bluuebunny/crossref_metadata_2025 huggingface dataset:
CHEMILUMINESCENCE IN THE PEROXIDATION OF TANNIC ACID
Authors: Slawinska Danuta , Slawinski Janusz , Polewski Krzysztof , Pukacki Wojciech
Published: January 2008

Abstract— Peroxidation of tannins with alkaline H2O2 is accompanied by weak chemiluminescence in the spectral region 480–800 nm. o‐Di and tri‐hydroxy groups of polyphenols undergo oxidation by a free‐radical mechanism and a green intermediate anion‐radical with absorption Δmax= 600 nm is formed. The radical mechanism is supported by the low activation energy 14–20 kJ/mol and the quenching effect of radical scavengers. The reaction of the green intermediate with peroxy anions is the chemiluminescence rate limiting step. In the presence of a‐hydroxy‐methylperoxide formed from H2O2 and formaldehyde, the alkaline peroxidation of tannins is accompanied by strong red luminescence (420–800 nm). The base catalyzed decomposition of peroxides gives only a weak red emission (460–800 nm). Light intensity is enhanced in D2O by a factor 6.5. Quenchers of O2(1Δg) and 1,3‐di‐phenylisobenzofurane diminish light intensity in non‐aqueous solutions. The data suggest 1O2 participation in the observed chemiluminescence. Thermo‐chemical calculations give —ΔH values from 250–1000 kJ/mol for one elementary reaction step which limits the mechanism of chemi‐enereization. Chemiexcitation of tannins is relevant to biochemical mechanisms of aerobic degradation of aromatic compounds, energy utilization as well as to defense and resistance processes in plants.
ELIMINATION OF THE EFFECT OF CONTAMINATING CO2 IN THE 18O‐LABELING OF THE CO2 PRODUCED IN BIOLUMINESCENT REACTIONS
Authors: Shimomura Osamu , Johnson Frank H.
Published: January 2008

Abstract— Although the mechanism of bioluminescent reactions in various species, such as fireflies, ostracod crustaceans (Cypridina), sea pansies (Renilla), and the deep‐sea shrimp Oplophorus, are thought to involve dioxetanone intermediates, studies reported in the past from different laboratories have included widely different experimental results, most likely due to various factors including the effects of contaminating CO2. With the improved technique employed in the present study, bioluminescent reactions of the firefly and Cypridina in 18O2 gas resulted in an incorporation of over 75% of 18O into one oxygen of the product CO2. with a reproducibility within a few per cent. When 13CO2. instead of the product CO2 of the bioluminescent reaction, was studied in an H218O medium, the exchange of one oxygen of 13CO2 with H2O was 64%. and the effect of contaminant CO2 amounted to 1418% of the total CO2. These results suggest that every molecule of CO2 formed in the bioluminescent reactions of the firefly and Cypridina had intially contained 1 oxygen atom derived from O2.
ACTION OF HYDROGEN PEROXIDE ON HUMAN FIBROBLAST IN CULTURE
Authors: Hoffmann M. Edwiges , Meneghini Rogerio
Published: January 2008

Abstract— Human fibroblasts in culture lose the capacity of proliferating when exposed to hydrogen peroxide in the concentration range of 1 to 10 μM. The toxicity of H2O2 to xeroderma pigmentosum cells (XP12RO). defective in excision repair of lesions produced by UV‐irradiation, was about twice as high as to cells proficient in excision repair (VA13). This compound produces single‐strand breaks in intracellular DNA but not in purified DNA. These breaks are in situ physical discontinuities rather than alkali‐labile bonds, and their generation occurs at the same extent at 4°C and 37° indicating that they are not produced by an endonuclease. The results favor the hypothesis that H2O2 reacts in the cell producing a radical species which brings about the formation of DNA single‐strand breaks. These breaks are effectively repaired by both XP12RO and VA13 fibroblasts. The possible reason for the lethality of H2O2 is discussed.
APPARATUS FOR RECORDING LIGHT FLASH INDUCED MEMBRANE VOLTAGE TRANSIENTS WITH 10 ns RESOLUTION
Authors: Huebner Jay S.
Published: January 2008

Abstract— Apparatus for recording voltage waveforms resulting from flash illumination of bilayer membranes with sorbed dyes or pigments are described. Time constants of light‐induced molecular events which displace electric charge in membranes can be taken directly from these waveforms. The waveforms induced across bilayer membranes by a carbocyanine dye and by chlorophyllin illustrate the apparatus performance. The risetime of the chlorophyllin induced photo‐voltages are ˜10ns.
STUDIES ON PLANT BILE PIGMENTS–6. PHOTOCHEMICALLY ASSISTED REACTION OF A‐DIHYDROBILINDIONE WITH NUCLEOPHILES AS A MODEL FOR PHYTOCHROME INTERCONVERSION
Authors: Krauss C. , Bubenzer C. , Scheer H.
Published: January 2008

Abstract— –From the A‐dihydrobilindione 3. the pyridinium derivatives 6a, b and analogues therwf have been obtained by a formal nucleophilic substitution. The reaction is rationalized as a photochemically assisted oxidation of 3 with a subsequent regioselective addition of pyridine at C‐5. By thermolysis. 6a.b yields back the parent bilin 3, together with an oxidation product. The significance of the reaction with respect to the phytochrome interconversion is discussed.
PHOTOSENSITIZED FORMATION OF SINGLET OXYGEN BY CHLOROPHYLL a IN NEUTRAL AQUEOUS MICELLAR SOLUTIONS WITH TRITON X‐100
Authors: Kraljić Ivan , Barboy Natalia , Leicknam Jean‐Pierre
Published: January 2008

Abstract— Singlet oxygen (lO2) formed in the photolysis of neutral aqueous micellar (with Triton X‐100) solution of chlorophyll a (dissolved inside the micelle) is detected in the aqueous phase by a test using imidazole in the presence of p‐nitrosodimethylaniline. The quantum yield of lO2 diffusing out of the micelle into the aqueous phase is also determined [θ(lO2) ⋍ 0.70–0.85].
PHOTOSENSITIZED FORMATION OF RNA‐PROTEIN CROSSLINKS IN AN INSECT EGG (SMITTZA SPEC., CHIRONOMIDAE, DIPTERA)*
Authors: Jackle Herbert , Kalthoff Klaus
Published: January 2008

Abstract—Upon irradiation of Smittia eggs with ultraviolet light (UV), the extractability of RNA with phenol decreased. The strongest decrease was observed after irradiation at 295 nm wavelength. After trypsin treatment, RNA could be recovered to the same degree as from unirradiated eggs. The extractability of RNA from irradiated eggs was not enhanced by formamide. dimethyl sulfoxide. high salt concentration or heat treatment. The results suggest that the UV‐mediated formation of RNA‐protein crosslinks in Smittia eggs involves the action of a photosensitizer.
POSITIONING OF AQUATIC MICROORGANISMS IN RESPONSE TO VISIBLE LIGHT AND SIMULATED SOLAR UV‐B IRRADIATION
Authors: Barcelo Jeanne A. , Calkins John
Published: January 2008

Abstract—

Three species of protozoans and two crustaceans were irradiated with simulated solar ultraviolet radiation to investigate their ability to detect and avoid UV‐B (320–280 nm). Horizontal and vertical movements to sheltered areas by these organisms suggest that UV‐B is an important environmental factor. UV‐B survival curves were determined which indicated the resistance for each organism studied. The tolerance correlated well with the positioning behavior (i.e. sensitive organisms avoided exposure by moving into sheltered areas whereas the more resistant organisms showed a less pronounced avoidance).
HETEROGENEITY IN THE THERMALLY‐INDUCED QUENCHING OF THE PHOSPHORESCENCE OF MULTI‐TRYPTOPHAN PROTEINS
Authors: Domanus Jerry , Strambini Giovanni B. , Galley William C.
Published: January 2008

Abstract— The steady‐state intensity and lifetime of the tryptophan phosphorescence from a number of globular proteins in 2:1 (v/v) glycerol buffer were monitored as a function of temperature. The phosphorescence lifetimes are essentially independent of the tryptophan local environment in rigid solution at temperatures < 170K, but vary markedly between proteins at temperatures at which the solutions become fluid. The ratio of steady‐state intensity to lifetime P/τ was found to be temperature independent despite the quenching for free tryptophan and the lone residue in myelin basic protein. Heterogeneity in the triplet quenching of the tryptophans in liver alcohol dehydrogenase and alkaline phosphatase were revealed as step‐like decreases in the ratio of P/T followed by plateau regions characterizing the homogeneous behavior of the more resistent tryptophans in the proteins. This heterogeneity exists not only between solvent‐exposed and buried residues, but reflects variations in the flexibility of the structure surrounding distinct buried tryptophans in the globular proteins.
ALPHA‐TERTHIENYL, A NON‐PHOTODYNAMIC PHOTOTOXIC COMPOUND
Authors: Kagan Jacques , Gabriel Robert , Reed Sally A.
Published: January 2008

Abstract— Alpha‐terthienyl (αT), a natural product first isolated in the plant Tagetes erecta (family Compositae), is the first member of a new class of phototoxic compounds, whose activity is not based on the generation of singlet oxygen. Its maximum activity against Candida utilis was at 370 nm, and was not affected by the presence of sodium azide. Furthermore, its phototoxicity against E.coliB cells was expressed under nitrogen, but not under oxygen. In the presence of UVA, radioactive αT formed covalent bonds with calf thymus DNA, and was also incorporated into the DNA of C. utilis. Two different methods proved that the photochemical interaction of αT and DNA did not involve cross linking of double strands.
RETINAL‐OPSIN LINKAGE OF CEPHALOPOD RHODOPSIN
Authors: Kito Yuji , Nashima Kazuko
Published: January 2008

Abstract— The pKa of the Schiff base of N‐retinylidene butylamine was determined in anionic (sodium dodecylsulfate), cationic (cetyltrimethylammonium bromide) and nonionic (polyoxyethylene (9) lauryl ether) detergent solutions. The pKa of the Schiff base was raised from 6.4 to 9.9 by the effect of the neighboring anion. The rise of the pKa was affected by the ion strength. Squid metarhodopsin behaved in a manner similar to the model Schiff base in the anionic detergent solution. The cationic group showed the opposite effect on the pKa of the Schiff base. The retinal Schiff base in rhodopsin might be heavily influenced by adjacent anionic groups. The nature of the interaction is discussed.
CHLOROPHYLL PHOTOCHEMISTRY IN CONDENSED MEDIA—I. TRIPLET STATE QUENCHING AND ELECTRON TRANSFER TO QUINONE IN CELLULOSE ACETATE FILMS*
Authors: Cheddar Glen , Castelli Francesco , Tollin Gordon
Published: January 2008

Abstract—

Chlorophyll‐a was incorporated into cellulose acetate films and the triplet state decay kinetics and electron transfer from triplet to p‐benzoquinone in aqueous solution was studied using laser flash photolysis and EPR. The triplet was found to decay by first order kinetics with a rate constant which was independent of Chl concentration. The triplet yield, however, was concentration dependent. These properties are due to quenching which occurs only at the singlet state level. In the presence of quinone, the triplet is quenched and, when the quinone is in an aqueous solution in contact with the film, Chl cation radical (C±) as well as the semiquinone anion radical (Q±) can be observed. The C decays by second order kinetics with a rate constant of 1.5 × 106M‐1 s‐1. Although triplet conversion to radicals is slightly lower in the films as compared to fluid solutions (˜ 3 times), the lifetimes of the radicals are greatly increased (˜ 103 times).
IRRADIATION IN THE FROZEN STATE: A TECHNIQUE FOR DIRECT PHOTOAFFINITY LABELING
Authors: Jr James J. Ferguson
Published: January 2008

Abstract—

UV irradiation of rabbit muscle phosphofructokinase (PFK) in the presence of adenosine 3′,5′‐cyclic phosphate (cAMP) resulted in the covalent attachment of this ligand molecule to the enzyme protein. Irradiation in the frozen ice state enhanced the rate of this incorporation more than 10‐fold above that achieved in aqueous solution, without significantly affecting the rate of photodestruction of the protein. [3H]‐cAMP and [32P]‐cAMP were each incorporated into PFK at identical rates in the frozen state. Rates of photoincorporation in the frozen and liquid states were both half‐maximal at a free ligand concentration approximately equal to the dissociation constant of cAMP and PFK. Adenosine diphosphate (ADP) and adenosine monophosphate (AMP), both of which are known to compete for cAMP binding to PFK, inhibited photoincorporation of cAMP. Guanosine monophosphate (GMP), inosine monophosphate (IMP), and guanosine 3′,5′‐cyclic phosphate (cGMP), which do not compete for cAMP binding, had no effect on photoincorporation of cAMP. Irradiation of [3H]‐AMP or [3H]‐ADP resulted in photoincorporation into PFK at 0°C, with enhancement at — 77°C similar to that noted with cAMP.
SOLVENT AND ACIDITY DEPENDENCE OF THE ABSORPTION AND FLUORESCENCE OF COUMESTROL*
Authors: Wolfbeis Otto S. , Schaffner Kurt
Published: January 2008

Abstract—

The UV absorption and fluorescence of the plant estrogen coumestrol (1) are markedly dependent on solvent and acidity. In neutral non‐aqueous solvents, emission occurs from the uncharged first excited singlet state. In aqueous solutions of 1, five species—the neutral form, the mono‐ and dianions, and the mono‐ and dications—were found and characterized by their UV absorptions, fluorescence (including lifetimes and quantum yields), and pK's of the ground and excited singlet states. The assignments are based on absorption, fluorescence and pK(*) data of coumestrol dimethyl ether (2), 3‐phenyl‐7‐hydroxy coumarin (3), 34′‐hydroxyphenyl coumarin (4), and appropriate model compounds from the literature. Variations in øF and, consequently, τF values are ascribed to excited state proton transfer processes. Fluorescence quantum yields as high as ca. 0.7 in most organic solvents and in certain pH ranges should render fluorimetry a suitable method for quantitative assays of this estrogen which is responsible for ‘clover disease’ in sheep.
THE PHOTOLYSIS RATES OF SOME DI‐ AND TRIPEPTIDES OF TRYPTOPHAN
Authors: Tassin J. D. , Borkman R. F.
Published: January 2008

Abstract—

We have measured the relative rates of photolysis of free tryptophan (trp), the dipeptides Gly‐Trp, Trp‐Gly, Leu‐Trp, and Trp‐Leu, and the tripeptides Gly‐Trp‐Gly and Leu‐Trp‐Leu. The photolyses were performed in neutral 0.1 mM aqueous solutions at 25°C using monochromatic 290 nm Xe arc radiation. Tryptophan loss was monitored by absorption, fluorescence and phosphorescence spectroscopy. The rate of tryptophan fluorescence loss was found to be different in the di‐and tripeptides than in tryptophan monomer. These rate differences depended on both the identity of the neighboring amino acid (gly or leu) and on the nature of the linkage, e.g., the rate of Gly‐Trp photolysis was more than 10 times greater than the rate of Trp‐Gly photolysis. Degassing was found to markedly reduce (factor of 8) the photolysis rates of Trp, Trp‐Gly, and Trp‐Leu, but degassing only slightly reduced (less than a factor of 2) the photolysis rates of the other di‐and tri‐peptides. Photochemical product structures were not determined, but absorption and fluorescence spectra were obtained and products could be inferred in some cases by comparison with data of previous workers. The products appeared to differ greatly among the various peptides studied; Trp, Trp‐Gly, and Trp‐Leu gave oxidation products, while Gly‐Trp and Leu‐Trp apparently gave ring closure products, not requiring oxygen.
EFFECTS OF ACRIDINE PLUS NEAR ULTRAVIOLET LIGHT ON ESCHERICHIA COLI MEMBRANES AND DNA IN VIVO
Authors: Wagner Stephen , Taylor William D. , Keith Alec , Snipes Wallace
Published: January 2008

Abstract—

Results from a variety of experiments indicate that photodynamic damage to E. coli treated with the hydrophobic photosensitizer acridine plus near‐UV light involves both cell membranes and DNA. Split‐dose survival experiments with various E. coli mutants reveal that cells defective in rec A, uvr A, or pol A functions are all capable of recovery from photodynamic damage. Alkaline sucrose gradient analysis of DNA from control and treated cells revealed that acridine plus near‐UV light treatment converts normal DNA into a more slowly sedimenting form. However, the normal DNA sedimentation properties are not restored under conditions where split‐dose recovery is effective. Several lines of evidence suggest that membrane damage may be important in the inactivation of cells by acridine plus near‐UV light. These include (a) a strong dependence of sensitivity on the fatty acid composition of the membranes; (b) a strong dependence of sensitivity on the osmolarity of the external medium; and (c) the extreme sensitivity of an E. coli mutant having a defect in its outer membrane barrier properties. Direct evidence that acridine plus near‐UV light damages cell membranes was provided by the observations that (a) the plasma membrane becomes permeable to o‐nitrophenyl‐ß‐D‐galactopyranoside and (b) the outer membrane becomes permeable to lysozyme after treatment. A notable result was that cells previously sensitized to lysozyme by exposure to acridine plus near‐UV light lose that sensitivity upon subsequent incubation. This strongly suggests that E. coli cells are capable of repairing damage localized in the outer membrane.
KINETIC STUDIES OF SELF‐SENSITIZED PHOTOOXYGENATION IN H2O AND D2O OF A WATER‐SOLUBLE RUBRENE DERIVATIVE
Authors: Aubry J. M. , Rigaudy J. , Cuong Nguyen Kim
Published: January 2008

Abstract A continuous argon laser has been used to study the self‐sensitized photooxidation of potassium rubrene‐2,3,8,9‐tetracarboxylate in oxygen‐saturated H2O and D2O. An analysis of the data obtained in concentrated solutions leads to an unexpected high value of the ratio of 1O2 lifetimes in D2O and H2O, Td2o/Th2o =17 ± 1. Results obtained in diluted aqueous solutions are interpreted in terms of a re‐encounter of 1O2 and ground state substrate molecules generated in the same triplet—triplet annihilation act.
EXCITATION‐ENERGY TRANSFER BETWEEN TYROSINE AND TRYPTOPHAN IN PROTEINS EVALUATED BY THE SIMULTANEOUS MEASUREMENT OF FLUORESCENCE AND ABSORBANCE
Authors: Saito Yoshio , Tachibana Hideki , Hayashi Hidechika , Wada Akiyoshi
Published: January 2008

Abstract— The efficiencies of the excitation–energy transfer from tyrosine to tryptophan residues in eight globular proteins in the native and denatured states are obtained by studying the wavelength dependence of the fluorescence quantum yield. The measurements are made over a wide wavelength range using a computer‐controlled spectrophotometer which can measure the fluorescence and absorbance simultaneously in one sample solution (Wada et al., 1980). The values of the energy transfer efficiencies ranged from 0.17 ± 0.12 to 0.69 ± 0.06 in the native state and from ‐0.04 ± 0.09 to 0.12 ± 0.06 in the denatured state. These values are considerably lower than the values reported by Kronman and Holmes (1971); in particular, an almost complete absence of energy transfer for the denatured state is shown.
ON THE POSSIBILITY OF PROTEIN–CHROMOPHORE CHARGE TRANSFER IN VISUAL PIGMENTS
Authors: Leclercq J.‐M. , Sandorfy C.
Published: January 2008

Abstract— Quantum chemical calculations have been performed on the retinylidene Schiff base assumed to be protonated or hydrogen bonded at the nitrogen and perturbed by a carboxylate ion at its β‐ionone end. The results indicate that weak charge transfer type bands might exist due to electron transfer from the carboxylate ion to the Schiff base and that the intense (π, π*) band in the visible spectrum might acquire a significant degree of charge transfer character.
STRUCTURAL STUDIES OF BROWN MEMBRANE BY X‐RAY DIFFRACTION, CIRCULAR DICHROISM AND ABSORPTION SPECTRA
Authors: Hiraki Kenji , Hamanaka Toshiaki , Mitsui Toshio , Kito Yuji
Published: January 2008

Abstract— Time course of formation and crystallization of bacteriorhodopsin upon the addition of retinal to brown apo‐membrane has been studied by X‐ray diffraction, circular dichroism (CD) spectra and absorption spectra. The rate of formation of bacteriorhodopsin decreases markedly at low pH (4.8) and low temperature (5°C). Furthermore, the formation of bacteriorhodopsin does not proceed in fully dried membranes. The half‐time of the increase of exciton CD band is about 70s at 17°C and pH 7.0, and is comparable to that of the formation of bacteriorhodopsins (∼48s). The crystallization of bacteriorhodopsin proceeds to a large extent within 30 min at pH 7.0 and 5°C.

The bilobed CD band of the brown holo‐membrane attributed to exciton coupling of bacteriorhodopsin molecules becomes negligibly small at pH 4.8, even though X‐ray diffraction pattern indicates the lattice structure to be similar to that of the native purple membrane.
INTERPRETATIONS OF THE SOLUTION AND ORIENTED FILM SPECTRA OF BROWN MEMBRANE OF HALOBACTERIUM HALOBIUM
Authors: Papadopoulos George K. , Cassim Joseph Y.
Published: January 2008

Abstract— The absorption and circular dichroic spectra of the brown holo‐membrane (retinal present) and apo‐membrane (retinal absent) of Halobacterium halobium in solution and oriented as a film have been studied over the accessible wavelength region, 800–183nm. Since the structure of the well‐studied purple membrane can be considered to be a modification of the structure of the brown membrane and much is known about the structure of the purple membrane, interpretations of the brown membrane spectra are based on our previous interpretations of similar studies of the purple membrane. The brown membrane contains two membrane proteins, bacteriorhodopsin and cytochrome b‐561 in a 3:1 molar ratio in contrast to the purple membrane which contains only bacteriorhodopsin. Main findings are (a) degenerate oscillator coupling (exciton) among the retinyl chromophores of the bacteriorhodopsins, (b) a relatively strong in‐plane interaction between the retinal and the bacteriorhodopsin apoprotein environment, possibly due to a dissymmetric static charge distribution, (c) the planes of the aromatic rings of some of the tryptophans must be nearly parallel to the plane of the membrane, (d) the helical axes of the bacterio‐opsin polypeptide segments are significantly tilted in respect to the normal to the membrane plane in contrast to the helical axes of the bacteriorhodopsin polypeptide segments which are nearly parallel to the normal, (e) no detectable interaction between the two membrane proteins, (f) the plane of the heme of the cytochrome cannot be parallel to the membrane plane and is most likely perpendicular to it. (g) the dipole moments of the two mutually perpendicular Soret porphyrin transitions of the heme are most likely oriented at an angle to the membrane plane, (h) there seems to be a significant reduction in the symmetry of the heme group in the environment of the apoprotein, (i) the possibility of a unique geometrical arrangement and resonance interaction between the Soret porphyrin and nearby cytochrome aromatic amino acid π–π* transitions, (j) the secondary structure of the cytochrome is significantly α‐helical, and (k) the helical axes of the cytochrome polypeptide segments are randomly oriented in respect to the normal to the membrane plane. A consequence of these findings is that the fine structures of the bacteriorhodopsins of the brown and purple membranes are very similar in spite of differences in the composition and the structure of the two membranes. In addition, the orientation of the helical segments of the bacteriorhodopsin polypeptides relative to the membrane plane in the brown and purple membranes can be regulated by the retinal–apoprotein interactions. Significance of this possible regulation in respect to the proton‐pumping function of these membranes is discussed.
MOLECULAR ASPECTS OF LIGHT‐INDUCED UPTAKE AND RELEASE OF PROTONS BY PURPLE MEMBRANES
Authors: Packer Lester , Quintanilha Alexandre T. , Carmeli Chanoch , Sullivan Paul D. , Scherrer Peter , Tristram Stephanie , Herz Jeffrey , Pfeifhofer Albert , Mehlhorn Rolf J.
Published: January 2008

Abstract— The precise molecular description of the time dependent steps in the uptake, translocation and release of protons by bacteriorhodopsin following photon absorption requires information on the time resolved changes in protonation of the side chains of specific amino acid residues and the correlation of these changes with photocycle kinetics. Thus far, the use of chemical modification to probe the role of amino acid side chains in this process has proven of value in demonstrating a role for tyrosine residues in release and uptake of protons associated with early and later stages (before and after M412 formation) of the photocycle. In addition, it has demonstrated the essential role of ionic interactions between negatively charged carboxyl groups and positively charged guanidinium groups of arginine, and amino groups of lysine. The transmembrane regulatory effect of ΔμH+ on the M412 species of the photocycle provides additional evidence for the participation of reversible protonation of amino acid side chains at the surfaces of the purple membrane in the mechanism of proton translocation. Thus, our studies relate molecular events of proton translocation to the bioenergetics of the purple membrane.
INHIBITION OF RESPIRATION AND LOSS OF MEMBRANE INTEGRITY BY SINGLET OXYGEN GENERATED BY A PHOTOSENSITIZED REACTION IN NEUROSPORA CRASSA CONIDIA
Authors: Shimizu‐Takahama Michiko , Egashira Takeshi , Takahama Umeo
Published: January 2008

Abstract— It was found that killing of Neurospora crassa conidia by singlet molecular oxygen generated by a photosensitized reaction in the presence of toluidine blue O, accompanied inhibition of respiration and uptake of the photosensitizing dye by conidia. Both the inactivation of respiration and the uptake of toluidine blue O were stimulated by deuterium oxide and suppressed by azide. Mitochondria of irradiated conidia were swollen and showed matrix of low density under an electron microscope.

These results suggest that singlet molecular oxygen induces the inhibition of respiration and the loss of membrane integrity of Neurospora conidia.
THE KINETICS OF REDUCTION OF CYTOCHROME c BY SEMI‐REDUCED FLAVIN
Authors: Salet C. , Land E. J. , Santus R.
Published: January 2008

Abstract— Flavin mononucleotide radicals, FMNH', generated by laser flash photolysis of FMN in the presence of the electron donors, histidine, guanosine monophosphate or EDTA, were found to reduce cytochrome c with an apparent rate constant of 6 ± 107M−1 s−1. These flash photolysis results were, however, complicated by the electron donor radicals formed simultaneously which, particularly with EDTA, also lead to reduction of cytochrome c. Pulse radiolysis of a nitrous oxide saturated aqueous solution of FMN containing a high concentration of HCOONa, leads to the exclusive formation of FMNH'. By adding small concentrations of cytochrome c to this solution, a rate constant of 4.0 ± 10−1M−1 s−1 was obtained for the reduction of cytochrome c by FMNH'. Replacement of the HCOONa by EDTA in such solutions leads to further routes for reduction of cytochrome c on radiolysis. as in the photolytic situation. The relevance of these results to flavin‐photosensitised reduction of cytochrome c and other components of the mitochondrial electron transport chain is discussed.
THE MASKING MODEL: A POSSIBLE EXPLANATION FOR VARIOUS EFFECTS OF NEAR‐UV RADIATION
Authors: Hartman Philip S.
Published: January 2008

Abstract—A general model is proposed to explain certain phenomena observed upon the near‐UV irradiation of biological materials. The model states that the ratio of two action spectra (e.g. in the presence or absence of histidine) does not accurately portray the absorption spectrum of the underlying chromophore. Rather, such a ratio is dictated by the relative amounts of two photoproducts. Both photoproducts are induced most efficiently at or below 300 nm. One photoproduct, sensitive to the presence of the variable agent (e.g. histidine), has a broader production spectrum than the other, which is induced independently of the variable agent. The first photoproduct is quantitatively more important at shorter wavelengths while the second dominates at longer wavelengths. An equation has been derived which defines the model in mathematical terms. Such a model might explain: (1) increased phage and bacterial inactivation in the presence of sublethal hydrogen peroxide concentrations; (2) the discrepancy between the inactivation action spectrum and absorption spectrum of psoralen; (3) histidine protection of transforming DNA inactivation; (4) phage T7 inactivation; (5) bacterial inactivation under anoxic conditions; (6) inactivation of DNA repair enzymes; and (7) photomutagenesis at low fiuence rates.
MOLECULAR HYDROGEN PRODUCTION BY UROPORPHYRIN AND COPROPORPHYRIN: A MODEL FOR THE ORIGIN OF PHOTOSYNTHETIC FUNCTION
Authors: Mercer–smith Janet A. , Mauzerall David
Published: January 2008

Abstract— Since life originated when the earth's atmosphere was still chemically reducing, the photooxidation of the prevalent reduced organic compounds and the emission of molecular hydrogen would have been a useful form of photosynthesis. If the biosynthetic pathway to chlorophyll recapitulates the evolutionary history of photosynthesis, then uroporphyrin served an early photosynthetic function. In the present study, ethylenediamine tetraacetic acid was oxidized by photoexcited uroporphyrin and coproporphyrin to produce molecular hydrogen in aqueous solution in the presence of colloidal platinum catalyst. In the presence of methyl viologen, a one‐electron carrier, the reaction is cyclic and hydrogen gas is produced at a constant rate. The evidence suggests that porphyrin radical intermediates rather than hydroporphyrin are active in the formation of molecular hydrogen. A coproporphyrin‐polyvinyl alcohol‐colloidal platinum polymer was used as a model for the evolving biological system for photosynthesis in which reactants are held in close proximity.
DITHIOPHENES AS SINGLET OXYGEN SENSITIZERS
Authors: Gommers F. J. , Barker J. , Wynberg H.
Published: January 2008

Abstract— The nematicidal compounds, 5‐methyl‐2,2′dithienyl, 5‐phenyl‐2,2′‐dithienyl and 5,5′‐dichloro‐2,2′‐dithienyl, generate singlet oxygen upon photoactivation with near‐UV light. Two chloro‐substituted dithienylethenes have similar properties that are farless efficient. The nematode Aphelenchus avenae was rapidly killed by the photoactivated dithienyls under aerobic but not under anaerobic conditions,indicating that nematicidal activity of these compounds is related to their sensitizing properties. Furthermore,these nematodes did not expire in the presence of these compounds maintained in the dark. Sensitizing properties were studied by following the inhibition ofglucose–6‐phosphate dehydrogenase by the photoactivated compounds and protection of enzyme activity by various additions. Only singlet oxygen quenchers were effective. The enzyme was inactivated 3 to 4 times faster in D20 compared to H20.Bleaching of p‐nitrosodimethylaniline in the presence of imidazole and the dithiophenes and a specific reaction with the olefin adamantylideneadamantane were additional evidence of generation of singlet oxygen by the photoactivated compounds.
DNA SYNTHESIS ON ØX174 TEMPLATE DAMAGED BY PROFLAVINE and LIGHT TREATMENT
Authors: Piette J. , Moore P. D.
Published: January 2008

Abstract— Onprimed–0X174 single‐stranded DNA photosensitized in the presence of proflavine, Escherichia coli DNA polymerase terminates DNA synthesis at the nucleotide preceding a guanine residue. This chain termination is visualized on a DNA sequencing gel. Our results show that (i) the major targets of the action of proflavine in the DNA are the guanine residues, (ii) there seems no preferential alteration of some residues and (iii) the rate of alteration is very high. We show that the loss of infectivity of 0X174 mediated by the photodynamic action of proflavine can be explained by a block in the DNA polymerisation reaction.
LOSS OF PHOTOREACTIVATION IN UV‐IRRADIATED CULTURED FISH CELLS UNDER DIFFERENT CONDITIONS
Authors: Mano Yukiko , Kator Kunihiko , Egami Nobuo
Published: January 2008

Abstract— CAF‐MM1 cells derived from a goldfish have photoreactivability for the damage induced by ultraviolet light (UV). When UV‐irradiated cells were incubated in the dark at 26AoC, the longest interval in which photoreactivation (PR) was observed (i.e. effective time for PR), measured by colony formation technique, was about 30 h after the UV irradiation. However, if the cells were incubated at 20AoC, the effective time was prolonged. Since each time appeared to correspond to the doubling time of the cells at each temperature, the loss of photoreactivability is suggested to be closely related to cell growth or progression of cell cycle. The loss of PR was not observed in the cells held in confluence up to 48 h after UV irradiation, in support of the above suggestion. Photoreactivating enzyme in growing CAF‐MM1 cells incubated in the dark for 24 h after UV irradiation was shown to be active, so that it is not possible that the cause of the loss of PR is change in the activity of photoreactivating enzyme.
THE EFFECT OF COORDINATING LIGANDS ON THE TRIPLET STATE OF CHLOROPHYLL
Authors: Clarke R. H. , Hotchandani S. , Jagannathan S. P. , Leblanc R. M.
Published: January 2008

Under laser excitation at 457.9 and 514.5 nm, a frozen solution of chlorophyll a in n‐octane displays fluorescence peak maxima at 2K that may be assigned to two distinct monomeric chlorophyll species. Using zero‐field fluorescence‐detected magnetic resonance the triplet state properties of the two chlorophyll species have been assigned to the monoligated and biligated chlorophyll monomer in which water serves as the ligand coordinated to the magnesium metal center. These triplet state properties for chlorophyll in solution are then utilized in interpreting triplet state results for in vivo chlorophylls associated with the light harvesting chlorophyll protein complex. It is shown that the triplet state data are consistent with attachment of the chlorophyll molecule to the protein site with a single ligand coordinated to the chlorophyll metal center.
IRRADIATION OF CIRCULAR DNA WITH 254 nm RADIATION OR SENSITIZATION IN THE PRESENCE OF Ag+ EVIDENCE FOR UNWINDING BY PHOTOPRODUCTS OTHER THAN PYRIMIDINE DIMERS
Authors: Ciarrocchi Giovanni , Sutherland Betsy M.
Published: January 2008

Abstract— Structural alterations of DNA irradiated with UV light were analyzed by the agarose gel technique. Relaxed, circular pAT 153 DNA molecules were sensitized by broad band radiation with a maximum at 313 nm in the presence of silver ions or irradiated with 254 nm light in buffer only. In both cases the electrophoretic mobility of DNA topoisomers was altered as a linear function of UV exposure. For DNA irradiated in the sensitized reaction the unwinding angle per site sensitive to Micrococcus luteus pyrimidine dimer endonuclease was found tobe–11.4°. This value is significantly smaller thanthe–14.3° already known for DNA topoisomers irradiated with 254 nm light. The irradiated DNAs were a very good substrate for the Escherichia coli photoreactivating enzyme (PRE). However, the photoenzymic removal of all sites sensitive to the endonuclease specific for pyrimidine dimers was not coupled to a full restoration of the original electrophoretic mobility. Thirty and 23% of the unwinding were still present in the photoreactivated topoisomers and the unwinding angles per pyrimidine dimer were then recalculatedas–10.1°and–8.7° for DNAs irradiated with 254 nm and sensitized, respectively. The limited difference between these two values could result from the different base composition of the pyrimidine dimers generated in the conditions of irradiation used. These results show that the tertiary structure of DNA is measureably altered by UV photodamages other than pyrimidine dimers.
ROLE OF THE supX GENE IN SENSITIZING Salmonella typhimurium CELLS TO RESPIRATION SHUTOFF INDUCED BY FAR ULTRAVIOLET IRRADIATION
Authors: Swenson Paul A. , Riester Laura , Palmer T. V.
Published: January 2008

Abstract— Salmonella typhimurium strains with supX mutations are known to be sensitive to ultraviolet (254 nm) irradiation (UV) and to be protected by plasmid pKM101. Wild type (supX+) cells shut off their respiration after UV and are protected against their shutoff by pKM101. Respiration and survival studies were carried out on several supX strains with different genetic backgrounds. The supX strains shut off their respiration after low fluences of UV. Plasmid pKM101 protected a supX 83 (nonsense mutation) strain against respiration shutoff and killing but did not protect a supX35 (deletion mutation) strain against respiration shutoff or killing. When each of the two supX genes were in the genetic backgrounds of the other, however, full protection was provided by pKM101. The supX35 strain not protected by pKM101 may have accummulated a modifying mutation. The supX locus is identical with one specifying topoisomerase I which removes negative superhelical turns from DNA. In the absence of this enzyme transcription of the DNA is increased. It is proposed that the exaggerated shutoff of respiration and increased killing of supX cells occurs because of the greater ease of transcription of an operon involved in UV‐induced respiration shutoff.
EFFECT OF PHOTOSELECTION UPON SATURATION AND THE DICHROIC RATIO IN FLASH EXPERIMENTS UPON EFFECTIVELY IMMOBILIZED SYSTEMS
Authors: Nagle J. F. , Bhattacharjee S. M. , Parodi L. A. , Lozier R. H.
Published: January 2008

Abstract— Flash spectroscopy of photochemical or photobiological systems, such as bacteriorhodopsin in purple membrane, for which the chromophore transition dipole moment does not undergo complete reorientation during the time of the flash, is considered as a function of light intensity. Due to photoselection, saturation proceeds very slowly with increasing flash intensity and the linear dichroic ratio decays rapidly from a maximum of three at zero flash intensity. Simple formulae are derived to describe these effects under stringent assumptions. Calculations are also performed which relax the assumptions by taking into account (i) non‐zero optical density, (ii) thermal decay of the photoproduct during the flash and (iii) non‐zero angle y between the initial chromophore and its photoproduct. Agreement with experiments on bacteriorhodopsin in purple membranes is excellent.
QUANTITATIVE MICROPHOTOMETRY AT THE CELLULAR LEVEL: A SIMPLE TECHNIQUE FOR MEASURING CHLOROPLAST MOVEMENTS IN VIVO*
Authors: Blairt Michael R. , Briggs Winslow R.
Published: January 2008

Abstract— A recording microphotometer was developed to permit quantitative analysis of light‐induced chloroplast aggregation in single filaments of the alga Vaucheria. Optical fibers were used both to irradiate the cells and to collect the transmitted light. Light transmittance was examined as a function of time at a fixed point along an algal filament. The photoresponse was stimulated by combining an additional actinic beam with the measuring beams such that both actinic and measuring beams followed the same optical path. The quasi‐opalescent properties of the optical fibers and dual‐wavelength measurements compensated for light scattering and variations in sample geometry.

Chloroplast aggregation, marked by a passive accumulation of organelles in the irradiated region of the cell, resulted in a decline of cell transmittance to 675 and 743 nm light. During stimulation with moderate intensities of actinic, 473 nm light the relative transmittance to 675 nm light (corrected for scattering, measured at 743 nm) fell below 0.1 within 5 min. The exponential form of this transmittance change as a function of time was consistent with changes in optical geometry of the aggregate during the photoresponse. It follows that the decay in algal transmittance can provide a measure of the rate of chloroplast accumulation in the light path.
THE INFLUENCE OF FLAVONOID SULFONATES ON THE FLUORESCENCE AND PHOTOCHEMISTRY OF FLAVYLIUM CATIONS
Authors: Santhanam Mahalingam , Hautala Richard R. , Sweeny James G. , Iacobucci Guillermo A.
Published: January 2008

Abstract— The effects of flavone sulfonic acid 9 andquercetin–5′‐sulfonic acid 10 on the luminescence spectra of eight flavylium salts have been determined. The non‐hydroxylated flavone 9 was found to enhance the luminescence of those flavylium salts, while the polyhydroxyflavonol 10 was shown to exert the opposite effect. These findings are rationalized in conjunction with prior observations on the enhancement and inhibition of the photodecomposition of anthocyanins exerted by 9 and 10, respectively.
PHOTOCHEMICAL REACTIONS OF DIBROMOTHYMOQUINONE: STRUCTURE AND INHIBITORY PROPERTIES OF THE PHOTOPRODUCT
Authors: Stidham Mark A. , Siedow James N.
Published: January 2008

Abstract— The chemical structure of the major product that resulted from illumination of ethanolic solutions of dibromothymoquinone was deduced using 13C‐and 1H‐nuclear magnetic resonance spectroscopy. The photoproduct is 2,5‐dibromo‐3‐allyl‐6‐methyl‐p‐dihydrobenzoquinone. The inhibition of photosynthetic electron transport by the photoreduced compound was found to be roughly equivalent to inhibition by nonirradiated dibromothymoquinone.
ULTRAVIOLET ACTION SPECTRA FOR AEROBIC AND ANAEROBIC INACTIVATION OF Escherichia coli STRAINS SPECIFICALLY SENSITIVE AND RESISTANT TO NEAR ULTRAVIOLET RADIATIONS
Authors: Peak Jennifer G. , Peak Meyrick J. , Tuveson Robert W.
Published: January 2008

Abstract— Action spectra for the lethal effects of ultraviolet light (254–434 nm) irradiation delivered under aerobic or anaerobic conditions to Escherichia coli RT2 (specifically sensitive to near‐UV radiation; > 320 nm) and E. coli RT4 (near‐UV resistant) were prepared. Negligible oxygen dependence was observed for both strains below about 315 nm. The oxygen enhancement ratio (OER) for RT4 increased above this wavelength to the longest wavelength used, whereas for RT2 there was a greater increase in the OER to a large peak at 365 nm, then a progressive decrease at longer wavelengths. The results are consistent with the possibility that the sensitivity of strain RT2 to near‐UV radiation may be due to hyperproduction of photosensitizer, operating via photodynamic type reactions involving excited species of oxygen.
REGULATION OF PROTOCHLOROPHYLL(IDE) LEVELS IN DARK‐GROWN NON‐DIVIDING Euglena—II. INFLUENCE OF UTILIZABLE SUBSTRATES AND INHIBITORS OF PROTEIN SYNTHESIS*
Authors: Alhadeff Myriam , Schiff Jerome A.
Published: January 2008

Abstract—

Dark‐grown cells of Euglena gracilis var. bacillaris incubated on resting medium for 7 days lose half of their extractable and phototransformable protochlorophyll(ide) [Pchl(ide)]. The readily‐utilized substrates glutamate and malate bring about a regeneration of both pools of Pchl(ide) to the levels found in growing cells, without causing cell division during the period of regeneration. Light does not cause a regeneration of total extractable Pchl(ide) to the levels found in growing cells, and the complete regeneration of phototransformable Pchl(ide) seen probably results from conversion of non‐transformable Pchl(ide) to transformable Pchl(ide). Optimal glutamate, malate, and light in any combination are no better in causing phototransformable Pchl(ide) regeneration than any one treatment alone, indicating that the Pchl(ide) pool size is limited by other factors. The regeneration of phototransformable Pchl(ide) induced by light or substrates is insensitive to inhibitors of protein synthesis on 80 S cytoplasmic ribosomes (cycloheximide) or on 70 S chloroplast ribosomes (streptomycin). Cycloheximide, however, induces the regeneration of phototransformable Pchl(ide) in darkness in the absencc of externally‐added substrates. Since cycloheximide is known to induce paramylum breakdown under the same conditions, it is likely that this process can provide internal substrates and/or reducing power for phototransformable Pchl(ide) regeneration. Possible mechanisms of regulation of formation of Pchl(ide)635 in Euglena are discussed and compared with regulation of Pchl(ide)650 in higher plants.
REACTION OF RETINOL AND RETINAL WITH SINGLET OXYGEN
Authors: Smith G. J.
Published: January 2008

Abstract— The rate constants for the reactions of all‐trans retinol and retinal with singlet oxygen were measured in a variety of solvents of different polarities. The rate constants increased with increasing solvent dielectric constant, which suggests that a charge transfer mechanism plays a part in the reaction. Further, the rate constant of reaction of singlet oxygen with retinal is greater than that with retinol. Since retinal has a lower ionization potential than retinol, these relative rates also support the hypothesis of charge transfer involvement in the reaction.
QUENCHING OF CHEMICALLY and ENZYMICALLY‐GENERATED TRIPLET ACETONE BY TYROSINE and 3,5‐DIHALOGENODERIVATIVES
Authors: Rivas‐Suárez Edy , Catalani Luiz H. , J. Etelvino , Bechara H , Cilento Giuseppe
Published: January 2008

Tyrosine and especially its 3,5‐dihalogenoderivatives quench acetone triplets. When the excited acetone is generated free in solution, the Stern‐Volmer plots for the quenching by these species, monitored via the sensitized emission of the 9,10‐dibromoanthracene‐2‐sulfonate ion, are linear. When triplet acetone is generated enzymically by the peroxidase‐catalyzed aerobic oxidation of isobutyral‐dehyde, the Stern‐Volmer plots for the quenching of the acetone phosphorescence curve upwards in the case of 3,5‐dibromotyrosine and even more markedly with 3,5‐diiodotyrosine. Quenching appears likely to occur by triplet‐triplet energy transfer and especially in the case of the phenoxide form, also by electron transfer. The curvature denotes a static contribution to quenching favoured by the enzyme.
BINDING OF RIBOFLAVIN TO LYSOZYME PROMOTED BY PEROXIDASE‐GENERATED TRIPLET ACETONE
Authors: Durán Nelson , Haun Marcela , De Toledo Sonia M. , Cilento Giuseppe , Silva Eduardo
Published: January 2008

When riboflavin and lysozyme are added to the 2‐methylpropanal/peroxidase/O2 system, which generates triplet acetone, an adduct is formed to a small extent. The adduct can be separated by gel filtration and is similar to that prepared by irradiating riboflavin in the presence of lysozyme.
PROBING PHOTODYNAMIC DAMAGE IN NUCLEIC ACIDS WITH A DAMAGE‐SPECIFIC DNA BINDING PROTEIN: A COMPARISON OF THE B and Z DNA CONFORMATIONS
Authors: Feldberg Ross S. , Brown Caroline , Carew Josephine A. , Lucas Judith L.
Published: January 2008

—We have employed a damage‐specific DNA binding protein from human cells as a probe for base damage in polymers irradiated with white light in the presence of methylene blue. Protein‐recognizable damage is introduced only into guanine‐containing polymers and quenching of damage introduction by H2O and sodium azide suggest the involvement of a singlet oxygen mechanism. Using poly d(G‐m5C), we have demonstrated that the left‐handed double helical Z conformation is much less susceptible to guanine photooxidation than is the usual B conformation. We speculate that this difference in reactivity may reflect steric hindrance at the purine C‐4 position and could provide some insight into the initial steps of the reaction between singlet oxygen and guanine in nucleic acid polymers.
CHAIN BREAKAGE ACCOMPANYING THE PHOTOLYSIS OF IdUrd‐DNA
Authors: Rahn R. O. , Sellin H. G.
Published: January 2008

Abstract DNA isolated from Escherichia coli and substituted with various amounts of iododeoxyuridine (12‐95%) was irradiated at either 265. 300 or 313 nm and the frequency of chain breakage measured by sedimentation in either neutral or alkaline sucrose gradients. The wavelength dependence of the photochemical cross section for chain breaks paralleled that for iodine loss, and the average frequency of chain breakage per halogen loss was 0.50 ± 0.07. Approximately 80‐90% of the breaks observed in alkali are alkali‐labile bonds and are not observed under neutral conditions. The presence of ethanol during irradiation reduced the frequency of chain breakage by more than an order of magnitude. These results are interpreted in terms of a model in which photo‐induced deiodination leads to the formation of a uracilyl radical which then abstracts a hydrogen atom from either a nearby sugar moiety or from another hydrogen donor such as ethanol. The resulting modified sugar can then rearrange to form either a clean chain break or an alkali‐labile bond.