bluuebunny/crossref_metadata_2025 huggingface dataset:
UNAMBIGUOUS EVIDENCE FOR THE PARTICIPATION OF SINGLET OXYGEN (1δ) IN PHOTODYNAMIC OXIDATION OF AMINO ACIDS
Authors: NILSSON R. , MERKEL P. B. , KEARNS D. R.
Published: January 2008

Abstract— A variety of experimental tests have been applied to the methylene‐blue‐sensitized photooxidation of amino acids to distinguish between singlet oxygen and non‐singlet oxidation mechanisms. Conventional flash photolysis and laser photolysis were used to measure the rate constants for the quenching of excited triplet sensitizer and singlet oxygen by the amino acids histidine. tryptophan and methionine and the nucleotide guanosine‐5′‐monophosphate. In the case of histidine, the rate constants alone rule out an oxidation mechanism involving direct reaction with excited dye. With the other amino acids, and with guanosine monophosphate, the oxidation rates might be accounted for by either mechanism. The inhibition of the photo‐oxidation of both tryptophan and methionine as well as histidine by the singlet‐oxygen quenchers N3− and tetramethylethylene suggests that these reactions occur via a singlet‐oxygen mechanism. A newly developed test of singlet oxygen reactions involving a comparison of photooxidation rates in normal and perdeuterated solvents has been used to establish that the photooxidation of tryptophan proceeds primarily by a singlet‐oxygen mechanism. These experiments appear to constitute the first proof that singlet oxygen is involved in the photooxidation of the three amino acids tryptophan, methionine and histidine.
ELECTRON TRANSFER FROM THE EXCITED STATE OF TYROSINE TO COMPOUNDS CONTAINING DISULFIDE LINKAGES
Authors: FEITELSON J. , HAYON E.
Published: January 2008

Abstract— The flash photolysis of aqueous solutions of tyrosine has been studied in the presence of various concentrations of the cyclic disulfide sodium lipoate (thioctic acid, Na+ salt). In addition to the formation of phenoxyl radicals and hydrated electrons (and possibly H atoms) from the photoionization of tyrosine, the characteristic spectrum of the radical anion RSSR‐ of lipoate was also observed in neutral as well as in alkaline solutions. From the dependence of these yields upon the concentration of lipoate, it was found that a long–lived triplet excited state of tyrosine, rather than the singlet excited state, is involved in these reactions. The negative radical ions RSSR‐ are formed by two distinct pathways: (a) Na+–lipoate reacts with the solvated electrons which are ejected from the tyrosine triplets 3Tyr → RO.+e‐aq+ H+ followed by e‐aq+ RSSR → RSSR‐, and (b) by direct interaction of lipoate with triplet excited tyrosine, resulting in the transfer of a negative charge from tyrosine to the disulfide linkage. At high lipoate concentrations, the singlet excited state of lipoate is quenched, k4= 1.6 × 1010M‐1 sec‐1, but this reaction does not lead to the formation of RSSR‐ radical ions.
MECHANISM OF PHOTOREDUCTION OF THIAZINE DYES BY EDTA STUDIED BY FLASH‐PHOTOLYSIS‐I
Authors: BONNEAU ROLAND , JOUSSOT‐DUBIEN JACQUES , FAURE JEAN
Published: January 2008

Abstract— The photoreduction of thiazine dyes by ethylene diamine tetraacetic acid (EDTA) was investigated by Rash photolysis. This reaction was found to occur according to a three‐step mechanism. the first being the formation of the dye triplet state followed, in weakly acid solutions, by protonation. During the second step, the triplet state of the dye disappears through two competing processes: spontaneous deactivation and reaction with EDTA, which leads to the semireduced dye. The third step leads to the leucodye. It is shown that the overall quantum yield of photoreduction is governed by the second step and can be calculated from the ratio of the rate constants of the two elementary processes involved in this step. This ratio was measured over a wide pH range.
ULTRAVIOLET IRRADIATION OF NUCLEIC ACIDS COMPLEXED WITH HEAVY ATOMS‐II. PHOSPHORESCENCE AND PHOTODIMERIZATION OF DNA COMPLEXED WITH Ag*
Authors: Rahn R. O. , Landry L. C.
Published: January 2008

Abstract— We have studied the luminescence (at 77°K) and photochemistry (at 298°K) of a variety of polynucleotides complexed with Ag+. In all cases we observed that Ag+ induces a ‘heavy atom effect’ as indicated by quenching of fluorescence, enhancement of phosphorescence, and reduction of triplet lifetimes. The enhancement by Ag+ of the phosphorescence intensity of poly (dT) and DNA paralleled a 20‐fold enhancement of the rate of thymine dimerization. These results suggest a possible triplet precursor for thymine dimerization in Ag+ complexes. Dimers were also made with a variety of triplet sensitizers, and Ag+ increased the dimer yield two‐ to four‐fold, depending on the sensitizer used.
PHOTODYNAMIC INACTIVATION OF LYSOZYME BY EOSIN
Authors: Kepka A. G. , Grossweiner L. I.
Published: January 2008

Abstract— It has been demonstrated that singlet oxygen is the major oxidizing entity in the photo‐dynamic inactivation of hen egg white lysozyme by eosin, using D2O to enhance the solvent‐induced decay lifetime, and azide ion as a specific scavenger. Two regimes of inactivation can be distinguished depending on whether the sensitizer is free or complexed to the enzyme. The kinetic analysis for free dye sensitization, based on photostationary measurements and inactivation quantum yields, indicates that at least 1 in 15 singlet oxygen interactions with lysozyme leads to loss of lytic activity. The direct attack of triplet eosin makes a lesser overall contribution in air‐saturated solutions, where 1 in 4 reactions induces inactivation. Lysozyme binds 1 eosin molecule from pH 4 to 12, leading to almost total quenching of the tryptophyl residue fluorescence without inhibition of the enzymic activity. The inactivation quantum yields indicate that singlet oxygen generated from the bound dye is the inactivating agent, but the dominant attack takes place with the complexed fraction of lysozyme molecules. The tryptophyl residue loss is the same or smaller in changing from H2O to D2O despite the 5–10 times increase in quantum yield, indicating that singlet oxygen inactivates also by reacting with residues other than tryptophan. The photochemical and fluorescence results are consistent with the the identification of tryptophyl site 108 with the eosin binding site and a reaction target for singlet oxygen. In a re‐examination of earlier work on eosin‐sensitized photo‐oxidation of I“, it has been found that singlet oxygen is the oxidizing agent in aerobic solutions.
THE QUENCHING OF TYROSINE AND TRYPTOPHAN FLUORESCENCE BY H2O AND D2O*
Authors: McGuire Robert , Feldman Isaac
Published: January 2008

Abstract— The quantum yields and lifetimes of the fluorescence of tyrosine and tryptophan were determined in D2O‐H2O and glycerol‐H2O solvent mixtures of varying composition from 10 vol.% to 100% H2O at 15°C. Forboth amino acids the ratio of the quantum yields in D2O and H2O (i.e., qD/qH) was smaller than the ratio of the corresponding lifetimes (D/H). For tyrosine the ratio of the quantum yields in glycerol and H2O (qG/qH) was also smaller than the corresponding G/H ratio, but for tryptophan qG/gHG/H. The proximity of the q vs. plots for tyrosine in the two solvent mixtures indicates that at 15°C neither D2O nor glycerol, in the pure state or when diluted with H2O, quench tyrosine significantly. However, H2O quenches tyrosine by a dynamic process, which increases both the radiative and the nonradiative rate constant. The quenching action is attributed to a tyrosine‐H2O exciplex, whose formation is independent of bulk viscosity and dielectric constant. Unlike tyrosine, tryptophan is quenched weakly by D2O by a static process at 15°C (i.e., involving no change in), but H2O quenches tryptophan much more efficiently by a dynamic process, which involves the nonradiative rate constant, but not the radiative constant. These results are explained on the basis of electrostatic complexation of the ammonium group to the carbon atom adjacent to the ring nitrogen with a lifetime which is longer thanin D2O but shorter thanin H2O, with solvent reorientation possibly also being an important factor in the quenching. This explanation is consistent with the fact that concentrated (8 M) urea increases q andof aqueous tryptophan ˜ 15–20%, while guanidine hydrochloride (6.4 M) has the opposite effect, i.e., it decreases q and t of tryptophan ˜ 15–20%, and with the fact that neither 8 M urea nor 6.4 M guanidine hydrochloride affects any fluorescence parameter of tyrosine at all.
QUANTUM MECHANICAL ANALYSIS OF ELECTRONIC TRANSITIONS IN SOME CYANINE DYE PHOTOSENSITIZERS
Authors: Weinstein Harel , Apfelderfer Benzion , Berg Robert A.
Published: January 2008

Abstract— INDO and CNDO/2 calculations of some cyanine dye photosensitizers are reported. The redistribution of electron charge density following various electronic transitions is analyzed and found to be localized mainly in the conjugated chains. The charge redistribution is shown to be strongly influenced by presence of the counter ion, which also proves to be a main factor in determination of the ionization energy values and symmetry of the molecular orbitals. The results suggest an ionization process different from the one considered in previous approaches, because the electron is shown here to leave the negative ion, with the conjugated cation acting as a “photon trap”. This situation is shown to provide a link between different models of optical sensitization. Results and assumptions from other methods, including the ‘electron gas’ models for the conjugated chain, are discussed in view of the counter‐ion effect and the chain–localized transitions found here.
PHOTOSYNTHETIC ENERGY TRANSFER REVERSIBLY INHIBITED BY HYDROSTATIC PRESSURE*
Authors: Schreiber Ulrich , Vidaver William
Published: January 2008

Abstract— Hydrostatic pressure is found to affect reversibly the emission spectra of Porphyra perforata. At 1200atm phycoerythrin and phycocyanin fluorescence show a remarkable increase, whereas at the same time chlorophyll a (Chl a) fluorescence decreases. Upon release of pressure the fluorescence intensities of the individual pigments return to their original levels. This effect indicates that hydrostatic pressure acts as a unique reversible inhibitor of energy transfer between phycobilins and Chi a in the chloroplast.

The effects of pressure and its release are relatively slow (minutes). It is suggested that pressure changes thylakoid membrane structure sufficiently to alter the critical distance between the phycobilisomes and Chl a, thus blocking the inductive resonance transfer of excitation energy.
THE PHOTOLYSIS OF CYSTINE IN ACIDIC AQUEOUS SOLUTION
Authors: Dixon C. J. , Grant D. W.
Published: January 2008

Abstract— Quantum yields of cysteine, ammonia, 1‐amino,1′‐oxo,2,2′‐dithiodipropionicacid (AODT–DPA), alanine, alanine 3‐sulphinic acid, cysteic acid, and serine have been determined in aqueous oxygenated and deaerated cystine solutions irradiated with 254 nm radiation. From the effect of methanol, ethanol and propanol‐2 on the quantum yields of cysteine, ammonia, AODT‐DPA and alanine, it is concluded that (a) the S–S bond is broken with high quantum efficiency, (b) C–S and C–N bonds do not undergo primary photolytic fission, and (c) all the AODT–DPA, but only about 12 per cent of the ammonia, is free‐radical in origin. The production of pyruvic acid at the expense of AODT–DPA in irradiated cystine solutions containing alanine provides further evidence that AODT–DPA has free‐radical precursors. Reaction schemes are proposed for the radical‐induced production of keto acid and ammonia in oxygenated and deaerated solutions.
PROTEIN COMPOSITION OF SPINACH CHLOROPLASTS AND THEIR PHOTOSYSTEM I AND PHOTOSYSTEM II SUBFRAGMENTS*
Authors: Klein Sigrid M. , Vernon Leo P.
Published: January 2008

Abstract— The proteins of spinach chloroplasts and their subfragments containing photosystem I and photosystem II, obtained by Triton X‐100 treatment or French‐pressure rupture, were separated by sodium dodecyl sulfate (SDS)‐acrylamide electrophoresis at pH 7·0 in phosphate buffer. The individual protein bands were identified where possible by comparing them with known, isolated and characterized proteins from chloroplasts, and their molecular weights were determined. The protein composition of the chloroplast fragments were correlated to the functional properties of these fragments. Distinct patterns were obtained for photosystem I and photosystem II particles. The major protein of photosystem II is expressed in the 23 kilodalton range and photosystem I proteins seem to be clustered mainly in the 50–70 kilodalton range.
CHLOROPHYLL ONE‐ELECTRON PHOTOCHEMISTRY‐I. PHOTOPRODUCTION OF THE CATION RADICALS OF CHLOROPHYLL AND BACTERIOCHLOROPHYLL IN SOLUTIONS AT LOW TEMPERATURES*
Authors: Harbour John R. , Tollin Gordon
Published: January 2008

Abstract— Electron spin resonance studies have shown that chlorophyll and bacteriochlorophyll can be photo‐oxidized in a variety of solvents via their lowest excited singlet states to produce cation radicals. Pheophytin does not undergo this reaction. The mechanism of this photoprocess and its implications for photosynthesis are discussed.
PHOTO‐OXIDATION SENSITIZED BY METHYLENE BLUE, THIOPYRONINE, AND PYRONINE‐IV. THE BEHAVIOUR OF THIOPYRONINE IN SUSPENSIONS OF BACTERIA*
Authors: Jacob Hans‐Egon
Published: January 2008

Abstract— In bacterial suspensions of Proteus mirabilis VI, at a cell concentration > 109/ml, a decrease in the concentration of oxidized (coloured) thiopyronine can be observed during aeration. The reduction of the dye to leucothiopyronine can be counteracted to only a small extent by aeration with oxygen, although aeration renders the redox potential of the suspension more positive than the polarographically determined half‐wave potential of the dye. This is caused by the fact that thiopyronine is reduced irreversibly by the bacteria. The decrease of thiopyronine concentration results in a decrease in the rate of photodynamic inactivation. Results obtained with thiopyronine are compared with those obtained with methylene blue: In suspensions of bacteria containing methylene blue, addition of oxygen inhibits reduction of the oxidized dye.

In addition, thiopyronine is adsorbed by Proteus bacteria quickly (within 1 min) and strongly (0·8 per cent of dry weight). The dye penetrates into the cell, but the share that remains on the cell surface is not yet known. Methylene blue is adsorbed to nearly the same extent. The adsorbed thiopyronine is bound strongly by the cells.

Sensibilisierte Photooxydation durch Methylenblau, Thiopyronin und Pyronin. IV. Zum Verhalten von Thiopyronin in Bakteriensuspensionen. Thiopyronin wird von Bakterien nahezu irreversibel reduziert. In Bakteriensuspensionen mit hohen Zellzahlen (> 109/ml) nimmt deshalb die Konzentration des oxydiert vorliegenden Farbstoffs laufend ab. Der Farbstoffreduktion kann durch Einleiten von Sauerstoff in die Bakteriensuspension nur geringfügig entgegengewirkt werden, obwohl dadurch das “Redoxpotential” der Suspension wesentlich positiver wird als das Reduktionspotential des Farbstoffs ist. Die beim Thiopyronin und beim Methylbenblau erhaltenen Ergebnisse werden miteinander verglichen. Insbesondere kann beim Methylenblau durch Sauerstoff‐anwesenheit die Reduktion völlig verhindert werden.

Weitere Ergebnisse sind: Das Thiopyronin wird von den Bakterienart Proteus mirabilis sehr schnell (innerhalb einer Minute) und in großem Umfang (Anteil am Trockengewicht etwa 0·8%) adsorbiert. Der Farbstoff gelangt auch ins Zellinnere. Welcher Anteil an der Zellbegrenzung verbleibt, ist nicht bekannt. Methylenblau wird etwa im gleichen Umfang wie Thiopyronin adsorbiert. Das von der Zelle adsorbierte Thiopyronin wird gegen einen Konzentrationsgradienten festgehalten.
THE MIDDLE ULTRAVIOLET REACHING THE GROUND*
Authors: Green A. E. S. , Sawada T. , Shettle E. P.
Published: January 2008

Abstract— We present a semi‐empirical analytic formula for calculating the direct, diffuse and global solar middle‐ultraviolet radiation (280–340 nm) reaching the ground. The formula accommodates variations in wavelength, solar angle, ozone thickness, aerosol thickness, ground albedo, ground elevation, and cloudiness. Analytic representations of biological action spectra are also presented for use in calculations of effective dose at any time of day. Our purpose is to provide a basis for estimating approximate changes in middle‐ultraviolet radiation levels reaching the ground caused by anthropogenic changes in the intervening atmosphere.
CORRELATION OF PHOTOREACTIVATION OF ULTRAVIOLET‐INDUCED KILLING WITH DIMER SPLITTING BEFORE AND AFTER DNA REPLICATION IN AN EXCISIONLESS STRAIN OF ESCHERICHIA COLI*
Authors: Kondo Sohei , Ikenaga Mituo , Jagger John
Published: January 2008

Abstract— Splitting of thymine‐containing dimers was compared quantitatively with photoreactivation (PR) of killing induced by ultraviolet radiation (254 nm) in a uvrA (excisionless) strain of E. coli. Immediately after irradiation, the splitting rate (number of dimers split/genome/unit PR dose) agreed well with the PR rate of the cells (rate of recovery from photoreactivable lethal damage converted into an ‘estimated’ number of dimers split/genome/unit PR dose). After 4 h of incubation of cells in nutrient medium, the maximal fraction of splittable dimers decreased, as did the maximal fraction of photoreactivable lethal damage. However, the initial splitting rate after incubation was equal to that before incubation. During the 4‐h incubation, the heavily irradiated uvrA cells did not divide but became filamentous and their DNA increased about 70 per cent. It is concluded that roughly half of the dimers in DNA that has replicated after ultraviolet irradiation are split as efficiently as those in DNA that has not replicated.
PHOTOASSOCIATION PHENOMENA IN CONCENTRATED ETHANOL SOLUTIONS OF 2‐AMINO‐PYRIMIDINE
Authors: Ferrara R. , Lenci F. , Neubacher H.
Published: January 2008

Abstract— Besides fluorescence and phosphorescence of the monomer, concentrated ethanol and water solutions of 2‐amino‐pyrimidine show an additional red‐shifted emission, whilst optical absorption spectra are independent of 2‐amino‐pyrimidine concentration. The maximum of this new band is red‐shifted about 4000 cm‐1 with respect to that of monomer emission. The dependence of the intensity of this bathochromic emission on concentration and on temperature suggests that 2‐amino‐pyrimidine excimers form in ethanol solutions. In aqueous solutions the photoassociation product seems to involve more than two base molecules.
MITOTIC ACCELERATION INDUCED IN GRASSHOPPER NEUROBLASTS BY SMALL DOSES OF MONOCHROMATIC ULTRAVIOLET RADIATION
Authors: Carlson J. Gordon , Stephens Ralph E.
Published: January 2008

Abstract—Neuroblasts of the grasshopper, Chortophaga viridifasciata (DeGeer), in culture were exposed to 4–15 J/m2 of monochromatic ultraviolet radiation in middle prophase and timed to prometaphase (breakdown of the nuclear membrane). At wavelengths 265 and 280 nm the times recorded for the treated cells were significantly less than those for the matched control cells. Wavelength 225 nm produced neither significant acceleration nor deceleration of mitotic rate.

Evidence from the present experiment does not implicate any particular chromophore in this response, though similar results of a previous microbeam study of neuroblasts point to the nucleic acid or protein of the nucleolus as the possible effective material.
FORMATION OF SEMIQUINONE RADICALS BY ULTRAVIOLET IRRADIATION OF PYRIMIDINES IN METHANOL
Authors: Castellano A. , Catteau J. P. , Lablache‐Combier A. , Allan G.
Published: January 2008

Abstract—Ultraviolet irradiation of pyrimidine and 4‐ and 5‐methylpyrimidine in methanol at 113 K gave the corresponding semiquinone radicals in a monophotonic process. It is likely that this process involves an n* triplet state of the photoexcited pyrimidines.
EFFECT OF SINGLET OXYGEN QUENCHERS ON OXIDATIVE DAMAGE TO LIPOSOMES INITIATED BY PHOTOSENSITIZATION OR BY RADIOFREQUENCY DISCHARGE
Authors: Anderson S. M. , Krinsky N. I. , Stone M. J. , Clagett D. C.
Published: January 2008

Abstract—Lipid model membrane systems, liposomes, may be oxidized by both toluidine blue Osensitized photo‐oxidation and radiofrequency‐discharge‐generated singiet oxygen. Oxidation can be followed by the appearance of lipid peroxides, malondialdehyde formation, and ultimately by the lysis of the liposomes. Inhibition of oxidation is observed in both systems using either β‐carotene or DABCO. These observations are consistent with the view that type II (singlet oxygen) reactions are involved in this photodynamic system.
ON THE LUMINESCENCE OF ESTROGENS
Authors: Weinreb A. , Werner A.
Published: January 2008

Abstract—The absorption, fluorescence, and phosphorescence of a series of estrogens is reported. The behavior of estrogens without a keto‐group is compared with that of the isolated phenylic, phenolic and naphtholic chromophores. In the latter two, attachment to the steroidal frame is inconsequential as regards their luminescent behavior. In all keto‐estrogens with the exception of equilenin there is a very strong transfer of excitation energy from the A ring chromophore to the keto group. The fluorescence of 6‐keto‐estradiol, which has a conjugated aromatic carbonyl chromophore, is apparently due to the rigidity of the steroid frame and exhibits a rather perculiar excitation spectrum.
FLUORESCENCE INDUCTION IN ALGAE AND CHLOROPLASTS
Authors: Lavergne Jerome
Published: January 2008

Abstract—The first phases of the fluorescence transient elicited by illumination of dark‐adapted algae or isolated chloroplasts (biphasic rise φ***v ‐ φI ‐ P) have previously been shown to be controlled by two quenchers: Q, the primary acceptor of Photosystem 2 interacting with the secondary acceptor pool A; and R, a non‐photochemical quencher which goes into a non‐quenching state as A is reduced.

The dependence of the kinetics of φ decay after illumination upon the redox state of A was studied. It is suggested that some of the centres are in a disconnected state, where electron transfer between Q and A is hindered, the amount of such centres being correlated to the reduction state of A. The implications of this hypothesis on the problem of the variation of the Q‐A‘equilibrium constant’ under different experimental conditions, and on Murata's ‘weak light effect’ are discussed.

The effect of 3‐(3,4 dichlorophenyl)‐1,1 dimethylurea (DCMU) on R is shown to depend upon the redox state of A. A DCMU‐induced shift of the midpoint potential of R may account for this dependence.

Evidence is given suggesting that the transient reduction of A which occurs in algae during the φI‐φP rise is controlled by an induction process on the acceptor side of Photosystem 1.
FURTHER STUDIES ON THE CRYSTAL‐VIOLET‐SENSITIZED PHOTOOXIDATION OF CYSTEINE TO CYSTEIC ACID
Authors: Gennari Giorgio , Cauzzo Giulio , Giulio
Published: January 2008

Abstract—Crystal violet sensitizes the selective photooxidation of cysteine to cysteic acid; hydrogen peroxide is also formed as an end product. The participation of singlet oxygen in the photoreaction has been ruled out, since exposure of cysteine to this reagent, generated by chemical or photochemical processes, gives only cystine as a product. The photoreaction is inhibited by radical scavengers such as hydroquinone and allylic alcohol. A mechanism is proposed involving hydrogen abstraction by the triplet dye from the thiol group of cysteine.
EXCISION REPAIR IN TETRAHYMENA: EVENTS FOLLOWING REFEEDING OF STARVED UV‐IRRADIATED CELLS
Authors: Mowat David , Pearlman Ronald E.
Published: January 2008

Abstract—Starvation of early‐log‐phase Tetrahymena pyriformis in non‐nutrient phosphate buffer for 24 h results in a 40 per cent increase in cell number, as well as a complete cessation of DNA synthesis. Low levels of DNA synthesis are detectable between 1 and 2h after starved cells are transferred to a nutrient medium. Larger amounts of DNA synthesis are detected after the first 2 h of refeeding, and one round of replication is complete 4.5 h after refeeding. Damage, caused by sublethal doses of UV radiation (254 nm) administered just prior to refeeding, to the DNA of starved Tetrahymena appears to be corrected by an excision‐repair process after refeeding of starved, irradiated cells. Changes in buoyant density of DNA synthesized, rate of DNA synthesis, and the chromatographic distribution of photoproducts were investigated following refeeding of starved, irradiated cells. Excision repair begins 1 h after refeeding and appears to be essentially complete within 7 h. During this time, thymine dimers produced by irradiation are removed. Semiconservative DNA synthesis commences 2–3 h after the first appearance of excision repair. In addition, between 3 and 8 h after refeeding, the rate of DNA synthesis in irradiated, refed cultures is much lower than the rate of DNA synthesis in unirradiated, refed cultures. Also, the specific activity in vitro of DNA polymerase from irradiated refed cells is very much greater than that of polymerase from unirradiated, refed cells.
ELECTRON TRANSFER IN PHOTOSENSITIZATION OF BIOMOLECULES BY ACRIDINE DYES
Authors: Vorst Albert Van DE , Lion Yves
Published: January 2008

Abstract— The photosensitization of some biomolecules by proflavine was studied using the technique of electron paramagnetic resonance. It was shown that this process is directly influenced by the relative molar concentration of dye and substrate. For some values of these concentrations, a singlet associated with a radical form of proflavine is observed. The appearance of this signal is discussed in terms of electron transfer from an ionized proflavine molecule directly to another neutral dye molecule or via a molecule of substrate as an intermediate. It is shown that this transfer is facilitated by stacking. These results were compared with radiolysis of the same kind of complexes in frozen aqueous solution.
PHOTOCHEMICAL FORMATION OF NITROXIDE RADICALS FROM CARCINOGENIC N‐METHYL‐N'‐NITRO‐N‐NITROSOGUANIDINE AND RELATED COMPOUNDS
Authors: Ioki Y. , Imamura A. , Nagata C. , Nakadate M.
Published: January 2008

Abstract— Potent carcinogenic N‐methyl‐N'‐nitro‐N‐nitrosoguanidine (MNNG) was found to be converted into a free radical by photoirradiation in organic solvents. The structure of the free radical produced was investigated by means of the electron paramagnetic resonance (EPR) method using isotope‐replaced compounds and also considering the results of the molecular orbital calculations. Upon illumination, release of the nitroso group and oxygen attack at the N‐methyl nitrogen occurred, and the radical was identified as a nitroxide radical. Similar types of nitroxide radical were obtained from other N‐alkyl‐N‐nitroso compounds, such as N‐ethyl‐, N‐propyl‐, and N‐butyl‐N'‐nitro‐N‐nitroso‐guanidine.
KINETIC ANALYSIS OF THE FLUORESCENCE INDUCTION IN 3‐(3,4‐DICHLOROPHENYL)‐1,1‐DIMETHYLUREA POISONED CHLOROPLASTS
Authors: Melis Anastasios , Homann Peter H.
Published: January 2008

Abstract— The size of the area over the fluorescence rise curve of chloroplasts is a measure of the total number of quanta utilized in photosystem II during the fluorescence induction, while the growth of the area reflects the progress of photochemical events. In the presence of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU), the growth kinetics of the area are affected by the reoxidation of the primary acceptor Q‐ with stored oxidizing charges on the donor side of system II.

At low light intensities, a slow component of this back reaction may limit the steady state fluorescence emission. At higher intensities, however, the fluorescence rise is limited solely by photochemical events, although fast thermochemical reactions like the immediate recombination of photochemically separated charges may affect the efficiency of the photochemistry.

A kinetic analysis of the area growth at moderate light intensities revealed that it occurred in two first order phases which were described by the rate constants kα and kβ. The biphasic nature suggested a sequential two‐electron reduction of the primary acceptor Q, or the presence of two different types of photochemical centers in system II. The rate constants were light intensity dependent. They also were affected by changes in pH, by an addition of NH2OH, or by a preillumination with short flashes prior to addition of DCMU. It is suggested that the pH of the medium, the presence of NH2OH, and the flash induced state Sn of the water splitting enzyme, control the values of kα and kβ by changing the rate constants of electron carrier interactions in the reaction center complex, with a resulting modification of the frequency of back reactions between the primary donor and the primary acceptor.
EXCISION OF PYRIMIDINE DIMERS FROM THE NUCLEAR DNA OF A HAPLOID RESPIRATION‐DEFICIENT (ρ) STRAIN OF SACCHAROMYCES CEREVISIAE
Authors: Waters R. , Moustacchi E.
Published: January 2008

Abstract— A haploid respiration‐deficient (ρ‐) mutant of Saccharomyces cerevisiae exhibits a lower ability to excise ultraviolet‐induced pyrimidine dimers in various post‐irradiation treatments as compared to the original respiration‐competent wild‐type strain. This decrease in excision may account for the inability of ρ‐ strains to show liquid‐holding recovery.
ISOLATION AND PARTIAL CHARACTERIZATION OF THE PHOTOCHEMICAL REACTION CENTER OF CHROMATIUM VINOSUM (STRAIN D)
Authors: Lin Lily , Thornber J. Philip
Published: January 2008

Abstract— –A preparation of the photochemical reaction center of Chromatiwn has been obtained by chromatography of lauryldimethylamineoxide‐solubilized chromatophores on hydroxylapatite and Sepharose columns. The procedure has yielded a reaction center preparation from both carotenoid‐containing and carotenoid‐deficient Chromatium cells. Preliminary analysis of the isolated component indicates that the photochemical reaction center of the Thiorhodaceae is homologous to that of the Athiorhodaceae. In particular, the near infrared absorption spectrum of the Chromatium reaction center preparation shows the same triple‐peaked spectrum observed for reaction center preparations from the Athiorhodaceae. The Chromatium preparation undergoes a rapid light‐induced oxidation and dark reduction of the reaction center. The ratio of the reaction center to the two membrane‐bound cytochromes (cytochrome c552 and c555) is greatly increased over the ratio observed in chromatophores or in other previously isolated, reaction center‐enriched subchromatophore fractions of this organism.
PHOTOCONTROL OF PHYTOCHROME DESTRUCTION IN GRASS SEEDLINGS. THE INFLUENCE OF WAVELENGTH AND IRRADIANCE
Authors: Schäfer E. , Lassig T.‐U. , Schopfer P.
Published: January 2008

Abstract— –The kinetics of phytochrome destruction in vivo of coleoptiles and mesocotyls of etiolated grass seedlings (Avena sativa L., Zea mays L.) in continuous light were investigated using wavelength and irradiance as experimental variables. In contrast to dicotyledonous seedlings, the destruction reaction of these monocotyledons is saturated at very low levels of the far‐red absorbing form of phytochrome, Pfr (e.g. at 1% of total phytochrome, corresponding to the photostationary state established by 727 nm light, in 2.5‐day‐old dark‐grown Avena). On the other hand, the first‐order rate constant of monocotyledon destruction may be at least one order of magnitude larger than in dicots, as indicated by the zero‐order rate measured in the presence of saturating amounts of Pfr (τl/2 1.5 min in Avena). At sub‐saturation Pfr levels, the destruction rate was found to be determined by the rate constants of the photoreactions over a wide range of wavelengths and irradiances. These results can be interpreted in terms of a destruction enzyme with high catalytic efficiency but limited availability.

Analysis of in vivo binding of phytochrome to a pelletable cell structure during destruction revealed that both the pelletable and the non‐pelletable fraction lose photoreversiblility with similar rates and thus provide no useful information with respect to a causal relationship between the two processes. However, due to the short half‐life of Pfr at sub‐saturation levels (which make the photoreactions and intermediary processes rate‐limiting for destruction even at relatively high irradiances) the existence of a similarly rapid dark‐reaction between the photoreactions producing Pfr and the destruction reaction could be demonstrated. This dark reaction displays the properties of Pfr binding to a receptor site.
SOME SPECTRAL CHARACTERISTICS OF THE LIGHT EMITTING SYSTEM OF THE POLYNOID WORMS
Authors: Lecuyer B. , Arrio B.
Published: January 2008

Abstract— The bioluminescence emission spectrum of the light emitted from the elytra of certain poly‐noid worms is similar to the fluorescence of the scales and to the fluorescence of flavins. In extracts the fluorescence is confined to the particulate fraction. Stimulation of bioluminescence from such particles was observed upon the addition of Fe2+ ions.
QUANTITATIVE EVIDENCE FOR ENZYMATICALLY‐INDUCED DNA DOUBLE‐STRAND BREAKS AS LETHAL LESIONS IN UV IRRADIATED pol+ AND polAl STRAINS OF E. COLI K‐12
Authors: Bonura Thomas , Smith Kendric C.
Published: January 2008

Abstract— We have recently reported that DNA double‐strand breaks arise enzymatically during the course of excision repair in uvr+ strains of Escherichia coli K‐12. Survival curves for ultraviolet (UV) irradiated E. coli K‐12 pol+ (JG139) and polA1 (JG138) strains have a pronounced shoulder region. The regions of the survival curves at which killing approaches exponential correspond to the fiuences at which DNA double‐strand breaks (assumed to be lethal events) accumulate linearly. Reducing the number of UV photoproducts either by photoreactivation or fluence fractionation results in an increase in survival and a decrease in the yield of DNA double‐strand breaks in both strains. These data support the hypothesis that enzymatically‐induced DNA double‐strand breaks may be the lesion ultimately responsible for UV‐induced cell killing in the pol+ strain of E. coli K‐12. and perhaps also in the polA1 strain.
THE PHOTOPEROXIDATION OF UNSATURATED ORGANIC MOLECULES—XV. O21δg QUENCHING BY BILIRUBIN AND BILIVERDIN
Authors: Stevens B. , Small R. D.
Published: January 2008

Abstract—The use of competitive methods with rubrene as reference acceptor provides values of the rate constants kBQ= 2.3 times 109/ mol‐1 s‐1 and kvq= 3.3 times 109 mol‐1 s‐1 for the physical quenching of O21δg, by bilirubin (in CCl4) and biliverdin (in CHCl3) respectively attributed to electron and energy transfer processes.

The rate constant kBR= 1.7 times 108/ mol‐1 s‐1 for bilirubin reaction with O21δg is considerably greater than that kvR 3 times 108 mol‐ s‐1 for the reaction of biliverdin which has identical O21δa, acceptor sites, and is attributed to a primary Type I oxidation process followed by a slower Type II addition of O21δg to the primary products.
DIRECT AND SENSITIZED PHOTOOXIDATION OF CYANINE DYES
Authors: Byers G. W. , Gross S. , Henrichs P. M.
Published: January 2008

Abstract—Direct photooxidation of cyanine dyes was found to be markedly enhanced by formation of hypsochromically shifted (H) aggregates. Singlet oxygen was found to attack many cyanines possessing low oxidation potentials with rate constants in excess of 108 t mol‐1 s‐1. Singlet oxygen attack on 3,3′‐diethyl‐8,10‐dimethylthiacarbocyanine yields carbonyl products consistent with 1,2 addition to the 2,8 bond of the methine chain.
ACTION SPECTRA FOR PHOTOACCUMULATION OF GREEN AND COLORLESS EUGLENA: EVIDENCE FOR IDENTIFICATION OF RECEPTOR PIGMENTS
Authors: Checcucci A. , Colombetti G. , Ferrara R. , Lenci F.
Published: January 2008

Abstract—Phototaxis action spectra have been determined in three different types of Euglena gracilis; green and dark‐bleached cells containing the stigma and streptomycin‐treated white mutant with an absorptionless stigma. In all three types of microorganisms the flavin containing paraflagellar body is present. The shape of the action spectrum is the same for the three types of cells and proportional to the absorption spectrum of flavoproteins. It has been shown that the structure of the action spectrum does not depend on the presence of screening organelles, on which, instead, depends the direction of the response to the light stimulus. It is concluded that the flavin chromophores present in the photoreceptor are the pigments responsible for phototaxis in Euglena gracilis.
TRIPLET ELECTRONIC STRUCTURE AND PHOTOREACTIVITY OF 8‐METHOXYPSORALEN*
Authors: Moore Thomas A. , Montgomery Alan B. , Kwiram Alvin L.
Published: January 2008

Psoralen and its derivatives are implicated in a variety of photobiological processes including skin‐sensitization in mammals, the experimental photochemotherapy of psoriasis, and photomutagenesis in bacteria. Although the various derivatives differ markedly in photoactivity, their excited triplet states as characterized by conventional luminescence spectroscopy are very similar and closely resemble that of the parent compound, coumarin, which is inactive as a skin sensitizer. Employing a more sensitive probe of triplet electronic structure, we have utilized optical detection of magnetic resonance to measure the zero‐field splittings in the triplet state of several psoralens and find a striking variation among the derivatives. D*, taken as a composite measure of the dipole‐dipole interaction of the unpaired electrons in the triplet state was found to be anomalously large, greater than 0.140 cm‐1, for the very active compounds, psoralen and 8‐methoxypsoralen, while D*= 0.124cm‐1 for the inactive, though smaller, coumarin molecule. Although 8‐hydroxypsoralen has a large D* value its inactivity as a skin‐sensitizer may be explained by the dissociation of the hydroxyl proton. The resulting (excited) triplet state anion has D*= 0.120 cm‐1.
INHIBITION OF UV‐INDUCED DNA STRAND BREAKAGE IN DICTYOSTELIUM DISCOIDEUM BY 2,4–DINITROPHENOL
Authors: Guialis A. , Deering R. A.
Published: January 2008

Abstract— In UV‐irradiated vegetative cultures of the cellular slime mold Dictyostelium discoideum NC‐4, single strand breaks appeared in the DNA very rapidly and at low temperatures (0–4°C). However, when these cells were incubated, prior to UV irradiation, in the presence of 2 mM 2,4‐dinitrophenol (DNP), an uncoupler of oxidative phosphorylation, breaks did not appear in the DNA. Extracts prepared from cells that had been incubated either in the presence or absence of DNP were tested for endonucleolytic activities on a UV‐irradiated exogenous DNA template (φX‐174 RF I). Results suggested that DNP might mediate its effect by interfering with the action of a UV‐specific endonuclease.
FLUOROMETRIC EVIDENCE FOR FLAVINS IN ISOLATED EYESPOTS OF EUGLENA GRACILIS VAR. BACILLARIS
Authors: Pagni Patricia G. Sperling , Walne Patricia L. , Wehry E. L.
Published: January 2008

Abstract— Fluorometric evidence suggesting the presence of flavins in isolated eyespots of Euglena gracilis var. bacillaris is reported for the first time. Fluorescence spectra of eyespots and flavin standards show maxima at 540nm and 530nm, respectively. Excitation spectra show matching major peaks at 360–370 nm and at 450nm. The addition of riboflavin standard to eyespot samples increases fluorescence intensity without major corresponding shifts in wavelength maxima. Photolysis of eyespot samples in the presence of EDTA effects a decrease in the fluorescence intensity; the fluorescence is quantitatively restored to its initial value by bubbling the photolyzed solution with air. Preliminary quantitative data, obtained by fluorescence measurements, indicate the presence of ca. 5 × 10‐4μg flavin/ml eyespot sample. While flavins have been hypothesized to be components of the photoreceptor system, they have been reported previously only in the paraflagellar bodies of intact cells. Emission and excitation data obtained by us for eyespots are similar to those previously reported by other investigators for paraflagellar bodies, but our studies now suggest the presence of flavins also in Euglena eyespots.
NEAR‐UV‐INDUCED BREAKS IN PHAGE DNA: SENSITIZATION BY HYDROGEN PEROXIDE (A TRYPTOPHAN PHOTOPRODUCT)
Authors: Ananthaswamy H. N. , Eisenstark A.
Published: January 2008

Abstract— Near‐UV irradiation of l‐tryptophan yields a large number of photoproducts. When this mixture is added to recombinationless (rec) mutants of bacteria, the cells are killed. The most toxic component of tryptophan photoproducts has been identified as hydrogen peroxide (H2O2). We now report that both tryptophan photoproducts and H2O2 sensitize phage DNA to near‐UV radiation resulting in enhanced killing as well as enhanced DNA breakages. We conclude that the in situ production of H2O2 via tryptophan photolysis may be an important biological event.
OXYGEN‐DEPENDENCE OF NEAR UV (365 NM) LETHALITY AND THE INTERACTION OF NEAR UV AND X‐RAYS IN TWO MAMMALIAN CELL LINES
Authors: Danpure Heather J. , Tyrrell Rex M.
Published: January 2008

Abstract— The colony‐forming ability of Chinese hamster cells (V‐79) and HeLa cells has been measured after near‐ultraviolet (UV) irradiation, predominantly at 365 nm. To avoid the production of toxic photoproducts, cells were irradiated in an inorganic buffer rather than in tissue culture medium. Under these circumstances near‐UV lethality was strongly oxygen‐dependent. Both cell lines were approximately 104 times more sensitive to 254 nm irradiation than to 365 nm radiation when irradiated aerobically. Pretreatment with 6 times 105 Jm‐2 365 nm radiation sensitised the HeLa, but not the V‐79 cell line to subsequent X‐irradiation. Pretreatment of cells with 17 Jm‐2 254 nm radiation, a dose calculated to produce twenty times more pyrimidine dimers than the 365 nm dose, produced only slight sensitisa‐tion to X‐rays. It is suggested that the sensitisation to X‐rays seen in the HeLa cells after 365 nm treatment is not the result of lesions induced in DNA by the near‐UV radiation, but may reflect the disruption of DNA‐repair systems.
IN VIVO INDUCTION OF 4‐THIOURIDINE‐CYTIDINE ADDUCTS IN tRNA OF E. COLI B/r BY NEAR‐ULTRAVIOLET RADIATION*
Authors: Ramabhadran T. V. , Fossum T. , Jagger J.
Published: January 2008

Abstract— Near‐ultraviolet (near‐UV; 320–405 nm) irradiation of Escherichia coli B/r induces the formation in vivo of 4Srd‐Cyd adducts in transfer RNA, as evidenced by (1) fluorescence spectrum changes of tRNA extracted from irradiated cells and reduced with NaBH4, (2) thin‐layer chromatography on cellulose of hydrolysates of trichloroacetic acid‐precipitable extracts of irradiated cells, and (3) comparison of these findings with adduct formation induced by near‐UV irradiation of purified mixed tRNA from E. coli.

The kinetics of induction of the 4Srd‐Cyd adduct in vivo, and the near‐UV fluences required, provide strong support for our earlier hypothesis that formation of these adducts is responsible for near‐UV‐induced growth delay in E. coli.
HETEROGENEITY OF THE PHOTOCHEMICAL CENTERS IN SYSTEM II OF CHLOROPLASTS*
Authors: Melis Anastasios , Homann Peter H.
Published: January 2008

Abstract— In 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) poisoned chloroplasts of algae and‘ higher plants the area over the fluorescence induction curve increases with biphasic first order kinetics (Melis and Homann, 1975). Two possibilities are considered to explain the biphasic nature of the area growth. The first is a sequential double reduction of the primary electron acceptor in system II while the second envisages a heterogeneity of its photochemical centers. The kinetic properties of the area growth after firing a single saturating flash proved to be incompatible with the predictions of the “sequential double reduction” model. This conclusion was corroborated by results obtained from a kinetic analysis of the area restoration process in the dark, and an analysis of the partially restored areas.

Assuming an existence of a heterogeneous pool of photochemical centers, the growth of the area over the fluorescence curve could be further analyzed to yield two components, a fast a‐component, and a relatively slow β‐component. The kinetic characteristics of these components, and the effect of a short saturating flash on their respective size, led to the conclusion that one type of photochemical center had a faster recombination rate of the photochemically separated charges and was less efficient in trapping excitation energy.
THE PHOTOSENSITIZED FORMATION AND REACTION OF SINGLET OXYGEN, O2*(1Δ), IN AQUEOUS MICELLAR SYSTEMS
Authors: Gorman A. A. , Lovering G. , Rodgers M. A. J.
Published: January 2008

Abstract— Oxygenated aqueous solutions of methylene blue containing dispersions of sodium dodecyl sulphate micelles with solubilised diphenyl isobenzofuran were irradiated with red light and the rate of loss of furan was followed over several min. The results are consistent with a mechanism in which singlet oxygen is produced by energy transfer from methylene blue triplet in the aqueous phase, and then diffuses to and penetrates the interior of the micelles where it reacts with the furan. The competition between this process and the natural decay of the excited oxygen has been examined and a β‐value of 9.7 times 10‐5M determined which is comparable to that for the same reaction in homogeneous solvents. A model of the system is proposed and its kinetic features discussed.
INHIBITION AND ENHANCEMENT OF SINGLET OXYGEN (‘Ag) DIMOL CHEMILUMINESCENCE
Authors: Deneke Carl F. , Krinsky Norman I.
Published: January 2008

Abstract— Various nitrogen containing compounds have previously been shown to quench singlet oxygen (10z). When measuring the dimol 1O2 light emission arising from the H2O2/OCI‐ reaction, we found that certain cyclic diamines increase the emission of light, while other amines were inhibitory. This increase of light emission was seen with both 1, 4diazabicyclo[2.2.2]octane and N, N'‐dimethylpi‐perazine but not with acyclic analogues. Sodium azide inhibited both the normal and enhanced light emission. The enhanced light emission shows spectral properties characteristic of lO2 dimol emission.
TRIARYLMETHANE DYE PHOTOCHROMISM: SPECTROSCOPY AND PHOTOCHEMISTRY OF BRILLIANT GREEN LEUCOCYANIDE
Authors: Geiger Margaret W. , Turro Nicholas J. , Waddell Walter H.
Published: January 2008

Abstract— The spectroscopy and photochemistry of brilliant green leucocyanide 1a were investigated at room and low temperature, in polar and nonpolar solvents. At 77 K, 1a exhibits solvent independent absorption, fluorescence (φf= 0.1), and phosphorescence (φp= 0.5). Solvent effects become important at room temperature; in polar solvents, φf, decreases and photodissociation yielding brilliant green dye 3 occurs [φdis,(EtOH) ˜0.91. Dye formation and 1a fluorescence can be quenched by 0.1 M crotononitrile. Attempts to sensitize dye formation with triplet sensitizers were unsuccessful. The spectroscopy of 3 was also examined.