bluuebunny/crossref_metadata_2025 huggingface dataset:
TOLUIDINE BLUE: THE MODE OF PHOTODYNAMIC ACTION IN YEAST CELLS
Authors: Ito Takashi
Published: January 2008

Abstract— Toluidine blue, a thiazine dye, was shown to have in vivo photodynamic activity through singlet oxygen (O21Δg) production. This was based mainly on the effective protection by N‐3 and the marked enhancement in D2O for the sensitized inactivation of yeast cells. The mode of the in vivo activity was, however, quite different from that of acridine orange, for which the singlet oxygen mechanism has also been proposed. The most characteristic feature in the toluidine blue‐sensitization was the total lack of the induction of gene conversion (at trp 5), while the survival went down below 10%. The non‐induction of genetic changes was confirmed at several pH's in the neutral region, whereas the inactivation was seen in parallel to the reported pH dependence of singlet oxygen production in vitro. Direct measurements by microspectrophotometry showed none of the toluidine blue was accumulated in the cell. It was also ascertained from acridine‐sensitized induction of gene conversion that toluidine blue never interfered with the binding of acridine orange to cellular DNA. These findings suggested that the unique mode of photodynamic activity of toluidine blue is attributable to its action from outside of the cell. Furthermore, comparisons between the photodynamically treated cells (with toluidine blue) and non‐treated cells with respect to the response to UV irradiation excluded certain cell functions relating to the expression of gene conversion from the possible damage sites. The photo‐reactivation process of UV induced gene conversion was not disturbed by the pre‐toluidine blue sensitition. In view of the foregoing results, the plasma membrane was tentatively suggested as the most likely site of damage.
THEORETICAL ANALYSIS OF THE PHOTOPHYSICAL PROPERTIES OF ε‐ADENINE AND THE RNAphe Y‐BASE
Authors: Evleth E. M. , Lerner D. A.
Published: January 2008

Abstract— …An analysis of the photophysical and theoretical properties of e‐adenine and the RNA Y‐base shows that these materials have a closer conceptual relationship to the indolizines than the purines.
SMALL SIGNAL ADMITTANCE OF METAL CHLOROPHYLL a|Hg PHOTOVOLTAIC SANDWICH CELLS
Authors: Corker G. A. , Lundström I.
Published: January 2008

Abstract— …The ac admittances of metal I chlorophyll a|Hg sandwich cells are shown to depend upon the chlorophyll (Chi) layer thickness, the aggregation state of the Chi, the light‐dark environment of the cells and the nature of the metal. The results suggest the presence of different but not independent charge transport processes in these cells. One process gives rise to a broad dispersion in the frequency dependent capacitance and conductance. This process is observed in all cells and is most readily ascribed to a hopping or tunneling of charge carriers across potential energy barriers. Another mechanism which is detected only with crystalline Chi and only with certain metal substrates is ascribed to interfacial polarization. A model circuit incorporating these interpretations yield calculated admittance data which approximate those measured experimentally.
ELECTROPHORETIC AND SPECTROPHOTOMETRIC STUDIES OF CHLOROPHYLL‐PROTEIN COMPLEXES FROM TOBACCO CHLOROPLASTS. ISOLATION OF A LIGHT HARVESTING PIGMENT PROTEIN COMPLEX WITH A MOLECULAR WEIGHT OF 70,000
Authors: Remy R. , Hoarau J. , Leclerc J. C.
Published: January 2008

Abstract— …After a short‐term solubilization with sodium dodecyl sulphate, chloroplast membranes of tobacco were separated by polyacrylamide gel electrophoresis into three chlorophyll‐protein complexes. In addition to the two major complexes termed I and IIc corresponding respectively to P700 chlorophyll a‐protein and light‐harvesting chlorophyll a/b‐protein described by Thornber (1975), a relatively stable complex termed IIa has been observed. This new complex has an apparent molecular weight of 70,000 daltons and possesses Chl a and b.

Complexes I, IIa and IIC have been isolated and precise spectroscopic analyses have been performed. Fourth derivative analyses of low temperature absorption spectra suggest that complex IIa seems more representative than IIC of chlorophyll a forms present in intact thylakoid membranes.

Moreover, the electrophoretic study reveals that CPI and CPII are composed of only one polypeptidic subunit with respective molecular weights of 68,000 and 24,000 daltons.
PHOTOTRANSFORMATIONS OF PHYTOCHROME
Authors: Kendrick R. E. , Spruit C. J. P.
Published: January 2008

Abstract— –Phytochrome is the photoreversible chromoprotein that controls many aspects of plant growth and development Phototransformations of the red absorbing form (Pr) and the far red absorbing form (Pfr) involve initial photoreactions followed by dark relaxation reactions. Techniques for the study of intermediates of phototransformation and the present picture of intermediates involved in the phototransformations of Pr and Pfr are outlined. The molecular natures of the phototransformations are reviewed in relationship to knowledge of the chemistry of the chromophore and apoprotein. The significance of phytochrome intermediates in understanding the physiology of phytochrome controlled responses is discussed.
CHLOROPHYLL METABOLISM IN ETIOLATED GHERKIN SEEDLINGS I. PHOTOINHIBITION OF CHLOROPHYLL ACCUMULATION
Authors: Dorsman A. , Elgersma O. , Meuer G. , Steuten L.
Published: January 2008

Abstract. Cotyledons of etiolated gherkin seedlings do not turn green upon transfer to high intensity red light (about 25 W/m2). A pre‐irradiation with high intensity red light has an after‐effect as chlorophyll accumulation during a subsequent exposure to white light (20 W/m2) is inhibited.

The capacity of protochlorophyll regeneration during a dark period depends on the length of a previous light period but is hardly affected by the light intensity. At high intensity light the rate of protochlorophyll regeneration, which also depends on the length of the foregoing irradiation, is lower than that at low intensity light only during the first 1.5h of the light period. It is concluded that high intensity red light inhibits chlorophyll accumulation mainly by photo‐bleaching of chlorophyll. The after‐effect is the result of a photooxidation which may lead to photo‐bleaching of newly formed chlorophyll in relatively low intensity light.

Photoinhibition of chlorophyll accumulation is accompanied by a disturbed development of etioplasts into chloroplasts.
THE FUNCTION OF PHYTOCHROME IN THE NATURAL ENVIRONMENT—I. CHARACTERIZATION OF DAYLIGHT FOR STUDIES IN PHOTOMORPHOGENESIS AND PHOTOPERIODISM
Authors: Holmes M. G. , Smith Harry
Published: January 2008

Abstract— The daily changes in spectral energy distribution of natural daylight, with special reference to the red and far‐red wayelength bands, are outlined. The effects of solar elevation and sky condition are described. The changes in the proportions of red and far‐red radiation in daylight which occur at sunrise and sunset are discussed in relation to the possible function of phytochrome in photoperiodic timing.
THE FUNCTION OF PHYTOCHROME IN THE NATURAL ENVIRONMENT—III. MEASUREMENT AND CALCULATION OF PHYTOCHROME PHOTOEQUILIBRIA
Authors: Smth Harry , Holmes M. G.
Published: January 2008

Abstract— Phytochrome photoequilibria have been measured in dark‐grown Phaseolus uulgaris L. and Cucurbita pepo I. hypocotyl hooks which had been exposed to various natural and artificial radiation sources. Mean phytochrome photoequilibria (φ) varied from 0.20 within a wheat canopy to 0.54 above, although lower values were occasionally observed in densely shaded areas. Greater variation in phyto chrome photoequilibria and lower levels of Pfr were recorded within a sugar beet canopy. The range of photoequilibria was φ= 0.04 in dense shade to φ= 0.54 above the canopy. Photoequilibrium was achieved within 5 s in mid‐day sunlight and approximately 30 s in dense canopy shade.

A close correlation was found between φ and the ratio of the quantum flux in the red and far‐red wavelength bands (ζ) in broad spectrum (400–800 nm) radiation. This relationship allows direct prediction of φ from a knowledge of ζ. Phytochrome showed greatest sensitivity to spectral changes in the range ζ= zero to ζ= 1.0, which is the range found in the natural environment.

The observations provide support for the hypothesis that phytochrome is involved in the detection of shading by plants.
PROTONATION AND DEPROTONATION EQUILIBRIA OF LUMICHROME
Authors: Laser N. , Feitelson J.
Published: January 2008

Abstract— In order to investigate the possibility of the tautomerization of alloxazine to isolloxazine in its ground state, the parameters affecting the redistribution of charges in the lumichrome molecule were studied. The absorption and emission spectra of lumichrome as a function of pH in the range H0= ‐ 6 to pH = 12 were recorded. At extreme pH conditions the spectra of lumichrome are similar to those of the isoalloxazine system. At high acid concentration (H0 < ‐ 3.0) the absorption spectrum of lumichrome protonated at N10, is practically identical to that of lumiflavin. The fluorescence quantum yield of the two cations is negligible at room temperature.

At pH = 10.5 lumichrome is deprotonated at positions N1 or N3, The two monoanions have different excitation spectra. Except for slight differences in the extinction coefficients, the absorption of the anion deprotonated at N3 is very similar to the lumichrome spectrum. The absorption spectra of the N1 monoanion and of the di‐anion are similar to the spectrum of lumiflavin except for a blue shift of about 20 nm. Furthermore, the emission spectrum of the N1 ‐monoanion is identical to that of the isoalloxazine system. These results indicate that the charge distribution in the lumichrome molecule depends on the protonation and deprotonation of the nitrogen atoms at positions 10 and l. Both processes cause a redistribution of charges so that an isoalloxazine ring system is formed.
THE EOSIN‐SENSITIZED PHOTOOXIDATION OF SUBSTITUTED PHENYLALANINES AND TYROSINES*
Authors: Rizzuto Frank , Spikes John D.
Published: January 2008

Abstract— The eosin‐sensitized photooxidation of tyrosine and a number of compounds related to tyrosine (substituted phenylalanines) was studied by steady‐state kinetic and flash photolysis techniques. In particular, the role of the phenolic group and the amino and carboxyl groups of the alanyl side chain in the photooxidation mechanism was investigated in detail. Several relationships between substrate structure and susceptibility to photooxidation as well as effects of substrate structure on photooxidation mechanisms were found.

For example, phenylalanine is not photooxidizable, hut substitution of electron‐donating (activating) groups such as‐OH (as in tyrosine) or‐NH2 (as in p‐aminophenylalanine) results in rapidly photooxidized derivatives. However, substituting deactivating groups such as—C1 (as in p‐chlorophenylalanine) or weakly activating groups such as ‐ OCH3 (as in 4‐methoxyphenylalanine) result in non‐photooxidiz‐able derivatives. Substitution of additional activating groups to the ring of hydroxy‐substituted phenylalanines results in increased rates of photooxidation, whereas additional deactivating groups result in decreased photooxidation rates.

The rate‐determining step in the photooxidation mechanism is shown to be dependent on the presence and position of an electron‐donating substituent on the benzenoid ring. Only minor involvement of the side chain amino and carboxyl groups was found. Both singlet oxygen and hydrogen abstraction mechanisms are involved in the eosin‐sensitized photooxidation of hydroxy‐substituted phenylalanines (e.g. tyrosine). The hydrogen abstraction mechanism probably predominates at both pH 8 and 11.
PHOTOPHYSICAL PROPERTIES OF PHYCOBILIPROTEINS FROM PHYCOBILISOMES: FLUORESCENCE LIFETIMES, QUANTUM YIELDS, AND POLARIZATION SPECTRA
Authors: Grabowski Jozef , Gantt Elisabeth
Published: January 2008

Abstract— Absorption and fluorescence polarization spectra, as well as absolute fluorescence quantum yields, and lifetimes of phycobiliproteins separated from intact phycobilisomes of Porphyridium cruentum, Nostoc sp. and Fremyella diplosiphon were measured. Two different types of phycoerythrin, in addition to phycocyanin and allophycocyanin, were separated from both Porphyridium cruentum and Nostoc sp. phycobilisomes. They were distinguishable by the shape of their absorption spectra, values of fluorescence quantum yields and their limiting polarization. Phycobilisomes of Fremyella diplosiphon had a type of phycoerythrin that was different from the above kinds. By the use of fluorescence quantum yields and lifetime data, the values of natural lifetimes, the decadic molar extinction coefficients, as well as Förster's critical distances R0 for excitation energy transfer, between phycobiliproteins in phycobilisomes, were estimated. The values obtained of Förster's critical distances indicate that for most efficient energy transfer from phycoerythrin to allophycocyanin, the outer layers of Porphyridium cruentum and Nostoc sp. phycobilisomes should be composed of bangiophycean, phycoerythrin and cyanophytan phycoerythrin‐II respectively.
OXYGEN‐INTERACTION LUMINESCENCE SPECTROSCOPY*
Authors: Khalil Gamal‐Eddin , Kasha Michael
Published: January 2008

Abstract— A new spectroscopic method has been developed in our laboratory for perturbation of singlet‐triplet transitions in organic molecules by O2. A dilute solution (10‐2‐10‐4M) of the molecule to be studied in various solvents is pressurized in a bomb with O2 at 100 atm (10MPa) for 3–10h. The pressure is released, the solution pipetted into a sample tube, sealed, and frozen to a rigid glass state at 77 K. Then the luminescence spectra and excitation spectra of the sample are scanned.

For benzene‐O2 we have evidence for a weak complex with a mild perturbation and a strong complex, with various new combination states. For the strong complex, the T1→ S emission and excitation spectrum is observed, and also the T2← S excitation spectrum. The T1→ S emission for the benzene‐O2 complex is seen as a highly resolved emission at 77 K in the glass solvent, but also at 298 K as a poorly resolved emission (induced triplet–triplet fluorescence in the complex). Various upconversion simultaneous transitions and downconversion simultaneous transitions are observed, e.g. (3Blu+1Σ+g), (3Blu+1Δg) upconversions, and the (3Blu+1Σ+g), (3Blu+1Δg) downconversions; thus, in the latter, the third π, π* triplet is revealed for the first time. A novel structure for the benzene–O2 strong complex is proposed as an anf jamel model.

For pyridine–O2 and perdeuteropyridine–O2 we observe the T1→ S emission for the first time; it is π, π* in character, analogous to benzene.
CHEMILUMINESCENCE AND THE FORMATION OF SINGLET OXYGEN IN THE OXIDATION OF CERTAIN POLYPHENOLS AND QUINONES
Authors: Slawinska Danuta
Published: January 2008

Abstract— The possibility of 1O2 (1Δg) participation in the oxidation of polyphenols and quinones has been investigated in two systems: (1) the system involving autooxidation leading to oxidative polymerization and destruction, and (2) the modified Trautz‐Schorigin reaction, i.e. oxidation of polyphenols and HCHO with H2O2 in concentrated alkaline solutions. The red band with maximum at 635 nm observed in chemiluminescence of pyrocatechol, adrenaline, pyrogallol, gallic acid, adrenochrome and p‐benzoquinone corresponds to the transition 2O2(1Δg) → 2O2(3Σ‐g). Emission bands in the range 475–540 nm arise from the superposition of the 2O2(1Δg) → 2O2(3Σ‐g) transition and radiative deactivation of excited oxidation products. In system (2) chemiluminescence has a broad band from 580 nm beyond 800 nm and much higher intensity than in system (1). Formaldehyde was found to enhance light emission in system (1) by a factor of about 30. The influence of solvents, including D2O in which 1O2 has varying lifetimes, on kinetics of chemiluminescence as well as quenching effect of β‐carotene, hydroquinone, cysteine, bilirubin and biliverdin strongly support the involvement of 1O2 in the chemiluminescence of both systems.
DETECTION OF OXYGEN RADICALS IN BIOLOGICAL REACTIONS
Authors: Bors Wolf , Saran Manfred , Lengfelder Edmund , Michel Christa , Fuchs Christine , Frenzel Christine
Published: January 2008

Abstract— Recent data are presented on the mechanisms or selected assay procedures for superoxide anions (O2‐) and hydroxyl radicals (OH). The systems discussed include the autoxidation of adrenalin to adrenochrome and other indole compounds, the oxidation of hydroxylamine to nitrite, the generation of ethylene from methional, and the scavenging of OH radicals by p‐nitroso‐dimethylaniline. The results are compared with other assay procedures to aid in the search for absolute and specific tests for these oxygen radicals. Particular emphasis is placed on the interrelation of 02‐ OH and hydrogen peroxide.
THE INVOLVEMENT OF1O2 IN THE INACTIVATION OF MIXED FUNCTION OXIDASE AND PEROXIDATION OF MEMBRANE LIPIDS DURING THE PHOTOSENSITIZED OXIDATION OF LIVER MICROSOMES
Authors: Rahimtula Anver D. , Hawco Fred J. , O'Brien Peter J.
Published: January 2008

Abstract— Dye sensitized photooxidation of rat liver microsomes results in inactivation of mixed function oxidase and peroxidation of the membrane lipids. Both the flavoenzyme NADPH: cytochrome P450 reductase and cytochrome P450 components of the mixed function oxidase were inactivated. Singlet oxygen was responsible for these effects as the inactivation was markedly enhanced if the microsomes were in D2O buffer during the irradiation. Singlet oxygen quenchers or traps also protected the microsomes against enzyme inactivation and lipid peroxidation. Antioxidants, whilst preventing the lipid peroxidation, did not protect cytochrome P450 from inactivation which suggests that lipid peroxidation was not responsible for cytochrome P450 inactivation.
THE OXIDATION OF ASCORBATE BY ELECTRON AFFINIC DRUGS AND CARCINOGENS
Authors: Biaglow John E. , Jacobson Birgit , Varnes Marie , Koch Cameron
Published: January 2008

Abstract— The nitrobenzenes, the carcinogens 4‐nitropyridine‐N‐oxide and 4‐nitro‐quinoline‐N‐oxide as well as the nitrofurans, also known to be carcinogenic, have been found to enhance the reaction of ascorbate with oxygen. The reaction results in the oxidation of ascorbate, the production of dehydroascorbate, superoxide radical, peroxide and water. The drugs are not reduced to stable intermediates during the oxidation but are recycled to their original state. The oxygen consumption is partially inhibited by either superoxide dismutase or catalase. If both superoxide dismutase and catalase are included in the reaction mixture, total oxygen consumption was equal to the amount expected for oxidation of ascorbate to dehydroascorbate and reduction of oxygen to water. The oxygen consumption was inhibited by ferricytochrome c. Semiquinones, nitro and hydroxylamine radicals, produced by electron transfer from ascorbate, reduce ferricytochrome c. These oxygen reactive radicals are responsible for the stimulation of oxygen utilization and ascorbate oxidation. In addition we have found that Ehrlich cells, containing catalase and superoxide dismutase, inhibit the drug catalyzed oxidation of ascorbate. The presence of cyanide, known to inhibit catalase and superoxide dismutase, abolished the cell effect for most of the drugs tested.
CYTOTOXIC REACTIONS OF FREE RADICAL SPECIES OF OXYGEN*
Authors: Borg Donald C. , Schaich K. M. , Jr J. J. Elmore , Bell J. A.
Published: January 2008

Abstract— We report on autooxidation reactions related to selective cell killing in vivo and present oxygen uptake and EPR data on the molecular nature of these changes, with a note on a reaction used to test for singlet oxygen.

Selective obliteration by 6‐hydroxydopamine, 6‐aminodopamine and their congeners of beta‐adrenergic cell receptors and of adrenergic and dopaminergic neurons in vivo and in vitro have been reported recently. These effects devolve from autoxidation of the compounds in situ after appropriate biological concentration, but it is unclear whether cytotoxicity is mediated by the reactive oxygen species themselves or by nucleophilic reactions of the product quinones. Because of the possibility of harnessing these reactions for a generalized “chemical surgery” if the former mechanism is operative, and because many other oxidative damage reactions involving unsaturated lipids of biomembranes seem to share similar autoxidative initiating and chain‐carrying steps, we have studied the autoxidation of ascorbate and other reductants catalyzed by polyhydroxy quinols related to 6‐hydroxydopamine. We find that superoxide anion mediation may or may not be important, depending on redox potentials and reaction kinetics of particular compounds. To the extent that the cellular toxicity of these compounds is oxidative in nature, it is facilitated by—and may depend upon—hydroxyl radical production due to Fenton‐type reactions. Likely Fenton reactants in vivo are hydrogen peroxide produced from the quinol‐catalyzed autoxidations and non‐heme iron reduced cyclically by superoxide anions from the same autoxidations.

Studies using flow systems adapted for EPR at 35 GHz have provided support for some of the reaction mechanisms proposed. In nonaqueous solvents eerie oxidation produced transient free radicals from hydrophobic diphenyl and isobenzo furans, which are often cited as “specific” probes for singlet oxygen detection in biochemistry.
DIFFERENTIAL CAUSES OF MUTATION AND KILLING IN ESCHERICHIA COLI AFTER PSORALEN PLUS LIGHT TREATMENT: MONOADDUCTS AND CROSS‐LINKS
Authors: Seki Takaharu , Nozu Keiichi , KONDO Sohei
Published: January 2008

Abstract— On treatment with 8‐methoxypsoralen plus near UV light, an excisionless (uvrB‐) strain of Escherichia coli showed about 3– and 10 times higher sensitivities to killing and mutation, respectively, than its parental strain. On re‐irradiation with near UV in the absence of unbound psoralen, the uvrB‐ strain pretreated with psoralen plus near UV showed a decrease in both survival and mutation. After treatment with psoralen plus near UV, re‐irradiation of T7 DNA in the absence of unbound psoralen caused an increase in the cross‐linked fraction with an equivalent decrease in the non‐cross‐linked fraction. From these and previous results, we conclude that monoadducts produced by treatment with psoralen plus near UV are converted to cross‐links by further irradiation and that, in E. coli, monoadducts are responsible for the mutation induced by psoralen‐plus‐light whereas cross‐links are the major cause of its lethal action.
CONTROL OF CHLOROPHYLL b BIOSYNTHESIS BY PHYTOCHROME
Authors: Oelze‐Karow H. , Mom H.
Published: January 2008

In the mustard seedling cotyledons, chlorophyll b appears from the very beginning in white light provided that a red light pulse pretreatment was given 12 h prior to the onset of white light. The red light pulses act through phytochrome. Without pretreatment no chlorophyll b is detectable at least during the first 60 min after the onset of white light (25°C). Biogenesis of chlorophyll b specifically depends on the action of phytochrome during the pre‐steady state period as well as during the steady state period of chlorophyll accumulation. In light pulse experiments, it was found that formation of chlorophyll b takes place stoichiometrically at the cost of chlorophyll(ide) a.
BIOSYNTHETIC PATHWAYS TO 6‐AMINOLEVULINIC ACID INDUCED BY BLUE LIGHT IN THE PIGMENT MUTANT C‐2A‘ OF SCENEDESMUS OBLIQUUS*
Authors: Klein Otto , Senger Horst
Published: January 2008

The X‐ray induced mutant C‐2A of Scenedesmus obliquus grows heterotrophically but forms only traces of chlorophyll in the dark. Upon illumination, baminolevulinic acid (ALA) is synthesized and chlorophyll is formed. These processes are blue light dependent and cease immediately when the cells are transferred back into darkness.

Addition of levulinic acid (LA) inhibits the light‐dependent formation of chlorophyll and causes accumulation of ALA by competitive inhibition of the ALA dehydratase (EC. 4.2.1.24). By feeding specifically labelled 14C precursors to the pigment mutant, inhibiting the ALA dehydratase with LA, accumulating, extracting and analyzing the ALA, two pathways leading towards ALA could be established: glycine and succinyl CoA can be condensed to ALA and the 5 carbon skeleton of glutamate can completely be incorporated into ALA via a second pathway.

The glycine‐succinyl CoA pathway dominates over the glutamate pathway, but both lead to chlorophyll formation.
PHYTOCHROME AND EFFECTS OF SHADING ON GROWTH OF WOODLAND PLANTS
Authors: Frankland B. , Letendre R. J.
Published: January 2008

qrowth of Circaea lutetiaim plants was studied in various locations in or near a mixed deciduous woodland. Morphological changes resulting from increased shading included increases in leaf area ratio, specific leaf area and specific water content. Parallel measurements with a spectroradi‐ometer confirmed that shading involved a reduction in both light fluence rate and light quality (e.g. red/far‐red ratio). Phytochrome Pfr/P status was also studied by spectrophotometric measurements on Avena seedling test material and by biological (Lactuca seed germination) assay. Attempts were made to demonstrate phytochrome controlled changes in plant morphology under controlled environment, using both end‐of‐day far‐red treatment and far‐red enrichment of the main light period. Effects of natural shading were most clearly simulated by varying light fluence rate while maintaining a constant but high red/far‐red ratio
PHYTOCHROME CONTROL OF THE DEVELOPMENT OF PHOTOPHOSPHORYLATION
Authors: Oelze‐Karow H. , Mom H.
Published: January 2008

In the cotyledons of the mustard (Sinapis ah L.) seedling the development of the capacity for photophosphorylation is strongly influenced by pretreatment of the seedling with red light pulses. The red light acts through phytochrome. After a red light pretreatment the capacity for photophosphorylation increases linearly with the chlorophyll content, at least up to 30 min after the onset of continuous white light. It is proposed that the reaction chain required for photophosphorylation is completed under the influence of phytochrome even in the absence of chlorophyll. As soon as chlorophyll becomes available photophosphorylation functions instantaneously. Without a red light pretreatment there is a lag of more than 15 min before photophosphorylation becomes detectable after the onset of continuous white light even though chlorophyll a is available. Although phytochrome strongly influences the rate of chlorophyll accumulation as well it is improbable that the control by phytochrome of development of photophosphorylation and of chlorophyll accumulation are causally connected.
UV INACTIVATION OF ENZYMES IN SUPRAMOLECULAR COMPLEXES OF BIOLOGICAL MEMBRANES. THE PHENOMENON OF PHOTOCHEMICAL ALLOTOPY
Authors: Konev S. V. , Volotovskij I. D. , Sheiko L. M.
Published: January 2008

Abstract. The photosensitivity of erythrocyte acetylcholinesterase (AChE) is different in its free and membrane‐bound states. The modification of the structure of membraneous lipids by phospholipases A2, C and D or by cholesterol depletion is accompanied by a change in AChE photosensitivity. UV light was demonstrated to induce cooperative structural transitions in the erythrocyte membrane. This follows from the data obtained by circular dichroism and solubilization in detergents. In contrast to free AChE, UV light acts on the membraneous enzyme as a mixed inhibitor (simultaneous change in Vmax and Km). The anomalous behaviour of membrane‐bound enzyme, termed the phenomenon of photochemical allotopy, is associated with a modification of the structure within the microenviron‐ment of the residual AChE. The phenomenon depends on membrane integrity, and disappears after treatment of erythrocyte ghosts with ultrasound, trypsin, phospholipases and neuraminidase and remains unchanged in cholesterol‐depleted membranes. The nature and localization of events responsible for this phenomenon are discussed.
PHOTOREACTIVATION OF RNA IN UV‐IRRADIATED INSECT EGGS (SMITTIA SP., CHIRONOMIDAE, DIPTERA) I. PHOTOSENSITIZED PRODUCTION AND LIGHT‐DEPENDENT DISAPPEARANCE OF PYRIMIDINE DIMERS*
Authors: Jäckle Herbert , Kalthoff Klaus
Published: January 2008

Abstract. Irradiation of Smittia eggs with UV during intravitelline cleavage causes the formation of pyrimidine dimers in the (largely ribosomal) RNA of the eggs. The yield of dimers is wavelength‐dependent in a way that strongly suggests the involvement of photosensitizing egg components. Illumination of UV‐irradiated eggs with light (380 or 400 nm) causes both photoreactivation of the eggs and mono‐merization of the pyrimidine dimers in their RNA. The photoreactivable sector of the biological damage is correlated with the amount of pyrimidine dimers present in the RNA after inactivation of the eggs with UV of different wavelengths. The data are regarded as the first direct evidence that the photoreactivation of a eukaryotic organism is correlated with the light‐dependent (and apparently enzymatic) monomerization of pyrimidine dimers in RNA.
ACTION SPECTRUM FOR OXYGEN‐DEPENDENT NEAR‐ULTRAVIOLET INDUCED CORNEAL DAMAGE*
Authors: Kurtin William E. , Zuclich Joseph A.
Published: January 2008

Abstract. An action spectrum for oxygen‐dependent corneal epithelial damage in the rhesus monkey is reported for the near UV wavelength range. The corneal threshold increases monotonically with wavelength throughout the near UV but exhibits a pronounced shoulder in the 340–350 nm region. This behavior is consistent with studies of effects of near UV radiation on bacterial cells. However, the work reported here is unique in that it examines the nature of near UV induced photochemical processes in mammalian cells in situ.
MYCOCHROME SYSTEM AND CONIDIAL DEVELOPMENT IN CERTAIN FUNGI IMPERFECTI
Authors: Kumagai Tadashi
Published: January 2008

Abstract. A photoreceptor system, “mycochrome”, is involved in a blue and near UV reversible photo‐reaction which in turn plays an important role in the photocontrol of conidial development in Alternaria tomato, Botrytis cinerea and Helminthosporium oryzae. Conidial development was controlled by alternating exposures to blue and near UV light with the final response being determined by the final light received. When the final light was near UV a conidium developed; when it was blue, conidiation was inhibited and a “sterile” conidiophore was formed. The effects of the two lights were alternatively reversible.

Blue and near UV reversible photoreaction was also found in a light‐minus‐dark difference spectrum of an intracellular particulate fraction isolated from dark‐grown mycelia of A. tomato, and two pigments, PB (blue absorbing type) and PNUV (near UV absorbing type), were contained in that photoreaction. PB was tightly bound to the particulate fraction and PNUV was either soluble in the cytoplasm or very loosely bound to the particulate fraction. Blue and near UV reversible photoreaction occurred only under the coexistence of PB and PNUV. That is, a dip in the near UV region and peak absorbance in the blue region was induced by irradiation with near UV light; however, both conditions were partially dissipated with a subsequent irradiation of blue light. These absorbance changes were revers‐ibly repeated by alternating doses of blue and near UV light. When molecular oxygen was introduced after exposure to near UV light, peak absorbance in the blue region rapidly disappeared, and these absorbance changes were repeatedly reversible. Similar results were obtained by treatment with sodium hydrosulfite and molecular oxygen.

Thus, it was concluded that the mycochrome system suggested in photo‐conidiation was consistent with certain active substances showing blue and near UV reversible absorbance changes and caused by photooxidation reduction reaction.
A PULSED LASER SYSTEM FOR THE STUDY OF MICRO‐SECOND DELAYED FLUORESCENCE FROM PLANTS
Authors: Groves Michael R.
Published: January 2008

Abstract—A new laser system is designed for the investigation of m̈S delayed fluorescence. This is intended to overcome some undesirable features present in other current designs, such as low actinic light fluxes and long illumination times, or slow responses owing to long turn‐off times of the stimulation source and the presence of fluorescence artifacts.

The system uses a pulsed argon‐ion laser and bears little resemblance to either the modified Becquerel phosphoroscope used by Lavorel (1971) or to those systems requiring shutters. Cheapness of design together with the ability to adjust such parameters as pulse duration easily, make this design attractive to most laboratories in which short (10 μs) high intensity (105 W m‐2) pulses with rapid (1.5 μs) turn‐off times and high on‐to‐off contrast ratios (106:1) are required.

Certain design criteria are strictly imposed in order to produce kinetic data that can be meaningfully analysed.
PHOTOSENSITIZATION OF AMINO ACIDS BY DI‐CYAN‐HEMIN: KINETIC AND EPR STUDIES
Authors: Cannistraro Salvatore , Jori Giulio , Van de Vorst Albert
Published: January 2008

Abstract— The low spin hemin derivative di‐cyan‐hemin can sensitize the photooxidation of amino acids. The efficiency of this dye as a photosensitizer is generally lower than that of other porphyrins such as hematoporphyrin in aqueous solution, but it is significantly enhanced by addition of ethanol. On the basis of the identified photooxidation end‐products of some amino acids, photooxidation kinetic data and EPR measurements, it appears that methionine is quantitatively converted to methionine sulfoxide by a pure Type II (singlet oxygen) mechanism, whereas in the case of cysteine and tryptophan a mixed Type ILType II mechanism is probably operative.
PHOTOCHEMISTRY OF THE BISBENZIMIDAZOLE DYE 33258 HOECHST WITH BROMODEOXYURIDINE AND ITS BIOLOGICAL EFFECTS ON BrdUrd‐SUBSTITUTED ESCHERICHIA COLI
Authors: Ben‐Hur E. , Prager A. , Riklis E.
Published: January 2008

Abstract— Exposure of BrdUrd‐substituted E. coli cells to 360 nm light in the presence of the bisbenzimi‐dazole dye 33258 Hoechst increases their sensitivity dramatically. Mutant cells deficient in excision repair of DNA damage (uur B) are more sensitive than wild type cells, indicating that the cells are able to repair this type of damage. However, they perform only a limited amount of liquid holding recovery (LHR). Exposure of the dye with BrdUrd to near UV light in solution results in the appearance of two BrdUrd derived photoproducts. One appears to be deoxyuridine, and the other — an adduct of BrdUrd‐dye. The adduct is acid labile and as a result only uracil is observed in acid‐hydrolyzates of DNA after exposure of BrdUrd‐substituted cells to 360 nm light in the presence of 33258 Hoechst. The production of uracil is linearly dependent on light exposure. Cells in which 85% of thymidine was replaced by BrdUrd are unable to remove more than 5–10% of uracil from their DNA during postirradiation incubation. However, when only 4% of thymidine is replaced, about 50% of the uracil is removed during 30min incubation after exposure. The results are consistent with our previous work, indicating that BrdUrd interferes with repair via excision‐resynthesis. A working hypothesis is suggested to explain this interference.
THERMODYNAMIC AND KINETIC LIMITATIONS ON THE CONVERSION OF SOLAR ENERGY INTO STORABLE CHEMICAL FREE‐ENERGY
Authors: Almgren Mats
Published: January 2008

Abstract— Energy‐storing reactions in a system after light excitation transform the system into a thermo‐dynamically metastable state. The effects of the microreversible back‐reaction on the net yield of the storage process and on the stability of the products are discussed. It is shown that the inevitable losses of photon energy in the conversion process may be estimated and considered as roughly independent of the threshold frequency of the system. The best attainable conversion efficiency as a function of the threshold absorption wavelength may then be estimated. Rough calculations show an ultimate efficiency of about 20% with the optimum threshold wavelength in the range 600–800 nm.

Photochemical production of fuel, like hydrogen from water, requires that more than one photon of the solar spectrum is used per product molecule formed. The low photon density of sunlight leads to troublesome stability requirements on the intermediates in the reaction mechanism. Some features of consecutive two‐photon mechanisms in organized systems and homogenous solutions are discussed.
PHOTOLYSIS AND HYDROLYSIS OF ADENOSINE 5‘‐PHOSPHATES
Authors: Goossen J. T. H. , Kloosterboer J. G.
Published: January 2008

Abstract— Mild acid hydrolysis of adenosine 5′‐di‐, tri‐ and tetra‐phosphate (ADP, ATP and ADTP) occurs predominantly in the side chain, yielding orthophosphate and adenosine 5′‐mono‐phosphate (AMP). Photolysis results in breaking of the 5′‐C—O—P bond, yielding orthophosphate for AMP and mainly condensed phosphates for ADP, ATP and ADTP, together with decomposition products of adenosine. The photolytic breaking of the 5′‐C—O—P bond is not enhanced by excitation of the strongly absorbing adenine ring followed by energy transfer but results from direct excitation of the very weakly absorbing ribosephosphate‐ moiety of the molecule. The arguments for this are: (i) cyclic adenosine 3'5′‐mono‐phosphate, which is sterically hindered for direct energy transfer from the adenine ring to the phosphate‐ester bond, is photolyzed at approximately the same rate as AMP, and (ii) the rate of disappearance of the strong absorption band due to the adenine ring is higher than the rate of liberation of orthophosphate.
AN INVESTIGATION OF RETINAL AS A SOURCE OF SINGLET OXYGEN
Authors: Delmelle M.
Published: January 2008

Abstract— All‐trans retinal is dissolved in alcohols and illuminated at 365 nm in the presence of a singlet oxygen acceptor, 2,5‐dimethylfuran. Illumination produces the photosensitized oxidation of the acceptor which is measured by the disappearance of its 215 nm absorption band. A kinetic study is carried out and βDMF is 1.6 × 10‐‐4M. The quantum yield of 1O2 production from the light‐excited retinal is estimated to 0.096. The retinal sensitized photooxidation of dimethylfuran is inhibited by a 1O2 quencher, 1,4‐diazabicyclo(2,2,2)‐octane, and enhanced by deuteration of the solvent. Deuterated solvents are known to increase 1O2 lifetime.

The production of 1O2 from retinal is briefly discussed in relation to the damage which may be induced by light in the visual cells.
IRRADIATION‐ENHANCED PHYTOCHROME PELLETABILITY IN AVENA: PIGMENT RELEASE BY Mg2+‐GRADIENT ELUTION
Authors: Quail Peter H.
Published: January 2008

Abstract— Gradient elution is used to facilitate controlled withdrawal of Mg2+ from phytochrome‐rich particulate fractions from irradiated Avena sativa L. shoots. The bound pigment from red‐irradiated tissue is released in a discrete band when the Mg2+ falls to just below 1 mM. This phytochrome has an apparent molecular weight of ˜300 kilodaltons upon gel filtration, indistinguishable from that of the unbound pigment in the same extract and from that in the 50,000 × g supernatant from non‐irradiated Avena. This indicates that the bound phytochrome is released as a soluble molecule at a Mg2+ concentration above that which permits release of the particulate binding partner from other particulate components. These findings appear to preclude the possibility that the phytochrome‐binding partner association can be selectively preserved at a Mg2+ level that would permit separation and analysis of phytochrome‐bearing particles without the complication of Mg2+‐induced membrane and RNP aggregation. “Cycled” Pfr (that from tissue irradiated with a red‐far red sequence prior to homogenization) is released at 0.1 to 0.2 mM Mg2+. This indicates that “cycled Pr is more tenaciously bound by the particulate fraction than is Pfr. This effect is photoreversible both by further in vivo and subsequent in vitro irradiations, suggesting that the state of the pigment, rather than of the binding partner, directly controls the tenacity of the interaction. Increasing concentrations of KCl release the pigment from the particulate fraction in the presence of 10 mM Mg2+; increasing Triton X100 concentrations do not. This confirms the ionic nature of the pigment‐particulate fraction interaction and indicates strongly that the phytochrome is located external to any membrane vesicles present (although not necessarily that it is bound directly to such vesicles). The data further suggest that phospholipid polar head groups are not primarily responsible for the binding.
TRANSFER OF EXCITATION ENERGY BETWEEN PORPHYRIN CENTERS OF A COVALENTLY‐LINKED DIMER*
Authors: Anton John A. , Loach Paul A. , Govindjee
Published: January 2008

Abstract— Three covalently‐linked porphyrin hybrid dimers were synthesized, each containing a metallotetraarylporphyrin [Zn(II), Cu(II), or Ni(II)], and a free base tetraarylporphyrin. Transfer of singlet excitation energy from the metalloporphyrin center to the free base porphyrin center was determined by measuring fluorescence properties. The Zn hybrid dimer displayed excellent intramolecular transfer of energy ( 85%) from the excited singlet state of the Zn(II) chromophore to the free base chromophore. No evidence for such transfer of the excited singlet state energy was found in the Ni(II) or Cu(II) analogues. From our experimental data, the fluorescence quantum yield of the Zn hybrid dimer was the same as for the free base monomer porphyrin (0.11; Seybold and Gouterman, 1969). Thus, the covalent attachment of another fluorescent porphyrin center effectively doubled the antenna size without decreasing the quantum yield even though the fluorescence quantum yield of the Zn(II) containing monomer was substantially less (0.03, according to Seybold and Gouterman, 1969) than that of the free base porphyrin.

The donor‐acceptor distance and the rate constant for energy transfer were calculated using the Forster equation. Assuming random orientation, a donor‐acceptor distance of 15 Å was calculated with an associated rate constant (kci) for energy transfer of 1.9 ± 109 s–1.
MODELS FOR BACTERIAL PHOTOSYNTHESIS: ELECTRON TRANSFER FROM PHOTOEXCITED SINGLET BACTERIOPHEOPHYTIN TO METHYL VIOLOGEN AND m‐DINITROBENZENE
Authors: Holten Dewey , Windsor Maurice W. , Parson William W. , Gouterman Martin
Published: January 2008

Abstract. As a model for the primary reactions of photosynthesis, we studied photochemical electron transfer from bacteriopheophytin (BPh) to methyl viologen (MVC12) and to m‐dinitrobenzene (m‐DNB) in solution. Both MVC12 and m‐DNB cause reductions in the lifetime of the first excited singlet state of BPh (BPh*), in the fluorescence quantum yield, and in the quantum yield of the triplet state, BPh +. The quenching of BPh* probably results from electron transfer, which generates short‐lived radical pairs involving the BPh radical cation (BPh+) and the reduced form of the quencher. Electron transfer from BPh* is thermodynamically favorable, but that from BPhT is not. From the magnitude of the quenching, we calculate rate constants for electron transfer in collision complexes formed between BPh* and MVC12 or m‐DNB. Measurements of the quantum yield of the free BPh+ radical indicate that about 3/4 of the [BPh+ MV+] radical pairs decay by reverse electron transfer, rather than dissociating to give the free radicals. Essentially all of the [BPh+m‐DNB +] radical pairs must decay by reverse electron transfer, because free BPh+ cannot be detected in this case. From these data, we estimate the rate constants for the reverse electron transfer reactions. The higher probability of dissociation in the [BPh+ MV+] radical pair can be explained by coulombic repulsion.

The rate of the primary electron transfer reaction in photosynthetic bacteria is comparable to that of forward electron transfer in the BPh* collision complexes. Reverse electron transfer, however, is at least 103‐times slower in the radical pair formed in the bacterial reaction center than it is in [BPh+m‐DNB−], and more than 104‐times slower than in [BPh+ MV+]. The explanation for this dramatic and crucially important difference remains unclear, but several possibilities are discussed.
ELECTRIC LINEAR DICHROISM OF P700 CHLOROPHYLL U‐PROTEIN COMPLEXES
Authors: Gagliano A. G. , Geacintov N. E. , Breton J. , Acker S. , Remy R.
Published: January 2008

Abstract— The P700 chlorophyll a‐protein complex (CPI) isolated from green plants was oriented in aqueous solutions using pulsed electric fields of up to 6700 V cm‐1. The electric linear dichroism spectrum is reported in the range of 400–720nm. Positive peaks in the linear dichroism ΔA=AI‐ A1 (where AI and A1 are the absorbance components in which the polarizer orientation is parallel and perpendicular with respect to the electric field. respectively) are observed at 443 and 686 nm. The ΔA signal at 686 nm is discussed in terms of either a specialized chlorophyll form absorbing at 686 nm. or due to an exciton component absorbing at the same wavelength.
EXCITED SINGLET AND TRIPLET PRODUCTS GENERATED FROM OXIDATION OF THE ‐CO‐CH‐ CONTAINING MOLECULES
Authors: Kamiya Isao , Sugimoto Takashi
Published: January 2008

Abstract— In a previous study. we found indirect chemiluminescence from air oxidation of various simple ketones in alkaline aprotic solvents containing 9,10‐diphenylanthracene and 9,10‐dibromoanthracene. By summarizing the experimental results. it was concluded that excited products. mainly in the triplet state. were generated from air oxidation of those simple compounds having a ‐CO‐CH‐group via dioxetane intermediates.

Recently. we have succeeded in observing an intense direct chemiluminescence due to the generation of the excited singlet product by the air oxidation of such anthracene derivatives having a ‐CO‐CH‐group as 9,10‐diisobutyrylanthracene and related compounds. The finding lends strong support to the hypothesis that dioxetane or dioxetanone may be the critical intermediate to give fluorescent singlet products.
ON THE FORMATION AND REACTIVITY OF DIOXIRANE INTERMEDIATES IN THE REACTION OF PEROXOANIONS WITH ORGANIC SUBSTRATES*
Authors: Edwards John O. , Pater Ruth H. , Curclf Ruggero , Furia Fulvio Di
Published: January 2008

Abstract— Kinetics and 18O‐labeling studies have provided evidence for the involvement of dioxirane intermediates (V) in the ketone‐catalysed decomposition of peroxomonosulfate (Caroate) HSO;. Reaction rates depend on ketone structure. In competition with catalysis of peroxide decomposition, the dioxirane intermediate is capable of oxidizing several organic and inorganic substrates. Thus, cis‐ and rrans‐cinnammic acids could be converted stereospecifically into the corresponding epoxides. Also, oxidation of phenylpropiolic acid, a substrate which is representative of weakly nucleophilic alkynes, could be carried out using the Caroatehetone oxidizing system. Under the conditions adopted, no oxidation of the substrates examined was found to occur in the absence of ketone. The possibility that formation of dioxathiirane intermediates (XXII) occurs following a side pathway in the reaction of Caroate with sulfoxides (which produces sulfones in high yield) has been explored. Preliminary experiments using 18O‐labeling of p‐tolyl phenylsulfoxide, however. failed to support this hypothesis. pointing out the need for further detailed studies.