followed single‐hit kinetics and a linear relationship was obtained in reciprocal plots of the inactivation rates vs the proflavine concentrations for both phage and isolated DNA. The phage photoinactivation rate was increased with an increase in the amount of proflavine bound to the phage DNA in a strong binding range (0.01‐0.04 proflavine/ nucleotide) as the total proflavine concentration was increased or the ionic strength decreased. Further, a phage‐specific factor was also found to affect the inactivation rate. The photodynamic treatment induced mutations in three phage strains from “amber” to “wild type” at a mutation rate per lethal hit of 0.3 times 10‐5 to 2.6 times 10‐5. In contrast to phage infectivity, the φ times 174 DNA infectivity was measurable only at a high multiplicity of infection, and its photoinactivation occurred only at high proflavine concentrations. The photoinactivation rate was enhanced either with a decrease in the multiplicity of infection or with the use of spheroplasts of recA mutants strains. The results are discussed in terms of the nature of and possible repair mechanisms of photodynamically induced lesions in φ times 174 phage DNA.