bluuebunny/crossref_metadata_2025 huggingface dataset:
PTHALOCYANINE‐INDUCED PHOTODYNAMIC CHANGES OF CYTOPLASMIC FREE CALCIUM IN CHINESE HAMSTER CELLS
Authors: Ben‐Hur E. , Dubbelman T.M.A.R. , Steveninck J. Van
Published: January 2008

Exposure to light of Chinese hamster cells preloaded with chloroaluminum phthalocyanine causes an immediate increase of cytoplasmic free calcium, [Ca2+]i, from about 0.2 μM to 1 μM within 5 min after illumination. This increase was dose‐dependent within the biological dose range, reaching a plateau at a dose that kills 99.5% of the cells. Fluoride addition prior to light exposure protected against cell killing and reduced the increase of [Ca2+]i. These findings raise the possibility that changes in [Ca2+]i after photodynamic treatment may be relevant to cell killing and/or other biological responses of the cells, e.g. release of eicosanoids.
CHRONIC ULTRAVIOLET RADIATION‐INDUCED INCREASE IN SKIN IRON and THE PHOTOPROTECTIVE EFFECT OF TOPICALLY APPLIED IRON CHELATORS 1,*
Authors: Bissett Donald L. , Chatterjee Ranjit , Hannon Daniel P.
Published: January 2008

In the skin of albino hairless mice (Skh:HR‐l) there is a basal level of non‐heme iron. Chronic exposure of mice to sub‐erythemal doses of ultraviolet (UV) B radiation results in an increased skin level of non‐heme iron. The iron increase may be the result of a UVB radiation‐induced increase in vascular permeability, which we measured in vivo with the dye marker Evans Blue. We also observed greater non‐heme iron in sun‐exposed vs non‐exposed body sites of human skin, suggesting that similar events occur in man.

Iron may have a role in skin photodamage by participating in formation of reactive oxygen species. These species have been implicated in skin photodamage. It is known that iron can contribute to oxygen radical production by acting catalytically in the formation of species such as hydroxyl radical. While the basal level of skin iron may be available for catalysis, the elevated iron content of UV‐exposed skin increases the potential for iron‐catalyzed radical production.

Topical application of certain iron chelators to Skh albino hairless mice dramatically delayed the onset of UVB radiation‐induced skin photodamage. Non‐chelating analogs provided no significant protection.
SIMULTANEOUS ESTABLISHMENT OF MONOCLONAL ANTIBODIES SPECIFIC FOR EITHER CYCLOBUTANE PYRIMIDINE DIMER OR (6‐4)PHOTOPRODUCT FROM THE SAME MOUSE IMMUNIZED WITH ULTRAVIOLET‐IRRADIATED DNA
Authors: Mori Toshio , Nakane Misa , Hattori Tsuyoshi , Matsunaga Tsukasa , Ihara Makoto , Nikaido Osamu
Published: January 2008

Six new monoclonal antibodies (TDM‐2, TDM‐3, 64M‐2, 64M‐3, 64M‐4 and 64M‐5) specific for ultraviolet (UV) induced DNA damage have been established. In the antibody characterization experiments, two TDM antibodies were found to show a dose‐dependent binding to UV‐irradiated DNA (UV‐DNA), decrease of binding to UV‐DNA after cyclobutane pyrimidine dimer photo‐reactivation, binding to DNA containing cyclobutane thymine dimers, and unchanged binding to UV‐DNA after photoisomerization of (6‐4)photoproducts to Dewar photoproducts. These results indicated that the epitope of TDM monoclonal antibodies was the cyclobutane pyrimidine dimer in DNA. On the other hand, four 64M antibodies were found to show a dose‐dependent binding to UV‐DNA, unchanged binding to UV‐DNA after cyclobutane pyrimidine dimer photoreactivation, undetectable binding to DNA containing thymine dimers, and decrease of binding to UV‐DNA after photoisomerization of (6‐4)photoproducts. These results indicated that the epitope of 64M antibodies was the (6‐4)photoproduct in DNA. This is the first report of the simultaneous establishment of monoclonal antibodies against the two different types of photolesions from the same mouse. By using these monoclonal antibodies, we have succeeded in measuring both cyclobutane pyrimidine dimers and (6‐4)photoproducts in the DNA from human primary cells irradiated with physiological UV doses.
ABSORPTION SPECTRAL SHIFTS OF CAROTENOIDS RELATED TO MEDIUM POLARIZABILITY
Authors: Andersson Per Ola , Gillbro Tomas , Ferguson Linda , Cogdell Richard J.
Published: January 2008

Abstract–Solvent induced absorption spectral shifts of the electronic transition from ground 1 Ag state to the excited 1Bu state in carotenoids have been studied. It is shown that the shift depends only on dispersion interactions in non‐polar solvents. In polar media there is just a small extra contribution to the red‐shift, due to other forms of interactions. The spectral shifts are well described by the theory, which expresses the shift relative to the gas phase value, as a function of solvent polarizability. The main conclusion is that the dominating mechanism behind the large red‐shifted absorbance of carotenoids in the proteinacous environment, in vivo, is the mutual polarizability interactions between the carotenoids and the surrounding medium. The solution‐phase values of the dipole moments of the lAg to 1Bu transitions and the differences of isotropic polarizability between 1Bu and lAg states of carotenoids in non‐polar solvents are calculated and found to be around 13 D and 360 Å3 respectively. From the great overlap of absorption spectra between carotenoids in quinoline and carotenoids in vivo in purple bacterial antenna complexes, it can be expected that the carotenoids are surrounded by several aromatic amino acids in vivo. Comparisons have been done between the exicted states in carotenoids and in linear conjugated polyenes.
PHOTOHEMOLYSIS SENSITIZED BY PSORALEN: RECIPROCITY LAW IS NOT FULFILLED
Authors: Potapenko A. Ya. , Agamalieva M. A. , Nagiev A. I. , Lysenko E. P. , Bezdetnaya L. N. , Sukhorukov V. L.
Published: January 2008

References

The effect of the intensity of ultraviolet‐A (UV‐A) radiation (366 nm) on delayed photo‐hemolysis sensitized by psoralen (PUV‐A hemolysis) was studied. It was shown that PUV‐A hemolysis induced by UV‐A radiation at low fluence rate (20 W m−2) develops according to the well‐known colloid‐osmotic mechanism: there was no threshold dose of PUV‐A treatment. After irradiation all the cells were hemolysed. The rate of PUV‐A hemolysis was proportional to the square of the fluence. Hemolysis was delayed in the presence of sucrose. When the fluence rate of UV‐A radiation was increased to 150 W m−2, the character of PUV‐A hemolysis changed drastically. A threshold fluence appeared, below which PUV‐A hemolysis was not induced. At fluences slightly exceeding the threshold, only part of the cells in the suspension were lysed. The dependence of the portion of hemolysing cells on fluence was S‐shaped. Increasing the fluence resulted in complete (100%) hemolysis. The rate of complete hemolysis decreased at higher fluences, but was many‐fold higher than the rate of low‐intensity PUV‐A hemolysis at equal fluences. The main features of high intensity PUV‐A hemolysis (dependences on fluence and temperature, effect of sucrose) were the same for the hemolysis induced by the addition of previously photooxidized psoralen. We suggest that high intensity PUV‐A hemolysis is induced with participation of photooxidized psoralen as an intermediate.
CYCLOBUTANE DIMERS AND (6‐4)PHOTOPRODUCTS IN HUMAN CELLS ARE MENDED WITH THE SAME PATCH SIZES
Authors: Cleaver James E. , Jen Jin , Charles Wayne C. , Mitchell David L.
Published: January 2008

The sizes of excision repair patches corresponding to excision of (6‐4) pyrimidine‐pyrimidone photoproducts and (5‐5,6–6) cyclobutane dimers have been independently determined by using bromodeoxyuridine substitution and density increases in isopycnic gradients of small DNA fragments. The two classes of photoproducts were distinguished by using (a) a xeroderma pigmentosum (XP) revertant cell line that excises (6‐4) photoproducts normally, but does not excise cyclobutane dimers from bulk DNA or from an actively transcribed sequence; (b) an XP cell line containing the denV gene of bacteriophage T4, which repairs only cyclobutane dimers by a unique glycosylase mechanism, and (c) normal cells analyzed during time intervals in which cyclobutane dimer repair is the main repair process in action. The patch sizes for the two lesions were similar under all conditions and were estimated to be approximately30–40 bases. These values are slightly larger than corresponding estimates for Escherichia coli and Saccharomyces cerevisiae but close to estimates from in vitro experiments with human cell extracts. The size of 30 bases may consequently be very close to the actual distance between cleavage sites made on either side of a photoproduct during repair.
PHOTOCYCLE KINETICS: ANALYSIS OF RAMAN DATA FROM BACTERIORHODOPSIN*
Authors: Nagle John F.
Published: January 2008

Abstract– A recently developed algorithm for analyzing photocycle kinetics was applied to recently obtained Raman data for the time course of bacteriorhodopsin (bR) and its intermediates, L, M, N and O. The algorithm allows all possible transitions between any of the intermediates in the kinetic model. The best fit to all the Raman data required the transitions L ↔ M ↔ N ↔ O ↔ bR and also the branch L↔N. The rates are moderately well determined and smooth as a function of pH. From the ratios of forward and backward rates the differences in free energy of the L, M and N states are no larger than 1.5 kcal. The possibility that only the sum of the L and N concentrations is well determined, but not the individual L and N concentrations, was investigated. The model L ↔ M ↔ N ↔ O ↔ bR satisfactorily fitted condensed L+N data and gave predicted individual L and N concentrations considerably different than those measured individually. The possibility of Raman invisible states, such as two Ms or two Ns was also investigated. Models with two Ns were not successful and it cannot yet confidently be concluded which model with two Ms is best. However, the model, L ↔ M1 ↔ M2 ↔ N ↔ O ↔ bR plus the branch L↔N, fits the data better with the same number of parameters as the best model with only one M intermediate. This provides strong support for two Ms in the bR photocycle.
FOURIER TRANSFORM INFRARED SPECTRAL STUDIES ON THE SCHIFF BASE MODE OF ALL‐trans BACTERIORHODOPSIN and ITS PHOTOINTERMEDIATES, K and L*
Authors: Maeda Akio , Sasaki Jun , Pfefferlé Jean‐Marc , Shichida Yoshinori , Yoshizawa Tôru
Published: January 2008

Abstract– Difference Fourier transform infrared spectra were recorded for bacteriorhodopsin upon irradiation at 230, 170 or 77 K, which gave, respectively, the spectrum of the M, L or K intermediate minus unphotolyzed all‐trans bacteriorhodopsin (denoted as BR). By replacement of the Schiff base nitrogen with 15N, or of either its hydrogen at N or C15 with deuterium, the vibrational bands related to the Schiff base were identified and the isotope‐shifts evaluated for BR, K and L. The 1348 cm−l band of BR and K and the 1400 cm−1 band of L were sensitive to each of these isotope substitutions. The 1254 cm−1 band of BR, the 1245 cm−1 band of K and the 1301 cm−1 band of L were sensitive to either N‐ or C15‐deuteration but not to 15N‐substitution. The N—D in‐plane bending vibration of K and L appeared at 969 and 997 cm−1, respectively, upon substitution with D2O. All the results show that L is larger in frequencies related to the N—H in‐plane bending vibration than K or BR and suggest that L has the strongest interaction with the protein. Among the bands containing an N—H bending vibration, the 1348 cm−1 band of K was more intense than the corresponding band of L at 1400 cm−1. The C15‐deuteration‐induced upshift of the 1245 cm−1 band of K was unobservable for the 1301 cm−1 band of L. Such differences between L and K might be brought about by a distortion in the retinal moiety close to the protonated Schiff base of the 13‐cis chromophore.
COOPERATIVITY OF THE DEHYDRATION BLUE‐SHIFT OF BACTERIORHODOPSIN*
Authors: Renthal Robert , Regalado Ruben
Published: January 2008

Abstract– Dehydration of purple membrane (PM) causes a hlue‐shift of the absorbance maximum from 570 nm to about 530 nm [Lazarev and Terpugov (1980) Biochim. Biophys. Acta590.324–338; Hildebrandt and Stockburger (1984) Biochemistry23,5539–5548]. The absorbance spectra of PM dried in films at pH 0, 7 and 11 were measured at controlled relative humidities (RH). At pH 7, a blue‐shift was observed similar to that previously reported. At pH 0(1M H2SO4) a reversible transition was observed from the “acid blue membrane” (maximum near 600 nm at 100% RH) to a blue‐shifted dehydrated pigment (maximum near 578 nm at 50% RH), with isosbestic points at 592 and 710 nm. At pH 11 (NaOH) the absorbance maximum shifted to 530 nm, similar to the dehydrated form at pH 7. The fraction of hydrated chromophore, Xh, was calculated (assuming only two chromophore states, hydrated and dehydrated) as a function of humidity and pH. The resulting curve at pH 7 showed a steep decline in Xh below 20% RH. Near this hydration level, water clusters on protein surfaces break up, causing side‐chain pK reversals. The Hill coefficient for the transition was about 2, indicating the minimum number of water molecules involved in a cooperative transition. The results suggest that as few as two water molecules are coordinated to the protonated retinal Schiff base of bacteriorhodopsin. A mechanism for the pH 7 dehydration blue‐shift is proposed, involving a pK reversal of the protonated Schiff base and a nearby carboxyl side chain. At pH 0, a sharp decline in Xh occurs between 100 and 70% RH. Near this hydration level, complete protein surface coverage by a water monolayer occurs. The Hill coefficient is about 20, suggesting involvement of a large region of the surface.
QUANTUM YIELD RATIO OF THE FORWARD and BACK LIGHT REACTIONS OF BACTERIORHODOPSIN T LOW TEMPERATURE and PHOTOSTEADY‐STATE CONCENTRATION OF THE BATHOPRODUCT K*
Authors: Balashov S. P. , Imasheva E. S. , Govindjee R. , Ebrey T. G.
Published: January 2008

The maximum photosteady state fraction of K, xKmax, and the ratio of the quantum yields of the forward and back light reactions, trans‐bacteriorhodopsin (bR) hArr; K, φbR/φK, were obtained by measuring the absorption changes produced by illumination of frozen water‐glycerol (1:2) suspensions of light‐adapted purple membrane at different wavelengths at ‐165°C. An independent method based on the second derivative of the absorption spectrum in the region of the β‐bands was also used. It was found that

The quantum yield ratio (0.66 ± 0.06) was found to be independent of excitation wavelength within experimental error in the range510–610 nm. The calculated absorption spectrum of K has its maximum at603–606 nm and an extinction 0.85 ± 0.03 that of bR. At shorter wavelengths there are P‐bands at 410, 354 and 336 rim. Using the data of Hurley et al. (Nature 270,540–542, 1977) on relative rates of rhodopsin bleaching and K formation, the quantum yield of K formation was determined to be 0.66 ± 0.04 at low temperature. The quantum efficiency of the back reaction was estimated to be 0.93 ± 0.07. These values of quantum efficiencies of the forward and back light reactions of bR at ‐ 165°C coincide with those recently obtained at room temperature. This indicates that the quantum efficiencies of both forward and back light reactions of bacteriorhodopsin are temperature independent down to ‐165°C.
ROTATIONAL DIFFUSION EFFECTS ON ABSORBANCE MEASUREMENTS: LIMITATIONS TO THE MAGIC‐ANGLE APPROACH*
Authors: Lewis J. W. , Kliger D. S.
Published: January 2008

Abstract–Optical absorbance changes are commonly used to characterize intermediates which appear in the bleaching sequence of rhodopsin and in the photocycle of bacteriorhodopsin. Absorbance changes can be caused by an intermediate's rotational diffusion, and when this occurs it can distort absorbance changes due to the structural evolution of intermediates. Linear polarization of an optical probe source at 54.7° (the magic angle) relative to the polarization direction of a linearly polarized actinic source has often been used to eliminate signals due to rotational diffusion. We used Jones calculus to investigate the validity of the magic‐angle strategy. Taylor expansion of the result in powers of the absorbances of the bleached ground state and of the intermediates leads to a relatively simple expression which can be used to determine whether rotational contributions are likely under various experimental conditions. This expression shows that in first order no dichroism‐dependent term appears in the absorbance measured at magic angle. In second order, however, linear dichroism contributes to signals. For the sequence of rhodopsin intermediates:

rhodopsin → bathorhodopsin BSI → lumirhodopsin.

where BSI is a recently discovered blue‐shifted intermediate, we determined the magnitude of the dichroism signals to be, on average, <2% of the true absorbance change due to the intermediates themselves (and hence undetectable). Freedom from dichroism artifacts in this case results from the fact that the transition dipoles of these intermediates are similar to that of rhodopsin. Larger and certainly detectable dichroism signals are predicted to occur, even at the magic angle, for later intermediates which have transition dipole moments which differ significantly from that of rhodopsin. Other strategies for eliminating rotational diffusion effects are compared to the magic‐angle approach.
EVIDENCE THAT THE REPELLENT RECEPTOR FORM OF SENSORY RHODOPSIN I IS AN ATTRACTANT SIGNALING STATE*
Authors: Yan Bing , Spudich John L.
Published: January 2008

Abstract– The lifetime of the Halobacterium halobium sensory rhodopsin I (SR‐I) photocycle intermediate S373 was modulated by incorporating retinal analogs into SR‐I apoprotein in vitro and in vivo. Photocycles by SR‐I analog pigments exhibit the same reaction scheme and similar formation rates, but different decay rates, of their S373‐like species as monitored by flash spectroscopy in membrane vesicle suspensions. The attractant receptor signaling efficiencies determined by physiological measurements are proportional to the lifetimes of the S373‐like intermediates, indicating that S373 is a physiological active conformation (signaling state) of the receptor. A model incorporating this finding into the SR‐I photocvcle is presented.
PICOSECOND FLUORESCENCE FROM PHYCOCYANIN 612
Authors: MALAK HENRYK , MACCOLL ROBERT
Published: January 2008

Abstract—

The biliprotein, phycocyanin 612, was purified from a cryptomonad,Hemiselmis virescens.The protein, which is an α2β2dimer having four spectrally different tetrapyrrole chromophores, was studied using picosecond fluorescence by exciting the various chromophores at three wavelengths, 565, 585 and 615 nm. These wavelengths were chosen to excite selectively the three highest energy chromophores. Decay times were measured as the excitation energy migrated from each of the three excited chromophores to the lowest‐energy chromophore. The ps decay times were found to be 9, 13, and 12 ps for excitations at 565, 585, and 615 nm, respectively. A comparison is made between phycocyanin 612 and phycocyanin 645 with regard to the causes of their differing absorption maxima.
CHEMIEXCITATION IN THE ARACHIDONIC ACID CASCADE
Authors: NASCIMENTO ANA LUCIA T. O. , CILENTO GIUSEPPE
Published: January 2008

Abstract—

As investigated in neutrophils, the very weak luminescence accompanying the arachidonic acid cascade is associated with the lipoxygenase pathway. The emission is dramatically enhanced by energy transfer to chlorophylla. The number of chlorophyll molecules excited to the fluorescent state per oxygen consumed, (the S1/O2ratio), equal to the product of the quantum yields of chemiexcitation and of energy transfer, is 5.4 × 10−6. The quantum yield of chemiexcitation is inferred to be higher than 1 × 10−3. The two most likely chemiexcitation routes point to triplet conjugated carbonyls as the most likely candidates for the excited species that transfer to chlorophyll. As such the emission intensity may reflect the level of hydroperoxyeicosatetraenoic acid. This is the first case where addition of a biotic substrate to a cellular system results in substantial generation of electronic excited states without any drastic loss of cell viability. Whether the formation of excited states in the arachidonic acid cascade in neutrophils is accidental or has a biological role is an open question.
A NEW METHOD OF DETERMINING INTRACELLULAR FREE Ca2+CONCENTRATION USING Quin2‐FLUORESCENCE
Authors: MIYOSHI NORIO , HARA KIYOAKI , KIMURA SHIRO , NAKANISHI KAZUO , FUKUDA MASARU
Published: January 2008

Abstract—

We determined intracellular free Ca2+ concentration by fluorescence spectroscopy and the time‐resolved measurements of 2‐[(2‐amino‐5‐methylphenoxy) methyl]‐6‐methoxy‐8‐aminoquinoline‐N, N, N′, N′‐tetraacetic acid, tetrapotassium salt (Quin2) incorporated in suspended mouse leukemia L1210 cells. The paper reports the following two points. (1) Various fluorescence spectrum patterns in cell suspensions dissolved with Quin2 acetoxy methylester were compared with those of the complex in buffer solution containing esterase. (2) The fluorescence lifetime of Quin2 bound to Ca2+ was approx. 4.5–11 times longer (10 ± 1 ns) than that (1.5 ± 0.5 ns) of Quin2. The fraction of the long lifetime component was plotted against the concentration of CaCl2 in buffer solution. From the results obtained, it was found that approx. 35 nM Ca2+ was contained in each L1210 cell.
PHOTOSENSITIZED LIPID PEROXIDATION AND ENZYME INACTIVATION BY MEMBRANE‐BOUND MEROCYANINE 540: REACTION MECHANISMS IN THE ABSENCE AND PRESENCE OF ASCORBATE*
Authors: BACHOWSKI GARY J. , PINTAR THOMAS J. , GIROTTI ALBERT W.
Published: January 2008

Abstract—

The lipophilic photosensitizing dye merocyanine 540 (MC540) is being studied intensively as an antitumor and antiviral agent. Since plasma membranes are believed to be the principal cellular targets of MC540‐mediated photodamage, we have studied membrane damage in a well characterized test system, the human erythrocyte ghost. When irradiated with white light, MC540‐sensitized ghosts accumulated lipid hydroperoxides (LOOHs derived from phospholipids and cholesterol) at a rate dependent on initial dye concentration. Neither desferrioxamine nor butylated hydroxytoluene inhibited LOOH formation, suggesting that Type I (iron‐mediated free radical) chemistry is not important. By contrast, azide inhibited the reaction in a dose‐dependent fashion, implicating a Type II (singlet oxygen, 1O2) mechanism. Stern‐Volmer analysis of the data gave a 1O2 quenching constant ∼50 times lower than that determined for an extramembranous target, lactate dehydrogenase (the latter value agreeing with literature values). This suggests that 1O2 reacts primarily at its membrane sites of origin and that azide has limited access to these sites. Using [14C]cholesterol‐labeled membranes and HPLC with radiodetection, we identified 3β‐hydroxy‐5α‐cholest‐6‐ene‐5‐hydroperoxide as the major cholesterol photoproduct, thereby confirming 1O2 intermediacy. Irradiation of MC540‐sensitized membranes in the presence of added iron and ascorbate resulted in a large burst of lipid peroxidation, as shown by thiobarbituric acid reactivity and appearance of 7‐hydroperoxycholesterol and 7‐hydroxycholesterol as major oxidation products. Amplification of MC540‐initiated lipid peroxidation by iron/ ascorbate (attributed to light‐independent reduction of nascent photoperoxides, with ensuing free radical chain reactions) could prove useful in augmenting MC540's phototherapeutic effects.
THE PHOTODEGRADATION OF PORPHYRINS IN CELLS CAN BE USED TO ESTIMATE THE LIFETIME OF SINGLET OXYGEN
Authors: MOAN JOHAN , BERG KRISTIAN
Published: January 2008

Abstract—

NHIK 3025 cells were incubated with Photofrin II (PII) and/or tetra (3‐hydroxyphenyl)porphyrin (3THPP) and exposed to light at either 400 or 420 nm, i. e. at the wavelengths of the maxima of the fluorescence excitation spectra of the two dyes. The kinetics of the photodegradation of the dyes were studied. When present separately in the cells the two dyes are photodegraded with a similar quantum yield. 3THPP is degraded 3–6 times more efficiently by light quanta absorbed by the fluorescent fraction of 3THPP than by light quanta absorbed by the fluorescent fraction of PII present in the same cells. The distance diffused by the reactive intermediate, supposedly mainly1O2, causing the photodegradation was estimated to be on the order of 0.01–0.02 μm, which corresponds to a lifetime of 0.01–0.04 μs of the intermediate in the cells. PII has binding sites at proteins in the cells as shown by an energy transfer band in the fluorescence excitation spectrum at 290 nm. During light exposure this band decays faster than the Soret band of PII under the present conditions. Photoproducts (1O2etc.) generated at one binding site contribute significantly in the destruction of remote binding sites.
EFFECT OF TRANSMEMBRANE POTENTIAL ON CHARGE PHOTOSEPARATION IN LIPOSOMES
Authors: NADTOCHENKO VICTOR A. , LAVRENTYEV ANTON I. , RUBTSOV IGOR V. , DENISOV NIKOLAI N. , BARANNIKOVA YANINA V. , NIKANDROV VITALY V. , KRASNOVSKY ALEXANDR. A.
Published: January 2008

Abstract—An unexpected transmembrane potential effect on the recombination rate of the pheophytin or bacteriopheophytin anion‐radicals (dissolved in membrane) and ascorbic ion‐radicals (dissolved in aqueous interior) has been established in liposomes. The influence of transmembrane potential on the recombination rate of Ru3+(dissolved in inner volume) and (C18H37)V+or (C14H29)V+(dissolved in membrane) was observed. The potential was created by a potassium concentration gradient between inner and outer volumes of liposomes in the presence of valinomycin. The effect of the potential was considered on the bases of: (1) it was determined by the diffusional drift of the hydrophobic radicals in a radial direction in the membrane, according to the direction of the electric field; (2) the electric field changed the rate constant of the electron transfer, owing to the effects on the free energy and electronic coupling. Our results show the first explanation to be preferable.
PHOTOREACTIVITY OF 5‐GERANOXYPSORALEN AND LACK OF PHOTOREACTION WITH DNA
Authors: MORLIÉRE P. , BAZIN M. , DUBERTRET L. , SANTUS R. , MELO T. SA E. , HÜPPE G. , HAIGLE J. , FORLOT P. , BERNARD A.
Published: January 2008

Abstract—5‐Geranoxypsoralen, commonly called bergamottin, a major furocoumarin contained in bergamot oil, is reportedin vitroas a highly photoreactive psoralen. In ethanol, it exhibits quite a high triplet state quantum yield (≅0.37). The triplet state is involved in subsequent photochemistry which depends on the initial concentration and on the presence of oxygen. In contrast to most psoralens, absorption and fluorescence data suggest that 5‐geranoxypsoralen does not interact with DNA in the dark. No UVA‐induced interstrand cross‐links in DNA were shown.
In vivo AND PHOTOPHYSICAL STUDIES ON PHOTOOXIDATIVE DAMAGE TO LENS PROTEINS AND THEIR PROTECTION BY RADIOPROTECTORS
Authors: ROBERTS JOAN E. , KINLEY JUDITH S. , YOUNG ANTONY R. , JENKINS GLORIA , ATHERTON STEPHEN J. , DILLON JAMES
Published: January 2008

Abstract— Photooxidation, whether initiated by an endogenous or exogenous sensitizer, is an important mechanism in light induced damage to the lens. One of the substrates for this damage is lens protein. A porphyrin sensitizer which binds to lens proteins [mesotetra(p‐sulfonatophenyl) porphyrin (TPPS)] was found to photooxidize Skh‐2 pigmented mice lens protein in vivo. Uroporphyrin, a model for a non‐binding photosensitizer, did not induce photooxidative damage to the mouse lens.

The radioprotector 3‐amino‐2‐hydroxypropyl phosphorothioate (WR‐77913) was investigated as an agent to retard or negate in vivo photooxidative damage to the lens. Intraperitoneal injections of WR‐77913 prior to irradiation reduced the TPPS induced photodestruction of lens protein in Skh‐2 pigmented mice.

The mechanism of protection was also investigated. Thiols were found to quench both the triplet state of porphyrins and the reactive intermediate singlet oxygen on the order of 105 and 106M‐1 s1 respectively. These are probably not fast enough to explain most of the protection afforded by thiols. An additional mechanism may be the accelerated photobleaching of porphyrins by thiols which protects tissue by reducing the absorptions due to the porphyrins.
CHLORIN AND PORPHYRIN DERIVATIVES AS POTENTIAL PHOTOSENSITIZERS IN PHOTODYNAMIC THERAPY
Authors: PANDEY RAVINDRA K. , BELLNIER DAVID A. , SMITH KEVIN M. , DOUGHERTY THOMAS J.
Published: January 2008

Abstract— In order to find a photosensitizer with better optical properties and pharmacokinetics than Photofrin II, a series of new photosensitizers related to methyl pheophorbide‐a and chlorin‐e6 were synthesized. These compounds absorb at substantially longer wavelengths (Λ max 660 nm) than does Photofrin II (630 nm) and show promise for use in photodynamic therapy. Among the porphyrins, we observed that long carbon chain ether derivatives are better photosensitizers than their ester analogs. These sensitizers were tested for in vivo photosensitizing activity vis‐a‐vis Photofrin II, using the standard screening system of DBA/2 mice bearing transplanted SMT/F tumors. Most of these photosensitizers were found to have better tumorcidal photosensitizing activity than Photofrin II and demonstrated more rapid attenuation of normal tissue photosensitivity with time after administration vis‐a‐vis Photofrin II.
BIOPHOTON EMISSION (ULTRAWEAK PHOTOEMISSION) FROM DARK ADAPTED SPINACH CHLOROPLASTS
Authors: HIDEG ÈVA , INABA HUMIO
Published: January 2008

Abstract— Biophoton emission (ultraweak photoemission) is observable in isolated spinach chloroplasts, even after several hours of dark adaptation. This spontaneous light emission is oxygen dependent, decreased by respiratory inhibitors such as cyanide or salycilhydroxamic acid, suppressed by p‐benzoquinone and enhanced by NADPH. We suggest that the respiratory chain of chloroplasts is involved in the series of redox reactions leading to the dark excitation of the emitter of biophotons, presumably chlorophyll molecules.

Biophoton emission is inhibited by superoxide dismutase, implying that the univalent reduction of molecular oxygen is associated with this process, in a yet unknown way.
4, 4′, 5′‐TRIMETHYL‐8‐AZAPSORALEN, A NEW‐PHOTOREACTIVE AND NON‐SKIN‐PHOTOTOXIC BIFUNCTIONAL BIOISOSTER OF PSORALEN
Authors: VEDALDI D. , DALL'ACQUA F. , CAFFIERI S. , BACCICHETTI F. , CARLASSARE F. , BORDIN F. , CHILIN A. , GUIOTTO A.
Published: January 2008

Abstract—Photochemical and photobiological properties of a new isoster of psoralen, 4, 4′, 5′‐trimethyl‐8‐azapsoralen (4, 4′, 5′‐TMAP), have been studied. This compound shows a high DNA‐photobinding rate, higher than that of 8‐methoxypsoralen (8‐MOP), forming both monoadducts and inter‐strand cross‐links. The yield of cross‐links, however, is markedly lower than that of 8‐MOP. Antiproliferative activity of 4, 4′, 5′‐TMAP, in terms of DNA synthesis inhibition in Ehrlich ascites tumor cells, is higher than that of 8‐MOP. Mutagenic activity onE. coliWP2 R46+ cells appeared similar to or even lower than that of 8‐MOP. This new compound applied on depilated guinea pig skin and irradiated with UVA did not show any skin‐phototoxicity. On the basis of these properties 4, 4′, 5′‐TMAP appears to be a potential photochemotherapeutic agent.
RESONANCE RAMAN AND SURFACE‐ENHANCED RESONANCE RAMAN SPECTROSCOPY OF HYPERICIN
Authors: Raser Lydia N. , Kolaczkowski Stephen V. , Cotton Therese M.
Published: January 2008

Abstract—

Hypericin has been found to exhibit a variety of photodynamic effects. To correlate biological activity with molecular structure, complete physical characterization of hypericin is required. The vibrational spectrum has been determined and resonance Raman and surface enhanced resonance Raman scattering spectra are reported. In addition, the Raman spectrum of a model compound has been studied to facilitate assignment of the vibrational modes of hypericin.
RETENTION AND PHOTOTOXICITY OF TETRA(4‐SULFONATOPHENYL)PORPHINE IN CULTIVATED HUMAN CELLS. THE EFFECT OF FRACTIONATION OF LIGHT
Authors: Berg Kristian , Madslien Kari , Moan Johan
Published: January 2008

Abstract—

Human cervix carcinoma cells of the line NHIK 3025 were incubated for 18 h with tetra(4‐sulfonatophenyl)porphine (TPPS4) and further incubated for 1–29 h in sensitizer free medium before exposure to light. After 1 h in sensitizer free medium only a 20% further loss of TPPS4was observed within the next 28 h. During the time in senzitizer free medium, each TPPS4molecule became more efficient in sensitizing single cells to photoinactivation. This enhanced photosensitizing efficiency of TPPS4correlated well with the enhanced fluorescence yield of TPPS4. In some experiments the cells were exposed to a light dose inactivating 10% of the cells after incubation for 1 h in sensitizer free medium and a second graded light dose given 4–28 h later. Exposure of the cells to the first light dose led to loss of 60% of TPPS4from the cells. Despite the significant loss of sensitizer from the cells the fluorescence yield of TPPS4from each cell was found to increase (e.g. by 100% 4 h after light exposure). The enhanced fluorescence yield of cell bound TPPS4was followed by a 1.6–2.5‐fold increase in sensitivity of each cell to a second light dose. Thus, a small light dose increased the photosensitivity of TPPS4‐loaded NHIK 3025 cells for several hours after the first light exposure. The advantageous effect of light fractionation was reduced by a significantly enhanced loss of sensitizer induced by the first light exposure. The optimal time between the two fractions of light seems to be 30–90 min.
In vitroANDin vivoULTRAVIOLET‐INDUCED ALTERATIONS OF OXY‐ AND DEOXYHEMOGLOBIN
Authors: Kollia N. , Baqer A. , Sadiq I. , Sayre R. M.
Published: January 2008

Abstract—

Ultraviolet (UV) radiation was found to convert oxyhemoglobin and deoxyhemoglobin stoichiometrically into methemoglobin and a met‐like product, respectively. The peak conversion efficiency for oxyhemoglobin occurred at 285 nm and decreased by a factor of 100 by 315 nm. The peak conversion efficiency for deoxyhemoglobin occurred at 290 nm and decreased by a factor of 30 by 320 nm. The transformation of oxyhemoglobin to methemoglobin was also documented in intact erythrocytes using UV‐B radiation. Finally, similar transformations were found to occur in human skin with UV‐B exposure but not on all volunteers tested. These results imply that methemoglobin will be formedin vivoon solar exposure and provide evidence that UV‐B photons reach the blood vessels.
PHOTOPHYSICAL PROPERTY OF SANGUINARINE IN THE EXCITED SINGLET STATE
Authors: Das A. , Nandi R. , Maiti M.
Published: January 2008

Abstract—

The photophysical property of the alkanolamine form of sanguinarine has been studied in aqueous and organic medium under various environmental conditions from the measurement of absorption, fluorescence and NMR spectroscopy. Alkanolamine fluorescence shows an excitation time dependent fluorescence quenching and the rate of quenching increases significantly with increasing pH and concentration of the species, while it decreases with increasing temperature. This phenomenon is explained by excited state intramolecular proton transfer from a 6‐O‐H group to the lone pair of nitrogen through the formation of zwitterion.
A LASER FLASH SPECTROSCOPY STUDY OF THE KINETICS OF ELECTRON TRANSFER FROM SPINACH PHOTOSYSTEM I TO SPINACH AND ALGAL FERREDOXINS
Authors: Hervás Manuel , Navarro José A. , Tollin Gordon
Published: January 2008

Abstract—

Laser flash absorption spectroscopy has been used to investigate the kinetics of electron transfer from P700 in Photosystem I (PSI)‐enriched particles from spinach to the ferredoxins from spinach and the green alga Monoraphidium braunii. Very similar behavior for the interaction of both ferredoxins with the PSI complex was observed, although the algal ferredoxin appears to be slightly more effective as an electron acceptor. For both proteins, a non‐linear protein concentration dependence of the rate constant for reduction was obtained, indicating complex formation preceding electron transfer. Estimates of 3 times 107M−1 s−1 and 140–180 s−l were obtained from these data for the second order rate constants for complex formation, and the limiting first order rate constants for electron transfer, respectively. At neutral pH, a biphasic dependence of the rate constant for ferredoxin reduction on the concentration of NaCl or MgCl2 was observed. This was interpreted in terms of the electrostatic interactions which occur between ferredoxin and the PSI membrane. In addition, magnesium cations appear to play a specific role in the interaction between PSI and ferredoxin. Thus, the addition of these ions under optimal conditions induces a 6‐f‐old increase in the electron transfer reaction rate constant, compared with a 2‐f‐old increase in the presence of an optimal amount of NaCI. This cannot be explained as arising from ionic strength effects. To our knowledge, this is the first time that a direct measurement of the rate constant for the reduction of ferredoxin by the PSI complex has been reported.
TRANSFORMATION OF A BOP‐HOP‐SOP‐I‐SOP‐II‐Halobacterium halobiumMUTANT TO BOP+: EFFECTS OF BACTERIORHODOPSIN PHOTOACTIVATION ON CELLULAR PROTON FLUXES AND SWIMMING BEHAVIOR
Authors: Yan Bin C , Cline Steven W. , Doolittle W. Ford , Spudich John L.
Published: January 2008

Abstract—

We have transformed Pho 81, aHalobacterium halobiurnmutant strain which does not contain any of the four retinylidene proteins known in this species, with thebopgene cluster to create Pho81BR, a BR'HR‐SR‐I‐SR‐11– strain. The absorption spectrum, pigment reconstitution process, light‐dark adaptation and photochemical reaction cycle of the expressed protein are indistinguishable from those of native bacteriorhodopsin (BR) in purple membrane of wild type strains. Strain Pho81BR permits for the first time characterization of effects of BR photoactivation alone on cell swimming behavior and energetics in the absence of the spectrally similar phototaxis receptor sensory rhodopsin I (SR‐I) and electrogenic chloride pump halorhodopsin (HR). A non‐adaptive upward shift in spontaneous swimming reversal frequency occurs following 3 s of continuous illumination of Pho81BR cells with green light (550 ± 20 nm). This effect is abolished by low concentrations of the proton ionophore carbonylcyanidem‐chlorophenylhydrazone. Although BR does not mediate phototaxis responses in energized Pho81BR cells under our culture conditions, proton pumping by BR in Pho81BR cells partially deenergized by inhibitors of respiration and adenosine triphosphate synthesis results in a small attractant response. Based on our measurements, we attribute the observed effects of BR photoactivation on swimming behavior to secondary consequences of electrogenic proton pumping on metabolic or signal transduction pathways, rather than to primary sensory signaling such as that mediated by SR‐I. Proton extrusion by BR activates gated proton influx ports resulting in net proton uptake in wild‐type cells. We observe a gated secondary proton influx also in Pho81BR which is deactivated byN, N'‐dicyclohexyl carbodiimide (DCCD) and heating, but is not affected by pre‐illumination. Based on previous studies, these properties exclude the known proton uptake from HR chloride pumping and the gated Na+/H+antiporter, and are consistent with H+‐ATPase activation. We do not observe a DCCD‐insensitive early proton inflow after illumination of Pho81BR cells, confirming that this previously reported proton inflow results from active chloride pumping by HR rather than from a change in the preexisting membrane potential.
PHOTOMORPHOGENIC PROCESSES IN THE AGRICULTURAL ENVIRONMENT
Authors: Ballaré Carlos L. , Scopel Ana L. , Sánchez Rodolfo A. , Radosevich Steven R.
Published: January 2008

Abstract—

We review recent advances in our understanding of how photomorphogenic mechanisms influence processes of significance for agriculture, including weed seed germination, acclimation to solar UV‐B radiation, and plant interactions in canopies.

It has been demonstrated recently that seeds of some weed species acquire the ability to germinate in response to very low photon fluences during burial. Short sunlight pulses perceived by seeds during tillage appear to be important signals of soil disturbance.

Regarding UV‐B acclimation there is increasing evidence for the involvement of a specific UV‐B photoreceptor in pigmentation and morphological responses to UV‐B. The protective role played by UV‐B‐induced flavonoids has been experimentally demonstrated.

Concerning plant interactions in canopies it has been shown that, by perceiving light signals through phytochrome and blue‐UV‐A photoreceptors, plants obtain information about the characteristics of the surrounding vegetation well before their resources are reduced as a consequence of neighbors' activities. There appears to be a large potential for improving cropping systems by manipulating the light environment or by changing the photomorphogenic behavior of crop plants. However, relatively little is known about how the expression and agronomic significance of photomorphogenic responses are influenced by other factors of the plant's environment.
EVENTS IN THE PHYTOCHROME MOLECULE AFTER IRRADIATION
Authors: Rüdiger Wolfhart
Published: January 2008

Abstract—

The photoconversion of Pr to Pfr has been investigated by a large number of investigators. We have previously demonstrated that Z,E isomerization of the tetrapyrrole chromophore is involved in the photoconversion. It is the best candidate for the primary photoreaction. Conformation and configuration of the Pr chromophore will be compared with that of chromophores in phycocyanin. The crystal structure of phycocyanin had been elucidated by x‐ray analysis. Proton transfer and/or Z, E isomerization of the tetrapyrrole are probably involved in different steps of the photoconversion in phytochrome and in photoreversible phycobiliproteins. Fluorescence decay kinetics of irradiated Pr and intermediate formation show heterogeneity. Possible reasons for this heterogeneity will be discussed.
SINGLET OXYGEN INDUCED DNA DAMAGE AND MUTAGENICITY IN A SINGLE‐STRANDED SV40‐BASED SHUTTLE VECTOR
Authors: Ribeiro D. T. , Madzak C. , Sarasin A. , Mascio P. DI , Sies H. , Menck C. F. M.
Published: January 2008

Abstract— The effects of singlet oxygen (1O2), generated by the thermal decomposition of water soluble NDPO2 (endoperoxide of the disodium 3,3'‐(1,4‐naphthylidene) dipropionate), on a single‐stranded shuttle vector were analysed. 1O2 induces a much higher level of breaks in the phosphodiester backbone of single‐stranded than double‐stranded DNA. This may be due to a higher accessibility of guanine residue, primarily damaged by 1O2. The damaged vector was transfected into monkey COS7 cells where single‐stranded DNA was converted to the double‐stranded replicative form DNA. After 3 days, extrachromosomal DNA was extracted and the plasmids rescued in E. coli to study mutagenesis. There is a significant increase in mutation frequency of damaged single‐stranded DNA in comparison to untreated DNA. It is concluded that 1O2 induces breaks in the backbone of single‐stranded DNA and that the 1O2‐damaged molecules are mutated after passage through mammalian cells.
A TEST OF THE SINGLET OXYGEN MECHANISM OF CATIONIC DYE PHOTOSENSITIZATION OF MITOCHONDRIAL DAMAGE
Authors: Bunting James R.
Published: January 2008

Abstract— Aromatic cationic dyes have a potential as photo‐chemotherapeutic agents because they are selectively concentrated into the mitochondria of cancerous cells. The mechanism of cytophototoxicity has been proposed to be primarily due to dye sensitized photogeneration of highly toxic singlet oxygen (1O2) at the mitochondria. We tested this hypothesis by measuring the relative phototoxicity of a collection of aromatic cationic dyes towards respiring rat‐liver mitochondria (RLM), upon addition of 514 nm laser light. Effectiveness of dye photosensitization towards destruction of RLM function was assayed by its effect on the RLM membrane potential. Three physical parameters of dye phototoxicity were independently measured and a relative phototoxicity calculated assuming adherence of mechanism to the 1O2 hypothesis. Quantum yields of dye sensitized 1O2 production were estimated, either from time‐resolved luminescence measurements of photosensitized 1O2 formed, or by comparing rates of photobleaching of 1O2 trap; the relative partition of dye into mitochondrial lipid was determined gravimetrically; and the optical density of dye was determined in a lipid like Triton X‐100 micellar environment. Under the assumption of the 1O2 hypothesis, these parameters were used to predict a relative phototoxicity which was compared with that observed. For 12 of the 14 dyes investigated, the observed and predicted phototoxicities were linearly correlated (r=0.85) suggesting support of the 1O2 hypothesis. Carbocyanines DiOC2(3) and DiSC2(3) did not correlate and were found to be 10 and 1000 times more potent than predicted, suggesting an additional factor at play in their phototoxicity.
PHEOPHORBIDEa‐INDUCED PHOTO‐OXIDATION OF CYTOCHROMEc: IMPLICATION FOR PHOTODYNAMIC THERAPY
Authors: Chernomorsky S. , Wong C. , Poretz R. D.
Published: January 2008

Abstract—Pheophorbidea‐induced photo‐oxidation,in vitro, of cytochrome c oxidase and cytochromecresults in irreversible modifications to both protein components. Photo‐oxidation of cytochromec, as exhibited by change in its heme oxidation state, displays exponential kinetics and is detected with a lag period. Both the photo‐induced inactivation of the enzyme, and destruction of the substrate ability of cytochromecoccur as complex multi‐process events. Under similar experimental conditions, the loss of the substrate capability of cytochrome c develops approximately three times faster than inactivation of the enzyme. The slight lag in the photo‐oxidation of cytochrome c is due to pheophorbidea‐induced superoxide production. However, the relative amount of photo‐oxidant produced is considerably more effective than the cytochrome c reducing capacity of the superoxide. Neither hydroxyl radical nor hydrogen peroxide are involved in the photo‐oxidation of the heme function. The possibilities of heme oxidation by a singlet oxygen mediated pathway or direct electron abstraction involving the heme or apoprotein are not excluded. It is proposed that a multi‐site oxidation of numerous reduced energy cofactors within cells may augment collateral enzyme inactivation in maximizing photosensitizer‐induced cytotoxicity. Accordingly, amphipathic photosensitizers, capable of accessing both lipid and aqueous compartments containing reduced cofactors, may be more effective agents for photodynamic therapy than those which exhibit a high specificity of subcellular localization.
MECHANISMS BEHIND THE RESISTANCE OF SPHEROIDS TO PHOTODYNAMIC TREATMENT: A FLOW CYTOMETRY STUDY
Authors: West Catharine M. L. , Moore James V.
Published: January 2008

Abstract—The influence of cell heterogeneity on response to photodynamic treatment (PDT) has been investigated using the human colon adenocarcinoma line WiDr, grown as spheroids and exposed to hematoporphyrin derivative. The spheroids show a marked spheroid size‐dependent resistance to PDT. Using a flow cytometer, cell sub‐populations have been separated, on the basis of drug fluorescence, from single cell suspensions prepared from 500 μm diameter spheroids. Cells low in fluorescence have been shown to be resistant to PDT, have a smaller median cell volume, and be enhanced in G1‐type cells. These cells also show reduced low density lipoprotein uptake. The results suggest that spheroid size‐dependent resistance to PDT is related to a decreasing growth fraction with increasing spheroid size. Heterogeneity of drug uptake could be a potential limitation to clinical PDT.