bluuebunny/crossref_metadata_2025 huggingface dataset:
FLASH PHOTOLYSIS STUDY OF ALIPHATIC AMINO ACIDS AND PEPTIDES IN AQUEOUS SOLUTION*
Authors: Mittal L. J. , Mittal J. P. , Hayon E.
Published: January 2008

Abstract— The intermediates produced in the photolysis of oxygen‐free aqueous solutions of a number of aliphatic amino acids and peptides were observed spectrophotometrically using the fast‐reaction technique of flash photolysis. Included among the compounds examined are the N‐acetyl derivatives of glycine, alanine, sarcosine, glutamic acid and glycylglycine; the esters and amides of these N‐acetyl compounds; diketopiperazines; the amino acids glycine, alanine and β‐alanine; and finally the oligopeptides di‐, tri‐ and tetraglycine. The direct optical excitation of these compounds was found to lead primarily to a photo‐induced decarboxylation reaction:

The transient spectra of the radicals produced have been identified. The quantum yields of these processes were found to be directly proportional to the pKa of the carboxyl groups of the corresponding ground‐state molecules, and hence to the concentration of the non‐ionized carboxylic acids. The φ's of these processes for the ionized acids were close to zero. The dependence of φ upon pH is correlated to the absorption spectra of these compounds. The quantum yields of the corresponding esters were lower but independent of pH. No intermediates were observed from excitation of the amine derivatives. Other photolytic reactions are suggested. The photo‐decarboxylation of alanine and diglycine were found to be monophotonic, while that of N‐acetyl alanine, N‐acetyl diglycine, and tetraglycine were found to be biphotonic. A triplet excited state precursor is indicated for the latter group of compounds. These and other results are discussed.
LASER FLASH PHOTOLYSIS OF RHODOPSIN AT ROOM TEMPERATURE
Authors: Bensasson R. , Land E. J. , Truscott T. G.
Published: January 2008

Abstract. Nanosecond flash photolysis of rhodopsin with 530 or 353 nm light produces an initial transient absorption spectrum with peaks at ˜57O and ˜420nm, and a subsequent transient species with a maximum absorption at 480 nm. These results are interpreted as the initial formation of prelumi‐rhodopsin (570 nm) followed by its conversion to lumirhodopsin (470 nm). The peak at 420 nm in the first transient may be due to either hypsorhodopsin or isorhodopsin.
USE OF THE DYE HOECHST 33258 IN A MODIFICATION OF THE BROMODEOXYURIDINE PHOTOLYSIS TECHNIQUE FOR THE ANALYSIS OF DNA REPAIR
Authors: Rosenstein Barry S. , Setlow R. B. , Ahmed Farid E.
Published: January 2008

Abstract— A modification of the bromodeoxyuridine photolysis technique is described in which the cells are treated with the fluorescent dye Hoechst 33258 to enhance the bromodeoxyuridine photolysis produced by 365 nm or by black light. Use of the modified assay overcomes several difficulties encountered in the original 313 nm photolysis technique and demonstrates that excision repair of damage produced in the DNA by 7,12‐dimethylbenz(fl)anthracene 5,6‐oxide takes place by a long patch type of repair pathway.
PHOTOELECTRON TRANSFER BETWEEN A CHARGED DERIVATIVE OF CHLOROPHYLL AND FERRICYANIDE AT THE LIPID BILAYER‐WATER INTERFACE
Authors: Losev A. , Mauzerall D.
Published: January 2008

Abstract— Flash illumination of a lipid bilayer containing a positively charge pigment: chlorophyll b cholyl hydrazone and separating two salt solutions, one of which contained ferricyanide, resulted in a photovoltage of ∼20mV, acceptor side negative. The positive charge on the pigment resulted in several novel effects. (1) The photo‐emf is twice that of chlorophyll a and five times that of chlorophyll b at a given concentration. A higher surface concentration of the charged derivative is the likely cause of this effect. (2) The pheophytin of chlorophyll b cholyl hydrazone produces about one‐half the photo emf of the magnesium derivative whereas pheophytin a or b produced only one‐tenth the signal. This may be a reflection of the changed redox potential of the cation chlorophyll b cholyl hydrazone. (3) A voltage drop of 100 mV across the membrane, the acceptor side negatively biased, causes a 3–4‐fold increase in the charge recombination rate. Biasing the acceptor side 100 mV positive has no effect. Chlorophyll a or b do not show this field effect. This asymmetric effect is explained as a movement of the more polar chlorophyll dication towards the water interface, leading to more rapid reaction with donor. Thus the kinetics of the charge reversal are a sensitive and specific probe of the polar interfacial region of the lipid bilayer‐water interface.
AMPLIFICATION OF PHOTODYNAMIC EFFECTS BY THE SYNERGISTIC ACTION OF UV‐B and TRYPTOPHAN
Authors: Halnak A. Al , Morliere P. , Santus R.
Published: January 2008

Abstract The formation of singlet oxygen by photodynamic agents is shown to be notably amplified by the combination of UV‐B radiations plus tryptophan in aqueous medium because of the formation of N‐formylkynurenine. a tryptophan photoproduct which is also a good photosensitizer. The biological implication of these effects is discussed.
THE TRANS → CIS PHOTOISOMERIZATION OF PROTONATED RETINYL SCHIFF BASES
Authors: Donahue Jean M. , Waddell Walter H.
Published: January 2008

Schiff bases were prepared from all‐trans‐retinal (I) and pyrrolidine perchlorate (II) and from I and n‐butyl amine, protonated with anhydrous hydrogen chloride gas, Ill. Initial quantum yields of trans→ cis photoisomerization (Φ°PI) were determined and primary photoproducts and product ratios were measured in aerated methanol. Φ°PI of all‐trans‐III is independent of excitation energy. All analyses were made using high‐pressure liquid chromatographic (LC) methods. It was necessary to hydrolize the Schiff bases to corresponding retinals prior to LC analysis.
ALPHA POLYMERASE INVOLVEMENT IN EXCISION REPAIR OF DAMAGE INDUCED BY SOLAR RADIATION AT DEFINED WAVELENGTHS IN HUMAN FIBROBLASTS
Authors: Tyrrell R. M. , Amaudruz F.
Published: January 2008

Abstract Cultured fibroblasts derived from normal human skin have been irradiated at a series of monochromatic wavelengths throughout the ultraviolet region and exposed to the specific α polymerase inhibitor, aphidicolin (1 μg/ml, 2 days) prior to assay for colony forming ability. Repair of 75‐80% of the lethal damage induced by UVC (254 nm) or UVB (302 nm, 313 nm) radiation is inhibited by aphidicolin suggesting that such damage is repaired by a common α polymerase dependent pathway. Exposure to aphidicolin after irradiation at longer UVA (334 nm, 365 nm) or a visible (405 nm) wavelength leads to slight protection from inactivation implying that the processing of damage induced in this wavelength region is quite distinct from that occurring at the shorter wavelengths and does not involve α polymerase.
A PHOTORECEPTOR SYSTEM REGULATING in vivo AND in vitro PHOSPHORYLATION OF A PEA PLASMA MEMBRANE PROTEIN
Authors: Short Timothy W. , Porst Markus , Brigg Winslow R.
Published: January 2008

Abstract

We have continued to characterize the blue light‐regulated phosphorylation of a 120 kDa pea plasma membrane protein thought to be involved in sensory transduction for phototropism (Short and Briggs, 1990, Plant Physiol.92, 179–185). By incubating pea stem sections in 32P‐phosphate, we show that the 120 kDa protein is phosphorylated in vivo only after blue light irradiation and that the photosensitive fluence range matches that for phototropism. Blue light induces phosphorylation of the protein in vitro as well, but the fluences required to elicit the response are at least 30‐fold higher. Triton solubilization of the plasma membrane vesicles does not further alter the fluence‐response relationship. Very little turnover was detected over 20 min phosphorylation time courses or by pulse‐chase experiments on unirradiated, blue light pulse‐irradiated, or continuously irradiated membranes. Experiments with a dark period intervening between irradiation and addition of adenosine triphosphate show the light‐induced change to persist for several minutes at 30°C. Agents that disrupt the normal photochemistry of flavins preferentially inhibit the light‐induced enhancement of phosphorylation, suggesting a flavin chromophore. However, exogenous free flavins do not affect the sensitivity of the response. Staphylococcus aureus V‐8 proteolysis of the phosphorylated protein from membranes subjected to a range of fluences before phosphorylation shows that the radiolabel on each of three peptides increases in proportion to the phosphorylation level of the undigested polypeptide. These studies may be valuable for assessing the nature of the photoreceptor and for unravelling the early sensory transduction steps in phototropism.
PHOTOOXIDATION AND ELECTRON‐TRANSFER PROCESSES IN FREE‐BASE TETRAPHENYLPORPHIN PROBED BY RESONANCE RAMAN SPECTROSCOPY
Authors: Saini G. S. S. , Chaudhury N. K. , Verma A. L.
Published: January 2008

Abstract

We report here the resonance Raman studies of photooxidation of free base tetraphenylporphin (H2TPP) in the presence of external electron acceptors such as CCl4 and chloranil under selective laser irradiation. From the dependence of photooxidation on the concentration of electron acceptors, polarity of solvents, excitation lines and temperatures, we have inferred that a weak triplet exciplex formed between the excited H2TPP and electron acceptor in non‐polar solvents serves as transient species and the light‐induced intermolecular charge transfer from H2TPP to the electron acceptor is the primary process involved in photooxidation. Observation of partial photooxidation in the rigid matrix at low temperatures has been interpreted to be due to long‐range quantum mechanical electron tunneling process. Almost complete photooxidation is observed in a soft matrix as the donor and acceptor molecules can attain favorable relative orientation and separation for electron transfer during the excited state lifetime of the exciplex.
PHOTOCHEMICAL MODIFICATIONS OF lac REPRESSOR: EFFECT OF EFFECTORS BINDING ON TRYPTOPHAN PHOTOOXIDATION
Authors: Spodheim‐Maurizot Mealanie , Charlier Michel , Helene Claude
Published: January 2008

Abstract— UV irradiation of lac repressor modifies the fluorescence of the protein and its binding to the inducer and to the operator. It has been previously shown that the total loss of fluorescence is due to photooxidation of, on average, one of the two tryptophyl residues of each protomer. The present work explains this observation by showing that N‐formylkynurenine formed at one site is responsible for the quenching of fluorescence of the other tryptophan via an energy transfer process. Consequently, no photoreaction occurs for the second tryptophyl residue. Photodamage of the two tryptophyl residues (in position 201 and 220) of each protomer were assayed by spectrofluorometric titration in the pH range from 8.5 to 5. For repressor alone, both residues are equally photodamaged. In the presence of the inducer isopropyl‐β‐D‐thio‐galactoside, IPTGt, residue 220 is completely protected, and tryptophan 201 is slightly more exposed to photooxidation. In the presence of antiinducer, residue 220 is only partially protected. Our results are discussed in terms of conformational changes triggered by the two types of ligands.
MITOCHONDRIAL DNA SYNTHESIS IN NON‐GROWTH CONDITION (LIQUID HOLDING) IN Saccharomyces cerevisiae. RELATION WITH GROWTH STAGES and MITOCHONDRIAL DNA REPAIR AFTER UV‐IRRADIATION
Authors: Heude Martine
Published: January 2008

Abstract— The synthesis of DNA as measured by incorporation of [14C]adenine in Saccharomyces cerevisiae liquid held in non‐growth conditions was followed in controls and UV‐irradiated cells. The incorporation into mitochondrial DNA relative to total DNA was higher in these conditions than that observed in growth medium, especially in liquid held stationary phase cells. The absolute amount of mitochondrial DNA synthesized during liquid holding was larger in exponential than in stationary phase cells and increased after UV‐irradiation.

The data reported here are discussed in relation to the effects of liquid holding on the UV‐induction of rho− mutants, such effects depending upon the growth stage of the cells at the time of irradiation. A correlation has been found between the initial ability of the cells to synthesize mitochondrial DNA in liquid holding conditions and their capacity to repair UV‐induced lesions in this DNA. We propose the hypothesis that the opposite effects of liquid holding on the UV‐induction of rho− mutants observed in exponential versus stationary phase cells are not due to the action of different repair pathways, but result essentially from quantitative differences in mtDNA synthesis.
PHOTOCHEMICAL BEHAVIOR OF BACTERIORHODOPSIN IMMOBILIZED IN NaCl PELLETS
Authors: Vodyanoy Vitaly , Karvaly Bela , Lanyi Janos K.
Published: January 2008

Abstract— Some photochemical reactions of bacteriorhodopsin (BR) embedded in NaCl pellets (BR‐NaCI) in the visible region are described here. BR in these preparations is a mixture of two classes of species: a drastically blue‐shifted form and the unchanged purple pigment. Depending on the illumination history of the BR before being immobilized, both kinds of BR could be demonstrated in light‐adapted (LA) and dark‐adapted (DA) forms, but light adaptation was not possible once the pellets were made. Analogously to BR suspensions, the light‐adapted blue‐shifted BRexhibited an a/l‐trans type photocycle, but the thermal steps were greatly slowed down (time constants 1 to 5 min). The parent species absorb at 506 nm. The DA blue‐shifted BR exhibited absorption changes resolved into two photoreactions, one all‐(rans‐ like (as in LA‐BR) and another, 13‐cw like, whose decay rate is also greatly slowed down (recovery time several hours). The parent species of the 13‐cis like cycle absorb at 480 nm. That pigment fraction in the pellets whose absorption was not blue‐shifted, also exhibited similar photoreactions to BR in suspension, but with an overall turnover rate only one order of magnitude slower. From a previous report (Lazarev and Terpugov, Biochim. Biophys. Acta590,324–338,1980) and this one, it appears that the very slow photocycles in NaCl‐BR of low moisture content originate from blue‐shifted chromophores rather than from unchanged BR.
PROPERTIES OF ROSE BENGAL: (X) NEW DERIVATIVES OF POLYMER‐ROSE BENGAL
Authors: Paczkowska B. , Paczkowski J , Neckers D. C.
Published: January 2008

Abstract— Polymer rose bengal derivatives are converted to their C‐6 ammonium salts. The φ1 O2 derived in CH2C12 is a function of the KB of the neutralizing amine.
A SIMPLE FIELD METHOD FOR MEASURING LIGHT QUALITY: SEASONAL CHANGES IN A TEMPERATE DECIDUOUS WOOD*
Authors: MacLellan Andrew J. , Frankland Barry
Published: January 2008

Abstract— Light was measured at 5 m intervals along a ground level transect through a mixed deciduous woodland in SE England. A simple method was developed to characterise the light environment, using measurements of photon fluence rate in the blue, photosynthetically active radiation (PAR) and near infrared regions of the spectrum. It was demonstrated that the two parameters, required to describe the state of the photoreceptor phytochrome the photostationary proportion of Pfr and the cycling rate, can be calculated from the quantities of PAR and IR light. These parameters as well as the amount of blue light were followed throughout the year along the woodland transect. The main seasonal changes are the fall and rise in the proportion of light which is PAR (and hence in the proportion of phytochrome as Pfr) associated with the appearance and disappearance of the green leaf canopy.
A REACTION BETWEEN PHEOPHYTIN and CHLOROPHYLL ADSORBED TO POLYETHYLENE‐TETRADECANE PARTICLES*
Authors: Seely G. R. , Senthilathipan V.
Published: January 2008

Abstract— When chlorophyll is adsorbed to polyethylene‐tetradecane particles along with ligating amphiphiles, and pheophytin is present also, a slow but irreversible photobleaching of the chlorophyll is observed in suspensions of the particles in aqueous media. It is suggested that the reaction starts by transfer of an electron from singlet excited chlorophyll to pheophytin and concludes by hydration and reduction of the chlorophyll radical cation.
CONFIGURATIONAL PHOTOISOMERIZATION OF BILIRUBIN IN VITRO–II. A COMPARATIVE STUDY OF PHOTOTHERAPY FLUORESCENT LAMPS AND LASERS
Authors: Agati Giovanni , Fusi Franco , Pratesi Riccardo
Published: January 2008

Abstract— A comparative investigation of configurational photoisomerization of bilirubin (Z.Z‐BR) bound to human serum albumin (HSA) in vitro produced by fluorescent lamps currently employed in phototherapy of neonatal jaundice has been carried out by using a fast absorbance technique. Photoequilibrium Z, E‐BR concentrations and rise‐times are reported. Similar measurements effected with monochromatic laser lines in the blue‐green spectral region are presented for comparison purposes.

Narrow‐spectrum fluorescent lamps (violet, special‐blue, filtered‐green) produce Z,E‐BR concentrations at photoequilibrium almost equal to those obtained with monochromatic lines. The photoequilibrium rise‐times, however, strongly depend on the spectral bandwidth of the excitation light. Special‐blue, daylight and green lamps produce Z,E‐BR concentrations = 34,31, and 12%, respectively. For green lamps, the intense UV‐blue‐Hg lines are responsible for more than 50% of Z,E‐BR concentration. Green light is found to be quite ineffective in forming Z,E isomers and very efficient in causing Z,E‐BR to revert to native Z.Z‐BR. Moreover, simultaneous irradiation of BR solution with special‐blue and green fluorescent lamps produces almost complete inhibition of the Z→E reaction at suitable green/blue intensity ratio.

On the basis of these results a possible mechanism is presented to explain the clinical success of fluorescent green lamp phototherapy and the greater production of structural BR isomers recently reported for green than that for white lamps.
QUALITATIVE KINETIC BEHAVIOR OF PHOTOCHEMICAL CASCADE SYSTEMS
Authors: Beach J. M. , Fager R. S.
Published: January 2008

Abstract— The equations describing concentration changes of cascading chemical intermediates after pulsed activation are discussed in terms of a matrix description of the entire unimolecular reaction sequence. Unidirectional unbranched and parallel branched cascades are treated in terms of relative pathway utilization. Qualitatively distinct kinetics are associated with these systems. Application to kinetic model selection for testing the bacteriorhodopsin photocycle is shown.
EXPERIMENTAL and THEORETICAL STUDIES OF SCHIFF BASE CHLOROPHYLLS
Authors: Maggiora Linda L. , Petke James D. , Gopal Dama , Iwamoto Reynold T. , Maggiora Gerald M.
Published: January 2008

Abstract— A protonated Schiff base of Ni (II)‐pyrochlorophyll a has been synthesized which exhibits a reversible bathochromic shift of 504 cm‐1 relative to Ni (II)‐pyrochlorophyll a. The magnitude of this shift lies between those observed for P700 and P680, the photoactive pigments of photosystems I and II in plants. Cyclic voltammetric measurements show that the protonated Schiff base is about 0.2 V more difficult to oxidize than its unprotonated form. These results suggest that a protonated Schiff base may be a better model for P680 than, as was originally assumed, for P700. In addition, the results of solvent and counterion effect studies show that microenvironmental perturbations in the neighborhood of the protonated Schiff base moiety are unlikely to induce further spectral shifts. Ab initio quantum mechanical calculations show a small hypsochromic shift rather than the observed bathochromic one, and the reasons for this discrepancy are discussed.
PICOSECOND LASER SPECTROSCOPY AND OPTICALLY DETECTED MAGNETIC RESONANCE ON A MODEL PHOTOSYNTHETIC SYSTEM
Authors: Hala J. , Searle G. F. W. , Schaafsma T. J. , Hoek A. van , Pancoska P. , Blaha K. , Vacek K.
Published: January 2008

Fluorescence‐detected magnetic resonance of triplets in zero magnetic field (FDMR), fluorescence fading (FF) due to triplet‐formation, both at 4.2 K, and prompt fluorescence decay kinetics (FDK) at room temperature have been measured for free pheophorbide‐a (f‐Pheo) and bound (b‐Pheo) to a synthetic polypeptide (L‐Lys‐L‐Ala‐L‐Ala)n, dissolved in dimethylformamide (DMF). Fluorescence decay kinetics measurements of f‐Pheo in DMF yielded 1‐5 ns lifetimes, for b‐Pheo in DMF a ~ 50 ps decay‐component was found emitting at 730–750 nm. Zero‐field splitting parameters |D| and |E| of the lowest triplet state T1 were determined from FDMR spectra as (337 and 24) 10‐4 cm‐1 for f‐Pheo and (359 and 25) 10‐4 cm‐1 for b‐Pheo, both in DMF. Decay rate constants of the three spin levels of T1 of b‐Pheo (Kx= 1200 50 s‐1, ky= 440 25 s‐1, kz= 80 5 s‐1) and relative steady‐state populations (Nx= 28 2%, Ny= 47 2%, Nz= 26 2%) determined from FF curves predict a fluorescence decrease at the D–E and D + E FDMR transitions, whereas experimentally a fluorescence increase is observed. The FDMR sign‐inversion results from singlet‐singlet energy transfer from b‐Pheo monomers to their aggregates, followed by fast intersystem crossing to T1. These results indicate that aggregates are formed by two or more b‐Pheo molecules at different positions on the folded polypeptide chain. This situation resembles that in chlorophyll‐proteins, containing low‐lying traps, resulting from interaction of chromophores with other chromophores and with the protein environment.
THE USE OF SPIN LABEL OXIMETRY IN THE STUDY OF PHOTODYNAMIC INACTIVATION OF CHINESE HAMSTER OVARY CELLS
Authors: Ankel Else , Felix Christopher C. , Kalyanaraman B.
Published: January 2008

Spin label oximetry has been used to study the effects of photosensitizer hematoporphyrin on oxygen consumption in Chinese hamster ovary cells. These measurements demonstrate that, in the presence of the sensitizer, there occurs (i) an increase in total oxygen consumption during irradiation and (ii) a decrease in oxygen consumption following irradiation. These results are attributed to the effects of photosensitized oxygen consumption and decreased cellular respiration due to cell inactivation. Thus the inhibition of oxygen consumption after irradiation was shown to correlate with decreased cell survival measured in cell culture experiments. Possible mechanisms of inactivation and extensions of the oximetric approach are discussed.
USE OF METABOLIC INHIBITORS TO INVESTIGATE THE EXCISION REPAIR OF PYRIMIDINE DIMERS AND NON‐DIMER DNA DAMAGES INDUCED IN HUMAN AND ICR 2A FROG CELLS BY SOLAR ULTRAVIOLET RADIATION
Authors: Chao Chuck C.‐K. , Rosenstein Barry S.
Published: January 2008

Abstract— ICR 2A frog and normal human skin fibroblasts were exposed to either 5 J/m2 of 254 nm UV or 50 kJ/m2 of the Mylar‐filtered solar UV wavelengths produced by a fluorescent sunlamp. Following these approximately equitoxic treatments, cells were incubated in medium containing the DNA synthesis inhibitors hydroxyurea (HU) and 1–β‐D‐arabinofuranosyl cytosine (ara C) for 0–20 min (human fibroblasts) or 0–4 h (frog cells) to accumulate DNA breaks resulting from enzymatic incision during excision repair. It was found that breaks were formed in human cells at about a 200‐f‐old higher rate compared with the ICR 2A cells indicating a relatively low capacity for excision repair in the frog cells. In addition, the rate of DNA break formation in solar UV‐irradiated cells was only one‐third of the level detected in 254 nm‐irradiated cells. This result is consistent with the conclusion that the pathway(s) involved in the repair of solar UV‐induced DNA damages differs from the repair of lesions produced in cells exposed to 254 nm UV.
SENSITIZER‐INDUCED CONFORMATIONAL CHANGES IN LENS CRYSTALLIN—II. PHOTODYNAMIC ACTION OF RIBOFLAVIN ON BOVINE α‐CRYSTALLIN
Authors: Bose Swapan K. , Mandal Krishnagopal , Chakrabarti Bireswar
Published: January 2008

Abstract— Photolysis of α‐crystallin in the presence of riboflavin under both aerobic and anaerobic conditions causes a rapid decrease in Trp emission; photooxidation most likely occurs via non‐covalent complex formation between the sensitizer molecule and the substrate. However, the change in the tertiary structure of the protein, as manifested in the near‐UV CD, is very different between aerobic and anaerobic photolysis. Riboflavin‐sensitized reaction under aerobic condition causes a major change in the microenvironments of thiol groups as well as in the near‐UV CD, whereas under anaerobic condition the change in the near‐UV CD is much less and SH‐group environments remain unaltered. The sensitizer in this photoinduced change in conformation of the protein is very selective and specific.
BIMANES—26. AN ELECTRON TRANSFER REACTION BETWEEN PHOTOSYSTEM I1 AND MONOBROMOBIMANE INDUCES STATIC CHLOROPHYLL a QUENCHING IN SPINACH CHLOROPLASTS
Authors: Melis Anastasios , Kosower Nechama S. , Crawford Nancy A. , Kirowa‐Eisner Emilia , Schwarz Miriam , Kosower Edward M.
Published: January 2008

Abstract— Monobromobimane in chloroplasts lowers both the quantum yield of system II photochemistry and the yield of chlorophyll a fluorescence. Illumination of the chloroplasts in the presence of monohromobimane is an absolute prerequisite to the manifestation of this phenomenon, which proceeds via the Photosystem II intermediate, the semiquinone radical anion, QA‐. The latter transfers an electron to monobromobimane to yield an anion radical (mBBr·), which may either lose bromide ion to yield a reactive radical (mB·), or acquire a proton and undergo further reduction, eventually forming syn‐(methyl, methyl) bimane. In turn, mB reacts with the protein of the light‐harvesting complex, to form a product which acts as static excitation energy quencher in the chlorophyll pigment bed of photosystem 11. Polarographic reduction of monobromobimane shows an adsorption wave at O V and two reduction waves. Prolonged reduction in water at ‐0.5 V yields syn‐(methyl, methyl) bimane (which is further reduced at more negative potentials) and bromide ion. Thus, both electrochemical and chloroplast‐induced reduction produce syn‐(methyl, methyl) bimane. Monobromobimane may then serve as a Photosystem II activated probe in elucidating the conformation of intrinsic thylakoid membrane polypeptides.
PHOTOCHROMIC SYNERGISM OF BACTERIORHODOPSIN‐ and HALORHODOPSIN‐MEDIATED PHOTOPHOSPHORYLATION IN Halobacterium halobium*
Authors: WAGNER Gottfried , Traulich Bernhard , Hartmann KarlM. , Oesterhelt Dieter
Published: January 2008

Quantitative action spectroscopy was performed in Halobacterium halobium. using four suited pigment mutants, namely the bacteriorhodopsin and halorhodopsin positive mutant strain M‐l (BR+, HR+), the bacteriorhodopsin positive but halorhodopsin negative strain M‐18 (BR+, HR‐), the bacteriorhodopsin negative but halorhodopsin positive strain L‐33 (BR‐, HR+), and the bacteriorhodopsin and halorhodopsin negative strain L‐07 (BR‐, HR+).

The approached questions were: First, photoenergetic synergism of halorhodopsin and bacteriorhodopsin in intact cells; second, photochromism and cellular function of the blue light‐absorbing intermediates, i.e. M‐412 and HR‐410 in bacteriorhodopsin and in halorhodopsin, respectively.

Dark‐adapted cells of mutant strain M‐l show wavelength‐dependency of quantum yield of photo‐phosphorylation, φATP. An 1.4‐fold enhancement was found at 575 nm wavelength where the long wavelength absorbance bands of bacteriorhodopsin and halorhodopsin intersect. The enhancement vanished after a 30 min pulse of orange light (600 Wm‐2 bandpass from 495 to 750 nm), but was restored after a 30 min pulse of blue light (100 Wm‐2 bandpass from 325 to 480 nm). Photoreversibility of this enhancement probably reflects phototransformation of halorhodopsin from its ground state into its inactive intermediate, HR‐410, and vice versa. The halorhodopsin‐mediated enhancement with maximum quantum yield of photophosphorylation, φATP= 0.06, i.e. a quantum requirement of = 17 photons/ATP, is partly substituted by a rise in phosphate potential and explained in terms of a voltage‐regulated gating effect on the H+‐driven ATP‐synthase, superimposed on the chemiosmotic mechanism of energy coupling.

The blue‐absorbing photochromic intermediate, M‐412 of bacteriorhodopsin, dissipates light energy upon photoexcitation that is reflected by a spectral decline in quantum yield of photophosphorylation to a minimum value of = 0.01 at 415 nm, i.e. a quantum requirement of = 100 photons/ATP.
SPECTRAL DEPENDENCE OF SOME UV‐B AND UV‐C RESPONSES OF Tetrahymena pyriformis IRRADIATED WITH DYE LASER GENERATED UV
Authors: Calkins John , Colley Ed , Wheeler John
Published: January 2008

Abstract— We have generated UV‐B and UV‐C radiations using a flashlamp driven tunable dye laser combined with frequency doubling crystals. Using this novel UV source, we have investigated lethality and its modification by growth phase, photoreactivation and caffeine in Tetrahymena pyriformis at 254 nm and from 260–315 nm in 5 nm steps. From the observed responses we have constructed action spectra for lethality, with or without caffeine (a repair inhibitor) and under conditions of photoreactivation. We have also estimated quantum efficiencies for these responses. Our observations suggest that complex changes in response occur at several wavelengths over the UV‐C and UV‐B regions.
A STUDY OF 1O2 PRODUCTION BY IMMOBILIZED SENSITIZER OUTSIDE THE SOLUTION. MEASUREMENT OF 1O2 GENERATION
Authors: Krishna C. Murali , Lion Yves , Riesz Peter
Published: January 2008

Abstract— Recently, a new technique of 1O2 generation has been described by Midden and Wang. The sensitizer is immobilized on silica gel particles which are attached on one surface of a glass plate which is placed, sensitizer‐side down, above a solution leaving a small air space between the sensitizer and the solution. Applying the principle of the technique, i.e. generation of 1O2 in the gas phase above the solution, we first improved the long‐term stability of the dye (rose bengal) by using double stock transparent tape instead of rubber cement. Under these conditions, although the initial rate of production was higher in rubber cement, the rate of production reached a plateau after 30 min, whereas with double stick transparent tape, the rate of generation was linear up to 100 min. This result was explained by the fact that silica glass beads are embedded in the cement which could lead to the bleaching reaction of the dye. Different reactions have been investigated, the bleaching of N,N‐dimethyl‐4‐nitrosoaniline (RNO) in the presence of imidazole, destruction of anthracenedipropionic acid, formation of a stable nitroxide from a sterically hindered secondary amine and the influence of pH on the nitroxide yield. The yield was measured to be 5 × 1012 molecules of singlet oxygen produced per second per cm2 from the surface of the plate using the RNO bleaching reaction. This method of generating 1O2 also seems promising for studying the killing of mammalian cells by 1O2 as the sole damaging species.
FURTHER CHARACTERIZATION OF ANESTHETIC‐TREATED PURPLE MEMBRANES
Authors: Henry Nathalie , Beaudoin Normand , Baribeau Johanne , Boucher François
Published: January 2008

Abstract— The absorption maximum of bacteriorhodopsin is shifted from 568 nm to 480 nm when halogenated volatile anesthetics (enflurane; halothane) are added to purple membranes. Analysis of the rate of formation of this new species upon addition of the anesthetic and of the back‐formation of native bacteriorhodopsin upon its removal indicate that in purple membranes, the dark‐adapted chromophore is much less reactive than its light‐adapted counterpart. Lipid‐soluble molecules thus have a lower accessibility to the dark‐adapted chromophore.

In addition, activity of the 480 nm bacteriorhodopsin was investigated. Flash and steady‐state photolysis experiments reveal that this blue shifted chromophore has full photochemical activity. It has a meta‐intermediate absorbing maximally at 380 nm. The photocycle ofBR–480 is mainly characterized by a slow decay of the “O” intermediate, enabling the direct observation of the branching reaction between the “M” intermediate and the parentBR–480 pigment.
SPECTROSCOPIC INVESTIGATION OF DIH YDRONICOTIN AMIDES‐II. DIHYDRONICOTINAMIDE ADENINE DINUCLEOTIDE COMPLEXES WITH DEHYDROGENASES
Authors: BAUMGARTEN BRIGITTE , HONES JOACHIM
Published: January 2008

Abstract— Detailed investigations are reported on absorption and fluorescence of dihydronicotinamide adenine dinucleotide in binary and ternary complexes with lactate dehydrogenase or malate dehydrogenase and substrates or substrate analogues. Polarity of the active site, as extracted from fluorescence maxima, reveals two types of dihydronicotinamide environment comparable to an aqueous and a dimethyl sulfoxide medium, respectively. Absorption maxima argue for absence of carboxamide/ acceptor hydrogen bonds in general. Vibrational fine structure in the absorption bands of some ternary complexes indicates the absence of carboxamide/donor hydrogen bonds. In these complexes, rotation of dihydronicotinamide within the binding site is established by means of fluorescence anisotropy decay.

These findings are interpreted in terms of the interaction between active site and dihydronicotinamide being highly specific for each individual complex. At the same time, they render any direct analogies between binding of reduced and oxidized coenzyme, and also between abortive and productive ternary complexes, highly problematical.
THE STABILITY OF LIGHT SOURCES: IMPLICATIONS FOR PHOTOBIOLOGICAL STUDIES
Authors: Diffey B. L.
Published: January 2008

Abstract— The radiation output of a number of different types of ultraviolet lamps, used unfiltered or in conjunction with optical filters, has been carefully monitored over the first1–2 h after switching on. It was shown that the spectral output can change significantly, particularly during the first 1/2 h, when lamps are used with filters. This may lead to errors in dosimetry if lamp output is monitored inappropriately.
INACTIVATION AND MUTATION INDUCTION TO 6‐THIOGUANINE RESISTANCE IN V79 HAMSTER FIBROBLASTS BY SIMULATED SUNLIGHT
Authors: Zölzer F. , Kiefer J. , Rase S.
Published: January 2008

Abstract— Risk estimates for an enhancement of ultraviolet radiation are frequently based on action spectra, in which case it is assumed that the different components of natural or artificial sunlight act independently and the overall effect can be derived by a simple summation procedure. Such an approach, however, may not always be justified and‐as shown earlier‐lead to a considerable underestimation of inactivation and mutation induction to 6‐thioguanine resistance by filtered ‘sunlamp’‐radiation. Here we report on experiments employing different kinds of simulated sunlight. A good agreement between theoretical and experimental results was found. The apparent contradiction can be resolved by an analysis for the spectral regions primarily responsible for the overall effect.
RHYTHMS IN BLUE‐LIGHT‐INDUCED CONIDIATION OF WILD TYPE AND A MUTANT STRAIN OF Trichoderma harzianum
Authors: DEITZER GERALD F. , Horwitz BENJAMIN A. , Gressel Jonathan
Published: January 2008

Abstract— Trichoderma harzianum normally requires light for conidiation. Conidiation of colonies grown in continuous light does not appear to be rhythmic, but sharp banding patterns are formed under light/dark cycles. A single pulse of blue light produces a sharp band of conidia that forms where the growing edge of the mycelia is located at the time when the light is given. A period of about 24 h is required following the light pulse to produce mature conidia. During this time colonies are insensitive to further induction by light. The fluence required to produce 50% saturation varies by a factor of about 3 depending on when the pulse is given. This change of sensitivity is rhythmic with a period length of approximately 27 h when grown on medium containing deoxycholate.

The pattern of conidiation in a mutant strain (B119), which is able to form conidia in the dark, is rhythmic and the period length is dependent on the composition of the medium. Addition of deoxycholate to the medium increased the interval between dark bands from 12 to 24 h. The rhythmic banding is suppressed in constant light and a double banding pattern is produced in light/dark cycles. A pulse of blue light induces a band of conidia in this mutant, as in the wild type, but it also delays the reappearance of the dark banding pattern. The extent of this delay depends on when the pulse is given and, although the period length of the dark conidiation rhythm is affected by deoxycholate, the effect of blue light on its phase is not. Of the various rhythmic responses of Trichoderma studied here. the delay in reappearance of the dark banding pattern in B119 is the most promising for further detailed studies, for example of wavelength and temperature dependence.
CHEMILUMINESCENCE AND FLUORESCENCE OF THE EUROPIUM IONS‐ADENINE NUCLEOTIDES SYSTEM AND ITS POSSIBLE BIOLOGICAL SIGNIFICANCE
Authors: ELBANOWSKI MARIAN , PAETZ MARIA , SIAWINSKI JANUSZ , CIEŚLA LESZEK
Published: January 2008

Abstract— Chemiluminescence of the Eu(II)/Eu(III)‐adenine nucleotide‐H2O2 system and fluorescence of the Eu(III)‐adenosine triphosphate system have been investigated. The spectral distribution of the chemiluminescence emission has shown an occurrence of three main bands (Λ=470–480,590–620 and ca. 700 nm). The energy transfer process from the adenosine triphosphate molecules to the Eu(III) ions has been observed in the fluorescence spectrum. The examined chemiluminescence and fluorescence spectra show that these both kinds of emission originate from the 5D***τ7F*** (n=1–4) transitions in the Eu(III) ions.
PORPHYRIN‐SENSITIZED PHOTOREACTIONS IN THE PRESENCE OF ASCORBATE: OXIDATION OF CELL MEMBRANE LIPIDS AND HYDROXYL RADICAL TRAPS
Authors: BACHOWSKI GARY J. , MOREHOUSE KIM M. , GIROTTI ALBERT W.
Published: January 2008

Abstract— Photooxidation reactions in ascorbate (AH)‐containing erythrocyte membrane suspensions have been studied in broad perspective by simultaneously monitoring lipid peroxidation in the membrane compartment and formation of hydrogen peroxide (H2O2) and hydroxyl radical (OH) in the aqueous compartment. Non‐bound uroporphyrin (UP) and membrane‐bound protoporphyrin (PP) were used as sensitizers. Photoreduction of UP to the radical anion (UP‐) was detected by electron spin resonance when UP/AH/membrane mixtures were irradiated anaerobically. Aerobic irradiation resulted in a strong AH‐‐stimulation of lipid peroxidation, H2O2 formation, and OH‐ generation (detected with 2‐deoxyribose (DOR) and the spin trap 5,5‐dimethyl‐l‐pyrroline‐N‐oxide). Use of diagnostic agents (e.g. catalase, desferrioxamine, mannitol) revealed that OH‐ is involved in light‐stimulated DOR oxidation, but not in lipid peroxidation. Similar irradiation in the presence of PP resulted in far greater lipid peroxidation than observed with UP, but less DOR oxidation, and insignificant accumulation of H2O2. This suggests that photoreduction of membrane‐bound PP is less efficient, possibly due to hindered access of AH‐.
FLUORESCENCE DECAY KINETICS and CHARACTERISTICS OF BIMOLECULAR EXCITON ANNIHILATION IN CHLOROPLASTS
Authors: France Lee , Geacintov Nicholas E. , Lin Su , Wittmershaus Bruce P. , Knox Robert S. , Breton Jacques
Published: January 2008

Abstract— The decay profiles of the fluorescence of dark‐adapted spinach chloroplasts (0A°C) excited with single 30 ps 532 nm laser pulses of varying intensities were measured with a low‐jitter streak camera system. By comparing the decay profiles of the fluorescence at low and high laser fluences, i.e. in the absence and presence, respectively, of dynamic bimolecular exciton‐exciton annihilation effects, the duration of such dynamic annihilation events can be estimated. A simple model suggests that the influence of bimolecular annihilation events on the fluorescence decay kinetics should disappear within a time interval corresponding to the low intensity, unimolecular lifetime of the exciton population which is subject to exciton‐exciton annihilation. The low intensity fluorescence decay profiles are characterized by three to four lifetimes (Reviewed by A. R. Holzwarth, Photochem. Photobiol. 43,707–725, 1986); it is shown here that only the shortest fluorescence components are subject to exciton annihilation, since the kinetics of the fluorescence decay are influenced by annihilations only within the initial 150–200 ps time interval after the excitation pulse. The amplitudes (but not the decay kinetics) of the longer‐lived fluorescence components are decreased at high levels of laser pulse excitations, suggesting that these components are derived from the shorter‐lived fluorescence decay components. The implications of these results are*discussed within the contexts of current models of the fluorescence in chloroplasts.
INTERACTION OF ENZYME‐GENERATED SPECIES WITH CHLOROPHYLL‐a AND PROBES BOUND TO SERUM ALBUMINS
Authors: Bohne Cornelia , Faljoni‐Alario Adelaide , Cilento Giuseppe
Published: January 2008

Abstract— The interaction of serum albumin‐bound acceptors with enzyme‐generated and protected triplet species was studied in two types of systems. Chlorophyll‐a bound to bovine and human serum albumins is efficiently excited by enzymatically generated triplet acetone and acetaldehyde. When the Chl‐a concentration is much lower than that of the albumin the interaction occurs with chlorophyll in an aggregate in which one Chl‐a is surrounded by several protein molecules. When the Chl‐a concentration is higher than that of the protein, the aggregate contains the proteins and fluorescent chlorophylls in a 1:1 ratio. The excess chlorophylls, although able to interact with the donors, are not fluorescent.

In another study, probes bound to various specific sites of serum albumins were used as quenchers of the enzymatically generated triplet acetone. The efficiency of quenching by all the bound probes is equal and in one case even stronger than for the free probes.

A model for the interaction of the excited species contained in the enzyme with the acceptor(s) located in the protein is proposed.

The present results provide further evidence that enzyme‐generated and protected triplet carbonyl species can interact through a collisional process with acceptors bound to or constituents of macromolecules.
THE CONTROL OF METABOLISM BY BLUE LIGHT IN Acetabularia mediterranea—II. SELECTIVE TRANSLATIONAL CONTROL AND DIFFERENTIAL DEGRADATION OF ENZYMES
Authors: Nickl Bernhard , Söllner Bruno , Schmid Rainer
Published: January 2008

Abstract— During prolonged continuous irradiation with red light the specific activity of uridine 5′‐diphosphoglucose (UDPG) pyrophosphorylase (uridine 5′‐triphosphate: glucose 1‐phosphate uridylyl‐transferase EC 2.7.7.9) decreased in Acetabularia mediterranea Lamouroux (=A. acetabulum (L.) Silva). Subsequent blue light restored the original activity within a comparatively short period of 3 to 4 days. Computer‐aided quantitative evaluation of density labelling experiments showed that the synthesis of the enzyme was accelerated about four‐fold during the period of activation by blue light. A similar increase in the rate of synthesis was found for hydroxypyruvate reductase (EC 1.1.1.81), a control enzyme that showed no blue light‐dependent changes in the specific activity under these conditions. The increase in the rate of enzyme synthesis was caused by an overall stimulation of the cytosolic translation. Degradation of UDPG pyrophosphorylase was unaffected by blue light, while the half life of hydroxypyruvate reductase was shortened about two‐fold compared to continuous red light. Thus, degradation of proteins appears to be selectively light dependent in Acetabularia.

Model calculations for enzyme amount and enzyme synthesis were carried out using the measurements of enzyme activity, rates of cytosolic protein synthesis, and degradation constants of the enzymes. Assuming that activities represented amounts of the given enzymes, these calculations indicated a selective activation of UDPG pyrophosphorylase synthesis by blue light since it did not coincide with the overall stimulation of protein synthesis in the cytosol, in contrast to hydroxypyruvate reductase.
THE PHOTOCHEMISTRY OF 3‐NITROBENZOYL AND 4‐NITROBENZOYL AZIDES: POSSIBLE REAGENTS FOR PHOTOAFFINITY LABELING
Authors: Woelfle Ingrid , Sauerwein Björn , Autrey Tom , Schuster Gary B.
Published: January 2008

Abstract— The photochemistry of 3‐ and 4‐nitrobenzoyl azides was studied to examine their suitability for use in photolabeling procedures. These aroyl azides absorb light in the near UV‐spectral region. Their irradiation leads both to photo‐Curtius rearrangement with formation of the analogous isocyan‐ates and to generation of nitrenes by loss of nitrogen. The chemical and spectroscopic properties of the aroyl nitrenes indicate that they are singlets in their ground states. These singlet nitrenes insert rapidly into unactivated, aliphatic carbon‐hydrogen bonds, trap nucleophiles, and add to olefins to form aziridines with retention of stereochemistry. Photolabeling agents based on these azides may offer some advantages over conventional agents for the labeling of lipophilic sites.
ACTION SPECTRA AND CHROMOPHORES FOR LETHAL PHOTOSENSITIZATION OF Candida albicans BY DNA MONOADDUCTS FORMED BY 8‐METHOXYPSORALEN AND MONOFUNCTIONAL FUROCOUMARINS
Authors: Baydoun Safa A. , Gibbs Neil K. , Young Antony R.
Published: January 2008

Abstract— The red‐shift of furocoumarin action spectra, compared with their absorption spectra, has been investigated. An action spectrum for 8‐methoxypsoralen (8‐MOP) monoadduct formation in the yeast Candida albicans has been determined. The yeast cells were initially exposed to sublethal doses of monochromatic UVA at different wavelengths. Monoadduct formation was monitored by growth inhibition induced, after washing out any unbound 8‐MOP, by re‐irradiation with a constant second (non‐lethal) dose of 330 nm radiation. A comparison between this action spectrum and the absorption spectrum of the dark complex of 8‐MOP and DNA was made. In addition, the action spectra of monoadduct formation of five monofunctional compounds including a coumarin derivative have been determined. These action spectra were compared with their respective DNA dark complex absorption spectra. In general, the peaks of the furocoumarin DNA dark complexes show a red‐shift when compared with the free furocoumarin molecule and the action spectra show peaks which correspond with the peaks of the dark complexes. Such data indicate that the DNA dark complex is the chromophore for growth inhibition in yeast rather than the free furocoumarin. The similarity of the 8‐MOP monoadduct formation action spectrum and 8‐MOP action spectra suggests that spectral dependence for the photobiological effects (including the red‐shift) is dependent on monoadduct formation rather than, as previously suggested by several authors, crosslink formation. The action spectrum for the coumarin derivative 4‐methyl N‐ethylpyrrolo (3,2‐g) coumarin (PCNEt) correlated well with the free molecule absorption spectrum rather than DNA dark complex indicating that the free molecule is the chromophore. This was supported by studies which showed that PCNEt photosensitization is oxygen dependent.
MECHANISTIC STUDIES OF THE PHOTOREACTION OF FLAVIN WITH N, N‐DIMETHYLPROPARGYLAMINE
Authors: FRANKE JÜRGEN , OTT ULRICH , KRAMER HORST E. A. , TRABER RAINER H.
Published: January 2008

Abstract Both photoexcited free flavin and protein‐bound flavin react with N, N‐dimethylpropargyla‐mine (DMPA) to yield dihydroflavin‐adducts which are not reoxidizable by oxygen. The mechanism of the photoreaction was reinvestigated by flash photolysis and continuous illumination experiments. We suggest that a mechanism occurs in which a flavosemiquinone and a DMPA radical result in the first photoinduced reaction. The flavin‐DMPA adducts are then formed by combinations of the two radicals.