bluuebunny/crossref_metadata_2025 huggingface dataset:
NANOSECOND LASER PHOTOLYSIS OF RHODOPSIN AND ISORHODOPSIN
Authors: Horwitz J. S. , Lewis J. W. , Powers M. A. , Kliger D. S.
Published: January 2008

Kinetic and spectral measurements have been carried out on the primary intermediate in the photolysis of rhodopsin and isorhodopsin, initiated by a 457 nm, 6 ns (FWHM) laser pulse. In rhodopsin the kinetic decay of bathorhodopsin was found to be 140 ± 15 ns at 20°C. The decay of bathorhodopsin to lumirhodopsin has an activation energy of 51 ± 4 kJ/mol (12.2 ± 1 kcal/mol). The decay kinetics of bathorhodopsin were found to be the same for rhodopsin in membrane and detergent solubilized suspensions. The kinetic decay of the batho product in the photolysis of isorhodopsin was found to be the same as rhodopsin.

The corrected transient spectrum 50 ns following excitation in rhodopsin has two peaks near 560 and 440 nm. A peak was also observed in isorhodopsin near 550 nm at 50 ns following excitation but no transient was observed in the blue. The 550 nm peak in isorhodopsin has an intensity similar to that in rhodopsin indicating that the quantum yields for the formation of batho products of rhodopsin and isorhodopsin are similar under the irradiation conditions used here. Transient spectra for rhodopsin and isorhodopsin 1 μs following excitation are also different. In isorhodopsin the corrected transient spectrum has a peak at 500 nm, similar to low temperature steady state irradiation spectra. The 1 μs transient spectrum in rhodopsin is more intense than in isorhodopsin and shows a peak at 475 nm.
OPTICAL PROPERTIES OF PHYTOCHROME IN THE BLUE‐ SPECTRAL REGION AS MEASURED IN VIVO AND IN VITRO
Authors: Epel B. L. , Horwuz B. A. , Baron O.
Published: January 2008

In the blue spectral region, the phototransformation difference spectrum of oat phytochrome extracted as Pfr differs from that of phytochrome extracted as Pr. The difference absorbance maximum for phytochrome extracted as Pfr is at 420 nm, while that extracted as Pr is at 412 nm. The phototransformation difference spectrum measured in the blue in oat coleoptile tips without inner leaves, corresponds very well with that of phytochrome as extracted in its Pfr form. There is, however, a slight apparent attenuation of the blue difference band relative to those in the red‐far‐red. In coleoptile tissue containing inner leaves, the blue difference band is relatively even more highly attenuated. A similar attenuation is observed in the blue, in the protochlorophyllide to chlorophyllide phototransformation difference spectrum. In the spectrum measured with excised coleoptile without inner leaves, there is a small attenuation, while in coleptile tissue with inner leaves the attentuation is nearly 9‐fold. These data suggest that the observed attenuation is probably artifactual. Neither instrumental non‐linearity nor fluorescence induced by the measuring beam could explain the observed attenuation. It is suggested that the observed attenuation is probably mainly the result of wavelength dependent scatter amplification, the amplification in the blue being attenuated by the high background absorption of other pigments in this region.
RED EMISSION FROM CHLOROPLASTS ELICITED BY ENZYME‐GENERATED TRIPLET ACETONE AND TRIPLET INDOLE‐3‐ALDEHYDE
Authors: Nassi Lilian , Cilento Giuseppe
Published: January 2008

—Enzyme‐generated triplet acetone and triplet indole‐3‐aldehyde transfer energy very efficiently to chloroplasts, as indicated by the intensity of the sensitized red emission that is observed. The intermediacy of excited species of oxygen (1O2, O2−, HO) has been excluded. Our results open the way for investigating energy transfer in architecturally organized systems in the absence of light.
INTRAMICELLAR QUENCHING OF 2,3‐DIMETHYLNAPHTHALENE FLUORESCENCE BY PEROXIDES and HYDROPEROXIDES
Authors: Encinas M. V. , Lissi E. A.
Published: January 2008

Hydrogen peroxide, t‐butyl hydroperoxide, di‐t‐butyl peroxide and dibenzoyl peroxide efficiently quench the fluorescence of 2,3‐dimethylnaphthalene incorporated into sodium dodecyl sulfate and cetyltrimethylammonium chloride micelles. Potassium persulfate only is effective when the probe is incorporated into a cationic micelle. The binding constant of the peroxides and the intramiccllar quenching rate constants have been evaluated for all the systems considered and the data are compared to that obtained in homogeneous solution. It is concluded that, even for processes which are not diffusion controlled, the quenching process is slower in the micelles.
CIRCANNUAL COURSE OF PHOTOMORPHOGENETIC REACTIVITY IN ETIOLATED BEAN SEEDLINGS
Authors: Spruyt E. , Maes L. , Verbelen J.‐P. , Moereels E. , De Greef J. A.
Published: January 2008

Hook opening and leaf expansion, measured 24 h after standard red light illumination, were considered as parameters determining the photoactivity of etiolated Phaseolus vulgaris L. seedlings. The experiment was repeated every h during one 17‐h period each month for 1 year. The mean values for each experimental period indicated that the photoactivity of the etiolated seedlings changed markedly throughout the year according to a seasonal pattern.
RESISTANCE OF THE SCRAPIE AGENT TO INACTIVATION BY PSORALENS
Authors: Mckinley MichaelP. , Masiarz FrankR. , Isaacs StephenT. , Hearst JohnE. , Prusiner StanleyB.
Published: January 2008

–In searching for a nucleic acid within the scrapie agent, we employed psoralens which penetrate the coats of most conventional viruses, form photoadducts with their genomes, and block replication of the viruses. Five psoralens, at concentrations up to 500 times greater than those required to inactivate conventional viruses, did not influence scrapie agent titers in partially purified preparations from murine spleen and hamster brain. 3H‐psoralens were used to monitor the formation of photoadducts within nucleic acid standards added to preparations of the scrapie agent. Since no inhibition of psoralen photoadduct formation was observed in these preparations, one of three possibilities seems likely: the scrapie agent is devoid of nucleic acid, the psoralens failed to penetrate the protein coat of the agent, or its nucleic acid is unreactive with psoralens.
SOME PHOTOPHYSICAL PROPERTIES OF 3‐CARBETHOXYPSORALEN, 8‐METHOXYPSORALEN and 5‐METHOXYPSORALEN TRIPLET STATES
Authors: Craw M. , Bensasson R. V. , Ronfard‐Haret J. C. , Melo M. T. Sae , Truscott T. G.
Published: January 2008

Abstract Triplet absorption spectra, extinction coefficients (ɛT), decay rates (K1), oxygen quenching rates (kq) and intersystem crossing yields (φT) for 3‐carbethoxypsoralen (3‐CPs). 8‐methoxypsoralcn (8‐MOP) and 5‐methoxypsoralen (5‐MOP) in methanol are reported. For 8‐MOP and 3‐CPs corresponding values are also reported with water as the solvent. Some photophysical data are also reported for 5‐MOP in water, but ɛT and φT were not obtained.

The phosphorescence spectra for these furocoumarin derivatives in ethanol at 77 K are reported together with the corresponding lowest triplet energy and lifetime. The values of the various photophysical properties obtained are compared with values reported by previous workers.
A DYE LASER SOURCE OF MONOCHROMATIC UV‐B and UV‐C RADIATIONS FOR BIOLOGICAL ACTION SPECTROSCOPY
Authors: Calkins John , Colley Ed , Hazle John , Hannan M. A.
Published: January 2008

Abstract We have used a flashlamp driven tunable dye laser as a radiation source for observing UV‐C and UV‐B action spectra of two eukaryotic microorganisms. The general nature of the irradiation system and various operating parameters are described. The laser produces the high power output required for UV‐B action spectroscopy; it is tunable throughout the UV‐B range with the very narrow bandwidth required for high resolution action spectra. The peak power density does not appear to reach the threshold of ‘two photon’ biological effects, a concern when using pulsed lasers for action spectroscopy. The laser is somewhat more expensive and considerably more difficult to operate compared with arc‐monochrometer systems; it is generally equal or greater in UV‐B power and has distinct advantages in tunability and bandwidth of the spectral output.
SUPEROXIDE RADICALS, SUPEROXIDE DISMUTASES and OXYGEN TOXICITY IN PLANTS
Authors: Rabinowitch Haim D. , Fridovich Irwin
Published: January 2008

Abstract In plants, as in other aerobic organisms, O2− is a commonly encountered intermediate of oxygen reduction and superoxide dismutases provide a defense against the potential cytotoxicity of this radical. The superoxide dismutases found in plants resemble those encountered in other organisms. Within chloroplasts one finds the CuZn enzyme, while mitochondria contain the Mn enzyme. Nymphaceae, ginkoaceae and cruciferae are unusual among plants, indeed among eukaryotes, in that they contain an iron superoxide dismutase. Bipyridylium herbicides, such as paraquat, exert their effect by diverting electron flow from photosystem I and thus increasing 02– production. Paraquat‐resistant genotypes of horseweed, tobacco and rye grass were found to contain elevated superoxide dismutase. This enzyme also appears to provide a defense against sulfur dioxide, sunscald and photooxidative death. The evidence supporting these statements and possible explanations are discussed.
THE TRIPLET AND RADICAL SPECIES OF HAEMATOPORPHYRIN AND SOME OF ITS DERIVATIVES
Authors: Bonnett R. , Lambert C. , Land E. J. , Scourides P. A. , Sinclair R. S. , Truscott T. G.
Published: January 2008

Abstract— Nanosecond laser flash photolysis and pulse radiolysis have been used to generate and characterise the triplet state, and semioxidised and semireduced radicals of haematoporphyrin, and three 0‐acyl compounds derived from it (the monoacetate, the diacetate and the disuccinate).

After 347 nm irradiation in water containing 2% Triton X‐100, haematoporphyrin forms the triplet state (φT= 0.92) and photoionises monophotonically (φI= 0.03). For the O‐acyl derivatives, φT approaches unity and photoionisation is reduced. In acetone the triplet yield of all four compounds are close to unity. The difference and corrected spectra for the triplet species are presented and decay rates (k1˜104s‐1) and oxygen quenching constants (kQ˜1.5times109M‐1s‐1) for the triplet state have been measured. The difference and corrected spectra for the semi‐reduced species in methanol and semi‐oxidised species in aqueous Triton X‐100 are presented.

The photophysical characteristics in fluid solution of haematoporphyrin and its 0‐acyl derivatives are rather similar to those previously recorded for other photosensitising porphyrins.
PHOTOCHEMICAL INACTIVATION OF SINGLE‐STRANDED VIRAL DNA IN THE PRESENCE OF UROCANIC ACID*
Authors: Tessman Irwin , Morrison H. , Bernasconi C. , Pandey G. , Ekanayake† L.
Published: January 2008

Abstract— Urocanic acid (UA) has previously been shown to react photochemically in vitro with N,N‐dimethylthymine. In this study, mixtures of UA and phage G4 single‐stranded DNA have been irradiated with UV light (λ≥ 254 nm) and the DNA assayed for infectivity. At the concentrations of UA employed (typically 5.4 × 10‐3M) there is extensive absorption of the incident light by the UA. The DNA is inactivated at rates greater than that predicted from the calculated shielding by UA, indicating that photosensitization is occurring. Photosensitization is also indicated by the fact that at high UA concentrations the inactivation rate does not decrease to zero but approaches a residual value. Furthermore, the ability to photoreactivate DNA that has been photolyzed in the presence of UA is much reduced relative to that observed upon photolysis of the DNA alone. UA is therefore responsible for the production of UV‐induced DNA lesions, which are resistant to photoreactivation.

A general analysis of the effects of photosensitization on the kinetics of UV inactivation is presented in an appendix.
THE PHOTOREDUCTION OF METHYLENE BLUE BY ARYLAMINOMETHANE‐SULFONATES
Authors: NEUMANN MIGUEL G. , MATTHEWS J. IOAN , BRASLAVSKYdR SILVIA E.
Published: January 2008

Abstract— The photoreduction of methylene blue in the presence of arylaminomethanesulfonates (RAMS = RC6H4NHCH2SO3Na) was studied by laser and conventional flash photolysis. These compounds quenched the methylene blue triplet deviating from a normal Stern‐Volmer behaviour. For low quencher concentrations, a Rehm‐Weller relationship was found between the kq's and the DLG's obtained for the electron transfer reactions. The lack of further quenching at higher [RAMS] is ascribed to the formation of a ground state ion pair between the dye and the anionic quencher which, on excitation, forms a triplet state unable to under go electron transfer for steric reasons. A second order decay rate constant was found for the semireduced species (MB') (ca. 5 × 109M‐1 s‐1, independent of the RAMS used) and is attributed to a proton transfer from the radical zwitterion (RC6H4NH CH2SO3−) to MB. The overall dependence on the substituent of the bleaching observed by continuous irradiation follows the triplet behaviour.
CHARGE TRANSFER COMPLEXES OF PHEOPHYTIN a WITH NITROAROMATICS. ELECTRON TRANSFER FROM EXCITED SINGLET OF PHEOPHYTIN a TO NITROAROMATICS
Authors: DROUPADI P. R. , KRISHNAN V.
Published: January 2008

Abstract— The interaction of pheophytin a (Pheo) with seven nitroaromatic acceptors of varying ring sizes and electron acceptor abilities has been studied both in the ground and excited states. The ground state association constants (K) of the 1: 1 complexes of donor (Pheo) and acceptors were found to increase with increasing electron affinities of the different acceptors. All the nitroaromatic compounds efficiently quench the singlet emission of Pheo and the quenching follows the Stern‐Volmer (SV) relationship. The SV constants (Ksv) for different quenchers follow the same order as that of the K values. The reduction potential of Pheo+/Pheo* obtained from the quenching data agrees well with the theoretically predicted value. A charge transfer interaction between the singlet excited state of Pheo and the nitroaromatics is suggested from the dependence of quenching rate constants on the electron affinities of the acceptors.
UV IRRADIATION OF WILD TYPE AND RADIATION‐SENSITIVE MUTANTS OF THE NEMATODE Caenorhabditis elegans: FERTILITIES, SURVIVAL, AND PARENTAL EFFECTS
Authors: HARTMAN PHILIP S.
Published: January 2008

Abstract— Survival after UV irradiation was examined in wild type and four radiation‐sensitive (rad) mutants of Caenorhabditis elegans. Synchronous populations were employed to assess radiation sensitivities at different developmental stages. In addition, the effects of irradiation on male and hermaphrodite fertilities were measured. Wild‐type sensitivity was maximal early in embryogenesis. Different age‐dependent patterns of radiation sensitivity were obtained with the rad mutants. The effects of parental genotype were also tested. A parental wild‐type allele was capable of quickly elevating the radiation resistance of embryos derived from homozygous rad hermaphrodites. In a second parental‐effect test, homozygous rad embryos displayed greater radiation resistance when derived from heterozygous rather than homozygous hermaphrodites. The results indicate that radiation sensitivity in this metazoan is determined by complex interactions of gene products.
THE ROLE OF OXYGEN IN PHOTOSENSITIZATIONS WITH POLYACETYLENES AND THIOPHENE DERIVATIVES
Authors: McLACHLAN D. , ARNASON T. , LAM J.
Published: January 2008

Abstract— The mechanism of photosensitization by polyacetylenes and biosynthetically derived thiophenes from species of the plant family Asteraceae was examined. With thiophenes photosensitization of yeast and E. coli occurred under aerobic but not anaerobic conditions. For similar experiments with polyacetylenes, both photodynamic and non‐photodynamic mechanisms were observed. While the relative toxicities of thiophenes and polyacetylenes under near UV radiation was in general similar, the in vitro generation of singlet oxygen was considerably less for polyacetylenes than thiophenes, which is additional evidence for the existence of an alternate mechanism of action in polyacetylene photosensitization. Rates of photodegradation of polyacetylenes are higher than for thiophenes suggesting that bond breaking/formation processes are more favored relative to energy transfer to oxygen for polyacetylenes than thiophenes.
A MICROSECOND KINETIC STUDY OF THE PHOTOGENERATED MEMBRANE POTENTIAL OF BACTERIORHODOPSIN WITH A FAST RESPONDING DYE
Authors: EHRENBERG BENJAMIN , MEIRI ZVI , LOEW LESLIE M.
Published: January 2008

Abstract— Bacteriorhodopsin is a light activated proton pump which generates proton and electric gradients across the cytoplasmic membrane of Halobacterium halobium. In this study, a dye whose fluorescence intensity responds rapidly to membrane potential was used to follow the evolution of the potential on liposomes reconstituted with bacteriorhodopsin, in the microseconds time domain. By comparing the formation kinetics of the potential to those of the long‐lived intermediate species in the bacteriorhodopsin photocycle, M412, both in H2O and 2H2O suspensions, we can draw the following conclusion: the electric potential onset time is 20 μs after initiation of the illumination. The triggering of the potential is not the formation of the M412 intermediate, which was hitherto considered to be the first species in the bacteriorhodopsin cycle which has an unprotonated Schiff base linkage at the retinal chromophore. Rather, the potential forms at the transition of the L550 intermediate to the species X which precedes M412 or even at the preceding conversion of K590 to L550.
THE FLUORESCENT PRODUCT OF SCALEWORM BIOLUMINESCENT REACTION: AN IN VITRO STUDY
Authors: FRESNEAU C. , ARRIO B. , LECUYER B. , DUPAIX A. , LESCURE N. , VOLFIN P.
Published: January 2008

Abstract— The fluorescence of scaleworms has been attributed by Harvey (1952) to a product of the bioluminescent reaction confined in the scales of these worms. We have purified this fluorescent molecule by gel filtration. This compound has an apparent low molecular weight as shown by polyacrylamide gel clectrophoresis in the presence of SDS. The yield of the fluorescent product, after gel filtration, varies with the stimulation of the bioluminescence, triggered either chemically or enzymatically. The fluorescence spectrum of the purified product is similar to the one observed in vivo, with a maximum centered at 520 nm. Consequently, the fluorescent compound isolated is likely the reaction product of the bioluminescent reaction.
MODIFYING FACTORS OF THE CELLULAR CONCENTRATION OF PHOTOLYASE MOLECULES IN Saccharomyces cerevisiae CELLS–I. EFFECTS OF TEMPERATURE AND LIGHT
Authors: Fukui Atsushi , Laskowski Wolfgang
Published: January 2008

Abstract— The effects of temperature and light on the cellular concentration of photoreactivating enzyme (PRE) molecules in haploid Saccharomyces cerevisiae cells were investigated. (1) Temperature effect: The number of active PRE molecules per cell (NPRE) in cells grown at 37°C was about 13% of that grown at 23°C, although the amount of proteins per cell remained the same. (2) Light effect: NPRE in cells grown in light was about 2.8 times larger than that grown in the dark. The value of NPRE in cells grown in the light decreased more rapidly during holding in buffer in the dark than in the light. The NPRE decrease during holding in buffer in the dark was more rapid in cells grown in the light than grown in the dark. A comparable decrease was observed after holding in buffer in the presence of cycloheximide. (3) In cells harboring a plasmid containing the gene PHR1, NPRE was larger in cells grown at 23 than at 30°C.
AN EXPERIMENTAL STUDY OF THE CHANGES IN PIGMENTATION IN HUMAN SKIN IN VIVO WITH VISIBLE AND NEAR INFRARED LIGHT
Authors: Kollias N. , Baqer A.
Published: January 2008

Abstract— The skin of the lower inner arm of volunteers was irradiated, with a 390–1700 nm light source, through a fiber optic bundle for times of up to 1.2 × 104 s and with powers of up to 0.35 W/cm2. Simultaneously with the irradiation, spectra (390–720 nm) of the remitted intensity were measured, while a 5.0 cm in diameter area of the skin around the fiber bundle was maintained at constant temperature, within 0.2°C. The generation of a photoproduct was observed and measured as changes in the remitted intensity within 600 s (10 min) of the start of irradiation.

The photoproduct formed was characterized by a weak absorption in the blue part of the spectrum (400–450 nm), leading to a bluish appearance in the irradiated area only. The color change appears as a two step process. It starts with a “soluble” photoproduct, which disappears, within 24 h after irradiation, and an “insoluble” photoproduct which appears with irradiation greater than 3 ×103 s (50 min). No spectral differences were detected between the two photoproducts. The “insoluble” photoproduct persists for periods of up to 8 weeks. The color change in the skin is immediate and there is no erythema associated with this color change.
PORPHYRIN PHOTOSENSITIZATION AND CAROTENOID PROTECTION IN MICE; IN VITRO AND IN VIVO STUDIES
Authors: Mathews‐Roth Micheline M.
Published: January 2008

Abstract Mice made porphyric with collidine received either of the pigments beta‐carotene or canthaxanthin. When the mice were exposed to ambient light and to weekly doses of black light, the treated animals developed less skinfold thickness than did porphyric mice receiving placebo, indicating some protection from photosensitization in the mice receiving pigments. Photosensitized inhibition of succinate oxidation in liver extracts prepared from porphyric mice was also reduced in those animals that had received the pigments. A singlet oxygen‐free radical trap, DPBF, was added to the isolated epidermis of collidine‐porphyric mice which had received either beta‐carotene, canthaxanthin or placebo. The absorbance of DPBF at 415 nm in epidermis prepared from mice receiving either of the pigments decreased less after light exposure of the prepared epidermis than did the absorbance of DPBF in epidermis prepared from porphyric mice receiving placebo and similarly light exposed. These experiments suggest that the administered carotenoids quenched to some degree photochemical reactions occurring in the porphyric epidermis.
POLARIZED UV‐ABSORPTION SPECTRA OF RETINAL ISOMERS—II. ON THE ASSIGNMENT OF THE LOW AND HIGH ENERGY ABSORPTION BANDS
Authors: Drikos G. , Rüppel H.
Published: January 2008

Abstract The polarized UV‐absorption spectra of all‐trans retinal and both crystal forms of 11‐cis, 12‐s‐cis retinal (presented in the previous paper, Part I) are analyzed using Lowry‐Hudson functions to describe the band profiles. The polarization ratios of the polarized bands is used to determine the direction of the corresponding transition moments. For all‐trans retinal the polarization spectra show that the absorption between 23 and 36 X 103 cm−1 is caused by three overlapping bands labeled S, A and B. For 11‐cis retinal the B‐band is also clearly resolved whereas the S and A bands are separated with much less certainty than for all‐trans retinal.

Comparing these bands with the excited state manifold resulting from semiempirical CI‐calculations including double excitations, the S‐band could be assigned to the 1Ag−→1Ag‐* and the A‐band to the 1Ag−→1Bu+* transition. However, no transition is found in this manifold which could positively be assigned to the B‐band because the transitions predicted in this spectral region have negligible oscillator strengths. In all the crystal spectra a further band C is observed around 39 X 103 cm−1 which is particularly pronounced in the case of 11‐cis retinal. For this band an assignment to the 1Ag−→1Ag+*‐transition is proposed.
ROLE OF ELECTRIC POLARIZATION IN THE THERMOLUMINESCENCE OF CHLOROPLASTS
Authors: Knox P. P. , Venediktov P. S. , Kononenko A. A. , Garab Gy. I. , Faludi‐Dániel Á.
Published: January 2008

Abstract Effect of an external electric field on thermoluminescence and thermodepolarization currents were studied in suspensions and dry films of pea chloroplasts. The external electric field was applied either during interrupted heating at a given temperature (“direct effect”) or was “stored” in the sample during cooling in the range –25°C and –70°C (“electret effect”).

It is shown that in chloroplast suspension both the luminescence burst upon “direct effect” and the new band peaking between –40°C and –50°C induced by the “electret effect” are accompanied by a preferential decrease in the intensity of the thermoluminescence band around +10°C.

A correlation was established between the polarized state of thylakoids and the thermoluminescence burst induced by the external field. In electret samples of chloroplast suspension the intensity of field induced low temperature thermoluminescence band under different experimental conditions varied in parallel with the intensity of thermodepolarization current. In dry films of chloroplasts, in addition to parallel changes in intensities of thermoluminescence and thermodepolarization current, also the peak positions shifted in the same manner when either humidity of samples or temperature of illumination and of application of external field were varied.

We conclude that the polarization state of thylakoid membrane, which can be governed by an external electric field, plays an important role in determining charge stabilization and recombination properties of photosynthetic units. Our results implicate that electric field induces conformational changes in the membranes which increases the frequency factor ascribed to the recombination processes.
ELECTROPHORETIC SEPARATION OF FUROCOUMARIN: DNA PHOTOADDUCTS
Authors: Calvin Noel M. , Hanawalt Philip C.
Published: January 2008

Abstract We describe a new approach for quantitating furocoumarin adducts in DNA using enzymatic hydrolysis followed by resolution and recovery of the adduct molecules by electrophoresis on polyacrylamide tube gels. The resolution of this method approaches that of high pressure liquid chromatography but at a considerably lower cost. Digestion conditions using DNase II and spleen phosphodiesterase II to yield mononucleotides and adducted bases were worked out for DNA containing 8‐methoxypsoralen or 4′‐hydroxymethyl‐4,5′,8‐trimethylpsoralen. The phosphatase activity of DNase II was shown to be much more active on dNMPs than on adducted bases. This can be exploited to reduce the background of radioactivity from labeled dNMP's trailing into the adduct peaks, thereby increasing the effective sensitivity of the technique when quantitating adducts made with non‐radioactive drug in labeled DNA. Since resolution of adducts requires dense (30%) acrylamide gels, we have devised a method for making extremely uniform high density gels by polymerization under static pressure. A continuous collection apparatus was constructed to recover material from gels. The identity of the resolved species was determined by several different methods, including analysis by HPLC.
FLUORESCENCE QUENCHING OF INDOLIC COMPOUNDS BY ALIPHATIC AMINO ACIDS. EVIDENCE FOR EXCITED STATE COMPLEXES
Authors: Bohorquez M. del V. , Cosa J. J. , Garcia N. A. , Previtali C. M.
Published: January 2008

Abstract The fluorescence quenching of indole, tryptophan, tryptamine and indole‐3‐acetic by aliphatic amino acids was studied. The bimolecular rate constant (kq) for the deactivation of the excited state was determined. The kq values were in the range 0.6 × 108–1.6 × 109M–1 S–1 and they increased in the order tryptophan < tryptamine < indole ≈ indole‐3‐acetic acid. When the rate constant was corrected for diffusion al effects a good linear correlation was found between the log (k'q) and the ionization equilibrium constant of the carboxylic group of the amino acid (pka1). This was interpreted as arising from a charge transfer mechanism in which the indole moiety acts as an electron donor and the carbonyl group of the amino acid as the acceptor.

The activation parameter for the quenching processes were also determined. The ΔH≠ values were in the range —4.0 to +4.0 kcal/mol and the ΔH≠ in the range –7 to –37 e.u. For the systems with lower values of kq negative values for ΔH≠ were observed. A good enthalpy‐entropy compensation was found with an isokinetic temperature of 229 K. These results suggest that a common mechanism is operating for all the systems and that it involves the formation of an excited state complex between the indolic compound and the amino acid.
PHOTOCHEMICAL EXCHANGE REACTIONS OF THYMINE, URACIL AND THEIR NUCLEOSIDES WITH SELECTED AMINO ACIDS
Authors: Shetlar Martin D. , Taylor John A. , Hom Kellie
Published: January 2008

The photoinduced exchange reactions of thymine with lysine at basic pH, using 254 nm light, have been studied. Three products have been isolated, namely, 6‐amino‐2‐(1‐thyminyl)hexanoic acid (Ia), 2‐amino‐6‐(1‐thyminyl)hexanoic acid (IIa) and 1‐amino‐5‐(1‐thyminyl)pentane (IIIa). Compound IIIa was shown to be a secondary product, produced by photochemical decarboxylation of Ia. Photochemical reaction of thymine with glycine and alanine at basic pH led, respectively, to formation of 2‐(1‐thyminyl)acetic acid (Ic) and 2‐(1‐thyminyl)propionic acid (Id). Compounds Ic and Id underwent photolysis to produce the decarboxylated secondary products 1‐methylthymine and 1‐ethylthymine, respectively. Thymidine reacts photochemically with glycine and alanine to produce the same products.

Irradiation of DNA in the presence of lysine at basic pH led to the formation of the same products formed in the thymine‐lysine system, namely Ia, IIa and IIIa.

Uracil was found to undergo analogous photochemical exchange reactions with lysine to form 6‐amino‐2‐(1‐uracilyl) hexanoic acid (Ib), and 2‐amino‐6‐(1‐uracilyl)hexanoic acid (IIb). Compound Ib was found to undergo photodecarboxylation to form 1‐amino‐5‐(1‐uracilyl)pentane (IIIb), analogous to the secondary photoreaction of Ia. Photoreaction of uracil with 1,5‐diaminopentane (cadaverine) likewise led to formation of IIIb.
A STUDY OF THE FLASH INDUCED 518 NM ABSORBANCE CHANGE KINETICS UNDER ANAEROBIC CONDITIONS
Authors: Popovic Radovan , Bruce Doug , Colbow Konrad , Vidaver William
Published: January 2008

The preillumination induced acceleration of the flash‐induced 518 nm absorbance change (ΔA518) decay was studied in lettuce leaves and chloroplasts. In leaves, the acceleration was inhibited by DCMU or reversibly by removal of oxygen. In chloroplasts with added ADP and phosphate and/or reconstructed electron transport, the acceleration was also inhibited by DCMU or the lack of O2.

Anaerobic inhibition of ΔA518 decay acceleration was no longer observed when hydroxylamine replaced water as electron donor to PSII. Anaerobiosis was also shown to reversibly inhibit the initial rate of FeCN reduction in chloroplasts. These results suggest the mechanism of anaerobic inhibition of ΔA518 decay acceleration to be associated with the O2 evolving system.
THE EFFECT OF MEDIUM POLARITY ON THE HEMATOPORPHYRIN‐SENSITIZED PHOTOOXIDATION OF l‐TRYPTOPHAN
Authors: Reddi Elena , Rodgers Michael A. J. , Spikes John D. , Jori Giulio
Published: January 2008

Abstract The 83 μM hematoporphyrin (HP)‐sensitized photooxidation of 0.1 mM tryptophan in aqueous solution buffered at pH 7.4 or in binary mixtures of phosphate buffer and organic solvents of higher (formamide) or lower (N,N‐dimethylformamide, methanol, ethanol, tetrahydrofuran) polarity proceeds by a pure singlet oxygen (1O2) mechanism as suggested by azide quenching experiments, the rate‐enhancing action of deuterated solvents, and the lack of any significant reaction between triplet HP and tryptophan. Both the first‐order rate constant of the photoprocess and the photooxidation quantum yield (φ= 0.011 in phosphate buffer at pH 7.4) increase when the medium polarity is increased (e.g. φ= 0.024 in 90% formamide); this results mainly from the greater quantum yield of 1O2 generation and the longer lifetime of 1O2. The intrinsic reactivity of 1O2 with tryptophan is independent of formamide concentration. A moderate decrease in the medium polarity (e.g. in the range 0‐30% methanol) enhances the efficiency of tryptophan photooxidation (φ= 0.014 in 30% methanol) as a result of the enhanced quantum yields of triplet HP and 1O2 formation. In contrast, the overall photooxidation rate is depressed at high concentrations of low‐polarity organic solvents (e.g. φ= 0.0039 in 90% methanol) due to a 5.5‐fold drop of the rate constant for the 1O2‐tryptophan reaction which counteracts the enhancement of the lifetime and quantum yield of triplet HP and 1O2. The solvent composition also affects the equilibria between monomeric and multimeric forms of HP. However, under our experimental conditions, the aggregation state of HP appears to exert only a minor influence on the efficiency of tryptophan photooxidation.
IMPROVED ANALYSIS OF TIME‐RESOLVED SINGLE PHOTON COUNTING FLUORESCENCE DATA OF EXCIMER/EXCIPLEX SYSTEMS USING A DUAL ANALYSIS ITERATED RECONVOLUTION PROGRAM ON A DEDICATED LABORATORY MICROCOMPUTER
Authors: Frye Stephen L. , Ko Jaeju , Halpern Arthur M.
Published: January 2008

Abstract A novel iterative reconvolution program for the simultaneous analysis of two sets of time‐resolved single photon counting (TRSPC) fluorescence data is described. Each set of data may be fit to a function containing up to three exponential terms and any of the parameters may be constrained to both sets. This dual analysis approach offers great advantages for the study of a coupled photokinetic scheme such as an excimer or exciplex system, both in terms of the accuracy of the results and in the simplicity and speed of the analysis.
ABSORPTION AND FLUORESCENCE STUDY OF TYROSINE‐DERIVED CROSSLINKING AMINO ACIDS FROM COLLAGEN
Authors: SAKURA S. , FUJIMOTO D.
Published: January 2008

Isotrityrosine, an isomer of trityrosine with an ether linkage, is a new crosslinking amino acid recently found in cuticle collagen of Ascaris lumbricoides. The absorption and fluorescence spectra of this new amino acid were examined and compared with other tyrosine‐derived crosslinking amino acids. Isotrityrosine showed UV absorption maximum at 283 nm in acidic and neutral solutions and at 303 nm in strongly basic solution. The wavelengths are almost the same with those at dityrosine and trityrosine. The values of pKa, for chromophore phenols are 7.5 and 11.0. This means that two proton dissociations occur progressively one by one. Boric acid did not have any influence on isotrityrosine, though the effect on dityrosine and trityrosine was substantial. These facts mentioned above may suggest structural inequality of two phenols in an ether‐linked isomer. The wavelength of emission maximum was 450 nm, which was the longest wavelength among relative compounds examined. The fluorescence quantum yield was as small as 0.027, and the value was about one‐tenth of those of dityrosine and trityrosine. Isotrityrosine was also found in cuticle collagen of other worms which belong to the phylum nematoda.
USE OF SYNTHETIC POLYNUCLEOTIDES TO CHARACTERISE AN ANTISERUM MADE AGAINST UV‐IRRADIATED DNA
Authors: L. Mitchell David , Clarkson Judith M.
Published: January 2008

UV—irradiated single‐stranded synthetic homopolymers were used to characterise an antiserum made against UV‐irradiated DNA. Using induction data obtained by reversed‐phase high performance liquid chromatography, the relative antigenicity of the polymers could be converted to relative binding affinity for each DNA photoproduct. Since no Pyr(6–4)Pyo adducts could be detected at 320 nm under these conditions, the affinity of the antiserum for this lesion could be compared with that for cyclobutane dimers. The relative binding capacity of Thy(6–4)Thy: Thy(5–6)Thy: Cyt(6–4)Cyt: Cyt(5–6)Cyt = 166: 1: 0.25: 0.062.
PROPERTIES OF A NEW STATE OF HEMATOPORPHYRIN IN DILUTE AQUEOUS SOLUTION
Authors: Ricchelli Fernanda , Grossweiner Leonard I.
Published: January 2008

Abstract —Dilute aqueous hematoporphyrin undergoes a transformation after standing at room temperature leading to a shift of the Soret peak from 395 nm to 405 nm, disappearance of visible bands I (610 nm) and IV (503 nm), a shift of the first emission band from 615 nm to 580 nm, and fluorescence polarization at room temperature. The transformation was accelerated by heating and was faster for more dilute solutions. It did not take place in ethanol, 99:1 glycerol‐water, or in small egg lecithin liposomes. It was rapid in SDS micelles and did not occur in CTAB and Triton X‐100 micelles. Low concentrations of divalent zinc and copper increased the rate of transformation, but the product was not the corresponding metal ion ligand. The transformation was fast with uroporphyrin I and fast but incomplete with hematoporphyrin derivative. The methyl esters of hematoporphyrin IX and uroporphyrin I did not transform. The tentative identification of the transformed product is a tightly‐bound linear micelle, oriented such that the central hydrogens of the free base monomer units are anti‐parallel.
ELECTRONICALLY EXCITED STATES IN MICROSOMAL MEMBRANES: USE OF CHLOROPHYLL‐a AS AN INDICATOR OF TRIPLET CARBONYLS
Authors: Cadenas Enrique , Siesi Helmut , Campa Ana , Cilento Giuseppe
Published: January 2008

Abstract —Chlorophyll‐a enhances the photoemission from the microsomeltert‐butyl hydroperoxide system without affecting the rates of O2 uptake and lipid peroxidation. This photoemission, due to energy transfer from triplet carbonyls to microsome‐bound chlorophyll‐a, shows that microsomal membranes produce a significant amount of excited triplet carbonyls during lipid peroxidation.
EFFECT OF DIETARY FAT LEVEL ON UV‐B INDUCED SKIN TUMORS, AND ANTI‐TUMOR ACTION OF β‐CAROTENE
Authors: Mathews‐Roth Micheline M. , Krinsky Norman I.
Published: January 2008

Abstract —Hairless mice (SKH‐hr strain) maintained on diets containing either 4.5 or 14.1% fat were exposed to UV‐B irradiation for a 16‐week period and tumor incidence was evaluated. The animals on the low fat diet developed tumors significantly more slowly and in smaller numbers than those on the high fat diet. In addition, a group of animals on a high fat diet (11.1%) were supplemented with β‐carotene in their food at a final level of 3%. At the end of the experiment there was no difference in the prevalence of tumors in the β‐carotene group, although these animals developed significantly fewer tumors per mouse than the control animals receiving 14.1% fat. These results would indicate that the fat level of the diet can decrease or eliminate the ability of β‐carotene to protect animals against UV‐B induced skin tumors.
PHOTOOXIDATION OF 3, 4‐DIHYDROXYPHENYLALANINE BY HEMATOPORPHYRIN IN AQUEOUS SOLUTIONS: AN ELECTRON SPIN RESONANCE STUDY USING 2, 2, 6, 6‐TETRAMETHYL‐4‐PIPERIDONE‐1‐OXYL (TEMPONE)
Authors: RESZKA K. , SEALY R. C.
Published: January 2008

Abstract— The oxidation of 3, 4‐dihydroxyphenylalanine (dopa) photosensitized by hematoporphyrin has been studied by ESR spectroscopy. The nitroxide free radical 2, 2, 6, 6‐tetramethyl‐4‐piperidone‐I‐oxyl (TEMPONE) is shown to be a convenient probe for monitoring oxygen consumption during the reaction. Isotope and azide effects on oxygen consumption suggest that photooxidation in D2O proceeds mainly by a singler oxygen mechanism, whereas in H2O both singlet oxygen and free radical mechanisms are important. The relative importance of these mechanisms can change as oxygen is consumed during the photoreaction. TEMPONE also can be used as an indicator of the presence of reducing radicals (in this case hematoporphyrin radical anions) in the system, but only at low oxygen levels: in aerated solutions efficient reaction of these radical ions with oxygen is proposed.
DIRECTIONS OF THE ELECTRONIC TRANSITION MOMENTS OF SYNTHETIC Yt BASE*
Authors: GRYCZYŃSKI I. , GRYCZYŃSKI Z. , KAWSKI A. , PASZYC S.
Published: January 2008

Abstract— Dichroism was measured for different electronic transitions (Sn←So) of Y‐4,9‐dihydro‐4,6‐dimethyl‐9‐oxo‐1H‐imidazo‐1,2‐a purine (Yt base) in anisotropic polyvinylalcohol (PVA) films. The directions of the electronic transition moments of the Yt base were determined based on the results obtained, applying the models of Tanizaki and Popov. The results were compared with relevant data obtained from quantum chemical calculations.
SPECTRAL PROPERTIES OF THE RHODOPSIN‐SYSTEM OF THE CRAYFISH Astacus leptodactylus
Authors: HAMACHER K. , STIEVE H.
Published: January 2008

Abstract— The absorption spectra of the membrane‐bound and of the digitonin‐solubilized visual pigment of crayfish Astacus leptodactylus were investigated by conventional spectrophotometry. A method was developed to isolate purified rhabdoms almost entirely free from screening pigments from a single retina. The quantity of isolated and purified rhabdoms from a single retina was sufficient to measure the absorption spectra of the visual pigment.

The absorption spectra of the chromoprotein system (R and M) show that both the membrane‐bound and the digitonin‐solubilized visual pigment isomers are stable at 0°C and pH 7.0. Rhodopsin and metarhodopsin are photoreversible under these conditions without any light‐induced denaturation. The difference spectra for the chromoprotein isomers and those of different photostationary states yield maximal values for ΔE at 570 and 485 nm.

At neutral pH, 0°C, Λmax of rhodopsin is 530 nm. Irradiation with light of Λ= 630 to 640 nm isomerizes rhodopsin nearly quantitatively to metarhodopsin with Λmax, of 500 nm. The molar extinction coefficient of metarhodopsin is greater than that of rhodopsin by a factor of ˜ 1.41. each measured at its respective Λmax Metarhodopsin can be isomerized to rhodopsin by irradiating at Λ > 630 nm. As the absorption spectra of the two chromoprotein isomers overlap, only part of the metarhodopsin can be reversed to rhodopsin. The maximal photoreversion can be achieved by irradiating at 460 nm. The stability of the digitonin‐solubilized chromoprotein is remarkably dependent on temperature. Warming the digitonin extract of rhabdoms from 0 to 20 or 30°C caused a shift of the rhodopsin spectrum to shorter wavelengths (Λmax= 485 nm) accompanied by a decrease of EΛmax by about 30%.
PHOTOCHEMISTRY OF PORPHYRINS: A MODEL FOR THE ORIGIN OF PHOTOSYNTHESIS*
Authors: MERCER‐SMITH JANET A. , MAUZERALL DAVID C.
Published: January 2008

Abstract— A series of porphyrins and catalysts has been prepared as a model for the origin of photosynthesis on the primordial earth. These compounds have been used to test the hypotheses that (1) the biosynthetic pathway to chlorophyll recapitulates the evolutionary history of photosynthesis, and (2) the proto‐photosynthetic function of biogenetic porphyrins (biosynthetic chlorophyll precursors) was the oxidation of organic molecules by photoexcited porphyrins with the attendant emission of molecular hydrogen.

This paper describes experiments in which photoexcited biogenetic porphyrins oxidize ethylenediamine tetraacetic acid (EDTA). The concomitant reduction of protons to hydrogen gas occurs in the presence of a colloidal platinum catalyst. The addition of methyl viologen, a one‐electron shuttle, increases the amount of molecular hydrogen generated during long irradiations and the quantum yield of hydrogen production. When the porphyrin and catalyst are held in association by molecular complexes, the increased efficiency of electron transfer produces higher yields of hydrogen gas.
TRIPLET FORMATION AND TRIPLET DECAY IN REACTION CENTERS FROM THE PHOTOSYNTHETIC BACTERIUM Rhodopseudomonas sphaeroides
Authors: SCHENCK C. C. , MATHIS P. , LUTZ M.
Published: January 2008

Abstract— In the reaction center of photosynthetic bacteria, with the primary ubiquinone reduced, the triplet state PR of the primary electron donor (a pair of bacteriochlorophylls named P) is PO ulated with a takes place in a few ns. We measured by flash absorption spectroscopy the influence of temperature on formation and decay kinetics of PR and 3Car in the reaction center of several strains of R. sphaeroides. The rate of triplet energy transfer, measured as the decay of PR after a flash, decreases when the temperature is lowered. Between 60 and 30 K the half‐time of energy transfer becomes longer than the 3Car half‐time decay (about 6 μs) and below 20 K the transfer is slower than the internal decay of PR (about 100 μs). In several cases it is clear that PR and 3Car decay independently and are not in thermal equilibrium. The singlet energy transfer from carotenoid to P occurs with a high efficiency at all temperatures.

The data can be accounted for on the basis of estimated energy levels of PR and 3Car, in the context of the equilibrium 3P ←3D where 3P is the localized triplet state of P‐870 and 3D is another triplet state. A reasonable kinetic scheme leads us to estimate that 3D is 0.0025 ± 0.005 eV above 3P. 3D may thus be the state observed by Shuvalov and Parson (1981). We propose that both triplet and singlet energy transfer between P and the carotenoid occur via a bacteriochlorophyll, to which the carotenoid should be tightly coupled via exchange interaction.
FURTHER CHARACTERIZATION OF MONOCLONAL ANTIBODY INDICATES SPECIFICITY FOR (6–4)‐DIPYRIMIDINE PHOTOPRODUCTS
Authors: Strickland P. T. , Nikaioo O. , Matsunaga T. , Boyle J. M.
Published: January 2008

Abstract

Monoclonal antibody aUVssDNA‐1 is produced by hybridoma cell line 25JF.C3B6 originally selected from cell fusions using spleen cells from mice immunized with UV‐irradiated polydeoxynucleotides (Strickland and Boyle, Photochem. Photobiol.34, 595–601, 1981). Original and subsequent studies of the binding characteristics of aUVssDNA‐1 indicated that it was specific for cyclobuta‐dithymidine photoproducts. Those investigations examined action spectrum, short‐wavelength photo‐reversal, nucleotide sequence effects, and photoreactivation using E. coli photolyase and incandescent tight. However, the more recent studies reported here examined acetophenone‐UV‐B photosensitization, UV‐B photoisomerization, and photoreactivation using cloned E. coli photolyase and filtered incandescent light. The results indicate that aUVssDNA‐1 recognizes photoproducts with characteristics of (6–4)‐dipyrimidines. Thus, previous studies in which relatively rapid repair of cyclobuta‐dithymidine photoproducts was inferred using this antibody, require re‐interpretation in light of these new findings.
EXCITED STATES OF DNA and ITS COMPONENTS AT ROOM TEMPERATURE–V. SPECTRAL, POLARIZATION and QUANTUM YIELD STUDIES OF CYTIDYLYL‐(3‘,5’)‐ADENOSINE
Authors: Shaar Casey S. , Morgan James P. , Daniels Malcolm
Published: January 2008

Abstract— The corrected normalized emission spectrum, quantum yield, and emission anisotropy are reported for partially‐stacked CpA excited at 266 nm. Utilizing parameters determined separately for cytidine and AMP, the emission spectrum of CpA is quantitatively resolved into components characteristic of the two monomers plus a red shifted emission characteristic of complex formation. The results fit accurately to a simple stacking model in which monomer‐like fluorescence originates only from the unstacked fraction and “complex” fluorescence from the stacked fraction. It is shown that the stacked fraction absorbs in a manner qualitatively distinct from the unstacked fraction and the “complex” emission is really the excited state of a ground state complex. This emission, which peaks at 440 nm and contains at least two species can be resolved into three Gaussian components. It is suggested that the emitting species may originate in distinct stacked conformations.