bluuebunny/crossref_metadata_2025 huggingface dataset:
HOST‐CELL REACTIVATION AND WEIGLE REACTIVATION OF ULTRAVIOLET‐IRRADIATED MYXOCOCCUS XANTHUS PHAGES
Authors: Grimm Klaus , Herdrich Klaus
Published: January 2008

Abstract— Myxococcus xanthus DZ1, and particularly M. xanthus B, show a phase variation resulting in tan and yellow pigmented colonies. M. xanthus XK is stable and yellow colonies occur only as rare mutants. The various M. xanthus strains exhibit different resistances to short wave UV. With the exception of M. xanthus XK the yellow types are more resistant than the tan types with the greatest difference found in M. xanthus B. This is probably partly responsible for the enrichment of yellow types during UV irradiation of M. xanthus B tan. By ICR mutagenesis a uvr mutant of Af. xanthus XK was isolated. Using this mutant it could be demonstrated that all strains, whether yellow or tan pigmented, are able to host‐cell reactivate UV irradiated phages Mxl and Mx4. The repair efficiency for irradiated Mxl is approximately 71 to 79% at a survival level of 10%. Weigle reactivation of phage Mx4 occurs in Af. xanthus XK and DZ1. The effect is most pronounced in M. xanthus XK with a repair efficiency of 44% at 1% survival. The uvr‐1 mutant is also able to W‐reactivate phage Mx4. Only the yellow phenotype of M. xanthus B is able to W reactivate the irradiated phage Mx4 ts27htf‐lhrm‐l with a similar efficiency to M. xanthus XK. M. xanthus B tan is therefore probably blocked in an inducible repair pathway. The phage Mx 1 is W‐reactivated by none of the M. xanthus strains used.
PROTECTION FROM VISIBLE LIGHT DAMAGE TO ENZYMES AND TRANSPORT IN ESCHERICHIA COLI*
Authors: D'Aoust J. Y. , Martin W. G. , Giroux J. , Schneider H.
Published: January 2008

Abstract— Cysteine, anthranilic acid and adenine, in decreasing order of effectiveness, protected flavo‐enzymes of E. coli against inactivation with high‐intensity, heterochromatic light above 400 nm. Cell suspensions illuminated for 40 min in the presence of cysteine retained 30, 40 and 55% of their succinate, l‐α‐glycerophosphate and d‐lactate dehydrogenase activities, whereas less than 10% activity could be detected in the absence of this protective agent. Different effects on respiration and transport systems were obtained with these protective agents. Adenine and anthranilic acid provided substantial protection of the glycine and methylthio‐ß‐d‐galactoside transport systems but failed to attenuate adverse light effects on respiration and phenylalanine uptake. Cysteine did not protect respiration and potentiated damage to selected transport systems. Our results suggest that flavins act as photosensitizers.
MOLECULAR PROBES: PHOTOISOMERIZATION OF OPTICALLY ACTIVE AZO COMPOUNDS
Authors: Kölle U. , Schätzle H. , Rau H.
Published: January 2008

Abstract— The azo group may be used as a probe to gain information about the molecular surroundings. The circular dichroism (CD) spectra of two azo steroids have been investigated in media of different viscosity and polarity. The CD spectra of the trans‐compounds are only slightly affected by the environment while those of the cis‐compounds are strongly dependent on the environment. Photoisomerization is analysed by absorption and ellipticity diagrams as tests for chromophoric and conformeric uniformity. Our results support an inversion mechanism of the photoisomerization of azo compounds.
INTERFACIAL CHARGE SEPARATION IN PHOTORECEPTOR MEMBRANES
Authors: Cafiso David S. , Hubbell Wayne L.
Published: January 2008

Abstract— A rapid change in an interfacial electric potential of isolated bovine rod outer‐segment disc membranes occurs upon illumination. This potential change, which has been detected by the use of spin labelled hydrophobic ions, apparently occurs within a low dielectric boundary region of the membrane near the external (cytoplasmic) surface and is positive with respect to the aqueous exterior of the disk. The magnitude of the potential change is pH and temperature dependent and appears with a first‐order half‐time of approximately 5 ms at 23°C. A simple model in which one positive charge per bleached rhodopsin is translocated from the cytoplasmic aqueous space into the membrane low dielectric boundary region readily accounts for all experimental observations. The similarity of the boundary potential change to the R2 phase of the early receptor potential suggests that the two have the same molecular origin.
CO‐OPERATION OF PERIPHERAL AND INTEGRAL MEMBRANE PROTEINS IN THE LIGHT DEPENDENT ACTIVATION OF ROD GTPase AND PHOSPHODIESTERASE
Authors: Shinozawa Takao , Bitensky Mark W.
Published: January 2008

Abstract— During the purification of light activated GTPase, we have observed that the GTPase activity is suddenly lost because of the separation of two components which are both needed for enzymatic activity. The G fraction or protein (apparent mol. wt 55000) can selectively bind GTP and is necessary for PDE activation by illuminated rhodopsin. However, the G fraction shows no GTPase activity unless it is supplemented by illuminated rhodopsin and the H fraction, a heat labile, trypsin resistant macro‐molecule with an apparent mol. wt of 53 000. The G and H fractions (and GTPase activity) show a significant increase in binding to bleached as compared with unbleached disc membranes.
SENSITIVITY OF MONONUCLEAR CELLS TO UV RADIATION: EFFECT ON SUBSEQUENT STIMULATION WITH PHYTOHEMAGGLUTININ
Authors: Morison Warwick L. , Parrish John A. , McAuliffe Daniel J. , Bloch Kurt J.
Published: January 2008

Abstract—

The ability of peripheral blood mononuclear cells to incorporate 3[H] thymidine into nuclear DNA following stimulation by phytohemagglutinin is reduced by prior exposure to UV radiation in vitro: the reduction is dose and wavelength dependent. The doses required to affect this function of mononuclear cells are higher than the doses required to reduce trypan blue dye exclusion, so that following exposure to radiation populations of cells that are unable to exclude trypan blue dye are still capable of responding to phytohemagglutinin. This finding indicates that trypan blue dye exclusion may not accurately reflect the viability of cells after exposure to UV radiation.
PHOTOMOVEMENT, PIGMENTATION AND UV‐B SENSITIVITY IN PLANARIA
Authors: Barcelo Jeanne A.
Published: January 2008

Abstract—

Four differently pigmented species of planarians were examined for UV‐B (Λ= 320 280 nm) tolerance and ability to delect and avoid UV‐B‐exposed areas. It was found that lighter‐pigmented species are more UV sensitive and that movement out of the UV‐B is directly related to UV sensitivity. Three species showed positioning preference corresponding to their pigmentation; the darker the species, the less avoidance of UV‐B. The white (unpigmented) species showed exceptional and very sensitive behavior.
ULTRAVIOLET LIGHT‐INDUCED INHIBITION OF CELL DIVISION AND DNA SYNTHESIS IN AXENICALLY GROWN REPAIR MUTANTS OF DICTYOSTELIUM DISCOIDEUM
Authors: Kielman J. K. , Deering R. A.
Published: January 2008

Abstract—

Cell division and DNA synthesis were studied during axenic growth following 254 nm ultraviolet light (UV) irradiation of a repair‐proficient parental strain (rad+, D10 colony formation = 195 J/m2) and two repair mutants (radC. D10= 50 J/m2; radB. D10= 5 J/m2) of Dictyostelium discoideum. Isopycnic CsCI gradients were used to distinguish uptake of labeled precursors into nuclear (n) and mitochondrial (m) DNA, using Netropsin to enhance the density resolution. In all strains, m‐DNA synthesis was inhibited to a lesser extent than was n‐DNA synthesis. For radC, which has been shown in other experiments to be slow in incision and dimer removal, the UV‐induced lags in division and n‐DNA synthesis were longer than for rad+. However, radB showed a more complex response. Although brief division lags were observed for < 10 J/m2, little immediate division lag was detected at greater fluences. Instead, a brief period of cell multiplication of up to but not exceeding two‐fold occurred, followed by a cessation of division, and then by lysis. Fluences that yielded extensive lags in n‐DNA synthesis in rad‐ and radC resulted in little detectable immediate postirradiation lag in n‐DNA synthesis in radB. However, later in the postirradiation period, when DNA synthesis had resumed in rad+ and radC. it gradually declined to near zero in radB. We conclude: (1) that the more extended lag in division and n‐DNA synthesis in radC is consistent with its slower rate of excision repair, and (2) that radB contains a defect resulting in less initial blockage of DNA replication by UV lesions.
ULTRAVIOLET ENHANCED REACTIVATION OF HERPES SIMPLEX VIRUS INACTIVATED BY DIFFERENT WAVELENGTHS OF UV RADIATION
Authors: Detsch Richard M. , Bryant F. Dudley , Moore Sharon P. , Coohill Thomas P.
Published: January 2008

Abstract—

The degree of ultraviolet enhanced reactivation (UVR) exhibited by mammalian cells when infected with Herpes simplex virus inactivated by different wavelengths of far ultraviolet (UV) radiation was measured. A wavelength dependence for this effect is presented over the wavelength region 238–297 nm. Within the limits of the deviations obtained, the degree of UVR exhibited is similar at each wavelength. This suggests that virus irradiated with different wavelengths of UV radiation received the same type of damage or that cells repaired the different types of viral damage with the same efficiency.
DNA DAMAGE AND REPAIR IN HUMAN CELLS EXPOSED TO SUNLIGHT
Authors: Parsons P. G. , Goss P.
Published: January 2008

Abstract—

Cultured human cells were treated with direct sunlight under conditions which minimised the hypertonic, hyperthermic and fixative effects of solar radiation. Sunlight produced similar levels of DNA strand breaks as equitoxic 254 nm UV in two fibroblast strains and a melanoma cell line, but DNA repair synthesis and inhibition of semiconservative DNA synthesis and of DNA chain elongation were significantly less for sunlight‐exposed cells. DNA breaks induced by sunlight were removed more rapidly. Thus, the repair of solar damage differs considerably from 254 nm UV repair. Glass‐filtered sunlight (> 320 nm) was not toxic to cells and did not induce repair synthesis but gave a low level of short‐lived DNA breaks and some inhibition of DNA chain elongation; thymidine uptake was enhanced. Filtered sunlight slightly enhanced UV‐induced repair synthesis and UV toxicity; photoreactivation of UV damage was not found. Attempts to transform human fibroblasts using sunlight, with or without phorbol ester, were unsuccessful.
STRUCTURE AND PHOTOBIOLOGICAL ACTIVITY OF 7‐CHLORO‐1,4‐BENZODIAZEPINES. STUDIES ON THE PHOTOTOXIC EFFECTS OF CHLORDIAZEPOXIDE, DESMETHYLCHLORDIAZEPOXIDE AND DEMOXEPAM USING A BACTERIAL INDICATOR SYSTEM
Authors: Cornelissen P. J. G. , Beijersbergen G. M. J. , Henegouwen Van , Mohn G. R.
Published: January 2008

Abstract—

The photobiological activity of chlordiazepoxide, an active ingredient of the drug Librium, which is known to induce phototoxic effects, and two of its metabolites, desmethylchlordiazepoxide and demoxepam, was investigated. Upon irradiation of these biologically active compounds with longwave UV light, the main decomposition product formed is an oxaziridine. Using a strain of Salmonella typhimurium as a test organism for cytotoxicity, it could be demonstrated that not only the drug itself, but also the major mammalian metabolites are phototoxic and, furthermore, that the respective oxaziridines are responsible for the toxic effects found upon irradiation. A close relationship appears to exist between the phototoxicity of the nitrones and the toxicity in the dark of their respective oxaziridines. Investigations of the photobiological activity of a few closely structurally related benzodiazepines could establish that a 4‐oxide moiety in the benzodiazepine nucleus is the structural characteristic responsible for the appearance of phototoxicity; in those compounds which contain a 4‐oxide in the benzodiazepine nucleus, photo‐decomposition to a toxic oxaziridine is observed, while the analogues lacking the 4‐oxide moiety do not show this characteristic and, therefore, no phototoxic effects can be observed. Finally, mutagenicity tests performed with the same bacterial indicator as used for phototoxic studies, and including chlorpromazine as a positive reference compound, indicate that under the present experimental conditions photoproducts formed upon irradiation of chlordiazepoxide and its metabolites with longwave UV light do not exert a mutagenic effect.
STEREOELECTRONIC PROPERTIES OF PHOTOSYNTHETIC AND RELATED SYSTEMS—VIII. AB INITIO QUANTUM MECHANICAL CHARACTERIZATION OF THE ELECTRONIC STRUCTURE AND SPECTRUM OF THE BACTERIOPHEOPHORBIDE a ANION RADICAL
Authors: Petke J. D. , Maggiora Gerald M. , Shipman Lester L. , Christoffersen Ralph E.
Published: January 2008

Abstract—

Ab initio configuration interaction wavefunctions and energies are reported for 16 doublet states of the anion radical of ethyl bacteriopheophorbide a (Et‐BPheo a‐˙), and are employed in an analysis of the electronic absorption spectrum.

The lowest excited doublet state D1 is predicted to lie 8601 cm‐1 above the ground state D0; the D1← D0 transition is nearly forbidden, with a computed oscillator strength f= 0.002. The visible absorption spectrum is shown to consist of transitions to three 2(π, π*) states, D2, D3, and D4. The D4← D0 transition (y‐polarized, f= 0.91) appears to account for observed intense absorption at 15 800 cm‐1.

The Soret band of Et‐BPheo a‐˙ is shown to consist of transitions to several 2(π,π*) states, D7‐D15. Transitions of particularly high intensity include D7← D0 (y‐polarized, f= 0.72), D10← D0 (y‐polarized, f= 1.1), D12← D0 (xy‐polarized, f= 0.86) and D15← D0 (y‐polarized, f= 0.83).

Spin density data and plots are used to describe and compare the general features of the unpaired spin distributions in D0 and D1, which are in reasonable agreement with other reported calculated values and available experimental data for D0.
OPTICAL‐MICROWAVE DOUBLE RESONANCE SPECTROSCOPY OF IN VIVO CHLOROPHYLL
Authors: Clarke Richard H. , Jagannathan Surya P. , Leenstra Willem R.
Published: January 2008

Abstract—

At low temperatures, chloroplast and subchloroplast preparations exhibit complex fluorescence spectra. Emission bands can be attributed to photosystem (PS) particles and various antenna‐chl proteins as well as solubilized chls. Initial results from a systematic study of the components of these fluorescence spectra via optical‐microwave double resonance spectroscopy are presently reported. Conclusions regarding possible structural features are discussed. Experiments on triplet sublevel decay rates yielded data consistent with an interpretation of triplet energy transfer within antenna fragments.
REPAIR OF PSORALEN PLUS NEAR ULTRAVIOLET LIGHT DAMAGE IN BACTERIOPHAGES T3 AND T4
Authors: Strike Peter , Wilbraham Hâf O. , Seeberg Erling
Published: January 2008

Abstract— Repair of T3 and T4 DNA damaged by treatment with 8‐methoxypsoralen plus near UV (PNUV) has been investigated. It is shown that the excision repair mechanisms of the host cell can repair a substantial fraction of the psoralen‐DNA mono‐adducts in T3 DNA, but cannot by themselves repair crosslinks. In contrast neither the excision repair system of the host nor the phage coded v gene endonuclease is involved in the repair of psoralen adducts in T4 DNA. Multiplicity reactivation is effective in the recovery of T4 DNA containing psoralen‐DNA mono‐adducts, but is ineffective in the recovery of crosslinked phages. Comparisons of the lethality of PNUV treatment and the number of crosslinks induced in T4 DNA show clearly that mono‐adducts are lethal to this phage. Both T3 and T4, however, appear to effectively repair many mono‐adducts by postreplicational repair.
THE pKa OF DIPROTONATED SEMIMETHYLENE BLUE, IN 5% ETHANOL AND 50% ACETONITRILE AQUEOUS SOLUTIONS
Authors: Kamat P. V. , Lichtin N. N.
Published: January 2008

Abstract— Semimethylene blue was generated by reductive quenching of triplet methylene blue, 3MBH2+, with diphenylamine at pH 0.62–3.4. A Q‐switched ruby laser flash‐photolysis‐kinetic spectro‐photometric apparatus was used to characterize the absorption spectrum of semimethylene blue from 350 to 900 nm and a number of physical constants at 25°C with μ= 0.4 M and Cl− as the anion. The specific rate of quenching of 3MBH2+ by DPA is 2.8 × 109M−1 s−1 in 5% EtOH‐95% water and 1.2×109M−1 s−1 in 50 v/v% aq. CH3CN. Corresponding efficiencies of net electron transfer are, respectively, 0.15 and 0.62. Spectral characteristics in 5% EtOH are, for MBH22±, λmax= 375 nm, ε375= 9000 M−1 cm−1; λmax= 880 nm, ε880= 12700 M−1 cm−1; for MBH±, λmax= 410 nm, ε410= 9800 M−1 cm−1, λmax= 880 nm, ε880= 33000 M−1 cm−1; for MBH± in 50 v/v% AN, λmax= 400 nm, ε400= 11000 M−1 cm−1 and λmax= 880 nm,ε880= 39000 M−1 cm−1. The pKa of MBH22ε calculated from the pH dependence of the absorption spectrum is 1.86 × 0.04 in 5% EtOH and 1.15 in 50 v/v% AN. Rate constants, kdecay, for reaction DPAH±+ with MBH22ε and MBH± in 5% EtOH are, respectively, 3.9 × 109 and 9.5 × 109M−1 s−1. The value of pKa of MBH22ε calculated from the dependence of kdecay on pH is 1.75 in 5% EtOH.
PHOTOPHYSICAL PROPERTIES OF NUCLEIC ACID COMPONENTS—II. EFFECT OF N, N'DIMETHYL SUBSTITUTION ON INTERSYSTEM CROSSING IN PYRIMIDINE BASES
Authors: Becker R. S. , Bensasson R. V. , Salet C.
Published: January 2008

Abstract— The intersystem crossing quantum yields to the lowest triplet states of N, N'dimethyluracil and N, N'dimethylthymine are 0.02 and ≥0.004, respectively. The very low yields are interpreted in terms of a 1(n, π*) to 1(π.π*) state order change compared with the unsubstituted parents.
DOES MEMBRANE ATTACKING PHOTODYNAMIC ACTION REFLECT THE SO‐CALLED PHASE TRANSITION?
Authors: Ito Takashi
Published: January 2008

Abstract— With Saccharomyces cerevisiae cells the temperature dependence of toluidine blue (TB) sensitized photodynamic inactivation was measured in the range 10–33°C using either H2O (pH 7.9) or 45% D2O (pH 6.8) as a solvent. Plots of ln(1/LD50) (LD50: light dose for 50% survival) as a function of the reciprocal of temperature could be fitted by two straight lines with a discontinuity at 21–22°C. In view of previous findings on TB‐cell interaction that TB sensitizes the cell, after long incubation, in the membrane rather than from outside the cell, it is suggested that the present results reflect the phase transition of lipid matrix.
ON THE ACRIDINE AND THIAZINE DYE SENSITIZED PHOTODYNAMIC INACTIVATION OF LYSOZYME—SINGLET OXYGEN SELF‐QUENCHING BY THE SENSITIZERS
Authors: Schmidt Hartmut , Al‐Ibrahim Ahmed , Dietzel Ursula , Bieker Ludwig
Published: January 2008

Abstract— The quantum yield of the photodynamic inactivation of lysozyme increases in the sequence acridine orange, methylene blue, proflavine and acriflavine (1:5:6:12). At least up to protein concentrations of 0.1 mM, singlet oxygen is exclusively responsible for the inactivation of the enzyme. For methylene blue, acriflavine and proflavine the quantum yields decrease considerably with increasing dye concentrations. From measurements in H2O and D2O buffer solutions it was concluded that in the case of methylene blue the effect is mainly caused by the quenching of singlet oxygen [rate constant (3–4) × 108M−1 s−1]. For the acridine sensitizers both singlet oxygen and dye triplet quenching processes have to be taken into consideration. It has been found that all sensitizers act as competitive inhibitors of the enzymatic reaction of lysozyme. However, the dye‐protein interaction near the active center cannot be responsible for the observed dye self‐quenching effect.
ULTRAVIOLET (254‐405 nm) ACTION SPECTRUM AND KINETIC STUDIES OF ALANINE UPTAKE IN ESCHERICHIA COLI B/R*
Authors: Sharma Rakesh C. , Jagger John
Published: January 2008

Abstract Uptake of ala in exponentially grown and starved cells of Escherichia coli B/r is inhibited by monochromatic far–UV (254–310 nm) and near UV (310–405 nm) light. The action spectrum for inhibition of ala uptake is similar to that found earlier for gly uptake, showing a maximum at 280 nm and a significant but much lower action throughout the near–UV region. The action spectra suggest that the chromophores for inactivation of ala and gly uptake lie in the carrier proteins and that these proteins are similar. Kinetic studies, in unirradiated bacteria, show that (a) the Km for ala uptake (11 μM) is about twice that for gly uptake (4.9 μM), (b) the Km for ala uptake does not change in the presence of gly, although the Kmax does decrease, and (c) other amino acids, such as ser and phe, have no effect on the Km or Vmax of the ala uptake system. These data suggest that ala and gly are transported by the same carrier protein, with the binding sites for ala and gly on different subunits.
INTERACTION OF 8‐METHOXYPSORALEN AND NEAR‐UV LIGHT CAUSES MUTATION AND CYTOTOXICITY IN MAMMALIAN CELLS
Authors: Schenley R. L. , Hsie A. W.
Published: January 2008

Abstract The interaction of near‐UV light and a photosensitizer, 8‐methoxypsoralen (8‐MOP), was studied in the Chinese hamster ovary cell/hypoxanthine‐guanine phosphoribosyl transferase system; cell survival (cloning efficiency) and mutation induction (resistance to 6‐thioguanine) were quantified. Exposure of cells to either 8‐MOP up to 20 μg/ml (93 μM) or near–UV light up to 40000 J/m2 had no effect on either survival or mutation frequency. Preincubation of cells with 8–MOP from 5 to 120 min prior to irradiation with various fluences did not affect cell survival or mutation frequency. Survival decreased and mutation frequency increased linearly when either the 8‐MOP concentration or fluence was increased while the other factor was held as a constant. Mutation frequency appears to show reciprocity relative to the product of 8‐MOP concentration times fluence of near–UV light [(μg/ml)·(J/m2)] throughout a range apparently limited by high cell lethality. The observed pooled data on mutation, f(x), as a function of (μg/ml)·(J/m2), x, fit a linear dose–response line, f(x) = (34.2 + 0.05 x) × 10‐6. Cell survival, however, does not appear to exhibit such reciprocity.
DNA‐DENATURING EFFECT OF IRRADIATED HYDROGEN PEROXIDE
Authors: Roth Daniel
Published: January 2008

Abstract By an acridine dye method for analyzing DNA conformation, it was shown that hydrogen peroxide, in conjunction with irradiation at wavelengths longer than 290 nm, exerted a denaturing effect on linear duplex DNA. The effect was dose–related to a disappearing limit of 10 μM hydrogen peroxide.
THE LIFETIME OF THE EXCITED SINGLET STATE OF β‐CAROTENE: CONSEQUENCES TO PHOTOSYNTHETIC LIGHT HARVESTING
Authors: Dallinger R. F. , Woodruff W. H. , Rodgers M. A. J.
Published: January 2008

Abstract The mechanism of singlet‐singlet energy transfer to chlorophyll from carotenoid auxiliary pigments in photosynthetic apparatus is considered. Transmittance studies and resonance‐enhanced Raman spectroscopy on a picosecond time scale lead to the conclusion that the de–excitation lifetime of the β‐carotene singlet state is not greater than one picosecond. This would require close contiguity on the part of the transferring partners.
FLASH‐INDUCED FAST CHANGE IN SURFACE POTENTIAL AND FLUIDITY OF PURPLE MEMBRANE STUDIED BY SPIN LABEL METHOD
Authors: Tokutomi Satoru , Iwasa Tatsuo , Yoshizawa Tǒru , Ohnishi Shun‐ichi
Published: January 2008

Abstract— Flash‐induced changes in surface potential and fluidity of purple membrane were studied by a spin label method. Changes in surface potential and fluidity were monitored by observing the distribution of charged and uncharged spin labels between the purple membrane and the aqueous phase.

On flash illumination, a transient hyperpolarization of the surface potential and a transient fluidization of the membrane hydrophobic region are induced. The former may probably reflect the proton movement near the purple membrane surface, while the latter may result from photo‐induced conformational changes of bacteriorhodopsin.

The two events are different in time course. The relationships between the two events, and the formation and decay of the intermediates of bacteriorhodopsin in the photoreaction cycle are discussed.
SOME OBSERVATIONS ON THE MORPHOGENESIS OF LATTICE STRUCTURE IN THE PURPLE MEMBRANE
Authors: Usukura Jiro , Yamada Eichi , Mukohata Yasuo
Published: January 2008

Abstract— The formation process of purple membrane was studied morphologically by freeze‐fracture and etching methods. The bacteria, H. halobium R1, cultured in the medium containing 2mM nicotine, did not show the hexagonal structure of purple membrane, but a particle free area was frequently observed in the plasma membrane. However, within 24h after returning to the normal medium, hexagonal and triclinic lattices with spacings of 6 to 8nm occurred as small patches on the P face of the plasma membrane. Furthermore, it was revealed that the retinal was not required for the formation of the two‐dimensional hexagonal lattice structure of purple membrane, since the mutant bacteria, H. halobium R1mW, lacking the ability of retinal synthesis, displayed a similar lattice. The other mutant, H. halobium R1mR, lacking the ability of bacterio‐opsin synthesis, never showed any highly ordered arrangement. This evidence suggests that membrane proteins other than bacterio‐opsin or bacteriorhodopsin do not form highly ordered lattices in the membrane.
ANALYSIS OF PRIMARY PHOTOCHEMICAL PROCESSES IN BACTERIORHODOPSIN
Authors: Dinur U. , Honig B. , Ottolenghi M.
Published: January 2008

Abstract— The sequence of primary events following light absorption by light adapted bacteriorhodopsin (bR570) is considered by analyzing recent picosecond absorption and emission data. The analysis is facilitated by theoretical calculations which allow us to characterize the properties of the first excited singlet state. It is concluded that excitation leads to the eventual population of a photochemically important nonfluorescent excited state (I) which decays into a photoproduct (J625)‐ In J625, which is most probably a ground state molecule, the chromophore has undergone a structural change, presumably trans→ 13‐cis isomerization. It is suggested that the subsequent process

reflects a relaxation of the protein environment involving proton transfer.
LIGHT‐INDUCED PROTON DISSOCIATION AND ASSOCIATION IN BACTERIORHODOPSIN
Authors: Takeuchi Yasuaki , Ohno Koki , Yoshida Masasuke , Nagano Kei
Published: January 2008

Abstract— Light‐induced proton release and uptake by acetylated and unmodified bacteriorhodopsin were measured. Bacteriorhodopsin, when illuminated, shows a net proton release at neutral and alkaline pH's, but in acidic pH, it shows an uptake of protons. In the presence of high concentrations of guanidine hydrochloride, light caused only proton release even in acidic pH and the maximum extent of the release was one proton per bacteriorhodopsin molecule around pH 8.

Acetylation of bacteriorhodopsin caused no alteration in the absorption spectrum of purple complex (bR570) and M412‐intermediate, but decreased the decay rate of the M412‐intermediate. Light‐induced release of protons was not observed even in neutral pH values, and only the proton uptake was noticed by acetylated purple membrane fragments. In high concentrations of guanidine hydrochloride, no proton uptake or release by illumination was observed. Vesicles were reconstituted from acetylated purple membrane. These vesicles had almost no ability for light‐induced proton transport. The role of amino group(s) in light‐induced proton release and transport through the purple membrane is discussed.
P588, A SECOND RETINAL‐CONTAINING PIGMENT IN HALOBACTERIUM HALOBIUM
Authors: Weber H. J. , Bogomolni R. A.
Published: January 2008

Abstract— Halobacterium mutant strains with defects in the biosynthesis of various pigments have been isolated. One of these strains, mutant ET‐15, is incapable of producing the light‐driven proton pump bacteriorhodopsin and the carotenoid bacterioruberin. However, ET‐15 synthesizes another photochemically active, retinal‐containing pigment, P588, which mediates light‐induced proton uptake enhanced by uncouplers. P588 and bacteriorhodopsin are simultaneously present in wild‐type cells grown under normal conditions; however, they can be distinguished by the following criteria.

They can be separated by independent mutational events.

Proton ionophores such as FCCP diminish bacteriorhodopsin‐driven proton translocation but enhance P588‐mediated proton flows. We define here proton translocations which can be diminished by the addition of uncouplers (e.g. FCCP) as ‘active’, others which can be enhanced by FCCP as ‘passive’.

The kinetic and spectral properties of the photocycle intermediates of bacteriorhodopsin and P588 are different.

The action spectrum for photocycling of P588 is red‐shifted with respect to that for bacteriorhodopsin.

A comparison of action spectra for proton translocations with that for photocycling links pigment P588 and light‐driven, passive proton uptake by ET‐15 envelope vesicles. When chemically bleached P588 was regenerated with all‐trans‐retinal, both photochemical activity and light‐induced proton inflow were restored to equal extents. This identifies P588 with the energizer for the passive proton flows.
LIGHT‐INDUCED LINEAR ACTION DICHROISM IN PHOTOREVERSIBLY PHOTOCHROMIC SENSOR PIGMENTS—I. THEORY
Authors: Björn Lars Olof
Published: January 2008

Abstract— With a photoreversibly photochromic regulator pigment such as phytochrome, linear action dichroism could theoretically be obtained after photoselection even if the molecules are initially randomly oriented: If randomly oriented Pfr (fed‐absorbing phytochrome) molecules are partially converted to Pfr (far‐red absorbing phytochrome) molecules by plane‐polarized red light, those molecules will preferentially be converted which have their ‘red’ transition moments nearly parallel to the electric vector of the red light. The effect of subsequent plane‐polarized far‐red light will depend on the plane of polarization. A general theory is developed for how this can be used to determine whether or not the transition moment changes direction during conversion. The pigment need not be isolated, since only physiological reactions (such as germination or chromatic adaptation) are measured.
EFFECT OF PHOSPHATE AND CHLORIDE ON THE PHOTODYNAMIC INACTIVATION OF YEAST CELLS
Authors: Moan J. , Kvello Stenström A. G.
Published: January 2008

Abstract— Yeast cells are inactivated by treatment with hematoporphyrin and light. The inactivation, which is mediated by singlet oxygen (1O2), is enhanced by the presence of phosphate and chloride. Neither phosphate nor chloride has any influence on the yield of 1O2. Possible mechanisms for the enhancement are briefly discussed.
PHOTOSENSITIZED OXIDATION IN THE OCULAR LENS: EVIDENCE FOR PHOTOSENSITIZERS ENDOGENOUS TO THE HUMAN LENS
Authors: Samuel Zigler J. , Goosey John D.
Published: January 2008

Abstract— Numerous investigators have attempted to associate near UV light exposure with various changes which occur to lens crystallins during aging and cataractogenesis. Recently we have shown in vitro that singlet oxygen mediated oxidation of lens crystallins produces effects very similar to those documented for crystallins from old or cataractous lenses and suggested that near UV photodynamic effects may play a major role in vivo in aging in the human lens. In the present work we demonstrate that certain oxidation products of tryptophan which have been identified in human lens can act as near UV photosensitizers, producing singlet oxygen. The insoluble protein fraction from human cataracts is shown to have the capacity to act as a photosensitizer. An age‐related increase in photosensitizing capacity is also demonstrated in the soluble crystallins from human lens. These findings are discussed with respect to development of pigmented nuclear cataracts.
A PHOTOSYSTEM I‐PHENOSAFRANINE SOLAR CELL
Authors: Bhardwaj R. , Pan R. L. , Gross E. L.
Published: January 2008

Abstract— We have previously developed a solar cell using the photochemistry of Photosystem I particles and flavin mononucleotide (Gross et al, 1978). We have now shown that phenosafranine (3,7‐diamine‐5 phenyl phenazine) is an acceptor of Photosystem I. We have used this compound to generate a photovoltage. The total power obtained was the sum of two photoreactions: the Photosystem I mediated photoreduction of phenosafranine and the direct photochemical reduction of phenosafranine by reducing agents such as EDTA or Tricine. An open circuit potential of 670 mV and a short circuit current of 1.6 mA (current density = 20 μA/cm2) were obtained. The front face power conversion efficiency of the cell was about 0.2% at 110 Wm−2 light intensity.
PHOTORESPONSIVE ARTIFICIAL MEMBRANE. REGULATION OF MEMBRANE PERMEABILITY OF LIPOSOMAL MEMBRANE BY PHOTOREVERSIBLE CIS‐TRANS ISOMERIZATION OF AZOBENZENES
Authors: Kano Kaji , Tanaka Yasuhiko , Ogawa Teiichiro , Shimomura Masatsugu , Kunitake Toyoki
Published: January 2008

Abstract— Photoresponsive artificial membranes have been prepared by embedding amphiphatic alkyl‐ammonium salts containing azobenzene chromophore in dipalmitoylphosphatidylcholine liposomes. The configurational change due to trans→cis photoisomerization of the azobenzene chromophore provided the perturbation of the membrane structure to result in the increase of the water and bromo‐thymol blue permeability of the liposomal membranes.
PHOTOSENSITIZATION BY DRUGS IN SURFACTANT SOLUTIONS
Authors: Moore Douglas E. , Burt Christopher D.
Published: January 2008

Abstract— Chlorpromazine, promazine, anthracene and furosemide were tested as photosensitizers using 365 nm UV light in micellar solutions of cationic, anionic and nonionic surfactants. In all cases, micelles enhanced the ability of these compounds to photosensitize the oxidation of 2,5‐dimethylfuran and the free radical polymerization of acrylamide. pH variation showed that the base form of chlorpromazine and the acid form of furosemide are the principal photosensitizing forms of these compounds. Rate differences between cationic and anionic surfactant media indicate the cation radical to be the major photochemical species formed from chlorpromazine and promazine in micellar media. Photodechlorination of chlorpromazine accounted for a significantly higher reactivity of chlorpromazine over promazine. Anthracene was found to be a very active photosensitizer by the singlet oxygen mechanism but also yielded a small concentration of cation radicals in micellar solution. In its neutral form, furosemide reacted strongly in both photooxidation and photopolymerization systems.

The implications of this study to drug‐induced photosensitivity are that (i) free radical reactions may play a major role, and (ii) these sensitizers are more reactive in a hydrophobic environment, suggesting that the cellular membrane or the hydrophobic surfaces of proteins or DNA are more important sites of action in photosensitivity.
ACTION SPECTRA FOR THE PHOTOLYSIS OF 5‐IODODEOXYURIDINE IN DNA AND RELATED MODEL SYSTEMS: EVIDENCE FOR SHORT‐RANGE ENERGY TRANSFER*
Authors: Rahn R. O. , Sellin H. G.
Published: January 2008

Abstract— A variety of polynucleotides containing 5‐iodouracil residues were irradiated in aqueous solution with wavelengths between 240 and 313 nm. From the rate of deiodination the photochemical cross sections (aB) were determined as a function of the irradiation wavelength (A). The expression was used to relate the observed values of B to the intrinsic quantum yield, φINT, and to the absorption cross sections, and for the iodinated and noniodinated residues, respectively. φINT is the probability an excited iodouracil residue will deiodinate, while the parameter b is a measure of the number of noniodinated bases which contribute their excitation energy to the deiodination process. For IdUrd and poly(5‐iodouridylic acid), the average values of φINT calculated from the experimental B values were 0.0202 and 0.0188, respectively, for irradiation in air. In native, denatured, and depurinated DNA in which IdUrd was substituted for 10% of the Thd, the average φINT values were 0.0069, 0.0088, and 0.0153, respectively, indicating an enhancement in φINT upon decreasing the order of the polynucleotide. In contrast, the average values of b bor the same set of compounds were found to be4, 2 and 0.4, respectively, indicating a decrease in b with decreasing polynucleotide order, i.e. a loss of base stacking decreases the extent of energy transfer. A value of b= 4 for native DNA is assumed to mean that the extent of energy transfer in native DNA is limited to four base donors per iodouracil residue serving as an energy trap.
AROMATIC AMINO ACIDS AND ULTRAVIOLET INDUCED PHOTO‐ELECTRIC EFFECTS IN BILAYER MEMBRANES
Authors: Huebner Jay S. , Arrieta Rodolfo T. , Millar David B.
Published: January 2008

Abstract— Ultraviolet light flashes induced voltage transients across bilayer lipid membranes when aromatic amino acids were adsorbed to one side of the membrane. These photo‐effects varied with the chromophore structure, the aqueous solution salt concentration, pH and oxygen partial pressure. These photo‐effects are attributed to the migration of electrically charged photochemical intermediates in the membrane, and provide a new method for studying the effects of UV light on membranes.
REACTIVATION OF UV‐ AND γ‐IRRADIATED HERPES VIRUS IN UV‐ AND X‐IRRADIATEDCV–1 CELLS
Authors: Takimoto Koichi , Niwa Ohtsura , Sugahara Tsutomu
Published: January 2008

Abstract— Enhanced reactivation of UV‐ and y‐irradiated herpes virus was investigated by the plaque assay onCV–1 monkey kidney monolayer cells irradiated with UV light or X‐rays. Both UV‐ and X‐irradiatedCV–1 cells showed enhancement of survival of UV‐irradiated virus, while little or no enhancement was detected for y‐irradiated virus assayed on UV‐ or X‐irradiated cells. The enhanced reactivation of UV‐irradiated virus was greater when virus infection was delayed 24 or 48 h, than for infection immediately following the irradiation of cells. It is demonstrable that the UV‐ or X‐irradiatedCV–1 cells are able to enhance the repair of UV damaged herpes virus DNA, but not of y‐ray damaged ones.
PYRIMIDINE DIMER FORMATION AND GERMINATION OF UV‐IRRADIATED SPORES OF DICTYOSTELIUM DISCOIDEUMNC–4 ANDys–13
Authors: Nozu K. , Ohnishi T. , Okaichi K.
Published: January 2008

Abstract— Survival, UV‐photoproducts and germination of UV‐irradiated spores of Dictyostelium discoi‐deum were studied on two strains,NC–4 andys–13. The spores ofNC–4 are about 35 times more resistant to UV thanys–13 spores at 10% survival. Pyrimidine dimers were formed in UV‐irradiated spores in both strains. No photoproducts other than pyrimidine dimers were detected. The formation of pyrimidine dimers in spores was about 2% in both strains at 800 J/m2. In the germination of spores, the conversion of spores into swollen spores was not affected by UV in both strains, but the emergence of amoebae from the swollen spores was suppressed, which was more distinctive inys–13 spores than inNC–4 spores. The emerged amoebae from the UV‐irradiatedNC–4 spores were viable, while those from theys–13 spores were inviable even when they succeeded in emergence.
DEPENDENCE OF Pfr/Ptot‐RATIOS ON LIGHT QUALITY and LIGHT QUANTITY
Authors: Jabben M. , Beggs C. , Schaufer E.
Published: January 2008

Abstract— Not only the spectral distribution of the light source determines the relative proportion of phytochrome in the Pfr(Pr) form, the Pfr/Ptot‐ratio also depends strongly on the fluence rate of the irradiation. This dependence has been observed in the cotyledons of etiolated mustard seedlings for blue light of fluence rates below 20 Wm‐2. It has also been observed for white light and seems to be a characteristic of the phytochrome system resulting from the involvement of phytochrome thermal reactions as well as Pr Pfr photoconversions. The fluence rate dependence of Pfr/Ptot‐ratios can be used to analyze the characteristic transformations of the phytochrome system. Phototransformations together with a fast thermal transformation (τ½⋍ 3min) are consistent with the results obtained for blue and white light.
TWO‐PHOTON INACTIVATION, PHOTOREACTIVATION AND PHOTOPROTECTION IN YEAST CELLS IRRADIATED BY 266 NM‐LASER RADIATION
Authors: Rubin L. B. , Burchuladze T. G. , Fraikin G. Y.
Published: January 2008

Abstract— The quadratic dependence of inactivation of yeast cells on laser fluence rate at 266 nm suggests the occurrence of two‐photon photochemical reactions in DNA, producing photoproducts similar to those found with ionizing radiation. Observations of a significant diminution of photoreacti‐vation and the disappearance of photoprotection at high laser fluence rates provide additional evidence for this.
SPIN‐TRAPPING and ESR STUDIES OF THE DIRECT PHOTOLYSIS OF AROMATIC AMINO ACIDS, DIPEPTIDES, TRIPEPTIDES and POLYPEPTIDES IN AQUEOUS SOLUTIONS—II. TYROSINE and RELATED COMPOUNDS
Authors: Lion Yves , Kuwabaraj Mikinori , Riesz Peter
Published: January 2008

Abstract— The UV‐photolysis of peptides containing tyrosine (Tyr) was investigated in aqueous solutions at room temperature at 220 and 265 nm. The short‐lived free radicals formed during photolysis were spin‐trapped by t‐nitrosobutane and identified by electron spin resonance. For N‐acetyl‐ and N‐formyl‐L‐Tyr and for peptides containing L‐Tyr as the middle residue, photolysis at 265 nm under neutral conditions produced mainly spin‐adducts due to the scission between the alpha carbon and the methylene group attached to the aromatic ring, while at 220 nm decarboxylation radicals were spin‐trapped. Photolysis of di‐ and tripeptides at 275 nm in alkaline solutions predominantly generated deamination radicals. The radicals produced in the photolysis of the oxidized A chain of insulin were tentatively characterized by comparison with the results for di‐ and tripeptides.
PHOTOCHEMISTRY IN HUMAN EPIDERMIS. A QUANTITATIVE APPROACH
Authors: Dubertret L. , Santus R. , Bazin M. , Melo T. de Sa e
Published: January 2008

Abstract— The good transmission of near UV or visible light by human epidermis obtained through mild suction blisters makes it possible to perform quantitative absorption spectroscopy on various photosensitizing dyes such as hematoporphyrin and methylene blue incorporated into the epidermis. The variety of microenvironments found in the skin modifies the photophysical properties of chromo‐phores as shown by optical absorption band red shifts resulting from chromophore‐macromolecule interactions. They also modify the primary photochemical processes as exemplified by measuring the photobleaching quantum yield of the diphenylisobenzofuran, a singlet oxygen probe. The relevance of this study to photomedicine is discussed; in particular, it is shown that some psoralens used in human photochemotherapy can induce photosensitized reactions involving molecular oxygen.
RADICAL GENERATION DURING THE ILLUMINATION OF AQUEOUS SUSPENSIONS OF TUNGSTEN OXIDE IN THE PRESENCE OF METHANOL, SODIUM FORMATE and SODIUM BICARBONATE. DETECTION BY SPIN TRAPPING
Authors: Aurian‐Blajeni B. , Halmann M. , Manassen J.
Published: January 2008

Abstract— Free radical intermediates appearing during illumination of aqueous suspensions of tungsten oxide were detected by electron spin resonance using the technique of spin trapping. Solutions irradiated contained methanol, formaldehyde, sodium formate and sodium hydrogen carbonate. Signals assigned to the spin adducts of the •H, •OH, •CO2‐ and •CH2OH radicals were found.
A COMPARISON OF THERMALLY INDUCED CHANGES IN SONICATED PHOSPHOLIPID AND SURFACTANT VESICLES BY MEANS OF INTRA‐MOLECULAR EXCIMER‐FORMING PROBE
Authors: Lukac Sava
Published: January 2008

Abstract The molecule (1,l'‐dipyrenyl)‐methyl ether (dipyme) was used for monitoring the bilayer fluidity of surfactant and sonicated phospholipid vesicles. In the latter systems, the observed transition temperatures (Tc) are identical with those found by different methods. Surfactant vesicles prepared from dioctadecyldimethylammonium bromide (DODAB) and dihexadecylphosphate (DHP) molecules manifest a similar fluidity of their bilayers as those of sonicated phospholipid vesicles below their Tc. However, unlike in phospholipid vesicles, there was no significant change of the bilayer structure above Tc observed in surfactant vesicles. DHP vesicles formed in pure water provide a different solubilization site for dipyme than those prepared in a buffer solution. Such sites are characterized by a relatively high local concentration of the probe and the appearance of the blue shifted spectrum of the excimer.
EFFECTS OF EXCITED‐STATE PROTON TRANSFER ON THE PHOSPHORESCENCE OF TYROSINE‐PHOSPHATE COMPLEXES
Authors: Schnarr Manfred , Helene Claude
Published: January 2008

Abstract Phosphate anions quench the fluorescence of tyrosine at room temperature as a result of an excited‐state proton transfer. At 77 K in frozen solutions the fluorescence of tyrosine is still quenched by phosphate anions but the phosphorescence emission is enhanced. No tyrosinate phosphorescence is detected. A mechanism is proposed to explain these results: excited‐state proton transfer from tyrosine to phosphates is followed by intersystem crossing in tyrosinate anions with subsequent back‐transfer of the proton in the triplet state.
PHOTODYNAMIC INHIBITION OF ESCHERICHIA COLI DNA POLYMERASE I BY 8‐METHOXYPSORALEN PLUS NEAR ULTRAVIOLET IRRADIATION
Authors: Granger Michèle , Toulme Francine , HÉLÉNE CLAUDE
Published: January 2008

Abstract Irradiation by UV‐A of E. coli DNA polymerase I in the presence of 8‐methoxypsoralen (8‐MOP) leads to a similar inactivation of the 5′→ 3’polymerase and 3’→ 5’exonuclease activities of the enzyme. The kinetics of inactivation depend on the psoralen concentration and on the duration of irradiation. The 5′→3’exonuclease activity is first slightly stimulated at short irradiation time in the presence of 8‐MOP; further irradiation leads to inhibition of this activity. The mechanism of the reactions involves oxygen as shown by the absence of any effect of UV irradiation when oxygen is removed. The results obtained in D2O, in oxygen‐saturated buffer or in the presence of singlet oxygen (1O2) quenchers show that 1O2 is one of the reactive intermediate species. Irradiation of homopolymers primed with oligomers in the presence of 8‐MOP inhibits their template and initiating capacity in the same dose range as that required to inactivate DNA polymerase I. Mono‐adducts of 8‐MOP with nucleic acid bases can act as inhibitors of both replication and initiation.
EFFECTS OF GLYCEROL UPON THE BIOLOGICAL ACTIONS OF NEAR‐ULTRAVIOLET LIGHT: SPECTRA AND CONCENTRATION DEPENDENCE FOR TRANSFORMING DNA AND FOR ESCHERICHIA COLI B/r
Authors: Peak J. G. , Peak M. J. , Foote C. S.
Published: January 2008

The concentration dependence for the protection of isolated transforming DNA and Escherichia coli by glycerol against 365‐nm monochromatic near‐ultraviolet light (UV) was measured. Glycerol protection saturates at a concentration of about 0.1 M for DNA and 1.0 M for E. coli. Action spectra for glycerol protection of transforming DNA (tryptophan and histidine markers) are similar to those obtained previously for diazobicyclo[2.2.2.˜octane (DABCO) protection, with protection reaching a maximum near 350‐nm UV and decreasing rapidly at wavelengths above and below 350 nm. However, glycerol protects against near‐UV about twice as efficiently as DABCO. The action spectrum for protection of E. coli by glycerol against the lethal effects of near‐UV was not the same as the spectrum for DNA since glycerol sensitized the cells, but not the DNA, at wavelengths longer than about 380 nm. A possible role of hydroxyl or other radicals was supported by the observation that benzoate also protected DNA against inactivation by 334‐nm UV.