bluuebunny/crossref_metadata_2025 huggingface dataset:
A NOVEL EFFECT OF UV‐B IN A HIGHER PLANT (SORGHUM VULGARE)
Authors: Drumm‐Herrel H. , Mohr H.
Published: January 2008

Abstract— Two non‐photosynthetic photoreceptors (phytochrome and the usual blue/UV light photoreceptor) were previously found to be involved in light‐mediated anthocyanin synthesis in the mesocotyl of Sorghum seedlings (Drumm and Mohr, 1978). The decisive point is that phytochrome can act only after a blue/UV light effect has occurred. On the other hand, the expression of the blue/UV light effect is controlled by phytochrome (‘obligatory sequential action’). A strong positive interaction between the blue/UV‐A and the UV‐B part of the spectrum was found, in addition to the above sequential action: an inductive effect of blue or UV‐A light can only express itself fully if short wavelength UV (approximately 300–320nm. UV‐B range) is also given, either after the blue/UV‐A light or simultaneously. Since even small amounts of the UV‐B are strongly effective it is probable that this effect plays a role under natural conditions and may not be considered as a mere laboratory artifact.
CARBON‐13 NUCLEAR MAGNETIC RESONANCE STUDIES ON 13C‐ENRICHED RETINALS EMBEDDED IN BACTERIORHODOPSIN
Authors: Yamaguchi Akihito , Unemoto Tsutomu , Ikegami Akira
Published: January 2008

Abstract— Both [15‐13C] and [14‐13C] all‐trans‐retinals were synthesized. Bacteriorhodopsin containing [14‐13C]retinal as a chromophore, when solubilized with octyl‐β‐D‐glucoside, showed characteristic resonances at 125 and 118 ppm from tetramethyl silane. The former was assigned to the signal from free retinal and the latter from protonated Sehiff base. When the bacteriorhodopsin was denatured in sodium dodecyl sulfate, the signal at 118 ppm disappeared, while the signal at 125 ppm rather increased.

In the case of bacteriorhodopsin containing [15‐13C]retinal, when solubilized with Triton X‐100, a characteristic resonance at 169 ppm was distinguishable as a shoulder peak superimposed on the broad signal of carbonyl carbons and it was assigned to the signal from the protonated Sehiff base. The other signal observed at 191 ppm was from free retinal.

These results suggested that the Sehiff base of bacteriorhodopsin is protonated in the dark.
PHOTOCHEMICAL REACTION OF 13‐CIS‐BACTERIORHODOPSIN STUDIED BY LOW TEMPERATURE SPECTROPHOTOMETRY
Authors: Iwasa Tatsuo , Tokunaga Fumio , Yoshizawa Tǒru
Published: January 2008

Abstract— The photoreaction cycle of 13‐cis‐bacteriorhodopsin (13‐cis‐bR) was investigated by low temperature spectrophotometry using two different preparations; 13‐cis‐bR constituted from bacterioopsin and 13‐cis‐retinal, and dark‐adapted bacteriorhodopsin (bRD), which is an equi‐molar mixture of 13‐cis‐bR and trans‐bR.

By irradiation with 500 nm light at — 190°C, 13‐cis‐bR was converted to its batho‐product, batho‐13‐cis‐bR (batho‐bR13), which is different from batho‐product from trans‐bR, batho‐bRt. On warming batho‐bR13 to ‐5°C in the dark, it completely changed to trans‐bR. We estimated the composition of 13‐cis‐bR and trans‐bR in the warmed sample spectrophotometrically and then the absorption spectrum of batho‐bR13 was calculated. The absorption maximum lies at 608 nm, 1250 cm−1 longer than that of 13‐cis‐bR; the molar extinction coefficient (ε) is about 74000 M−1 cm−1, larger than that of 13‐cis‐bR (52000 M−1 cm−1).

On the warming the sample containing batho‐bR13 formed by irradiating 13‐cis‐bR or bRD at — 190°C, we could not detect other intermediates such as the lumi‐ or meta‐intermediates seen in trans‐bR system.
THE WHITE MEMBRANE OF CRYSTALLINE BACTERIOOPSIN IN HALOBACTERIUM HALOBIUM STRAIN R1mW AND ITS CONVERSION INTO PURPLE MEMBRANE BY EXOGENOUS RETINAL
Authors: Mukohata Yasuo , Sugiyama Yasuo , Kaji Yoshio , Usukura Jiro , Yamada Eichi
Published: January 2008

Abstract— A new strain isolated from Halobacterium halobium designated R1mW, contained negligible amounts of isoprenoid pigments, had a yellowish white color due to respiratory pigments and showed no proton movement in response to light. However, addition of all‐trans‐retinal converted R1mW into purple cells. Formation of both halorhodopsin and bacteriorhodopsin was indicated by induction of light‐dependent proton uptake and release, respectively. Both haloopsin and bacterioopsin were thus postulated to be present in R1mW. Electron micrographs of freeze‐fractured cytoplasmic membranes revealed patches in a hexagonal array of trimeric particles, comparable to the purple membrane structure.

These white membrane patches were isolated by procedures similar to those for the purple membrane. The white membrane's buoyant density was about 1.18 g/m/, and its main component migrated on sodium dodecylsulfate polyacrylamide gels at the same rate as bacteriorhodopsin. The white membrane showed only a small absorption peak at ∼410nm due to contaminating respiratory pigments and a strong absorption at around 275 nm and shorter wavelengths. The white membrane was thus considered to be mainly composed of bacterioopsin, which was readily converted into bacteriorhodopsin by an addition of all‐trans‐retinal.

The absorption and CD spectra of the white membrane were measured before and after addition of retinal. The molar extinction coefficient of dark‐adapted bacteriorhodopsin formed was determined to be 53000M−1 cm−1 at 560 nm from retinal binding studies. The CD spectrum of the white membrane was negligible in the visible region but showed several bands assigned to aromatic and backbone structures in the UV region. Retinal addition caused considerable changes in the spectrum, yielding the CD spectrum of crystalline purple membrane bacteriorhodopsin. The white membrane thus appears to be a preparation suitable for structure‐function studies of bacteriorhodopsin.
A COMPARISON OF FLUORESCENCE QUENCHING AND FLUORESCENCE DECAY STUDIES WITH TRYPTOPHAN
Authors: Eftink M. R. , Ghiron C. A.
Published: January 2008

Abstract— The quenching of the fluorescence of aqueous tryptophan solutions has been studied as a function of emission wavelength using acrylamide as a collisional quencher. Our quenching studies are consistent with recent observations of the heterogeneity of tryptophan fluorescence, but they show a slight discrepancy when compared to certain analyses of the decay of tryptophan fluorescence in terms of two components.
OXYGEN REQUIREMENT FOR NEAR‐UV MEDIATED CYTOXICITY OF α‐TERTHIENYL TO ESCHERICHIA COLI AND SACCHAROMYCES CEREVISIAE
Authors: Arnason T. , Chan G. F. Q. , Wat C. K. , Downum K. , Towers G. H. N.
Published: January 2008

Abstract— The photosensitizing activity of α‐terthienyl, a naturally occurring compound from Tagetes has been studied. Fluence‐response curves for the effect of α‐terthienyl and near‐UV radiation on Escherichia coli have been prepared. Photosensitization of E. coli was enhanced in aerobic as compared to anaerobic conditions and exogenous superoxide dismutase had a slight protective effect. Sodium azide, a quencher of 1O2, protected yeast cells from photosensitization with α‐terthienyl. The available evidence suggests that α‐terthienyl acts as a photodynamic sensitizer in vivo.
ENERGY TRANSFER IN A LIGHT‐HARVESTING CAROTENOID‐CHLOROPHYLL c‐CHLOROPHYLL a‐PROTEIN OF PHAEODACTYLUM TRICORNUTUM
Authors: Gugliemelli L. A. , Dutton H. J. , Jursinic P. A. , Segelman H. W.
Published: January 2008

Abstract— The marine diatom Phaeodactylum tricornutum was readily disrupted in 0.1 N Tris‐HCl buffer, pH 7.8, in a Braun Model MSK cell homogenizer at 0‐5°C. Treatment of the suspension with sodium lauryol sarcosinate (3 molecules per 10000 daltons of protein) at 5°C in the dark and subsequent centrifugations produced a pigmented, protein fraction whose excitation spectrum exhibited energy transfer from carotenoids to chlorophyll a (Chi a). Disruption of the pigment‐protein complex by heating in 1% sodium dodecylsulfate resulted in loss of energy transfer. For each Chi a molecule this fraction had 1 Chi c, 4 fucoxanthin, and 6.7 accessory pigment molecules. Presence of the accessory complex of Photosystem II in this preparation is suggested by the high xanthophyll content. Further, based on Chl a concentrations, this fraction had about 18 times more apparent fluorescence emission at 680 nm when excited at 470 nm than the intact cells.
CIS‐TRANS PHOTOISOMERIZATION OF ABSCISIC ACID
Authors: Brabham Dale E. , Biggs R. H.
Published: January 2008

Abstract— An important regulator of numerous physiological processes in higher plants is abscisic acid (ABA), which is photoisomerized from the more biologically active cis isomer to the nearly inactive trans isomer by natural sunlight. It is possible that this photoisomerization is a UV control mechanism in functions regulated by ABA.

The quantum yields of both the cis to trans and trans to cis photoisomerizations were measured by an initial velocities method under various conditions of pH and oxygen concentration at room temperature. The yield for photoisomerization of cis‐ABA ranged from 0.25 at pH 3.0 to 0.11 at pH 7.0. Oxygen partially quenched the process. The quantum yield varies only slightly with wavelength.

The quantum yield of photolysis of cis‐ABA is reported for pH 3.0 as 0.06. This yield also varies slightly with wavelength and is relatively insensitive to oxygen. This relatively high yield explains the loss of potency of ABA during UV irradiation.

Phosphorescence of cis‐ and trans‐ABA is observed in methanol at 77 K. Onset of the emission is at 350 nm. The emission spectra is the same for both isomers.

From these results a mechanism of UV action on plants based on the photoisomerization of the inactive trans‐ABA to the biologically active cis isomer is proposed.
KINETICS OF FUROCOUMARIN PHOTOSENSITIZATION OF DNA TO NEAR‐ULTRAVIOLET RADIATION
Authors: Grossweiner L. I.
Published: January 2008

Abstract— The kinetics of DNA photoadduct formation induced by irradiation with near‐ultraviolet in the presence of furocoumarin photosensitizers has been analyzed for systems of differing repair competance and for light sources of arbitrary spectral intensity distributions. The results are exemplified by applications to published data on DNA photoadduct yields in vitro and in vivo and Escherichia coli survival curves.
THE EFFECT OF ALIPHATIC ALCOHOLS ON FLUORESCENCE QUENCHING AND FLUORESCENCE POLARIZATION OF LUMINESCENCE PROBES IN HEXADECYLTRIMETHYLAMMONIUM BROMIDE MICELLES
Authors: Turro Nicholas J. , Tanimoto Yoshifumi
Published: January 2008

Abstract— The fluorescence quenching of the indole chromophore by NO−2 and the fluorescence depolarization of several luminescence probes in aqueous solutions containing hexadecyltrimethylammonium bromide (HDTBr) were measured as a function of added C2–C4 aliphatic alcohol concentration. The fluorescence decay profiles of pyrene in the micellar solutions were also measured to estimate the aggregation number of the micelles. The addition of n‐butyl alcohol significantly reduces the fluorescence quenching rate and the aggregation number and increases the extent of fluorescence depolarization in HDTBr micellar systems. The addition of ethyl alcohol shows a similar but smaller effect.
PATHWAYS FOR PHOTIC ENTRAINMENT OF MAMMALIAN CIRCADIAN RHYTHMS*
Authors: Rusak Benjamin , Boulos Ziad
Published: January 2008

Abstract— Photic entrainment of mammalian circadian rhythms is mediated exclusively by the retina. Several retinofugal pathways may be involved in the mediation of entrainment and other effects of light on the circadian system. The retinohypothalamic tract (RHT) is sufficient for entrainment, but other visual projections are capable of mediating either driving or entraining effects of light after RHT interruption in rats and hamsters. Interruption of the primary or accessory optic tracts can modify several features of light entrainment, suggesting their involvement in normal entrainment in hamsters. Retinofugal projections appear to interact in a complex fashion to produce the features of normal photic entrainment.
INTENSITY DEPENDENCE OF FLUOROPHORE PHOTOBLEACHING BY A STEPPED‐INTENSITY SLOW‐BLEACH EXPERIMENT
Authors: Lanni Frederick , Ware B. R.
Published: January 2008

Abstract— We describe a simple method for determination of the dependence of fluorophore photo‐bleaching on the intensity of the incident light. A sample of fluorophore is illuminated uniformly with an intensity which is sufficient only to bleach a small fraction of the fluorophore during a fluorescence lifetime period. The long‐term decay of fluorescence due to photobleaching is monitored before and after a stepped increase in the incident intensity. The order of the photobleaching reaction is determined by taking the ratio of the logarithms of the limiting values of the slope of the fluorescence bleaching curve and the absolute fluorescence change. The method is applied to fluorescein, bound to dextran or ovalbumin, in aqueous solution, and the order of the reaction in both cases is shown to be unity.
THE PHOTOPHYSICAL AND PHOTOCHEMICAL PROCESSES OF TRYPTOPHAN IN INTERACTION WITH POLYNUCLEOTIDES: LASER FLASH PHOTOLYSIS STUDY
Authors: Le Doan T. , Toulme J. J. , Santus R. , Hélène C.
Published: January 2008

Abstract— The influence of nucleotides or polynucleotides on the photophysics and the photochemistry of tryptophan (Trp) derivatives has been investigated in aqueous solutions using the 265 nm laser flash photolysis technique. In solutions containing mixtures of N‐acetyltryptophanamide and uridine monophosphate (UMP) or mercurated dUMP, the Trp triplet and the hydrated electron (eaq) are quenched at almost diffusion controlled rates by the nucleotides leading to uracil reduction. Lysyl‐tryptophyl‐α‐lysine (Lys‐Trp‐Lys) forms stable complexes in solution with normal or mercurated poly(uridylic acid) [poly(U)]. In the Poly(rU)‐Lys‐Trp‐Lys complex the Trp triplet state is completely quenched, whereas the Trp triplet formation quantum yield is enhanced in complexes with mercurated poly(U). In this last case, the ‘heavy atom effect’ is characterized by a shortening of the Trp triplet lifetime in agreement with low temperature experiments. Our results also show that photoionization of Trp does occur in the complexed state with both polymers. The eaq lifetime is however longer with the complexed than with the free peptide.
FLUORESCENCE AND PHOTOOXIDATION OF 1—ANILINONAPHTHALENE—8—SULFONIC ACID IN REVERSED MICELLAR SOLUTIONS AND THE EFFECT OF CCl4
Authors: Miyoshi N. , Tomita G.
Published: January 2008

Abstract— The 1‐anilinonaphthalene‐8‐sulfonic acid solubilized in dodecylammonium propionate reversed micellar cyclohexanic solutions, emitted a strong fluorescence, and was photooxidized under aerobic conditions. Carbon tetrachloride (CCl4) highly quenched the fluorescence and remarkably enhanced the oxidation reaction. The fluorescence quenching obeyed the Stern‐Volmer relation, and the photooxidation was caused by the singlet oxygen generated by the photosensitization of the dye. From the kinetic analysis, it was known that the intersystem crossing rate from the dye excited singlet to triplet was enhanced by CCl4. Carbon tetrachloride did not quench the triplet state. The ratio of quantum yields for the oxidation in the presence and absence of CCl4 was independent of the oxygen concentration in the reaction mixture. The fluorescence quenching constant and the intersystem crossing rate were obtained at various solubilized water contents.
PHOTOCHEMISTRY OF ALL‐TRANS‐ AND 13‐CIS‐14,15‐DIDEUTERIORETINAL
Authors: Waddell Walter H. , Chihara Kohji , Younes Usama E.
Published: January 2008

Abstract— All‐trans‐ and 13‐cis‐14,15‐dideuterioretinal were synthesized and their solution photochemistry examined. Quantum yields of trans→cis or cis→ trans photoisomerization and the number and ratio of primary photoproducts, determined by high pressure liquid chromatographic analysis, are essentially identical to that of their corresponding retinal isomer. The C‐14, C‐15 carbon‐hydrogen modes play no particularly important role in the deactivation of electronically excited linear polyenes related to retinal.
OXYGEN QUENCHING OF CHLOROPHYLL FLUORESCENCE IN CHLOROPLASTS
Authors: Vidaver William , Popovic Radovan , Bruce Douglas , Colbow Konrad
Published: January 2008

Abstract— Three phases of chlorophyll a fluorescence quenching by O2 are observed in green plants. The effects of various inhibitors on photosynthetic partial processes in chloroplasts were investigated in attempts to (1) localize the O2‐quenching sites and (2) assess possible physiological significance of O2‐quenching. Our results localize the most sensitive (and presumably functionally important) phase to a site between plastoquinone and the photosystem I acceptor, chlorophyll (P700), possibly plastocyanin. It is suggested that PC may transfer electrons to oxygen in addition to P700.
PHOTOTRANSFORMATION KINETICS OF UNDEGRADED OAT AND PEA PHYTOCHROME INITIATED BY LASER FLASH EXCITATION OF THE RED‐ABSORBING FORM
Authors: Cordonnier M.‐M. , Mathis P. , Pratt L. H.
Published: January 2008

Abstract— Phototransformation at 2°C of the red‐absorbing form of phytochrome (Pr) to the far‐redabsorbing form (Pfr) was studied with both undegraded oat (Avena sativa L., cv. Garry) and undergraded pea Pisum sativum L., cv. Alaska) phytochrome. Phototransformation was initiated by a 15‐ns laser pulse with maximum emission near 600 nm and output power of 30 mJ. The first resolvable transformation intermediate exhibited relative to Pr a maximum absorbance increase near 700 nm and was fully present at the earliest time measured, which was 60 ns after the flash. This intermediate absorbance decayed by two reactions for oat phytochrome (half‐lives of 11 and 140 μs assuming parallel reactions) and by three for pea phytochrome (half‐lives of 14, 280 and 1600 μs assuming parallel reactions). The kinetics of the slowest reaction for pea phytochrome, however, might be somewhat distorted by an instrument artifact. The appearance of the far‐red‐absorbing phytochrome, as monitored by absorbance increase at 720 nm, occurred by at least two reactions for both oat (half‐lives of 47 and 250 ms assuming parallel reactions) and pea (half‐lives of 170 and 770 ms assuming parallel reactions) phytochrome. The possibility of slower reactions was not tested. Assays for possible proteolysis of the phytochrome samples studied here indicated that the presence of degraded phytochrome could not account for the observed multiphasic kinetics except possibly for one phase of the triphasic intermediate decay seen with pea phytochrome.
SOME PROPERTIES OF THE TRIPLET EXCITED STATE OF THE PHOTOSENSITIZING FUROCOUMARIN: 3‐CARBETHOXYPSORALEN
Authors: Ronfard‐Haret J. C. , Averbeck D. , Bensasson R. V. , Bisagni E. , Land E. J.
Published: January 2008

Abstract— 3‐Carbethoxypsoralen (3‐CPs) has been tested in the photochemotherapy of psoriasis. It only forms monoadducts with DNA and is being considered as a non‐carcinogenic alternative to 8‐MOP which itself forms DNA crosslinks that arc difficult to repair. Using laser flash photolysis or pulse radiolysis, the triplet state of 3‐CPs, a possible intermediate in photosensitization, has been generated in several solvents: ethanol, water and benzene. The triplet lifetime, extinction coefficient and quantum efficiency of formation have been measured. Triplet reactivities towards (i) the solvents used, (ii) 3‐CPs, (iii) oxygen, (iv) tryptophan and (v) tyrosine, leading, respectively, to photoadditions with water, ethanol and 3‐CPs, to 1O2, semioxidized tryptophan and semioxidized tyrosine, (vi) thymine and (vii) uracil have been investigated. The dark binding of 3‐CPs to DNA has been studied by comparing the reactivity of eaq‐ with free 3‐CPs, free DNA and the 3‐CPs DNA complex. Some photophysical and photochemical properties of 4′,5′di‐hydro‐3‐carbethoxypsoralen(DH–3‐CPs), model of the main fluorescent photo‐product of 3‐CPs, have also been investigated. Biological consequences of the photochemical properties of 3‐CPs andDH–3‐CPs have been studied in a cellular system (haploid yeast).
ANALYSIS OF Pfr DESTRUCTION IN AMARANTHUS CAUDATUS L EVIDENCE FOR TWO POOLS OF PHYTOCHROME*
Authors: Brockmann J. , Schaufer E.
Published: January 2008

Abstract— Kinetics of the destruction of the far red absorbing form of phytochrome (Pfr), measured by in vivo spectroscopy, show two phases: after a saturating red light pulse, rapid first order decay results in the loss of most, but not all, of the detectable Prr; decay of the rest is much slower. The concentration of the more stable Pfr is positively correlated to the concentration of the total Pfr established at time zero. The linear relationship between total and ‘stable’ Pfr exludes the existence of a threshold level of Pfr for fast destruction. Photoconversion of the Pr (red absorbing form of phytochrome) present during the slow decay, by exposure to a second light pulse, is followed by fast destruction of most of the newly formed P,r, whereas some Pfr formed by the first pulse still remains. The experiment suggests that not all Pfr molecules are accessible to the same destruction mechanism, i.e. there are two populations of PfI.
THE PHOTOOXIDATION OF 8‐METHOXYPSORALEN
Authors: Wasserman H. H. , Berdahl D. R.
Published: January 2008

Abstract— The photooxidation of 8‐methoxypsoralen has been studied. Enhancement of the reaction rate in deuterated solvents is in accord with the involvement of singlet oxygen. Several photoproducts including 6‐formyl‐7‐hydroxy‐8‐methoxycoumarin and polymer are formed. Low temperature nuclear magnetic resonance spectroscopy studies give evidence of a peroxidic intermediate.
ENHANCED SENSITIVITY TO THE LETHAL AND MUTAGENIC EFFECTS OF PHOTOSENSITIZING ACTION OF CHLORPROMAZINE IN ETHYLENEDIAMINETETRAACETATE‐TREATED ESCHERICHIA COLI
Authors: Yonei Shuji , Todo Takeshi
Published: January 2008

Abstract— Ethylenediaminetetraacetate (EDTA) treatment of Escherichia coli H/r30 (Arg‐) enhanced cell sensitivity to the lethal and mutagenic effects of the photosensitizing action of chlorpromazine (CPZ). The most obvious effect of EDTA on the fluence‐survival curve was an elimination of the shoulder. In the absence of EDTA, CPZ plus near‐UV radiation did not induce the reversion from arginine‐auxo‐troph to autotroph of E. coli H/r30. However, when EDTA (5 mM)‐treated cells were subjected to CPZ plus near‐UV radiation, the induced reversion frequency increased with time of irradiation. It is concluded that the enhanced penetration of CPZ into E. coli cells by EDTA facilitates the drug binding to DNA within the cells upon near‐UV irradiation and that this is the cause for the enhanced photosensitized lethal and mutagenic effects of CPZ.
PRIMARY PROCESSES IN THE PHOTOCHEMISTRY OF AQUEOUS SULPHACETAMIDE: A LASER FLASH PHOTOLYSIS and PULSE RADIOLYSIS STUDY
Authors: Land Edward J. , Navaratnam Suppiah , Parsons Barry J. , Phillips Glyn O.
Published: January 2008

Abstract— The spectra have been measured of the transient species formed in the nanosecond flash photolysis of aqueous solutions of sulphacetamide under a variety of conditions. In addition to the excited triplet state, the cation radical and the solvated electron were observed. The ionisation of aqueous sulphacetamide was found to occur by a biphotonic process. The extinction coefficient of the cation radical of sulphacetamide was determined by both laser flash photolysis and pulse radiolysis techniques, a value of 1.9 times 103 dm3mol‐1cm‐1 being obtained. The rate of electron reaction with sulphacetamide and the anion radical spectrum were also determined by the two techniques, good agreement being obtained. The spectrum of the product of the reaction of the superoxide anion radical and the corresponding rate constant have also been determined. A possible mechanism of photosensitized skin reaction due to sulphacetamide is discussed.
QUANTUM YIELD and EQUILIBRIUM POSITION OF THE CONFIGURATIONAL PHOTOISOMERIZATION OF BILIRUBIN BOUND TO HUMAN SERUM ALBUMIN*
Authors: Lamola Angelo A. , Flores Jorge , Doleiden Franklin H.
Published: January 2008

Abstract— At low fluence rates it is possible to observe a photoequilibrium between Z,Z‐bilirubin(BR) and its E isomers(collectively called PBR) bound to human serum albumin(HSA).For excitation centered at 465 nm, the fraction of PBR/HSA in the photoequilibrium mixture was observed to be 0.22 + 0.02. The quantum yield for conversion of BR/HSA to PBR/HSA was found to be 0.20 0.02. The equality of the quantum yield value and the fraction of PBR/HSA in the photoequilibrium mixture is consistent with a simple mechanism for the photoisomerization in which optically excited singlet states of BR and PBR convert rapidly and with virtually total efficiency to a common excited intermediate with twisted geometry that subsequently decays to BR and PBR in the ratio 4:1, respectively. Quantum yields for other photoprocesses of BR bound to HSA are much lower than that for configur‐ational isomerization. The central role suggested for configurational isomerization in the phototherapy for neonatal hyperbilirubinemia is supported by these observations.
RECOVERY FROM INHIBITION BY UV‐IRRADIATION OF ORNITHINE DECARBOXYLASE INDUCTION IN HUMAN CELLS: IMPLICATION OF EXCISION REPAIR
Authors: Ben‐Hur E. , Prager A. , Buonaguro F.
Published: January 2008

Abstract— Exposure of stationary‐phase human breast carcinoma(T–47D) cells to far‐UV light (254 nm) inhibited the appearance of induced ornithine decarboxylase (ODC) activity. The fluence response curve had a shoulder (D4= 2 J m‐2) followed by an exponential decline (D0= 4.2 Jm‐2). The cells could recover from this inhibition when the stimulus of induction of ODC was delayed for20–24 h after irradiation. Hydroxyurea (HU) when present at 3 mM during the recovery period eliminated completely the ability of the cells to recover. This effect of HU on ODC induction was partially reversed by 50nM of the four deoxyribonucleosides required for DNA synthesis. Neither HU nor the deoxyribonucleosides by themselves affected ODC induction in unirradiated cells. Since HU inhibited the recovery from potentially lethal UV damage and is a known inhibitor of excision repair, we interpret the above results to mean that recovery from UV‐induced inhibition of ODC induction depends on excision‐repair of DNA damage. This interpretation is strongly supported by the finding that specific photolysis of 5‐bromodeoxyuridine, incorporated into DNA during the recovery period, inhibited recovery of ODC induction from inhibition by UV light.
NONRECIPROCAL SYNERGISTIC LETHAL INTERACTION BETWEEN 365‐nm and 405‐nm RADIATION IN WILD TYPE and uvrA STRAINS OF ESCHERICHIA COLI*
Authors: Webb Robert B. , Brown Mickey S. , Ley Ronald D.
Published: January 2008

Abstract— Lethality by 405‐nm radiation in three repair‐proficient and two uvrA strains of Escherichia coli that belong to two isogenic series was greatly enhanced by prior exposures to 365‐nm radiation at fluences greater than 1 times 106Jm‐2. Fluences at 365 nm that yielded a surviving fraction of 0.10 (>1 times 106 Jm‐2) in the 5 strains tested resulted in the following 405‐nm fluence enhancement factors (FEF, ratio of the 405‐nm F37 in the absence of a prior 365‐nm irradiation to that in the presence): strain K.12 AB1157 (wild type), 8.7; strain B/r (wild type), 52; strain WP2 (wild type), 25; strain WP2s (uvrA), 13; strain K.12 AB1886 (uvrA), 15. The maximal 405‐nm FEF value obtained after a prior 365‐nm irradiation at greater fluences was 83 in the wild‐type strain B/r. Enhancement of anoxic 405‐nm radiation after a prior aerobic 365‐nm exposure was not detectable, suggesting that prior aerobic irradiation at 365‐nm increased the effects of damage produced at 405 nm by means of an oxygen‐dependent process. Single‐strand breaks (or alkali‐labile bonds) were produced by 405‐nm radiation at 3.0 times 10‐5 breaks per 2.5 times 109 daltons per Jm‐2 in the polA strain P3478; pyrimidine dimers were not detected by biological assay (photoreactivation) at 405 nm. Although the introduction of different DNA lesions produced by 365‐ and 405‐nm radiations cannot be ruled out, we propose that the strong synergistic effect of 365‐nm irradiation on 405‐nm lethality is the consequence of pronounced inhibition by 365‐nm radiation of components of the DNA‐repair systems that can mend or bypass damage produced by 405‐nm radiation.
SPECTRAL PERTURBATIONS OF THE AEQUOREA GREEN‐FLUORESCENT PROTEIN
Authors: Ward William W. , Prentice Hugh J. , Roth Amy F. , Cody Chris W. , Reeves Sue C.
Published: January 2008

Abstract— In the jellyfish Aequorea, the green‐fluorescent protein (GFP) functions as the in vivo bio‐luminescence emitter via energy transfer from the photoprotein aequorin. Accumulated evidence has indicated that the Aequorea GFP is a relatively inflexible protein. Present evidence, however, indicates that the chromophore environment is readily accessible to a variety of external perturbants. Native Aequorea GFP has an absorbance maximum at 395 nm and a shoulder at 470 nm. In low ionic strength buffer at neutral pH and room temperature the 395/470 nm absorbance ratio is about 2.0. We show that this ratio is highly variable depending upon temperature, ionic strength, protein concentration, and pH. A maximum ratio of 6.5 (at a protein concentration of 18.6 mg/m/) and minimum of 0.42 (at a pH of 12.2) have been measured. In the latter case, the resulting absorption and excitation spectra resemble those of Renilla GFP in spectral shape (but not wavelength maximum). In all cases as the perturbant is varied the resulting spectra pass through a sharp isosbestic point, suggesting a relatively simple two‐state mechanism. These spectral perturbations are fully reversible. On the basis of these results, we suggest that the chromophore binding site is conformationally flexible. pH‐Dependent changes in the near‐UV and visible circular dichroism spectra plus spectrophotometric titration of tyrosine residues lend additional support to this hypothesis.
DIRECT OBSERVATION OF ELECTRON TRANSFER ACROSS A LIPID BILAYER: PULSED LASER PHOTOLYSIS OF AN ASYMMETRIC VESICLE SYSTEM CONTAINING CHLOROPHYLL, METHYL VIOLOGEN AND EDTA*
Authors: Ford William E. , Tollin Gordon
Published: January 2008

Abstract— Suspensions of vesicles composed of chlorophyll a (Chi) and phospholipid that were asymmetric with respect to aqueous solutions of methyl viologen (MV2+), an electron acceptor, and EDTA, an electron donor, were investigated using both flash and steady‐state photolysis techniques. It was shown that Chl‐photosensitized electron transfer occurred across the walls of the vesicles from EDTA to MV2+. Flash photolysis indicated that MV2+ dissolved in the interior aqueous compartments of the vesicles oxidized only those triplet excited state Chi molecules that were dissolved in the inner monolayers of the vesicle walls. The resultant radical products, Chi+ and MV+, recombined with a halftime of the order of 10‐4s. EDTA, added externally to the vesicles, competed effectively with MV+ as a reducing agent for Chl+. This places a lower limit of 104 s‐1 on the rate constant for transmembrane electron transfer. Compartmentalization by the vesicle wall of the competing pathways for the reduction of Chi+ resulted in a nonlinear dependence of the rate constant of Chl+ decay on EDTA concentration. The magnitude of the rate constant of electron transfer through the membrane and the way that the kinetics of Chl+ decay depended on the concentration of Chi in the membrane strongly suggest that the electron transfer occurred by electron exchange between Chi and Chl+.
THE Py SCALE OF SOLVENT POLARITIES. SOLVENT EFFECTS ON THE VIBRONIC FINE STRUCTURE OF PYRENE FLUORESCENCE and EMPIRICAL CORRELATIONS WITH ET and Y VALUES
Authors: Dong Dao Cong , Winnik Mitchell A.
Published: January 2008

Abstract— Pyrene fluorescence spectra have been run in 62 solvents of widely differing solvent polarity. As has been noted previously, the intensity ratio of the first (the 0–0 band) and third bands in vibronic fine structure of these spectra are very sensitive to solvent polarity. These I1/I3 values, however, are not sensitive to hydrogen bonding aspects of solvent‐solute interactions. Correlations are reported with Winstein's Y values and with Dimrotb's ET values. On this basis the I1/I3 values for pyrene fluorescence are suggested as the basis for a new empirical scale of solvent polarity, called the Py scale, which offers certain conveniences over other scales of solvent polarity.
MONOFUNCTIONAL COVALENT PHOTOBINDING OF DICTAMNINE, A FUROQUINOLINE ALKALOID, TO DNA AS TARGET IN VITRO
Authors: Pfyffer Gaby E. , Panfil Irma , Towers G. H. N.
Published: January 2008

Abstract— The naturally occurring furoquinoline alkaloid, dictamnine, is phototoxic to Gram‐positive bacteria, yeasts and filamentous fungi in the presence of long‐wave UV light. Prior to photobinding to DNA dictamnine forms a complex with the macromolecule in the dark. Photobinding to DNA is shown with [3H]‐dictamnine. In contradiction to an earlier finding, dictamnine proved to be incapable of forming interstrand crossiinkages with native DNA. This fact was ascertained by the use of methods additional to hydroxyapatite column chromatography, e.g. alkaline sucrose gradient centrifugation and hyperchromicity tests. The alkaloid therefore represents a new monofunctional photoreagent towards DNA in vitro. It is assumed that it binds through its furyl‐C=C to DNA. The inability to form crosslinks may be attributed to the stability of the lateral aromatic nucleus. As no photoreactivity against human erythrocytes could be observed, it is possible that nucleic acids represent the major target of damage in vivo.
THE ACTION SPECTRUM (313–435 nm) FOR KILLING HOECHST 33258 TREATED CHINESE HAMSTER OVARY CELLS CONTAINING BROMODEOXYURIDINE SUBSTITUTED DNA
Authors: Rosenstein Barry S.
Published: January 2008

Abstract— The action spectrum (313–435 nm) for killing Chinese hamster ovary cells containing bromo‐deoxyuridine substituted DNA and treated with Hoechst 33258 was very similar to the absorption spectrum of the dye bound to chromatin, indicating that sensitization was mediated through direct absorption of radiation by the dye. The ratio of sensitization cross sections for 365 nm (plus dye) to 313 nm (no dye) was approx. 30 while this ratio for strand breakage was about one. These results are in agreement with the hypothesis that strand breaks are not the major class of lethal photoproducts induced via Hoechst 33258 sensitization.
POLYNOIDIN: A MEMBRANE PHOTOPROTEIN ISOLATED FROM THE BIOLUMINESCENT SYSTEM OF SCALE‐WORMS
Authors: Nicolas Marie‐Therese , Bassot Jean‐Marie , Shimomura Osamu
Published: January 2008

Abstract— In order to isolate and purify the luminescence system of scale‐worms, the scales were homogenized and extracted in the presence of Triton X‐100. After chromatography on Bio‐Gel A‐5m, Sephadex G‐75 and DEAE‐cellulose, a single peak in luminescence activity was obtained. It showed properties of a membrane protein having a high mol. wt (about 500000) with characteristics of a photoprotein. The photoprotein, for which we suggest the name polynoidin, emits light in response to several reagents that can produce superoxide or hydroxyl radicals, such as H2O2 plus Fe2+, but the luminescence is not triggered by Ca2 +. Oxygen is an absolute requirement for the luminescent reaction. The luminescence has a maximum at 510 nm. The photoprotein is not fluorescent when excited at 350 nm either before or after the luminescent reaction, thus differing distinctly from the green‐fluorescent riboflavin in photosomes which is easily separated at the first step of the purification. We suggest a mechanism of the in vivo luminescence of scale worms in which the production of superoxide or hydroxyl radicals by the oxidation of reduced riboflavin could be regulated by Ca2+.
CHLOROPLAST PIGMENTS and THEIR BIOSYNTHESIS IN RELATION TO LIGHT INTENSITY*
Authors: Grumbach Karl H. , Lichtenthaler Hartmut K.
Published: January 2008

Abstract— Depending on the light intensity that they received during growth, radish seedlings altered not only the pigment and quinone composition of the thylakoid membrane but also the chloroplast ultrastructure. In strong light, sun chloroplasts of radish were very similar to those from sun leaves of beech trees, while those developed under under dim light possessed a typical shade chloroplast. Radish shade chloroplasts contained a higher chlorophyll content and a higher concentration of xanthophylls resulting in a lower xanthophyll to carotene ratio as compared to sun chloroplasts. Chloroplasts from radish grown in strong light showed a much higher activity in their terpenoid metabolism than plastids from shade plants. Chlorophylls and carotenoids which are involved in the absorption of light and the transfer of energy during photosynthesis were labeled by [3H]‐mevalonate to a much higher degree in plastids from sun leaves as compared to plastids from shade leaves. This shows that in strong light where pigments are continuously broken down and resynthesized in order to maintain photosynthesis, chlorophylls and carotenoids exhibit a much higher turnover rate than the pigments of shade plants.
EFFECTS OF BLUE‐LIGHT ON PYRUVATE KINASE ACTIVITY DURING CHLOROPLAST DEVELOPMENT OF UNICELLULAR GREEN ALGAE*
Authors: Ruyters Günter
Published: January 2008

Abstract— In analysing the stimulating effect of blue‐light on respiration and carbohydrate degradation of green algae, the author demonstrated a dual light‐effect on pyruvate kinase (E.C. 2.7.1.40.) of the chlorophyll‐free, carotenoid‐containing mutant. No. 20, of Chlorella vulgaris. This dual effect consists first in an enhancement of the maximal velocity of the enzyme reaction, and second in an increase in the affinity towards the substrate phosphoenolpyruvate. Attempts to elucidate the importance of this enhanced enzyme activity led to the assumption that it might be seen in correspondence with chloroplast development. To support this assumption, the influence of short‐wave visible radiation on pyruvate kinase of Scenedesmus C‐2A' was investigated, a mutant, yellow in the dark, but forming a functioning chloroplast under blue‐light conditions. Indeed, it could be shown that in this organism the substrate affinity of pyruvate kinase is increased during the blue‐light‐mediated greening process and that the dependencies of this blue‐light effect on the age of culture, light intensity, and duration of light treatment are in good agreement with the corresponding data for the Chorella mutant. The results thus support the assumption that the light‐enhancement of pyruvate kinase in the yellow Chlorella mutant. No. 20, may be a remaining part of the blue‐light‐controlled chloroplast development found in some other algae and mutants like e.g. Scenedesmus C‐2A'.
THE IN VIVO SPECTROPHOTOMETRIC ASSAY OF PHYTOCHROME IN TWO MATURE DICOTYLEDONOUS PLANTS*
Authors: Kilsby C. A. H. , Johnson C. B.
Published: January 2008

Abstract— Mature Sinapis alba L. and Impatiens parviflora DC. were treated with the herbicide norfiuorazon prior to development of the third or second leaf, respectively. This treatment yielded a partially bleached plant capable of normal growth and development. The bleached leaves were used for spectrophotometric phytochrome assay. In mature plants an almost constant level of phytochrome is maintained under continuous white light. The dark kinetics and the response of the phytochrome system to light of various qualities provide further evidence of the stable character of the phytochrome system.
CORRELATION BETWEEN INACTIVATION OF HUMAN CELLS and NUMBERS OF PYRIMIDINE DIMERS INDUCED BY A SUN LAMP and 254 nm RADIATION
Authors: Kantor G. J. , Setlow R. B.
Published: January 2008

Abstract— Nondividing human fibroblasts are inactivated by radiation from a source (a Westinghouse sun lamp) that simulates the UV spectrum of sunlight. Survival curves determined for a DNA excision repair‐proficient and a repair‐deficient strain (XP12BE) are related to those determined using germicidal light (254 nm) by constant fluence modification factors. In addition, the same fraction of XP12BE cells are killed per pyrimidine dimer by 254 nm and sun lamp light. These results, when related to other survival and photoreactivation studies, suggest that the mechanism for inactivation of nondividing human cells by sun lamp light is the same as that by 254 nm and that pyrimidine dimers are the major responsible photolesion. Repair reverses some of the lethal effects of this light. We suggest that these conclusions apply to sunlight‐irradiated skin cells in vivo.
PEROXIDASE‐GENERATED TRIPLET INDOLE‐3‐ALDEHYDE ADDS TO URIDINE BASES AND EXCITES THE 4‐THIOURIDINE GROUP IN t‐RNAPhe
Authors: Mello Maricilda P. De , Toledo Sonia M. De , Aoyama Hiroshi , Sarkar Hemanta K. , Cilento Guiseppe , Durán Nelson
Published: January 2008

Abstract Triplet indole‐3‐aldehyde generated by the peroxidase catalyzed aerobic oxidation of indole‐3‐acetic acid adds to t‐RNAphe with an efficiency which can reach 20% of the theoretical value based upon the substrate. The reaction occurs with uridine groups and is of the Paterno‐Büchi type. Magnesium ions reduced addition and increased the sensitized emission from the 4‐thiouridine group. Our results, coupled with available biological data obtained with selectively labeled indole‐3‐acetic acid, support the hypothesis that formation of triplet indole‐3‐aldehyde is at the root of the biological effects of indole‐3‐acetic acid.
PHOTOSENSITIZED DEGRADATION OF DNA BY DAUNOMYCIN
Authors: Gray Peter J. , Phillips Don R. , Wedd Anthony G.
Published: January 2008

Abstract Visible irradiation of DNA‐daunomycin solutions resulted in a decrease of viscosity of the DNA and an increase of the rate of denaturation of DNA in formaldehyde. These changes are consistent with the induction of single‐strand breaks in the DNA, some of which pair to cause fragmentation of the DNA. The DNA damage increases with drug: nucleotide ratio up to 0.2 and is diminished beyond that range. The damage also increases with ionic strength up to 0.6 M and is diminished above that value. These results suggest that the non‐intercalated form of the drug is involved in the photosensitization process. Radicals that are produced accompanying the degradation have been trapped by 5,5‐dimeth‐yl‐l‐pyrroline‐1‐oxide and identified as hydroxyl radicals from their ESR spectrum. The DNA photosensitized damage is completely inhibited when hydroxyl radicals are removed by the spin‐trap, suggesting a direct role for the hydroxyl radicals in the DNA photosensitized degradation process. The implications of the photosensitized DNA damage and the production of hydroxyl radicals in this process are discussed with respect to the medical uses and chemotherapeutic role of daunomycin.
COAL TAR PHOTOTOXICITY: ACTIVE COMPOUNDS AND ACTION SPECTRA*
Authors: Kochevar I. E. , Armstrong R. B. , Einbinder J. , Walther R. R. , Harber L. C.
Published: January 2008

Abstract Eight compounds present in crude coal tar were tested for phototoxicity on guinea‐pig skin. Four concentrations (5 μM to 5 mM) of each compound in ethanol were applied to the dorsal surface of 6 guinea‐pigs. Each animal received 1.0 x 105 j/m2 of UVA radiation. The erythematous (phototoxic) response was evaluated after 20 h. Pyrene, anthracene and fluoranthene were strongly phototoxic. Acridine was markedly less phototoxic. Action spectra based on erythema as an endpoint were determined in guinea‐pigs for anthracene, pyrene and fluoranthene. Each compound was applied to 5 animals which received irradiations from 274 to 502 nm in 12 nm bands for 3, 6, 9, 12 and 15 min. The maximum erythema response to anthracene was observed between 346 and 382 nm, to fluoranthene between 322 and 382 nm and to pyrene between 322 and 358 nm.
ON THE CHROMOPHORE CONFIGURATION OF METARHODOPSIN II
Authors: Pande Jayanti , Pande Ajay , Callender R. H.
Published: January 2008

Abstract The nature of the chromophore configuration of metarhodopsin II (meta II) has been a subject of recent controversy. Earlier resonance Raman results from this laboratory had indicated that meta II has an unprotonated Schiff base linkage between the chromophore and apoprotein. It has been argued, on the other hand, that the Raman evidence does not exclude a non‐covalently bound retinal chromophore. In this communication we present additional evidence and further arguments in favor of our earlier conclusion regarding the state of the chromophore in meta II.
EXCITATION OF CHLOROPLASTS INDUCED BY PHENYLACETALDEHYDE
Authors: Nassi Lilian , Cilento Giuseppe
Published: January 2008

Abstract Chloroplasts promote a slow oxygen consumption by phenylacetaldehyde. The latter elicits a sustained red emission and induces reduction of tetrazolium blue. Addition of horseradish peroxidase greatly increases both O2 uptake and the initial light emission, but has little or no effect upon the reduction of tetrazolium blue. These results indicate that chlorophylls in chloroplasts can be efficiently excited in the absence of light.
PHOTOCHEMICAL REACTIONS OF DIBROMOTHYMOQUINONE
Authors: Caspar Tim , Siedow James N.
Published: January 2008

Abstract The photosynthetic electron transport inhibitor dibromothymoquinone was found to mediate the photoreduction of horse heart cytochrome c in aqueous solution. This process appears to involve the reduction of dibromothymoquinone to the corresponding hydroquinone followed by direct electron transfer to cytochrome c. A subsequent‘autoxidation’of the reduced cytochrome c takes place which requires the presence of both oxygen and quinone. Irradiation of ethanolic stock solutions of dibromothymoquinone generates a hydroquinone species which is (1) capable of reducing cytochrome c directly in aqueous solution in the dark and (2) chemically distinct from the parent compound. This photore‐duced species is stabilized in ethanolic solution but undergoes autoxidation (t1/2= 24 s) when placed in an aqueous medium. Because dibromothymoquinone is used in photosynthetic studies, some care must be taken to avoid complications which might arise from the above reactions; suitable precautions are discussed.
NEW PHOTOSYSTEM I ELECTRON ACCEPTORS: IMPROVEMENT OF HYDROGEN PHOTOPRODUCTION BY CHLOROPLASTS *
Authors: Cuendet Pierre , Grätzel Michael
Published: January 2008

AbstractFour novel electron carriers (two zwitterionic bipyridyls, dicarboxyl colbalticinium and sodium metatungstate), which are negatively charged in their reduced form, have been tested as photo‐system I acceptors and as mediators of H2evolution. Measurements of O2uptake, anaerobic photoreduction rates and stationary concentrations of reduced species under continuous illumination indicate that Coulombic interactions control the electron transfer between the photosynthetic membrane and the mediators. Both rates of forward transfer and back reaction (electron cycling) seem to depend on the charge of the electron carrier. The low concentration of anionic species in the diffuse layer associated with the membrane could explain our results. Hydrogen evolution rates obtained with these four mediators used as electron relays between the photosynthetic membrane and colloidal platinum catalyst are higher than with methylviologen. This improvement of the conversion efficiency parallels the high steady state accumulation of reduced carriers favoured by their negative charge. It is also shown that these synthetic mediators, except metatungstate, are able to evolve hydrogen with an hydrogenase isolated fromDesulfovibrio desulfuricans.