bluuebunny/crossref_metadata_2025 huggingface dataset:
LUMINESCENCE STUDIES ON FORMYCIN, ITS AGLYCONE, AND THEIR N‐METHYL DERIVATIVES: TAUTOMERISM, SITES OF PROTONATION AND PHOTOTAUTOMERISM
Authors: Wierzchowski Jacek , Shugar David
Published: January 2008

Abstract— A detailed study has been made of the luminescence spectra of 3‐β‐d‐ribofuranosyl‐7‐amino‐pyrazolo(4,3‐d)pyrimidine (formycin A), 3‐propyl‐7‐aminopyrazolo(4,3‐d)pyrimidine (7APP), and their various N‐methyl derivatives, at room temperature and in methanol‐water glasses at 77 K. Comparisons of the foregoing, together with the observed dependence of the emission spectra of formycin and 7APP on excitation wavelength, demonstrated that these consist of two tautomeric species, N(1)H and N(2)H, both of which emit at 300 and 77 K. The two tautomers may be distinguished by the location of the emission maxima, especially for phosphorescence, and quantum yields for emission.

Comparisons of the emission spectra of the protonated forms of 7APP and its N‐methyl derivatives showed that the fluorescence of the cations of 7APP and its N,‐ and N2‐methyl derivatives originates from the forms protonated on N(4). By contrast, the forms protonated on N(6) contribute appreciably to the phosphorescence at 77 K. On the basis of the emission spectra at 77 K, it is concluded that the major tautomeric form of the formycin cation is N(1)H,N(4)H+, but there is also some contribution by the form N(2)H,N(4)H+.

In acid medium at room temperature, there is photodissociation of a proton from the pyrazole ring of the formycin cation. This leads to formation in the state S! of the tautomeric species N(4)H, which does not exist in the ground state. This conclusion, similar to that previously reported for the analogous isomeric 4‐aminopyrazolo(3,4‐d)pyrimidines, is derived from a comparison of the fluorescence spectra of the cations of formycin and N4‐methylformycin, which exhibit two bands at 375 and 440 nm, the latter corresponding to the emission of the neutral form of N,i‐methylformycin. The proposed mechanism of phototautomerization is supported by a study of solvent and salt effects.
A LASER FLASH KINETIC SPECTROPHOTOMETRIC EXAMINATION OF THE DYNAMICS OF SINGLET OXYGEN IN UNILAMMELLAR VESICLES
Authors: Rodgers Michael A. J. , Bates Anne L.
Published: January 2008

Abstract— The kinetic properties of O2(1Δg) have been examined in unilamellar vesicle dispersions composed of didodecyldimethylammonium bromide, di‐n‐octadecyl phosphate and egg lecithin. Light absorbing sensitizers 2‐acetonaphthone, methylene blue and a methylene blue derivative of enhanced water‐solubility were used. The rate parameters for singlet oxygen were monitored by observing the time profile of the bleaching of the reactive substrates diphenylisobenzofuran and anthracene dipropionate. The natural lifetime of O2(1Δg) in D2O‐based suspensions was shown to be 46/JS in good agreement with that found earlier for D2O alone and D2O‐based micelle systems. The bimolecular rate constants for reaction with diphenylisobenzofuran and dimethylindole (both lipid‐bound) and histidine (water‐bound) were also in close conformity with the values found earlier in micellar media. Kinetic spectrophotometry has been shown to be a useful technique for examining rate parameters in these heterogeneous media.
THE ACTION SPECTRA FOR PHOTOREACTIVATION AND PHOTOREPAIR IN ICR 2A FROG CELLS
Authors: Rosenstein Barry S.
Published: January 2008

Abstract— Action spectra for photoreactivation (enhancement of colony forming ability) and photorepair (monomerization of pyrimidine dimers in DNA) were obtained for ICR 2A frog cells over the334–577 lira range. These spectra were very similar with peaks at 435 nm and little effectiveness at wavele.
ENHANCING EFFECT OF ASCORBATE ON TOLUIDINE BLUE‐PHOTOSENSITIZATION OF YEAST CELLS
Authors: Ito Atsushi , Ito Takashi
Published: January 2008

Abstract— Using toluidine blue, a potent photosensitizer with a 1O2 dominated mechanism in yeast cell inactivation, it was found that addition of ascorbate to the sensitizer‐cell mixture during illumination enhanced the inactivation. The enhancement required the presence of oxygen in the reaction mixture. The same enhancement was observed with methylene blue and thionine but not with xanthenes (Rose Bengal and eosin Y). The consumption of O2 and ascorbate seemed coupled in the enhancement. From the observation that the presence of ascorbate for a very short time (1 s) in the reaction mixture was enough to exhibit the same enhancement, it was concluded that the ascorbate enhancement processes are probably initiated in bulk medium, not intracellularly. The ascorbate enhancement may be a combined consequence of the high electron‐accepting property of triplet toluidine blue and the strong tendency of ascorbate to act as an electron donor. The role of oxygen was not specified whether it was directly involved in the photoinactivation of cells. Addition of N J appeared to suppress the photoinacti‐vation only in the higher fluence region where ascorbate had been consumed. Thus the ascorbate enhancement seems to occur under low fluence conditions and may probably be independent of the singlet oxygen mechanism.
PHOTOOXIDATION OF 8‐METHOXYPSORALEN WITH SINGLET OXYGEN*
Authors: Logani M. K. , Austin W. A. , Shah B. , Davies R. E.
Published: January 2008

Abstract— The in vitro photooxidation of 8‐methoxypsoralen (8‐MOP) with singlet oxygen is studied. Irradiation of 8‐MOP(295–400 or320–400 nm) in the presence of oxygen for 72 h results in the formation of a product (1.4%) which is identified as 6‐formyl‐7‐hydroxy‐8‐methoxycoumarin by aid of IR, NMR, MS and co‐chromatography with an authentic sample. A study of this reaction in the presence of l,4‐diazobicyclo(2,2,2)octane, a singlet oxygen scavenger, indicates the involvement of 1O2 in the formation of this compound. In addition to this, formation of a novel dimer of 8‐MOP is reported.
PHOTO‐CIDNP STUDY OF ADENYLYL‐CONTAINING DEOXY‐DINUCLEOTIDES. PAIR SUBSTITUTION EFFECTS DUE TO INTRAMOLECULAR CATION RADICAL DEPROTONATION
Authors: Schleich T. , Scheek R. M. , Stob S. , Alma N. C. M. , Hilbers C. W. , Kaptein R.
Published: January 2008

Abstract— 360 MHz 1H photo‐CIDNP spectra of several adenylyl containing deoxy dinucleotides show that fast deprotonation at the 6‐amino group of the adenylyl radical cation can occur via two intramolecular routes. One is mediated by the 5′‐phosphomonoester group and only occurs for the pdA moiety at the 3′ end of the dinucleotide, e.g. in pdTpdA and pdApdA; molecular model building studies reveal that fluctuations away from the B‐DNA like conformation are involved. In the second route the deprotonation is catalyzed by N‐l located on an adjacent adenine ring, like in dApdA and pdApdA; it probably occurs for both adenylyl units in a stacked conformation. This fast deprotonation leads to the observation of negative polarization for the adenineH–8 as was observed in the case of adenosine 5‐monophosphate in the presence of added phosphate.
HYDRODYNAMIC EFFECTS IN THE PHOTOSENSITIZED LYSIS OF LIPOSOMES*
Authors: Grossweiner Leonard I. , Grossweiner James B.
Published: January 2008

Abstract— The photosensitized lysis of phosphatidylcholine liposomes incorporating methylene blue in the membrane or in the presence of external methylene blue is promoted by hydrodynamic agitation concurrent with or subsequent to irradiation with red light. The results implicate the attack of singlet oxygen on an unsaturated lipid component as the key photochemical step, which is followed by additional membrane damage induced by hydrodynamic action.
SINGLE‐STRAND BREAKS INDUCED IN BACILLUS SUBTILIS DNA BY ULTRAVIOLET LIGHT: ACTION SPECTRUM and PROPERTIES
Authors: Peak M. J. , Peak J. G.
Published: January 2008

Abstract— The induction of single‐strand breaks (alkali‐labile bonds plus frank breaks) in the DNA of Bacillus subtilis irradiated in vivo by monochromatic UV light at wavelengths from 254 to 434 nm was measured. The spectrum consists of a major far‐UV (below 320 nm) component and a minor near‐UV shoulder. A mutant deficient in DNA polymerase I accumulates breaks caused by near‐UV (above 320 nm) wavelengths faster than the wild‐type strain proficient in polymerase I. Measurable breaks in extracted DNA are induced at a higher frequency than those induced in vivo. Anoxia, glycerol, and diazobicyclo (2.2.2.) octane inhibit break formation in extracted DNA. Alkali‐labile bonds induced by 365‐nm UV radiation are largely (78%) covalent bond chain breaks, the remainder consists of true alkali‐labile bonds, probably apurinic and apyrimidinic sites.
PIGMENT ORGANIZATION IN THE LIGHT‐HARVESTING CHLOROPHYLL‐a/b PROTEIN COMPLEX OF LETTUCE CHLOROPLASTS. EVIDENCE OBTAINED FROM PROTECTION OF THE CHLOROPHYLLS AGAINST PROTON ATTACK and FROM EXCITATION ENERGY TRANSFER
Authors: Siefermann‐Harms Dorothea , Ninnemann Helga
Published: January 2008

Abstract—The light‐harvesting Chl‐a/b protein complex (LHC) ofLactuca sativaL. was examined for pigment content, excitation energy transfer and behavior under acidic conditions:

(1) Lettuce LHC contains Chl‐a, Chl‐b and xanthophylls (lutein, neoxanthin, lactucaxanthin, viola‐xanthin) at a molar ratio of 6:4:3; their contribution to the absorbance of the LHC between 390 and 530 nm is estimated to be about 31% (Chl‐a), 26% (Chl‐h) and 43% (xanthophylls).

(2) Energy transfer from xanthophylls and Chl‐fe to Chl‐a takes place at 100% transfer efficiency.

(3) LHC exhibits an unusual acid stability: in contrast to complexes of photosystem I or II, LHC‐bound chlorophylls are not converted to phaeophytin and LHC apoprotein is not denatured at pH 1.5; also, energy transfer is maintained.

(4) Pronase or trypsin treatment do not affect acid stability and energy transfer.

(5) Treatments that break down acid stability (heat, urea or TritonX–100) also inhibit energy transfer.

The coincidental breakdown of energy transfer and acid stability points at one underlying process, namely, the breakdown of a structure that enables protection of chlorophylls from proton attack and close contiguity of xanthophylls and chlorophylls as required for energy transfer. Dense packing of xanthophylls and chlorophylls within lipophilic crevices of the LHC is suggested.
FLAVIN SENSITIZED PHOTOOXIDATION OF (POLY)AMINO ACIDS: FATE OF THE PHOTOSUBSTRATE
Authors: Armstrong Jacqueline S. , Hemmerich Peter , Traber Rainer
Published: January 2008

Abstract—With respect to literature data, which seemed to be contradictory, we examined the fate of ethylenediaminetetraacetate (EDTA) and nitrilotriacetate (NTA) in flavin‐sensitized photooxidation reactions by quantitation of all possible products, i.e. CO2by acidimetric titration, CH2O by colometry and glyoxylate enzymatically; N‐methyl groups were quantified by1H‐NMR.

Nitrilotriacetate yields 100% oxidative photodecarboxylation with CH2O formation, while EDTA behaves quite differently, yielding quantitative amounts of CO2and glyoxylate, but no CH2O. The electron balance in this reaction is found to be maintained by co‐formation of one equivalent >N‐CH3. From these data it is concluded that the photooxidation of the structural element >NCH2C02containing a tertiary nitrogen atom, occurs by electron transfer, followed by decarboxylation. The neutral radical that is formed is reductant and will give off an electron equivalent to yield the easily hydrolysed structural element >N+= CH2.

With EDTA, containing the fragment –O2CCH2>NCH2CH2N< CH2CO2–, the electron transfer towards flavin is strongly favoured by stabilisation of a cisoid mesomeric radical cation (02cch2>+NCH2CH2NCH2CO2o2cch2>NCH2CH2N+CH2CO2), which, after loss of CO2undergoes internal 1,6‐hydrogen shift to yield the more stable radical:CH2>CH2CH2N CH2CO2CH2lt NCH2CH2NHCO2. The latter radical will easily be oxidized to the iminium ion >N*= CH‐C02‐. which in turn hydrolyses to glyoxylate.

Chelation of EDTA by metal cations prevents the 1,6‐hydrogen shift, and leads to the product pattern obtained in the NTA photoreaction.
PHOTOMIMETIC EFFECT OF SEROTONIN ON YEAST CELLS IRRADIATED BY FAR‐UV RADIATION
Authors: Marina G. Y. Fraikin , Strakhovskaya G. , Rubin Leonid B.
Published: January 2008

Abstract— The effect of serotonin on the survival of far‐UV irradiated cells of the yeast Candida guillier‐mondii was studied. Serotonin was found to have a photomimetic property. Preincubation of cells with serotonin results in protection against far‐UV inactivation, whereas the post‐radiation treatment with serotonin causes a potentiation of far‐UV lethality. Both effects are similar to those produced by near‐UV (334 nm) radiation. The observations provide support to the idea advanced by us previously that photosynthesized serotonin is the underlying cause of the two effects of near‐UV radiation, photo‐protection and potentiation of far‐UV lethality. Experiments with an excision‐deficient strain of the yeast Saccharomyces cerevisiae suggest that the effect of serotonin is by its binding to DNA.
PHOTOREACTIONS OF THE CHROMOPHORE CATIONS OF DENATURED SPECIES OF C‐PHYCOCYANIN AND ALLOPHYCOCYANIN
Authors: Kok Jacob de
Published: January 2008

Abstract— C‐phycocyanin dissolved in buffer containing 75% ethylene glycol (vol/vol) shows photorevers‐ible reactions which are ascribed to the interconversion by light of two species: PCr, PCg. After denaturation with formic acid, the chromophore cation of PCg, can be irreversibly photoconverted to that of PCr A conversion of the chromophore of denatured PCg, to that of denatured PCr also occurs after adjustment of the pH to about 8. Under the same conditions the chromophore of allophycocyanin shows similar reactions. Moreover, the reactions of the chromophores of the denatured species of these phycobiliproteins are similar to the reactions of the chromophore of the denatured species Pfr of photochrome.
ALTERATIONS IN DNA IRRADIATED WITH ULTRAVIOLET RADIATION—I. THE FORMATION PROCESS OF CYCLOBUTYLPYRIMIDINE DIMERS: CROSS SECTIONS, ACTION SPECTRA and QUANTUM YIELDS
Authors: Garcés F. , Dávila C. A.
Published: January 2008

Abstract— We have determined the dimerization and monomerization cross sections of the Thy < > Thy (cyclobutyl dimer of thymine and thymine) and the Cyt < > Thy (cyclobutyl dimer of cytosine and thymine) dimers in Escherichia coti [3H]‐DNA ([3H]‐thymine labeled DNA) at five wavelengths in the range 240–300 nm. It may be concluded from the dimerization action spectra for the two dimers that the excitation of Thy (thymine) is mainly responsible for the photochemical dimerization reaction in both cases. The calculated quantum yields of dimerization and monomerization are also presented in this paper and several questions, raised by the results obtained at 300 nm, are discussed.
SPIN‐TRAPPING and ESR STUDIES OF THE DIRECT PHOTOLYSIS OF AROMATIC AMINO ACIDS, DIPEPTIDES, TRIPEPTIDES and POLYPEPTIDES IN AQUEOUS SOLUTIONS—III. TRYPTOPHAN and RELATED COMPOUNDS
Authors: Lion Yves , Kuwabara Mikinori , Riesz Peter
Published: January 2008

Abstract— The UV photolysis of tryptophan (Trp) and Trp‐containing peptides in aerated aqueous solutions has been studied by ESR and spin‐trapping techniques using f‐nitrosobutane as the spin‐trap. The photolysis of Trp alone at 290 nm gave rise to the addition of the spin‐trap to carbon 3 of the indole ring. A large ESR signal from the hydronitroxide spin‐adduct was also observed revealing the formation of hydrated electrons. Generally, the photolysis of Trp‐containing dipeptides generated the deamination radical of the N‐terminal amino acid followed by addition to the spin‐trap. In the case of lysyl‐Trp, a deamination radical from the side chain of lysine was proposed. A sensitization experiment with Trp as sensitizer and glycine (Gly) as substrate led to the generation of the deamination radical of Gly. Most of the observed free radicals resulting from the photolysis of Trp‐containing peptides can be explained in terms of hydrated electrons reacting with the carbonyl group followed by deamination of the N‐terminus.
SYNTHESIS and SPECTRA OF TRICYANOVINYL INDOLES
Authors: Johnston David Samuel
Published: January 2008

Abstract— Indole and tetracyanoethylene form a purple charge transfer complex which decomposes into 3‐tricyanovinyI indole and hydrogen cyanide in neutral or basic media. In acid media, 2‐tricyanovinyI indole is formed. 3‐Tricyanovinyl indole has an intense visible absorption at 460 nm, the 2‐isomer is colourless. It is suggested that the visible absorption of 3‐tricyanovinyl indole is due to intramolecular charge transfer and that such a transition is not observed in the case of the 2‐isomer because of a higher excited state energy.
PHOTOGENERATION OF SUPEROXIDE ION and HYDROGEN PEROXIDE FROM TRYPTOPHAN and ITS PHOTOOXIDATION PRODUCTS: THE ROLE OF 3a‐HYDROPEROXYPYRROLIDINOINDOLE*
Authors: Inoue Kenzo , Matsuur Teruo , Saito Isao
Published: January 2008

Abstract— Mechanism of the photogeneration of hydrogen peroxide and superoxide ion from tryptophan (Trp) and its photooxidation products was investigated. Near‐ultraviolet irradiation of 3a‐hydro‐peroxypyrrolidinoindole, an intermediate in the photooxidation of Trp, has been shown to generate hydrogen peroxide efficiently under aerobic conditions. Irradiation of N‐formylkynurenine in the presence of 3α‐hydroxypyrrolidinoindole also produced hydrogen peroxide. The formation of superoxide ion in both reactions has been confirmed, whereas the reaction of Trp with chemically generated singlet oxygen did not produce any detectable amount of superoxide ion.
THE EFFECT OF MEMBRANE FATTY ACID COMPOSITION ON THE NEAR‐UV (300–400 nm) SENSITIVITY OF ESCHERICHIA COLI K1060
Authors: Klamen Debra L. , Tuveson R. W.
Published: January 2008

Abstract— The near‐UV (NUV, 300 400 nm) sensitivity of logarithmically growing Escherichia coli cells of the fatty acid auxotroph K1060 increases with the number of carbon‐carbon double bonds in the fatty acid used as supplement. Cultures of K.1060 grown to stationary phase on unsaturated fatty acids of the same chain length but differing in the number of carbon‐carbon double bonds per molecule differed only marginally in their NUV sensitivity. The clear NUV‐sensitizing effect of increasing double bonds in the fatty acid supplement used to support logarithmic growth implies that the membrane may be an important NUV target only for logarithmically growing cells. Based on these observations, our previous suggestion that inefficient conversion of fatty acids in the membrane to their cyclopropane analogs as an explanation for the NUV‐sensitizing effect of the nur mutation on stationary E. coli cell populations must be wrong.
THE EFFECT OF CYTOKININS ON GROWTH and PIGMENT ACCUMULATION OF RADISH SEEDLINGS (RAPHANUS SATIVUS L.) GROWN IN THE DARK and AT DIFFERENT LIGHT QUANTA FLUENCE RATES*
Authors: Buschmann Claus , Lichtenthaler Hartmut K.
Published: January 2008

Abstract— The dependency of cytokinin effects upon irradiance was studied with radish seedlings (Raphanus sativus L. cv. Saxa Treib). Kinetin (6‐furfurylamino‐purine) or BAP (6‐benzylamino‐purine) were applied via the roots of plants growing either in continuous darkness or under high (90 Wm‐2) or low intensity white light (10Wm‐2). Apart from the different development of plants at low and high fluence rates, the following cytokinin effects were found:

(1) Both cytokinins acted in a similar manner on growth characteristics and pigment accumulation at high and low light conditions, BAP being in many cases more effective than kinetin.

(2) When compared with the control, the cytokinins suppressed hypocotyl and root lengthening in the dark and light‐grown plants. In darkness they led to increased cotyledon areas, whereas in the light the leaf expansion was suppressed.

(3) In the etiolated and low light grown plants, the anthocyanin content of the hypocotyls was enhanced due to the action of cytokinins, whereas under high light the anthocyanin accumulation was decreased.

(4) In the cotyledons of etiolated plants, more phototransformable protochlorophyll(ide) and more carotenoids were formed when cytokinins were present. In green leaves the carotenoid content was diminished due to the action of cytokinins, particularly in plants grown in strong light. The chlorophyll a/b ratio was increased in the cytokinin‐treated plants in most cases.

The results suggest a light dependency of the cytokinin effects. It is believed that the response of a plant towards exogenously applied cytokinins is similar to that with high intensity light.
PHYTOCHROME CONTROL OF DEGREENING OF ATTACHED COTYLEDONS and PRIMARY LEAVES OF MUSTARD (SINAPIS ALBA L.) SEEDLINGS*
Authors: Biswal U. C. , Kasemir H. , Mohr H.
Published: January 2008

Abstract— Mustard (Sinapis alba L.) seedlings were grown on moistened vermiculite without added nutrients for 17 days in medium white light (4.6 lx). During this period cotyledons as well as primary leaves expressed signs of senescence as defined by the loss of chlorophyll(ide) a (‘degreening’). While degreening was detectable 9 days after sowing in the cotyledons it was not measurable before 15 days after sowing in the primary leaves. Phytochrome retards the loss of chlorophyll(ide) a in both organs; however, it does not change the temporal pattern of greening and degreening.
BLUE LIGHT INDUCED PHOTOTRANSFORMATION OF PHYTOCHROME IN THE PRESENCE OF FLAVIN*
Authors: Sarkar Hemanta K. , Song Pill‐Soon
Published: January 2008

Abstract— Irradiation of the Pr form of phytochrome in the presence of flavin mononucleotide (FMN) which absorbs the actinic blue light yields Pfr at a rate greater than that in the absence of FMN. The actinic blue light absorbed by FMN enhances the phototransformation of Pr via the energy transfer from the former to the latter. On the other hand, the photoreversion of Pfr was inhibited by the presence of FMN when illuminated with blue light. The lack of photo‐enhancement of the reversion of Pr, by blue light suggests that the Pfr chromophore (acceptor) transition dipole is virtually perpendicular to the FMN transition dipole, as the result of a chromophore reorientation in the Pr→Pfr phototransformation. The fact that blue light absorbed by flavin preferentially enhances the forward phototransformation of phytochrome while inhibiting the reversion may have an important implication in the high irradiance responses in plants in terms of a preferential accumulation of Pfr by blue light excitation.
PHOTOMORPHOGENETIC REACTIONS and THEIR RELATION TO TIME*
Authors: Verbelen Jean‐Pierre , Spruyt Eric , Moereels Edith , Greef Jan A. de
Published: January 2008

Abstract— Hook‐opening and leaf expansion were selected as a measure of the photoactivity of etiolated Phaseolus vulgaris L. seedlings. The experimental procedure consisted of a standard red illumination, followed by a 24‐h reaction period. The magnitude of both morphogenic responses was dependent upon the time of day when the light pulse was given. The photoactivity of the etiolated seedlings changed rhythmically with a periodicity of about 6 h.
SPECIFIC PHOTOREGULATION BY PHYTOCHROME OF EPINASTY and LIGHT‐INDUCED ETHYLENE PRODUCTION IN MARCHANTIA POLYMORPHA*
Authors: Veroustraete F. , Fredericq H. , Wiemeersch L. Van , Greef J. De
Published: January 2008

Abstract— A study is made of the influence of phytochrome on light‐induced ethylene production and epinasty in green Marchantia polymorpha thalli. Ethylene production of thalli irradiated with terminal far‐red is not substantially affected by the presence or absence of CO2, in contrast with the controls which show a clearcut CO2 dependency. Photoreversibility and fiuence response data indicate the involvement of the low energy red'far‐red reversible type of phytochrome action for both the light‐induced ethylene production and the control of epinasty. The far‐red effect is further characterized by a difference in escape from reversibility between light‐induced ethylene production and the elimination of epinasty.
MODEL STUDIES ON PHOTODYNAMIC CROSS‐LINKING
Authors: Verweu H. , Steveninck J. van
Published: January 2008

Abstract— A model system is described for studying photodynamic protein cross‐linking. It appeared that several different types of cross‐links are possible between photooxidized amino acid residues—especially histidine—and functional groups in proteins.
EFFECT OF LIQUID HOLDING ON THE REPAIR OF PHOTOINDUCED DAMAGES IN ACRIFLAVINE SENSITIZED ESCHERICHIA COLI CELLS
Authors: Basu Sreeradha , Bagchi B.
Published: January 2008

Abstract— Damage caused by visible light in the presence of acriflavine can be repaired in various strains of Escherichia coli possessing one or the other repair mechanism. The number of viable cells of the irradiated E. coli cultures increases on holding in buffer. The results of liquid holding suggest that the major role played by holding in liquid medium is the removal of dye molecules from inside the cells; this would create a favourable condition for recovery during subsequent incubation.
PHOTOINACTIVATION OF ENZYMES BY LINEAR AND ANGULAR FUROCOUMARINS
Authors: Veronese F. M. , Schiavon O. , Bevilacqua R. , Bordin F. , Rodighiero G.
Published: January 2008

Abstract Furocoumarins with linear (psoralen, 8‐methylpsoralen, 8‐methoxypsoralen and 3‐carbethox‐ypsoralen) and angular molecular structures (angelicin and 4,5'‐dimethylangelicin) were found to inactivate enzymes to different extents through UV‐A irradiation. Moreover, enzymes with different structures (glutamate dehydrogenase, lysozyme, 6‐phosphogluconate dehydrogenase, enolase, thermoly‐sine and ribonuclease) are inactivated to different extents by the same furocoumarin. UV‐A irradiation produces both covalent incorporation of the furocoumarins into the protein molecule and photodegra‐dation of amino acid residues; the latter phenomenon seems to be mainly responsible for the photoinactivation process. A close correlation was found between the capacity of the furocoumarins to photoinactivate enzymes and their capacity to modify free amino acids.

A study of the effects of quenchers of various forms of activated oxygen on the photoinactivation of glutamate dehydrogenase, used as a model enzyme, and psoralen and 8‐methylpsoralen as a reference for furocoumarins, showed that singlet oxygen is the species most involved in the photoinactivation process.
THE INTERACTION OF 8‐AZIDOETHIDIUM AND tRNA
Authors: Bertrand Nancy J. , KEARNs David R.
Published: January 2008

Abstract Optical spectroscopy and proton nuclear magnetic resonance spectroscopy have been used to investigate the non‐covalent and covalent binding of 8‐azidoethidium (8‐azido‐3‐amino‐5‐ethyl‐6‐phe‐nyl‐phenanthridium) with transfer RNA (tRNA) molecules. The nuclear magnetic resonance measurements demonstrate that ethidium and ethidium monoazide bind to the same unique binding site on tRNA molecules. However, the optical studies demonstrate that the photochemical reaction between ethidium monoazide and tRNA generates at least three different photoproducts. One of the covalent photoproducts has fluorescence properties which mimic those of intercalated, non‐covalently bound ethidium, but it is produced only in about 10% yield. The major photoproduct(s) is(are) virtually non‐fluorescent. The ethidium monoazide photochemistry with tRNA molecules is obviously complex and this may complicate its use as a photolabel of polynucleotides.
PHOTOSENSITIZATION BY ANTIMALARIAL DRUGS
Authors: Moore Douglas E. , Hemmens Violet J.
Published: January 2008

Abstract The antimalarial drugs, chloroquine, hydroxychloroquine, quinine, quinacrine, amodiaquine and primaquine and the local anaesthetic, dibucaine, were tested for in vitro photosensitizing capability by irradiation with 365 nm UV light in aqueous solutions. The ability of these compounds to photosensitize the oxidation of 2,5‐dimethylfuran, histidine, tryptophan or xanthine, and to initiate the free radical polymerization of acrylamide was examined in the pH range 2‐12. Chloroquine and hydroxychloroquine show maximal photooxidative behaviour when in the monocation form at pH 9, in contrast to quinine which is extremely efficient as the dication below pH 4. This pattern appears to relate to the fluorescence yield as a function of pH. Chloroquine in the monocation or neutral form was found to undergo dechlorination upon irradiation, and this correlates directly with its ability to initiate photo‐polymerization of acrylamide. Quinine also gives rise to small polymerization rates, attributed to photo‐ionization in the quinoline ring, yielding a cation radical. Amodiaquine, primaquine and quinacrine do not have significant photochemical activity in aqueous solution. Dibucaine exhibits a strong photosensitizing capability at low pH, similar to quinine.
STUDIES ON THE CAPACITY OF pR IN VITRO TO PHOTOCONVERT TO THE LONG‐WVELENGTH Ffr‐FORM. A SURVEY FO TEN PLANT SPECIES*
Authors: Baron O. , Epel B. L.
Published: January 2008

Studies on the capacity of Pr in uitro to photoconvert to the long wavelength in uioo‐like Pfr form were performed with extracts from 10 species. Red irradiation, immediately after extraction of crude extracts from 9 species, photoconverted Pr to long‐wavelength Pfr with an absorbance maximum around 735 nm. Red irradiation of soybean extracts, however, photoconverted Pr to short‐wavelength Pfr, with an absorbance maximum at 725 nm. Red irradiation given later than 1.5‐2 h after extraction, to extracts of oats, pea, cucumber, radish, sunflower and soybean, photoconverted Pr to a short‐wavelength Pfr species with an absorbance maximum around 725 nm. In crude extracts of barley, corn, wheat and zucchini, red irradiation, even after a long dark‐incubation period at 4°C of up to 48 h, photoconverted Pr to long‐wavelength Pfr with an absorbance maximum around 735 nm. After incubation at 25°C for 3 h, however, Pr from barley also photoconverted to the short‐wavelength form. It is suggested that in the group exemplified by oats, Pr rapidly undergoes an alteration following extraction, which results in the loss of the capacity of Pr to photoconvert to long‐wavelength Pfr. In contrast, in extracts from the group exemplified by barley, Pr is much more stable and retains the capacity to photoconvert to long‐wavelength Pfr for much longer periods.
LETHALITY IN REPAIR‐PROFICIENT ESCHERICHIA COLI AFTER 365 nm ULTRAVIOLET LIGHT IRRADIATION IS DEPENDENT ON FLUENCE RATE
Authors: Peak J. G. , Peak M. J.
Published: January 2008

Abstract Reciprocity (total applied fluence produces the same response, regardless of the fiuence rate) for the lethal effects caused by 365 and 254 nm ultraviolet light (UV) was studied for repair‐proficient and ‐deficient Escherichia coli strains. In the repair‐proficient strain, E. coli WP2 uvrA*recA*, reciprocity after 365 nm UV was only observed at fluence rates of about 750 Wm‐2 and above. Below this rate, the cells became increasingly sensitive as the fluence rate was decreased. Similar lack of reciprocity was obtained whether the cells were exposed at 0 or 25°C. The double repair‐defective mutant, E. coli WP100 uvrA recA, showed complete reciprocity after 365 nm UV over the same range of fluence rates measured for the repair‐proficient strain. For 254 nm UV, complete reciprocity occurred in both strains over a range of fluence rates differing by an order of magnitude.
TYPE I AND TYPE II MECHANISMS IN THE PHOTOSENSITIZED LYSIS OF PHOSPHATIDYLCHOLINE LIPOSOMES BY HEMATOPORPHYRIN
Authors: Grossweiner L. I. , Patel A. S. , Grossweiner J. B.
Published: January 2008

Abstract The lysis of phosphatidylcholine (PC) liposomes was sensitized to visible light (>500nm) by hematoporphyrin (HP) incorporated in the liposomes (0.09‐1.5%, wt/wt) or in the external buffer (1‐15 μM). The lytic mechanism changed from the Type II pathway mediated by singlet oxygen (1O2) at low HP concentrations to the anoxic, Type I pathway at high HP concentrations. Spectral measurements of HP in aqueous and organic solvents indicate that the HP was not aggregated (monomers and/or dimers) for Type II sensitization and aggregated for Type I conditions. High concentrations of azide (>0.1 M) or DABCO (>0.5 M) were protective with high HP concentration under oxic and anoxic conditions, which cannot involve the scavenging of 1O2. Feasible protective mechanisms are quenching of the HP triplet state by high azide and repair of the damaged membrane by DABCO via an electron transfer process. There was significant protection against lysis under Type I conditions by low concentrations of ferricyanide (>1 mM), indicative of an electron transfer mechanism. The incorporation of 22 mol % cholesterol in PC liposomes with 1% HP had no effect on the lytic efficiency for oxic and anoxic conditions. Dipalmitoylphosphatidylcholine liposomes incorporating 1% HP showed negligible photosensitized lysis at 50°C compared with PC liposomes with 1% HP at 25°C. The promotion of photosensitized lysis by hydrodynamic agitation observed in prior work with methylene blue (Grossweiner and Grossweiner, 1982) was significant with HP sensitization for both Type I and Type II conditions. Actinometry with PC liposomes incorporating 1% HP indicated that photosensitized lysis was very inefficient, requiring many absorbed quanta per lysed liposome. Preliminary experiments with crude hematoporphyrin derivative (Hpd) showed similar concentration effects on lytic efficiency, where PC liposomes incorporating 0.1% (wt/wt) Hpd were strongly sensitized by oxygen, whereas sensitization by oxygen was insignificant with 3.1% Hpd. The results with HP and crude Hpd indicate that lytic damage in a biomembrane does not necessarily require oxygenation.
POSTIRRADIATION PROPERTIES OF A UV‐SENSITIVE VARIANT OF CHO
Authors: Wood Richard D. , De Veciana Margarita , ‐Tincknell Bonnie Presson
Published: January 2008

Abstract A UV‐hypersensitive mutant of Chinese hamster ovary (CHO) cells, termed 43‐3B, has been used in a comparative study with the wild type CHO in order to determine the involvement of repair in several postirradiation phenomena. 43‐3B has the same growth rate and chromosome number as the wild type CHO‐9. It is hypersensitive to UV irradiation (D0 of 0.3 J/m2 as compared to 3.2 J/m2 for the wild type). 43‐3B shows only about 17% of the UV‐stimulated unscheduled DNA repair synthesis of CHO‐9 as measured by autoradiography. When breaks in supercoiled chromatin are measured after UV by the nucleoid sedimentation method, the mutant appears to be capable of carrying out only limited incision. A much reduced ability to recover control rates of semiconservative DNA synthesis after UV irradiation was observed in the repair‐deficient 43‐3B cell line, suggesting that the removal of UV‐induced replication blocks by excision repair is the most important factor in allowing recovery of UV‐inhibited DNA synthesis. Recovery of colony‐forming ability between fractionated UV exposures was observed in the wild type CHO‐9, but little recovery was seen in 43‐3B. This indicates that excision repair capability can also be important in split‐fluence recovery.
ERYTHEMA AND MELANOGENESIS ACTION SPECTRA OF NORMAL HUMAN SKIN *
Authors: Parrish John A. , Jaenicke Kurt F. , Anderson R. Rox
Published: January 2008

AbstractThe action spectra for delayed erythema and melanogenesis in Caucasian human skin are determined for wavelengths between 250 and 435 nm. The untanned skin of very fair volunteers was observed after single exposures to a range of fluences of monochromatic radiation. At wavelengths longer than 300 nm the two action spectra are indistinguishable, and at wavelengths shorter than 300 nm, they are of similar shape despite a distinct separation. This suggests a common or similar chromophore for initiation of the vascular and pigmentary responses to UV. A broad minimum in the action spectra occurs near 280 nm, a maximum near 296 nm, and for wavelengths longer than 300 nm, increasingly larger fluences of radiation are required to induce delayed erythema and melanogenesis. Between 304 and 334 nm both action spectra exhibit a rapid decrease of almost three orders of magnitude. In contrast, between 334 and 405 nm the spectra decrease by only one order of magnitude, and there is a suggestion of a small maximum at or near 365 nm. Different chromophores, sites of damage, or response mechanisms may be responsible for induction of delayed erythema at these longer wavelengths. After spectral corrections for the optical effects of the stratum corneum, the shape and magnitude of the action spectra are grossly consistent with a mechanism in which DNA is the primary chromophore initiating the response pathways for wavelengths less than 313 nm. Whatever the actual basis for these action spectra may be, they are of practical significance in predicting skin response to sources of ultraviolet radiation.
ZERO FIELD OPTICAL DETECTION OF MAGNETIC RESONANCE OF TRIPLET STATE OF CHLOROPHYLL a IN LIPID BILAYER VESICLES
Authors: Hotchandani S. , Leblanc R. M. , Clarke R. H. , Fragata M.
Published: January 2008

Abstract The zero‐field ODMR of triplet state of chlorophyll a incorporated in phosphatidylcholine (PC) vesicles (Chi a: PC = 1:100) has been carried out. The zero‐field ODMR frequencies and intersystem crossing rate constants have been measured at various fluorescence wavelengths. The ODMR data suggest that the chlorophyll is present in mono‐ and biligated species. The nature of the ligand and the role of the medium (phospholipid) are also discussed.
REGENERATION OF NAD+ AND NADP+ COFACTORS BY PHOTOSENSITIZED ELECTRON TRANSFER
Authors: Julliard M. , Le Petit J.
Published: January 2008

Abstract The irradiation with visible light of photosensitizer dyes like methylene blue or N‐methyl phenazonium methyl sulfate leads to the oxidation of reduced coenzymes such as pyridine nucleotides (NADH or NADPH). This photoredox reaction can be used to regenerate the oxidized form of these coenzymes in enzymatic reactions and total consumption of a substrate with catalytic amounts of enzyme, coenzyme and photosensitizer can be performed. The process has been studied on two common enzymatic reactions: ethanol oxidation by alcohol‐NAD + ‐oxidoreductase and gluconate‐6‐phosphate oxidation by 6‐phospho‐D‐gluconate‐NADP+‐2‐oxidoreductase. In the first case, a turnover number of 1125 has been obtained for the photoregeneration of NAD + from NADH.
DAMAGE BY SOLAR RADIATION AT DEFINED WAVELENGTHS. INVOLVEMENT OF INDUCIBLE REPAIR SYSTEMS
Authors: Menezes Salatiel , Tyrrell Rex M.
Published: January 2008

Abstract The susceptibility of bacteriophage damaged by solar‐ultraviolet (UV, 290‐380 nm) radiations at denned wavelengths and by radiation at a visible wavelength (405 nm) to the Weigle reactivation system induced by far‐UV (254 nm) irradiation of the host cell has been studied in a repair competent strain of Escherichia coli. The sector of inducible repair diminishes with wavelength, being very small after 313 nm irradiation and absent after irradiation at longer wavelengths. However, irradiation of bacteria at wavelengths as long as 313 nm induces a bacteriophage reactivation system as effectively as radiation at 254 nm in both the repair competent and an excision deficient host cell. At longer wavelengths pre‐irradiation of the repair competent host cell enhances reactivation of 254 nm irradiated bacteriophage but the reactivation is smaller and the process quite distinct from that induced in the 254‐313 nm region. We conclude that, with increasing wavelength, damage induced by solar UV radiations becomes increasingly less susceptible to repair systems induced by far‐UV (pyrimidine dimers) and that this type of inducible repair system is no longer induced by wavelengths longer than 313 nm.
LETHALITY AND THE INDUCTION AND REPAIR OF DNA DAMAGE IN FAR, MID OR NEAR UV‐IRRADIATED HUMAN FIBROBLASTS: COMPARISON OF EFFECTS IN NORMAL, XERODERMA PIGMENTOSUM AND BLOOM'S SYNDROME CELLS
Authors: Smith P. J. , Paterson M. C.
Published: January 2008

Abstract Using normal human fibroblasts we have determined the ability of far (254 nm), mid (310 nm) or near (365 nm) UV radiation to: (i) induce pyrimidine dimers (detected as UV endonuclease sensitive sites) and DNA single‐strand breaks (detected in alkali); (ii) elicit excision repair, monitored as unscheduled DNA synthesis (UDS); and (iii) reduce colony‐forming ability. Unscheduled DNA synthesis studies were also performed on dimer excision‐defective xeroderma pigmentosum (XP) cells, and the survival studies were extended to include XP and Bloom's syndrome (BS) strains. UV‐induced cell killing in normal, BS and XP cells was found to relate to an equivalent dimer load per genome after 254 or 310 nm exposure, whereas at 365 nm the lethal effects of non‐dimer damage appeared to predominate. Lethality could not be correlated with DNA strand breakage at any wavelength. The two XP strains examined showed the same relative UDS repair deficiency at the two shorter wavelengths in keeping with a predominant role for pyrimidine dimer repair in the expression of UDS. However, UDS was not detected in 365 nm UV‐irradiated normal and XP cells despite dimer induction; this effect was due to the inhibition of DNA repair functions since 365 nm UV‐irradiated normal cells showed reduced capacity to perform UDS subsequent to challenge with 254 nm UV radiation.

In short, the near UV component of sunlight apparently induces biologically important non‐dimer damage in human cells and inhibits DNA repair processes, two actions which should be considered when assessing the deleterious actions of solar UV.
FORMATION OF NON‐VIABLE SPORES OF DICTYOSTELIUM DISCOIDEUM BY UV‐IRRADIATION AND CAFFEINE
Authors: Ohnishi Takeo , Hazama Masumi , Okaichi Kumio , Nozu Keiichi
Published: January 2008

Abstract We have characterized the spores formed from amoeboid cells of the wild type strain of Dictyostelium discoideum after UV‐irradiation. Cell differentiation in the presence of caffeine after a fluence of 300 J/m2 resulted in a population of spores which was 98% non‐viable. The UV‐irradiation did not affect the conversion of the spores to swollen spores but did affect the conversion of swollen spores to amoeboid cells. When the germination of the spores was done without caffeine, we detected only a small effect on conversion of swollen spores to amoeboid cells and on the beginning of growth. On the other hand, in the presence of caffeine, the spores had a remarkable delay in both. It was also shown that few, if any, pyrimidine dimers exist in the DNA of the non‐viable spores. Possible mechanisms of formation of non‐viable spores are discussed.
EFFECT OF CHRONIC UV EXPOSURE ON EPIDERMAL TRANSMISSION IN MICE*
Authors: Gruul F. R. de , Leun J. C. vander
Published: January 2008

In connection with an investigation on UV‐tumorigenesis in hairless mice, the question arose in what way the epidermal transmission changes under chronic UV exposure. At regular time intervals, epidermal sheets of these mice were optically probed, i.e. the specimen was irradiated perpendicularly to its surface with a collimated monochromatic beam of 313, 302 or 297 nm and the transmission was measured in forward direction and a small angle around it. The optical probe measurement was sensitive to epidermal changes and easy to perform; it correlated well with thickness and total transmission of the epidermal sheet.

As a result it was found that over the dose range investigated the logarithm of the epidermal transmission at 297 nm was a simple linear function of the daily UV dose and the time of treatment. Calculations, in which this result is combined with data on UV‐tumorigenesis over the same dose range, show that the change in epidermal transmission is sufficiently large to have an important bearing on the dose‐response relationship for tumorigenesis by chronic UV exposure.
QUANTUM EFFICIENCY AND PHOTOSENSITIVITY OF THE RHODOPSIN ⇌ METARHODOPSIN CONVERSION IN CRAYFISH PHOTORECEPTORS
Authors: Cronin Thomas W. , Goldsmith Timothy H.
Published: January 2008

Photosensitivity (Kλ) of a visual pigment is the product of the molecular absorption coefficient (αλ) and the quantum efficiency for photoconversion (γ). Among the invertebrates, many visual pigments are stable not only in the rhodopsin (R) conformation but also as the photoproduct, metarhodopsin (M), We here employ a method for determining the photosensitivities of the two stable pigments of a rhodopsin‐metarhodopsin pair, using kinetic analysis of fluorescence from metarhodopsin combined with measurements of spectral absorption made before and after saturation at the isosbestic wavelength of the pigment pair. A curve fitting technique, in which a theoretical function is scaled for best fit to the measured absorption spectrum of the photosteady‐state mixture, yields values for the photosensitivity of rhodopsin at λ.max, the ratio of quantum efficiencies for rhodopsin—metarhodopsin interconversion, and the fractional composition of the steady‐state mixture. With knowledge of the molecular extinction coefficient, the absolute values of quantum efficiency can be calculated. For crayfish (Orconectes, Procambarus) rhodopsin, measured in isolated rhabdoms, Kmax= 1.05 x 10‐16 cm2 at 535 nm with >7λR→M0.69. These values are similar to the photosensitivity and quantum efficiency of bleaching of vertebrate rhodopsins in digitonin solution (Dartnall, 1972). For the metarhodopsin, Kmax= 1.02 x 10‐16 cm2 at 510 nm, and λM‐R= 0.49.
PHOTOKINETIC ASPECTS OF SPECIFIC HYDROGEN BONDING IN ALL‐TRANS RETINAL AT ROOM TEMPERATURE
Authors: Das P. K. , Hug G. L.
Published: January 2008

Room‐temperature hydrogen‐bonding of all‐trans retinal (ATR) with 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) in cyclohexane results in fluorescence enhancement and triplet yield quenching; these effects, as well as the associated absorption spectral changes in both ground and triplet states and the kinetics of H‐bonding in the triplet state, have been studied by steady‐state absorption‐emission and laser flash‐photolytic transient measurements. The fluorescence enhancement is predominantly controlled by the H‐bonding in the ground state (static interaction) and gives a value of 440 M‐1 for the corresponding equilibrium constant which is very similar to the value (420 M‐1) obtained from the analysis of absorption spectral data as a function of [HFIP˜. The quantum yield of triplet occupation (øT) of the H‐bonded complex, ATR‐HFIP, in cyclohexane is non‐negligible and is about one‐third of øT of free ATR. The kinetic data of H‐bonding equilibration in the triplet state, observable on a nanosecond time scale, indicate that the triplet ATR is a stronger base than the ground state as far as H‐bonding with HFIP is concerned.
PICOSECOND TIME RESOLVED ENERGY TRANSFER IN ISOLATED PHYCOBILISOMES FROM RHODELLA VIOLACEA (RHODOPHYCEAE)*
Authors: Holzwarth Alfred R. , Wendler Joachim , Wehrmeyer Werner
Published: January 2008

Energy‐transfer kinetics in isolated phycobilisomes (PBS) of the red algaRhodella violaceahave been measured by detecting both ground state recovery and fluorescene rise or decay using a synchronously pumped cavity‐dumped dye laser as excitation source. For the first time the constituent phycobiliproteins of PBS have been excited selectively, thus allowing the kinetics of both directly and indirectly excited pigments to be followed. Energy‐transfer between the phyeobiliproteins, which was found to proceed extremely fast, is governed by nonexponential kinetics at low excitation intensities. When analyzed in a biexponential model, the main components of the fluorescence of B‐phycoerythrin (B‐PE) and C‐phycocyanin (C‐PC) decay with τ= 34 ps and τ= 25 ps, respectively. Evidence is presented that transfer between the biliprotein pigments is close to a single‐step process with some contribution of homotransfer. Fluorescence quantum yields of PBS have been determined as a function of the excitation wavelength and were found to reflect a dissociation equilibrium involving ca. 10% dissociated PBS at the concentrations studied.
OBSERVATION OF C‐S BOND CLEAVAGE IN THE PHOTOLYSIS OF A 2‐AMINO‐Δ2‐THIAZOLINE DERIVATIVE
Authors: CORVAL A. , Gaude D. , Jardon P. , Gautron R.
Published: January 2008

Photoirradiation of 2‐benzoylamino‐Δ2‐thiazoline in outgassed toluene and cyclohexane solutions leads to N‐ethyl‐N'‐benzoyl thiourea after a C‐S bond cleavage in the thiazohne group. This photoreaction occurs from the first excited triplet state of the 2‐amino‐Δ2‐thiazoline derivative.