bluuebunny/crossref_metadata_2025 huggingface dataset:
EFFECT OF COLD STORAGE ON INACTIVATION OF ESCHERICHIA COLI BY 313 nm IRRADIATION
Authors: Newman C.
Published: January 2008

Abstract. Data are presented showing that the inactivation response of exponential phase Escherichia coli to 313 nm irradiation is affected by previous storage of cells at 3°C in M9 buffer. A similar effect of cold storage on the far‐UV inactivation response was not observed. Cold storage alone causes exponential loss in cell viability. After 0.95 days, cell viability is only about 15% of that observed immediately after exposure of cells to cold incubation. However, irradiation at 313 nm causes reactivation of these cold‐inactivated bacteria.
RETINAL SENSITIZED PHOTODYNAMIC DAMAGE TO LIPOSOMES
Authors: Delmelle M.
Published: January 2008

Abstract. All trans‐retinal has been introduced (2 mol %) into artificial membranes made up of egg lecithin, cholesterol and dicetyl phosphate. Illumination of retinal‐enriched liposomes at 365 nm induced photodynamic damages; it triggered the sensitized oxidation of the lipids measured by the appearance of a 233 nm absorption band or by the formation of malonyl dialdehyde. Illumination produced an increase of the membrane fluidity detected with the spin label technique and led also to the lysis of the liposomes as revealed by the release of entrapped chromate ions or by changes in light scattering. Singlet oxygen is involved in these photodynamic effects. The results have been discussed in connection with the light damage phenomena which may afflict the rod outer segment membranes.
MULTIPLE EXCITATIONS AND THE YIELD OF CHLOROPHYLL a FLUORESCENCE IN PHOTOSYNTHETIC SYSTEMS
Authors: Mauzerall D.
Published: January 2008

Abstract. Analysis of the effect of multiple excitations on chlorophyll a fluorescence yields in the green alga Chlorella reveals several distinct reactions. The first excitation in dark‐z‐adapted units produces photochemistry and the high yield state with a rise time of 35 ns. It is ascribed to a change in coupling between the antenna pigments and the photochemical trap. The second hit produces with the same quantum yield a quenched state which changes to the high yield state with a rise time of 4 μs. This is ascribed to the formation and the decay of a particular carotenoid triplet state near the funnel or antenna‐trap junction. Further hits produce enhanced quenching assigned to mobile triplets with lifetimes in the order of 100 ns. The fluorescence yield decreases monotonically with increasing excitations during the 7 ns pulse. This effect can be adequately ascribed to annihilation of excitations with lifetimes longer than the trapping time, or by a unique model of a multi‐trapped unit. The latter model is favored by arguments based both on the absence of a local maximum in the graph of fluorescence yield vs excitation energy and on the fact that the high yield state shows a different behaviour on multiple excitation, fit by a single‐trapped unit. This analysis is related to that used in experiments with ps flashes and is applied to the qualitatively different bacterial system.
ACID‐BASE EQUILIBRIA OF THE EXCITED SINGLET AND TRIPLET STATES AND THE SEMI‐REDUCED FORM OF ACRIDINE ORANGE
Authors: Kellmann Arlette , Lion Yves
Published: January 2008

Abstract— The acid‐base equilibria of the excited singlet and triplet states of acridine orange (AO) were studied by flash‐photolysis and fluorometric methods. The dye is a stronger base in the first excited singlet state (pKs= 13.3) than in the triplet and ground states (pKr= 10.3: pKc, = 10.2); acridine orange follows the trend observed with some other heterocyclic compounds, viz. pKs >pKr= pK,c. At room temperature, an anomalous fluorescence occurs from the dye in basic media: the assignment of this emission is discussed.

The semi‐reduced dye was studied as a function of pH. In a large pH range (3–14), only the protolytic equilibrium between the cationic (AOH2+) and the neutral (AOH) radicals was observed; the pK value corresponding to this equilibrium was found to be in the range of pH 5–6.
SOME ONE ELECTRON REDUCTION PRODUCTS OF FLAVIN ANALOGS: CYANOISOALLOXAZINES AND DEAZAISOALLOXAZINES
Authors: Tollin Gordon , Chan Rebecca L. , Malefyt Thomas R. , Bruice Thomas C.
Published: January 2008

Abstract— 8‐Cyanoisoalloxazines have been previously shown to form highly stable radical species at basic pH. We have measured the electron spin resonance (EPR) spectra of the radical forms of 8‐cyano‐10‐methyl‐3‐sulfopropylisoalloxazine (I) at both acidic and basic pH. In both cases. the EPR spectra are similar to those obtained from unsubstituted isoalloxazines. with no indication of hyperfine splitting due to the cyano nitrogen. Laser photolysis of I in the presence of EDTA at basic pH generates two radical species. One of these decays rapidly by a first‐order process to produce thc stable radical. The rate of this decay depends upon the initial flavin concentration, thus suggesting a reaction of the radical with oxidized isoalloxazine. The rates of reaction of the radical species with added oxidants (O2, ferricyanide), and the pH‐dependence of stable radical formation, indicate that the rapidly‐decaying species is the anion radical of I, and that the stable radical is formed by its reaction with oxidized flavin. Laser photolysis of I at acidic pH, as well as of 8‐cyano‐5‐deaza‐isoalloxazine at acidic or basic pH, does not generate stable radical species. I‐Deazaisoalloxazines do not give radical transients at all upon laser photolysis.
DNA STRAND BREAKS IN MAMMALIAN CELLS EXPOSED TO LIGHT IN THE PRESENCE OF RIBOFLAVIN AND TRYPTOPHAN
Authors: Hoffmann M. Edwiges , Meneghini Rogerio
Published: January 2008

Abstract— When mammalian cells were exposed to visible‐fluorescent light or near‐UV light in the medium containing riboflavin and L‐tryptophan, single‐strand breaks appeared in their DNA. This did not occur if either riboflavin or tryptophan was omitted from the medium. The same effect was observed when cells were added to the pre‐irradiated medium, indicating that a stable photoproduct was responsible. The induced DNA lesions were shown to be equally repairable in both excision proficient and defective (xeroderma pigmentosum) human cell lines. The active photoproduct formed was shown to be hydrogen peroxide. The possible relationship between these results and the near‐UV induced killing of mammalian cells is discussed.
QUANTUM YIELD OF PHOTOHYDRATION FOR DIMETHYLURACIL. CONCENTRATION AND WAVELENGTH DEPENDENCE*
Authors: Rahn Ronald O. , Sellin Helen G.
Published: January 2008

Abstract— The quantum yields for the photohydration of dimethyluracil were determined for concentrations in the range 5 × 10‐‐1‐‐1 × 10‐‐3M by use of 240–280 nm irradiation. The average quantum yield (0.0139 f 0.0005) was independent of both concentration and irradiation wavelength.
QUENCHING OF TYROSINE FLUORESCENCE BY PHOSPHATE IONS: A MODEL STUDY FOR PROTEIN‐NUCLEIC ACID COMPLEXES
Authors: Alev‐Behmoaras Tula , Toulme Jean‐Jacques , Hélène Claude
Published: January 2008

Abstract— In order to test the ability of phosphate groups to quench the tyrosine fluorescence in nucleic acid‐protein complexes, we have studied the effect of several phosphate ions on the fluorescence of tyrosine derivatives. Mono and bianions (H2PO4 and HPO42–) which are good proton acceptors quenched the fluorescence of all the phenolic compounds studied except that of O‐methyl tyrosine. With the other derivatives (tyrosine, N‐acetyl tyrosinamide and lysyl‐tyrosyl‐α lysine) fluorescence inhibition was accompanied by the appearance of a long wavelength emission (345 nm) attributed to tyrosinate anions. The quenching of tyrosine emission was due to the deprotonation of the phenolic group promoted in the excited state by phosphate ions and leading to the weakly fluorescent tyrosinate ion. Mono and dianions of phosphate mono ester inhibited tyrosine fluorescence as did unesterified phosphates. However, phosphate diester did not have any effect on the fluorescence of tyrosine derivatives. We conclude from this study that in nucleic acid‐protein complexes phosphate groups are not able to quench tyrosine fluorescence except at the end of polynucleotide chains. Since monoester and diester monoanions have a different behavior, we propose that quenching of tyrosine fluorescence by monoanions requires the formation of two hydrogen bonds. This complex cannot form with diesters which consequently do not quench tyrosine fluorescence.
LIGHT EFFECTS IN YEAST: PERSISTING OSCILLATIONS IN CELL DIVISION ACTIVITY AND AMINO ACID TRANSPORT IN CULTURES OF SACCHAROMYCES CEREYISIAE ENTRAINED BY LIGHT‐DARK CYCLES*
Authors: Edmunds Leland N. , Apter Ray I. , Rosenthal Philip J. , Shen Win‐Kuang , Woodward John R.
Published: January 2008

Abstract— In addition to the direct inhibitory effects of visible light (cool‐white fluorescent, < 3500 lux) on growth and amino acid transport previously reported for cultures of the yeast Saccharomyces cereui‐siae (strain Y185 rho+) grown at 12°C in medium containing glucose, yeast carbon base, KH2PO4, ammonium ion and proline, we have found evidence for endogenous, light‐entrainable, self‐sustaining circadian and ultradian oscillators underlying both cell division and transport activity. Diurnal light (⋍ 3000 lux) cycles (LD), imposed on cultures previously grown in the dark, phased or synchronized cell number increase to a 24‐h period with bud release being confined primarily to the dark intervals (although not necessarily every cell divided during any given division ‘burst’). The observed division or budding rhythm freeran with a circadian period (⋍26h) only approximating 24 h for a number of days in constant darkness (DD) following prior entrainment by LD, thereby implicating an endogenous circadian clock. Further, a similar light‐entrainable circadian rhythm in the uptake of “C‐histidine or 14C‐lysine occurred in nondividing (or very slowly dividing) cultures during the “stationary” (infradian) phase of growth synchronized by a 24‐h LD cycle and then released into DD for as long as 10 days. Some experiments revealed a bimodal (ultradian) periodicity in both LD and DD with secondary peaks or shoulders occurring at intervals of ⋍12h, corresponding approximately to subjective ‘dawn’ and ‘dusk’. Transport in cultures of the Y185 rho‐ petite mutant, which lacks cytochromes a/a3, b and cl, could not be synchronized by LD cycles, a finding that is consistent with the hypothesis that these chromophores may be primary photoreceptors for synchronization of rhythms in this microorganism.
RHODOPSIN: ITS MOLECULAR SUBSTRUCTURE AND PHOSPHOLIPID INTERACTIONS*
Authors: Litman Burton J.
Published: January 2008

Abstract—Rhodopsin in retinal rod outer segment disc membranes, was proteolyzed by treatment with papain. This treatment left three fragments of apparent mol wt of 26,000, 19,000 and 10,000 in the membrane. The circular dichroism (CD) of solubilized, proteolyzed rhodopsin, in both the UV and visible spectral regions, was essentially identical to that of native rhodopsin. This indicates that the retinal binding site configuration is essentially unchanged by proteolysis and that the proteolyzed form of rhodopsin retained the helical content of native rhodopsin. Far UV CD measurements on the fragments indicate that the secondary structural features of the proteolyzed complex were largely maintained when the complex was dissociated. This finding suggests that the proteolytic fragments represent independently stabilized domains within rhodopsin.

Measurements of the dependence of the activation free energy of the unfolding of opsin (as determined by the rate of loss of regenerability of opsin) and the meta I to meta II transition on the level of phospholipid associated with opsin and rhodopsin. respectively, have allowed for a determination of the mode of stabilization of these proteins by phospholipid. This dependence has been shown to have a linear form for opsin and rhodopsin. Hence, it appears that the stabilization of the tertiary structure of both solubilized opsin and rhodopsin is attributable to the sum of their interactions with individual phospholipid molecules, interacting with the protein in a non‐cooperative manner.
CELL CYCLE MAPPING BY IRRADIATING CELLS WITH BROMOSUBSTITUTED DNA SEGMENTS
Authors: Torre C. de la , Gonzalez‐Fernandez A.
Published: January 2008

Abstract—The role of chromatin replicated at restricted S intervals in further interphase progression has been analyzed by bromosubstitution followed by black light irradiation (313 nm peak) in a naturally synchronous population rendered binucleate by a caffeine pulse in Allium cepa L. root meristems.

Interphase completion is preferentially halted when irradiating cells with bromosubstituted chromatin which is replicated at the 3rd and 4th interval of an S period artificially divided into 5 portions. The treatment apparently inhibits transcription of the bromosubstituted DNA segments. The failure in the transcription of these segments may be related to the transition point located at early G2 in these cells. where protein synthesis is needed in order to reach mitosis.
MIGRATION OF SINGLET EXCITATION ENERGY FROM ACRIDINE ORANGE‐10‐DODECYL BROMIDE TO METHYLENE BLUE IN MICELLES
Authors: Usui Yoshiharu , Gotou Akie
Published: January 2008

Abstract—

The efficient energy transfer occurred from photoexcited singlet stale of acridine orange‐10‐dodecyl bromide dissolved in SDS micelles to methylene blue absorbed on the micelle surface. The sensitized fluorescence of methylene blue was effectively quenched by the addition of a small amount of ethanol and with the increase in temperature.
PHOTODEGRADATION OF PHAEOMELANIN: AN IN VITRO MODEL
Authors: Agin Patricia Poh , Sayre Robert M. , Chedekel Miles R.
Published: January 2008

Abstract— A new in vitro model system for studying the photochemistry and photobiology of melanins in epidermal tissue has been developed. The photochemistry of phaeomelanin in this model system follows the same course as in pH 8.0 aqueous buffered solutions, i.e. photodegradation accompanied by production of superoxide radicals. These photoreactions may be effectively quenched by application of a broad spectrum sunscreen prior to irradiation.
TRYPTOPHAN EMISSION FROM HUMAN HEMOGLOBIN AND ITS ISOLATED SUBUNITS
Authors: Alpert Bernard , Jameson David M. , Weber Gregorio
Published: January 2008

Abstract— The emission spectra of human adult hemoglobin A0 and its isolated α and ß subunits were obtained using a highly sensitive photon‐counting spectrofluorometer. The quantum yields of the emissions, relative to free tryptophan, were also measured as well as the excitation polarization spectra for hemoglobin A0 and apohemoglobin. The fluorophore bis‐ANS was utilized to probe for the presence of apoproteins in the hemoprotein preparations. The work suggests that tryptophan may be useful as an intrinsic probe to study dynamical processes in hemoglobin.
PHOTOCHEMISTRY OF THE REACTION CENTERS OF SYSTEM II UNDER REPETITIVE FLASH GROUP EXCITATION IN ISOLATED CHLOROPLASTS
Authors: Eckert H. J. , Renger G.
Published: January 2008

Abstract— Absorption changes induced in isolated chloroplasts by excitation with repetitive flash groups have been measured at 690 nm, indicating the photochemical turnover of chlorophyll‐aII (Chl‐αn), and at 480 nm and 513 nm respectively, reflecting via electrochromic effect the formation of a transmembrane electric field. The data are compared with measurements of oxygen evolution. In chloroplasts with practically fully intact oxygen evolving capacity it was found:

1. The initial amplitude of the 690 nm absorption change induced by the second flash as a function of the time tv between the first and second flash of a group increases with a half life of about 35 µs. On the other hand, the average oxygen yield due to the second flash as a function of the time tv rises with a half life of about 600 µs (and a kinetics in the ms‐range of minor extent), confirming the data of Vater et al. (1968).

2. Under far red background illumination, where contributions due to PS I in the µs‐range can be excluded, the difference spectrum in the red of the absorption changes induced by the first flash corresponds with that of the absorption changes induced by the second flash fired 200 µ after the first flash.

3. The pattern of the absorption changes at 690 nm induced by repetitive double flash groups at tv= 200 µs does not markedly change in normal chloroplasts by the presence of DBMIB†. Similar 690 nm absorption changes occur in trypsin treated chloroplasts, independent of the presence of DCMU.

4. The fast regeneration in the µs‐range of Chl‐an is also observed in the third flash of a triple flash group at a time tv= 200 µs between the flashes of the group.

5. The initial amplitudes of the absorption changes with a decay kinetics slower than 100 µs induced by the second flash at 480 nm and 513 nm, respectively, as a function of the time t, between the first and second flash of a group, are characterized by a recovery half‐time of about 600 µs, confirming earlier measurements at 520 nm (Witt and Zickler, 1974).

On the basis of these results it is inferred that there does exist a photoreaction of Chl‐αn., with an electron acceptor, referred to as Xa, other than the ‘primary’ plastoquinone acceptor X320, if X320 persists in its reduced state. Under conditions of X320 being in the reduced state, this photochemical reaction was shown to be highly dissipative with respect to charging up the watersplitting enzyme system Y. Furthermore, this Chl‐an‐photoreaction with Xa does not lead to a vectorial transmembrane charge separation, which is stable for more than a few microseconds. Different models for the functional and structural organization of PS II are discussed.
PHOTOCHEMISTRY OF PHEOMELANIN: ACTION SPECTRUM FOR SUPEROXIDE PRODUCTION
Authors: Chedekel Miles R. , Agin Patricia Poh , Sayre Robert M.
Published: January 2008

Abstract— The action spectrum for superoxide production from aerated aqueous solutions of pheomela‐nin was determined by utilizing the nitroblue tetrazolium‐superoxide dismutase assay for superoxide. Superoxide production was greatest in the UVC regions, but continued well into the visible wavelengths. The marked increase in superoxide production noted in the UVC‐UVB regions of the spectrum suggests that superoxide production may be involved in a number of actinic disorders in fair‐skinned humans.
A SHORT‐LIVED INTERMEDIATE IN THE PHOTO‐ENZYMATIC REDUCTION OF PROTOCHLOROPHYLL(IDE) INTO CHLOROPHYLL(IDE) AT A PHYSIOLOGICAL TEMPERATURE
Authors: Franck Fabrics , Mathis Paul
Published: January 2008

Abstract—

The reduction of protochlorophyll(ide) into chlorophyll(ide) has been studied by flash absorption spectroscopy at 21°C, with a time resolution of 0.5 µs. The absorption changes have been recorded in the range 670–720 nm after the first and subsequent flashes given to an extract of etiolated bean leaves.

At 695 nm the flash‐induced absorption increase has its maximum value immediately after the flash and then partly decays with a half‐time of about 7–10 µs. A complementary behaviour is observed at 675 nm where the absorption change is very small at time zero and then increases to a stationary value with a half‐time of about 6–9 µs. From measurements at several wavelengths it is concluded that a species with an absorption peak around 695 nm is formed immediately after the flash and is then transformed into a stable species with an absorption peak around 675 nm. Measurements at lower temperatures, down to—50°C, show that the transformation is much slowed down at decreased temperatures. The species absorbing at 695 nm (P695) is attributed to an intermediate in the photoreduction of protochlorophyll(ide) P639,650 into chlorophyll(ide) P676.

When the protochlorophyll(ide) is photoreduced before the flash illumination, the newly formed chlorophyll(ide) gets to a triplet state, which decays with a half‐time of 15 µs at 21°C. This result shows that carotenoid molecules do not exert their protective role at this stage of chlorophyll (Chi) formation.
THE INVOLVEMENT OF WATER AT THE RETINAL BINDING SITE IN RHODOPSIN AND EARLY LIGHT‐INDUCED INTRAMOLECULAR PROTON TRANSFER
Authors: Rafferty Charles N. , Shichi Hitoshi
Published: January 2008

Abstract Extensive dehydration of air‐dried films of bovine rod outer segment membranes induces fully reversible changes in the absorption spectrum of rhodopsin, indicative of deprotonation of the retinylidene Schiff base in more than 50% of the rhodopsin molecules in the sample. This suggests that water is involved at the site of the Schiff base protonation in rhodopsin. In contrast, the spectrum of metarhodopsin I is resistant to similar dehydrating conditions, implying a significant difference in the mechanism for protonation in metarhodopsin I. The photochemistry of dehydrated membranes was also explored. Photoexcitation of deprotonated rhodopsin (λmax 390 nm) induces a large bathochromic shift of the chromophore. The major photoproduct at room temperature was spectrally similar to metarhodopsin I (λmax, 478 nm). These findings suggest that intramolecular proton transfer involving the Schiff base proton may occur in the earlier stages of the visual cycle, prior to or during the formation of metarhodopsin I.
PHOTOCHEMISTRY OF ANTHRAQUINONE‐2,6‐DISODIUM SULPHONATE IN AQUEOUS SOLUTION
Authors: Harriman Anthony , Mills Andrew
Published: January 2008

Abstract— Irradiation of anthraquinone‐2,6‐disodium sulphonate in aqueous solution leads to formation of hydroxyquinone and semiquinone, which undergoes disproportionation to form the fully reduced hydroquinone. The quantum yield for formation of the semiquinone depends upon pH, the results being attributed to the relative efficiency with which the various acid/base forms of the hydroquinone react with quinone. The photoreaction does not involve production of hydroxyl radicals and luminescence studies suggest that the quantum yield for formation of the triplet state is unity. Indeed, flash photolysis studies indicate the presence of a short‐lived triplet (τ < 1 μs) which reacts with water to form a photosolvolate (τ= 5 μs) which, in turn, decays to form the observed products. These findings are in agreement with a mechanism previously proposed by Stonehill.
RATE PARAMETERS FOR THE QUENCHING OF SINGLET OXYGEN BY WATER‐SOLUBLE AND LIPID‐SOLUBLE SUBSTRATES IN AQUEOUS AND MICELLAR SYSTEMS
Authors: Lindig Barbara A. , Rodgers Michael A. J.
Published: January 2008

Abstract— The laser flash photolysis method has been used to determine the bimolecular rate constants for the reaction between O2(1Δ9) and several lipid‐soluble and water‐soluble substrates. Values for lipid‐soluble substrates have been obtained using aqueous dispersions of surfactants above the critical micelle concentration with 1,3 diphenylisobenzofuran as monitor of singlet oxygen. Under these conditions the hydrophobic substances are solubilized by the micellar phase. For substrates which are water‐soluble, 9,10‐anthracene dipropionic acid disodium salt was used as singlet oxygen monitor. For several substances, the values obtained are comparable to the values found in homogeneous nonaqueous solutions. In cases where significant differences have been found these have been rationalized according to the individual case. The only major unexpected result concerned β‐carotene which, in micellar dispersion, failed to react at all with O2(1Δ9) This may be due to multi‐molecular aggregations occurring in the polar medium. The work described herein shows clearly that, under appropriate conditions, singlet oxygen kinetics can be effectively followed in aqueous solutions by time resolved methods. The indiscriminate use of β‐carotene as a quencher of O2(1Δ9)in mainly aqueous media is questioned.
PHOTOPHYSICAL AND PHOTOSENSITIZING PROPERTIES OF 2‐AMINO‐4 PTERIDINONE: A NATURAL PIGMENT
Authors: Chahidi C. , Aubailly M. , Momzikoff A. , Bazin M. , Santus R.
Published: January 2008

Abstract— The characteristics of the fluorescence and phosphorescence emission of 2‐amino‐4 (3H) pteridinone (or pterin) in aqueous solutions are pH dependent. The room temperature fluorescence quantum yield is low and is maximum at pH = 10 (φF∼ 0.057). The 77K phosphorescence emission consists of two overlapping emissions originating from τ* triplet states. In agreement with low temperature results, the 353nm laser flash photolysis makes it possible to detect at pH 9.2, two transient triplet absorptions (τ1∼ 0.3 μs and τ2∼ 2.3 μs). The longer lived triplet is characterized by φTM∼ 0.20 and ∼ (550nm) = 2000 M−1 cm−1. It reacts with the solvent forming the semireduced pterin with a quantum yield φR∼ 0.06. The photosensitizing properties of pterin have been studied by laser flash spectroscopy and steady state irradiations. Photoreactions implying singlet oxygen formation are shown to occur. Laser flash spectroscopy indicates that the pterin triplet is reduced by amino acids and nucleic acid bases. Corresponding bimolecular reaction rate constants have been measured.
QUENCHING OF PEROXIDIZED LUMINOL CHEMILUMINESCENCE BY REDUCED PYRIDINE NUCLEOTIDES
Authors: Wong Joseph K. , Salin Marvin L.
Published: January 2008

Abstract— Reduced pyridine nucleotides were observed to cause a delay as well as a diminution of light emission from peroxidized luminol at pH 6.5. Other reductants were found to have similar effects. Neither superoxide nor hydroxyl radical scavengers quenched chemiluminescence of luminol in the presence of horseradish peroxidase and H2O2. A scheme in which reductants such as NADH and NADPH prevent peroxidase from oxidizing luminol to aminophthalate is proposed. Moreover, it is concluded that neither O2−nor OH’ play a role in the peroxidation of luminol by horseradish peroxidase.
ACTION SPECTRUM FOR THE PHOTOINHIBITION OF BIOLUMINESCENCE IN THE MARINE DINOFLAGELLATE DISSODINIUM LUNULA
Authors: Hamman J. P. , Biggley W. H. , Seliger H. H.
Published: January 2008

Abstract— The fractional photoinhibition of the mechanically stimulable bioluminescence in the vacuolar dinoflagellate Dissodinium lunula is proportional to the logarithm of the exposure. The action spectrum for this photoinhibition has been determined by measuring threshold exposures in absolute units of photons cm−2. The threshold exposure at the wavelength of maximum sensitivity, 450 nm, was 2 ± 10−2 photons cm−2. The action spectrum is consistent with absorption by a blue light receptor pigment shielded by a nonphotoactive pigment which absorbs in the region of the bioluminescence emission spectrum. It is suggested that there may be some selective advantage for this absorbing pigment in the vacuolar dinoflagellates in order to prevent the organisms from being photoinhibited by their own bioluminescence.
PHOTOSENSITIVITY IN CAROTENOIDLESS MUTANTS OF MICROCOCCUS LUTEUS (SARCINA LUTE A): NON‐PHOTODYNAMIC MENAQUINONE DESTRUCTION IN WHITE LIGHT
Authors: Prebble John N.
Published: January 2008

–The photosensitivity of a carotenoidless mutant strain has been examined in terms of its loss of viability and loss of menaquinone when subjected to high intensity visible light. Cell viability and menaquinone are protected by cyanide (an inhibitor of cytochrome oxidation), by malate (a substrate for the respiratory chain) and by nitrogen although the protection of menaquinone is less in nitrogen. Evidence is presented in support of the view that oxidised membrane‐bound menaquinone is more photolabile in visible light than the reduced form. Loss of menaquinone is seen as the primary cause of death in these obligately aerobic carotenoidless cells and the role of oxygen as indirect by converting reduced menaquinone to the oxidised form. Evidence is also presented that the cause of cell death in red light in the presence of an exogenous photosensitizer, toluidine blue, is different from that in white light.
EVIDENCE AGAINST A PHOTOPROTECTIVE COMPONENT OF PHOTOREACTIVATION IN SACCHAROMYCES CEREVISIAE
Authors: MacQuillan Anthony M. , Green Gisele , Perry William G.
Published: January 2008

Abstract— Photoreactivation‐deficient (phr−) mutants of Saccharomyces cerevisiae were shown to lack in vitro DNA‐photolyase activity. A phr− mutant was then compared with a phr+ strain for near‐UV induced photoprotection from far‐UV irradiation. Neither strain exhibited a photoprotective effect.
THE CIRCULAR DICHROISM OF SODIUM CHOLATE SOLUBILIZED RHODOPSIN
Authors: Wagner J. , Smith E. , Cusanovich M. A.
Published: January 2008

Abstract— The near UV and visible circular dichroism (CD) spectra of rhodopsin solubilized and purified in sodium cholate have been determined. The CD properties of rhodopsin in 2 and 20mg/ml sodium cholate are substantially different in terms of the α band to β band ratio, and sensitivity of the near UV CD spectra to bleaching. Rhodopsin in 2mg/ml sodium cholate will regenerate (11‐cis‐retinal + opsin → rhodopsin) and has a CD spectrum similar to rhodopsin in rod outer segment membranes and digitonin which will also regenerate. On the other hand rhodopsin in 20mg/ml sodium cholate will not regenerate and has CD properties similar to other nonregenerable detergents (cetyltri‐methylammonium salts and emulphogene). These results indicate that CD reflects the conformational integrity of functional (regenerable) rhodopsin and that sodium cholate can reversibly alter the conformation of rhodopsin. Finally the results further support the validity of using sodium cholate solubilized rhodopsin as a model system for studies on the structure and function of rhodopsin.
ACTION SPECTRUM AND THRESHOLD SENSITIVITY OF ENTRAINMENT OF ORCADIAN RUNNING ACTIVITY IN THE COCKROACH PERIPLANETA AMERICANA
Authors: Mote Michael I. , Black Kenneth R.
Published: January 2008

Abstract— The interaction between the compound eye and the circadian timing system for running activity in the cockroach, Periplaneta americana, has been investigated by measuring the action spectrum for entrainment of such behavior by imposed photic stimuli. Test wavelengths were selected which spanned the spectral range of the dichromatic retina of this insect and intensities of such lights for which half of a population of animals failed to be entrained (threshold) were determined. Stimuli were presented either with a 12:12 light–dark regime or for 12h/day on a continuous background of orange light. The latter procedure altered the balance of sensitivity in the two groups of color receptors in the eye. A comparison of the resulting action spectra and the spectral sensitivities of receptors and visual interneurons measured under similar conditions suggest that the entrainment mechanism is dominated by the receptor group most sensitive to long wavelength light. Furthermore, the eye‐clock mechanism shows an extraordinarily high sensitivity to such stimuli. We estimate that a mean flux of about 5 photons/eye/s is sufficient to entrain the behavior. The implications of these results are discussed.
PHOTOLYSIS OF MELANIN PRECURSORS: FORMATION OF SEMIQUINONE RADICALS AND THEIR COMPLEXATION WITH DIAMAGNETIC METAL IONS
Authors: Felix Christopher C. , Sealy Roger C.
Published: January 2008

Abstract— Semiquinone free radicals have been generated by the UV photolysis of aqueous solutions of melanin precursors (catechols and catecholamines) and characterized by electron spin resonance (ESR) spectroscopy. Hyperfine parameters of the semiquinones are sensitive to the nature of the substituents on the aromatic ring, reflecting (i) the ionization state of the substituent; (ii) restricted rotation of methylene protons; and (iii) the presence of a chiral carbon center. In the presence of complexing metal ions (Zn2+, Cd2+) the semiquinones form chelate complexes whose ESR spectra differ from those of the uncomplexed radicals. Satellite peaks demonstrating hyperfine coupling to metal isotopes (67Zn, 111Cd and 113Cd) present in natural abundance were detected in several instances. Concentrations of metal complexes are much higher than those of the uncomplexed radicals, suggesting that diamagnetic metal ions may be useful in identifying the presence of semiquinone radicals of this kind in various systems.
FLAVIN TRIPLET QUENCHING AND SEMIQUINONE FORMATION BY ALIPHATIC α‐SUBSTITUTED ACETIC ACIDS: INTERMEDIATES IN FLAVIN‐SENSITIZED PHOTODECARBOXYLATION*
Authors: Ahmad Iqbal , Tollin Gordon
Published: January 2008

Abstract—The quenching of flavin excited states and the production of radical intermediates by aliphatic α‐substituted acetic acids have been investigated using fluorescence and laser photolysis measurements. Stern‐Volmer quenching constants for the flavin triplet are 2–4 orders of magnitude smaller than those found previously for aromatic acids. At the high substrate concentrations required to obtain triplet quenching, singlet quenching, probably via exciplex formation, is also observed. When triplet and radical yields are quantitated, it is found that, for pyruvate, glyoxylate and lactate, quenching occurs virtually exclusively by a one‐electron transfer mechanism. This supports the contention that the flavin‐sensitized photodecarboxylation of these acids proceeds via a radical mechanism.
ENHANCEMENT OF ULTRAVIOLET OR N‐METHYL‐N'‐ NITRO‐N‐NITROSOGUANIDINE SENSITIVITY OF DICTYOSTELIUM DISCOIDEUM BY 3‐AMINOBENZAMIDE
Authors: Ohnishi T. , Eimoto H. , Okaichi K.
Published: January 2008

Abstract— The amoeboid cells of Dktyostelium discoideumNC–4 possess a 3‐aminobenzamide(3‐ABA)‐sensitive repair mechanism for DNA damages induced by UV‐irradiation or N‐methyl‐N'‐nitro‐N‐nitrosoguanidine (MNNG)‐treatment. We have studied the effect of 3‐ABA on each step of excision repair in the UV‐ irradiated cells. Although the nicking of DNA‐strand and the excision of pyrimidine dimcrs are insensitive to 3‐ABA, the rejoining of DNA strand‐breaks is sensitive. The frequency of mutation induced by UV‐irradiation or MNNG‐treatment is depressed by 3‐ABA. The mechanisms of repair inhibition by 3‐ABA are discussed.
PHYTOCHROME‐MEDIATED PHOTOTROPISM AND DIFFERENT DICHROIC ORIENTATION OF Pr AND Pfr IN PROTONEMATA OF THE FERN ADIANTUM CAPILLUS‐VENERIS L.
Authors: Kadota Akeo , Wada Masamitsu , Furuya Masaki
Published: January 2008

Abstract— Single‐celled protonemata of Adiantum capillus‐veneris were cultured under continuous red light for 6 days and then in the dark for 15 h. Brief local exposure of a flank (5 times 20 /mi) of the subapical region of a protonema to a microbeam of red light effectively induced a phototropic response toward the irradiated side. The degree of the response was dependent upon the fluence of the red light. Red/far‐red reversibility was typically observed in this photoreaction, showing that phytochrome was the photo‐receptive pigment. When the flank was irradiated with a microbeam of linearly polarized red and far‐red light, red light with an electrical vector parallel to the cell surface was most effective. However, the far‐red light effect was most prominent when its electrical vector was normal to the cell surface. These polarized light effects indicate the different dichroic orientation of Pr (red‐light‐absorbing form of phytochrome) and Pr (far‐red‐light‐absorbing form of phytochrome) at the cell flank.
PHOTOIONIZATION OF MELANIN PRECURSORS: AN ELECTRON SPIN RESONANCE INVESTIGATION USING THE SPIN TRAP 5,5‐DIMETHYL‐1‐PYRROLINE‐1‐OXIDE (DMPO)
Authors: Kalyanaraman B. , Felix C. C. , Sealy R. C.
Published: January 2008

Abstract The photoionization of 3,4‐dihydroxyphenylalanine (dopa) and catechol has been studied by electron spin resonance spectroscopy using the free radical scavenger 5,5‐dimethyI‐1‐pyrroline‐1 ‐oxide as a spin trap for hydrated electrons and hydrogen atoms. The photochemistry of these materials is shown to resemble tyrosine in that both photoionization and photohomolysis (to give H) occur, with photoionization predominating (by a factor of 2.6 for dopa). Ionization of one of the phenolic hydroxyl groups increases the yield of radicals by a factor of 2. Action spectra and quantum yields for radical production are reported.
BACTERIORHODOPSIN AND THE SENSORY PIGMENT OF THE PHOTOSYSTEM 565 INHALOBACTERIUM HALOBIUM
Authors: Schimz Angelika , Sperling Walter , Hildebrand Eilo , Köhler‐hahn Dorothea
Published: January 2008

AbstractBlocking in vivo synthesis of retinal by addition of nicotine to the culture medium leads to the loss of photobehavior inHalobacterium halobium.Addition ofrrans‐retinol or frans‐retinol2(3,4‐dehy‐droretinol) restores the responses to light decreases in the green‐yellow spectral range. Action spectra of the reconstituted retinal‐ and retinal2‐photosystem show maximal sensitivity at 565 and 580 nm, respectively. Addition of retinol or retinol2also restores the formation of bacteriorhodopsin (BR) or bacteriorhodopsin2(BR2= 3,4‐dehydroretinal‐bacterio‐opsin complex). The absorption spectra of BR and BR2, measured in isolated membranes, as well as in living bacteria, show maxima at 568 nm (BR) and at about 600 nm (BR2), respectively. Comparison of the action spectrum of the retinal2‐containing sensory photosystem with the absorption spectrum of BR2suggests that a retinal pigment different from BR is responsible for the photosensory behavior to green‐yellow light.
PHOTOOXIDATION AND SINGLET OXYGEN SENSITIZATION BY PROTOPORPHYRIN IX AND ITS PHOTOOXIDATION PRODUCTS
Authors: Cox G. Sidney , Bobillier Christiane , Whitten David G.
Published: January 2008

Protoporphyrin IX and its various ester derivatives have been previously shown to undergo self‐sensitized photooxygenation to yield hydroxyaldehydes (photoprotoporphyrin) and mono‐ and diformyl deuteroporphyrin derivatives. In the present study the photoreactions of these products in the presence of oxygen have been investigated. All of the photooxidation products are themselves good sensitizers of singlet oxygen. In addition spin trapping experiments indicate these products can produce superoxide in low‐to‐moderate efficiency by an excited state electron transfer process. The photo‐products themselves are somewhat more stable to photooxidation than protoporphyrin IX itself. The two monoformyl‐monovinyl deuteroporphyrins have been found to undergo further photooxidation at the vinyl groups to yield primarily monoformyl hydroxyaldehydes in a reaction mainly involving singlet oxygen analogous to the initial reaction of protoporphyrin IX.
UV‐INDUCED DNA DEGRADATION IN THE CYANOBACTERIUM SYNECHOCYSTIS PCC 6308
Authors: O'Brien Philip A. , Houghton James A.
Published: January 2008

Ultraviolet radiation‐induced DNA degradation has been demonstrated in the unicellular cyanobacterium Synechocystis PCC 6308. The extent of DNA degradation was greatly reduced by inhibition of DNA replication by preirradiation dark incubation and degradation was completely inhibited by exposure of irradiated cells to photoreactivating wavelengths. DNA degradation was not observed when irradiated cells were incubated in the presence of the excision repair inhibitors caffeine and acriflavin, suggesting that degradation is a manifestation of excision repair of pyrimidine dimers in Synechocystis. Increasing UV fluences resulted in an increase in the final extent of DNA degradation. However, at higher fluences degradation was inhibited, suggesting saturation of the excision repair system. Incubation of irradiated cells under conditions which inhibit protein synthesis greatly increased the extent of DNA degradation and the time over which it occurred. Exposure of cells to a sublethal fluence of UV greatly reduced the extent of DNA degradation produced by a challenge fluence administered after 24 h incubation providing evidence for inducible DNA repair activity in cyanobacteria.
MODE OF ACTION OF α‐TERTHIENYL ON ESCHERICHIA COLI: EVIDENCE FOR A PHOTODYNAMIC EFFECT ON MEMBRANES
Authors: Downum K. R. , Hancock R. E. W. , Towers G. H. N.
Published: January 2008

The photodynamic effects of α‐terthienyl (αT) in near‐UV light (UV‐A) onEscherichia colishowed close agreement with the light absorption of αT at different wavelengths suggesting that αT is the primary absorbing molecule responsible for the photosensitized reaction. Studies with DNA repair deficient mutants ofE. coliindicated that the bactericidal action of αT/UV‐A was not mediated by DNA damage, in direct contrast to the well‐known photosensitizer, 8‐methoxypsoralen. By using a closed borosilicate glass reaction vessel and various gas mixtures, it was demonstrated that photosensitization of bothE. coliand a more resistant bacterium,Pseudomonas aeruginosa, was absolutely dependent on the presence of oxygen. The rate of killing by αT/UV‐A showed a rather small dependence on preincubation temperatures, with quite rapid killing at 5°C, suggesting that the movement of αT across the cytoplasmic membrane ofE. coliis not the rate limiting step in killing and perhaps is not even necessary for killing. Sodium dodecyl sulphate‐polyacrylamide gels of cell membrane proteins after 15 and 30min of treatment with αT/UV‐A showed substantial random crosslinking of these proteins. The results taken overall suggest that αT is a photodynamic photosensitizer which exerts its primary effect at the level of the cytoplasmic membrane.
LIGHT‐INDUCED REDOXCYCLES OF FLAVINS IN VARIOUS ALCOHOL/ACETIC ACID MIXTURES
Authors: Schmidt Werner
Published: January 2008

Abstract— By dual wavelength absorption spectroscopy and fluorimetry. a flavin photo‐redoxcycle never reported before has been observed in solvents composed of alcohols (methanol, ethanol, benzyl alcohol) and acetic acid. This cycle consists of a fast anaerobic photoreduction with a subsequent rcoxidation of the flavin as a dark reaction. The photoreduction process is not sensitive to the prescnce of water (up to 50 vol%), in contrast to the reoxidizing process, which is completely inhibited by 10 vol% of water. Furthermore. this photocycle is inhibited by esters. Negative activation energies of about 20 kJ/mol for both photoreduction and oxidation indicate complex molecular mechanisms. It is proposed that photoreduction of the flavin produces a highly volatile oxidizing agent responsible for the subsequent reoxidation. Photoreducing and oxidizing species remain to be identified.
PHOTOREACTION OF 8‐METHOXYPSORALEN WITH THYMIDINE
Authors: Shim Sang Chul , Kim Yong Zu
Published: January 2008

Abstract—The photoreaction of 8‐methoxypsoralen (8‐MOP) with thymidine in solid film state yielded two 4′, 5′‐monoadducts (a pair of diastereomers) and three 3,4‐monoadducts. The stereochemistry of two 4′, 5′‐monoadducts was found to becis‐synandtrans‐synand one 3,4‐monoadduct wascis‐anti.In addition to these monoadducts, 3,4‐, 4′, 5′‐biadducts were also formed during the reaction, but the isolation of each isomer of these adducts was not successful; however, the formation of these biadducts was confirmed by UV, IR, TLC and photosplitting experiments.
INDUCIBLE POSTREPLICATION REPAIR IS RESPONSIBLE FOR MINIMAL MEDIUM RECOVERY IN UV‐IRRADIATED Escherichia coliK–12
Authors: Sharma Rakesh C. , Smith Kendric C.
Published: January 2008

Abstract— Ultraviolet (UV)‐irradiated Escherichia coliK–12 uvrA cells showed higher survival if plated on minimal growth medium rather than on rich growth medium, i.e., they showed minimal medium recovery (MMR). A 2‐hour treatment of UV‐irradiated cells with rifampicin inhibited the subsequent expression of MMR, and produced a large reduction in survival. We have recently isolated a new mutant (mmrA1) that does not show MMR. The mmrA mutation protected UV‐irradiated uvrA cells from the effect of rich growth medium on survival, but not from the effect of rifampicin on survival. DNA daughter‐strand gap (DSG) repair in UV‐irradiated (4 J/m2) uvrA cells was inhibited to the same degree whether rich growth medium was added immediately after irradiation or after 10 min of postirradiation incubation in minimal growth medium. However, chloramphenicol added immediately after irradiation greatly reduced this repair; there was less reduction if it was added 10 min after UV irradiation. These findings suggest that MMR is an inducible repair phenomenon, and that rich growth medium inhibits this repair process itself rather than its induction.
PHOTO ACTIVATION OF ISOFLAVONOID PHYTOALEXINS: INVOLVEMENT OF FREE RADICALS
Authors: Bakker J. , Gommers F. J. , Smits L. , Fuchst A. , Vries F. W. de
Published: January 2008

Abstract— Upon irradiation with ultraviolet light the isoflavonoid phytoalexins phaseollin, 3,6a, 9‐trihydroxypterocarpan, glyceollin, tuberosin and pisatin, but not medicarpin, brought about inactivation ofglucose–6‐phosphate dehydrogenase in an in vitro assay system. Photoinactivation of the enzyme by photoactivated pisatin in air‐saturated solutions was hardly affected by singlet oxygen quenchers such as NaN3, bovine serum albumin, histidine or methionine. Neither addition of the hydroxyl radical scavengers mannitol, Na‐benzoate and ethanol nor the presence of catalase or supcroxide dismutase protected the enzyme against photoinactivation, suggesting that OH, H2O2 and O2 are not the reactive oxygen species involved. However, the free radical scavenger S‐(2‐amino‐ethyl)isothiouronium bromide hydrobromide (AET) protected the enzyme against inactivation by photoactivated pisatin. Direct evidence for the generation of free radicals was obtained by ESR measurements of solutions of phaseollin, pisatin and medicarpin in hexane irradiated with ultraviolet light in the presence or absence of O2. Phaseollin produced the most stable free radicals, whereas medicarpin hardly gave rise to free radical formation; pisatin took a somewhat intermediate position by producing a strong ESR signal which, however, decayed rather quickly. Photodegradation of all phytoalexins, except for medicarpin, was accompanied with loss of fungitoxicity, as shown in thin‐layer chromatographic bioassays, and formation of new products.

These results indicate free radical formation as the causative process for photoinactivation of enzymes by photoactivated isoflavonoid phytoalexins.
SITE‐SELECTION SPECTROSCOPY OF CHLOROPHYLL b IN MEMBRANES OF LECITHIN VESICLES AND IN OTHER SOLVENTS
Authors: Fünfschilling J. , Walz D.
Published: January 2008

Abstract— Site‐selection fluorescence spectra of chlorophyll b in membranes of lecithin vesicles and in the solvents ethanol, n‐butanol, n‐butyl acetate, 2‐methyl tetrahydrofuran and toluene are presented. The spectra in vesicles display zero‐phonon lines as pronounced as those in the best organic glasses. The characteristics of the distributions of O—O transition energies and of the electron‐phonon couplings allow to infer the position of the chlorophyll molecule in the membrane of vesicles. It is thus found that the chromophore of chlorophyll b is situated in the layer formed by the ester moieties of the lecithins, i. e. close to the surface of the membrane but not in direct contact with the aqueous phase.
SINGLET EMISSION STUDIES ON PORPHYRINS APPENDED WITH HETEROCYCLIC BASES
Authors: Suriyanarayanan P. , Krishnan V.
Published: January 2008

Abstract— Porphyrins appended in the meso positions with 1,2‐diazole, indole and quinoline are shown to exhibit enhanced fluorescence quantum yields relative to meso tetraphenyl porphyrin. The singlet emission yields decrease with the number of appended heterocyclic bases. An intramolecular charge transfer resonance mechanism has been advanced to interpret these results.
CONSECUTIVE FORMATION OF SENSORY PHOTOSYSTEMS IN GROWINGHalobacterium halobium
Authors: Hildebrand Eilo , Schimz Angelika
Published: January 2008

Abstract—The sensory photosystems PS 370 and PS 565 ofHalobacierium halobiumare actively degraded in the early growth phase and later resynthesized. Neither degradation nor resynthesis is correlated to the rate of cell division. The reappearance of photosensory activity requiresde novosynthesis of proteins which are most likely directly involved in the sensory pathway. PS 370 appears earlier than PS 565 and thus may be studied independently of PS 565, before the latter is synthesized, or by blocking the synthesis of PS 565 with puromycin after PS 370 has appeared. The action spectrum of PS 370 alone shows the same maximum as the spectrum obtained when PS 565 is present. Carotenoids, which act as accessory pigments of PS 370, do not shift its activity peak. Also the maximum of PS 565 is not influenced by PS 370. We conclude that the maxima of the action spectra of PS 370 and PS 56.5 truely reflect the absorption maxima of the sensory retinal pigmentsP–370 andP–565.