bluuebunny/crossref_metadata_2025 huggingface dataset:
PHOTOADDITION OF 8‐METHOXYPSORALEN TO E. coli DNA POLYMERASE I. ROLE OF PSORALEN PHOTO‐ADDUCTS IN THE PHOTOSENSITIZED ALTERATIONS OF POL I ENZYMATIC ACTIVITIES
Authors: Granger Michele , Héène Claude
Published: January 2008

Abstract— We have previously demonstrated that 8‐methoxypsoralen (8‐MOP)‡ plus UVA is able to inactivate the three enzymatic activities of E. coli DNA polymerase I and that oxygen is required for these reactions (M. Granger et al., (1982) Photochem. Photobiol., 36, 175–180). We now show that UV‐A irradiation produces a covalent incorporation of the psoralen derivative into the enzyme either in the presence or in the absence of oxygen. The excited psoralen binds directly to the protein in an oxygen‐independent reaction; no complex was detected in the absence of irradiation. Fluorescence measurements reveal that at least two photoadducts are formed.

The 8‐MOP‐photomodified enzyme is still fully active but further irradiation leads to an inhibition of the 5′→ 3′ polymerase activity whereas the 5′→ 3′ exonuclease activity is not affected. A major part of the inhibition reaction is shown to be oxygen‐dependent but singlet oxygen quenchers have no effect on the kinetics. This oxygen‐dependent reaction is attributed to a photosensitization, due to covalently bound 8‐MOP, of neighbouring amino acids through an intermediate reactive oxygen species which is not singlet oxygen. The oxygen‐independent reaction is attributed to a direct photosensitization through, for example, a radical mechanism.
PROMOTIONAL EFFECTS OF ULTRAVIOLET RADIATION ON HUMAN BASAL AND SQUAMOUS CELL CARCINOMA
Authors: Rundel R. D.
Published: January 2008

Abstract— Recent data on the incidence of basal and squamous cell skin cancer among Caucasians in eight regions of the United States have been analyzed. Principal conclusions are that (1) ultraviolet radiation is an effective promoter of non‐melanoma skin tumors; (2) the probability of a skin tumor becoming observable in an individual of some given age is well described by the log‐normal distribution: (3) the fluence‐response relation for both basal and squamous cell tumors is linear with a positive intercept, although the parameter values are clearly different for the two types; (4) a 1% ozone layer depletion would lead to an eventual 1.7% increase in basal cell carcinoma, and a 2.3% increase in squamous cell carcinoma.
ASCORBIC ACID AS A PHOTOOXIDATION INHIBITOR
Authors: Rooney Michael L.
Published: January 2008

Abstract— The rate constant for total quenching of singlet oxygen by ascorbic acid has been determined using the inhibition of the bleaching of 9, 10‐dimethylanthracene by AA in pyridine. The rate constant was 8.4 × 10‐6M‐1 s‐1, as determined photochemically, and 1.06 10‐7M‐1 s‐1 as determined in a dark reaction.
REGULATION OF PROTOCHLOROPHYLL(IDE) LEVELS IN DARK‐GROWN NON‐DIVIDING Euglena—I. CONTROL BY LIGHT*
Authors: Alhadeff Myriam , Coronado Roberto , Figueroa Nara , Schiff Jerome A.
Published: January 2008

Abstract—

Dark‐grown cells of Euglena gracilis var. bacillaris contain low levels of protochlorophyll(ide) [Pchl(ide)] which absorbs at 635 nm in vivo. When growing cells are placed on a resting medium, cell division ceases after 3 days and the levels of total extractable and phototransformable Pchl(ide) decrease, reaching a new plateau at one‐half the original concentration by 7 days of resting. Phototransformable Pchl(ide) can be induced to regenerate to the original levels found in dark‐grown cells by treatment with light. The optimum conditions are 40 min of white light (0.2–0.3 W/m2) followed by 1 h of darkness. Although reciprocity between fluence rate and duration of illumination was not observed in this system, it was possible to determine the effectiveness of various spectral regions for the regeneration of phototransformable Pchl(ide) as a function of fluence rate. Blue light (400–510 nm) was most effective followed closely by green (490–590 nm); red light (610–720 nm) was relatively ineffective. The results suggest that phototransformable Pchl(ide) is regulated to achieve the levels ordinarily found in dark‐grown cells and that the blue photoreceptor system, rather than Pchl(ide) itself, is probably the light receptor for Pchl(ide) regeneration.
PHYTOCHROME CONTROL OF ITS OWN SYNTHESIS IN Sorghum vulgare AND Avena sativa
Authors: Otto V. , Mousinger E. , Sauter M. , Schäfer E.
Published: January 2008

Abstract—

The accumulation of phytochrome in the dark was measured for Avena sativa seedlings after a white light pretreatment and for Sorghum vulgare seedlings after continuous red or far‐red light treatments, using the herbicide Norflurazon to prevent greening under continuous irradiation. In both cases the accumulation of phytochrome depends on the state of the phytochrome at the light‐dark transition: high Pfr levels (red light pulse) led to a slower rate of phytochrome accumulation than lower Pfr levels (long wavelength far‐red (RG 9) light pulse). Poly‐(A+)‐RNA was isolated fromA. sativa seedlings grown for 48 h in darkness + 24 h WL + light pulse (5 min) (red, RG 9 light, red followed by RG 9 light or RG 9 followed by red light pulse) + 19 h darkness. The poly‐(A+)‐RNA was translated in a rabbit reticulocyte lysate system and the translation products were immunoprecipitated by specific anti‐phytochrome antibodies. It was demonstrated that the activity of mRNA coding for phytochrome was under phytochrome control.
THE TRIPLET EXTINCTION COEFFICIENTS OF SOME BACTERIAL CAROTENOIDS
Authors: Cogdell R. J. , Land E. J. , Truscott T. G.
Published: January 2008

Abstract—

The extinction coefficients of the triplet states of the bacterial carotenoids, neurosporenc (Λmax 489 nm). sphcroidene (Λmax 510 nm). spheroidenone (Λmax 550 nm) and spirilloxanthin (Λmax 550 nm) in cyclohexane have been determined to be 27.4. 30.9. 6.06 and 9.20 × 104 dm3 mol−1 cm1, respectively. These values were obtained by an energy transfer technique using a range of carotenoid concentrations. For the three that had been studied earlier, the extinctions now obtained are suhstantially higher than prcviously reported.
FLAVIN‐SENSITIZED PHOTODYNAMIC MODIFICATION OF MULTISUBUNIT PROTEINS
Authors: McCarron Sara H. , Tu Shiao‐Chun
Published: January 2008

Abstract— Riboflavin 5'‐phosphate (FMN)‐sensitized photodynamic modifications of multisubunit alcohol dchydrogenase, bacterial luciferase. L‐glutamate dehydrogenase, and catalase all lead to significant formation of crosslinked species. On the contrary, irradiation of monomeric lysozyme, trypsin inhibitor, trypsin, and bovine serum albumin in the presence of FMN yields either no or only trace amounts of polymerized molecules. Photodynamic modifications thus appear to be much more efficient in crosslinking proteins with quaternary structures in their native forms. While no photodegradations of other proteins were found, FMN‐sensitized modifications of the nonidentical dimeric (αß) bacterial luciferase resulted in the formation of two degraded fragments as well as two polymerized species. Singlet oxygen is shown to be involved in the photopolymerization of luciferase but it is unclear whether singlet oxygen is the sole species active in initiating the crosslinking reaction(s). FMN also sensitizes effective inactivations of luciferase which can be attributed to actions of singlet oxygen, triplet FMN, H2O2. and superoxide anion. Photodynamic inactivation of luciferase proceeds faster than photopolymerization; these processes are thus not coupled.
1H AND 13C PHOTO‐CIDNP STUDY OF AQUEOUS CHLORPROMAZINE AND ANALOGS*
Authors: Marko J. , Vermeersch G. , Febvay‐Garot N. , Caplain S. , Lablache‐Comboer A.
Published: January 2008

Abstract— The photochemical reaction in aqueous solutions of several phenothiazines with an N‐alkylamine chain, and their salts, is studied by means of Chemically Induced Dynamic Nuclear Polarization (CIDNP)¶. The particular behaviour of chlorpromazine hydrochloride is outlined and evidence is shown for the existence of a substitution product with the solvent at the α‐carbon atom of the side‐chain, and an aldehydic derivative resulting in the cleavage of that one. Radical‐ions pairs of CPZ are involved in both processes.
PHOTO‐EXCITED TRIPLET STATE OF DIMERIC CHLOROPHYLL a IN 3‐METHYLPENTANE RIGID MATRIX AT 77 K STUDIED BY FLASH PHOTOLYSIS
Authors: Hoshino M. , Imamura M. , Koike K. , Kikuchi K. , Kokubun H.
Published: January 2008

Abstract— Flash photolysis studies of dimeric and monomeric chlorophyll a were carried out at 77 K. The triplet‐triplet absorption spectrum of the dimeric chlorophyll a in 3‐methylpentane at 77 K is interpreted as a sum of the spectra of chlorophyll a in the ground and triplet states. The dimeric chlorophyll a in the triplet state is considered to have the half‐excited structure at 77 K without photodisaggregation owing to high viscosity of the solvent.
WAVELENGTH DEPENDENCE OF INACTIVATION and MUTAGENESIS IN HAPLOID YEAST CELLS OF DIFFERENT SENSITIVITIES
Authors: Zölzer F. , Kiefer J.
Published: January 2008

The wavelength dependence of inactivation and mutagenesis in the range between 254 and 313 nm was investigated in haploid cells of the yeast Saccharomyces cerevisiae. The action spectra for a wild type and an excision deficient mutant essentially corresponded to those for bacteria and mammalian cells. There were, however, minor differences. The ratio of mutagenic to lethal action decreased with increasing wavelength in the wild type, but remained constant in the excision deficient mutant. This is discussed in terms of error‐prone and erro‐free repair. For both inactivation and mutagensis, photorcactivability was lower with longer wavelengths in the wild type, but did not change in the excision deficient mutant. Implications for the role of pyrimidine dimers are considered.
SINGLE‐STRAND DNA BREAKS INDUCED BY 365 NM RADIATION IN ESCHERICHIA COLI STRAINS DIFFERING IN SENSITIVITY TO NEAR and FAR UV
Authors: Tuveson R. W. , Peak J. G. , Peak M. J.
Published: January 2008

The gene mutation nur has been shown specifically to sensitize Escherichia coli stationary phase cells to inactivation by broad spectrum near‐UV (NUV) radiation. In the work reported here, E. coli strains RT1. RT2, RT3, and RT4, carrying the 4 possible combinations of recA1, recA+, nur, and nur+, were exposed to monochromatic NUV (365 nm). The strains carrying the nur allele (RT1 and RT2) were more sensitive to inactivation by this wavelength and exhibited considerably more single strand break's (SSB's) than the strains carrying the nur+ allele (RT3 and RT4). As predicted, following X‐irradiation the strains carrying the recA1 allele (RT1 and RT3) were more sensitive than the recA+ strains (RT2 and RT4). We conclude that the enhanced SSB's observed in strains RT1 and RT2 following monochromatic NUV irradiation correlated with the nur mutation and are unrelated to the recA1 mutation.
IDENTIFICATION OF A LUMAZINE PROTEIN FROM PHOTOBACTERIUM LEIOGNATHI BY COHERENT ANTI‐STOKES RAMAN SPECTROSCOPY
Authors: Vervoort Jacques , O'Kane Dennis J. , Carreira Lionel A. , Lee John
Published: January 2008

The vibrational fingerprint in the frequency region 1700‐1100 cm‐1 has been obtained for a fluorescent protein purified from the bioluminescent bacterium Photobacterium leiognathi. using the technique of resonance coherent anti‐Stokes Raman scattering. The frequencies of the 4 prominent modes are the same as for lumazine protein purified from Photobacterium phosphoreum, and for an authentic sample of 6,7‐dimethyl‐8‐ribityllumazine. The fluorophore in the new protein, therefore, must have the same chemical structure. The absence of frequency shifts between the free and bound ligand, in contrast to observations of fiavoproteins, implies that the lumazine ring undergoes no changes in hydrogen bonding between the free and protein‐bound ligand in its ground electronic state. However, changes in relative intensities of two modes are seen, arising from differences in interactions in the excited state, and this is also reflected by differences in fluorescence properties.
LIQUID‐CRYSTALLINE PHASE TRANSITION OF MONOMOLECULAR LAYERS OF CHLOROPHYLL a*
Authors: Heithiert H. , Ballschmiter K. , Mohwald H.
Published: January 2008

Monomolecular layers of chlorophyll a at the air‐water interface were investigated by absorption spectroscopy and simultaneous thermodynamic measurements. Whereas at temperatures near 20°C at all pressures, only a liquid phase exists, at a temperature of 4°C, a liquid‐crystalline phase transition is observed at a surface pressure of 5 dynes/cm. Pressure‐induced changes in the chlorophyll arrangement become evident from a drastic change in the absorption spectra, accompanying the phase transition. The crystalline phase exhibits an extremely narrow absorption band (halfwidth below 9 nm) centered at 698 nm, indicative of a coplanar chlorophyll arrangement in a well‐ordered environment. It is highly probable that in these model membranes a chlorophyll arrrangement could be established that is equivalent to the one proposed for the reaction center P700.
HEMATOPORPHYRIN PHOTOSENSITIZATION OF SERUM ALBUMIN and SUBTILISIN BPN'
Authors: Richard Philippe , Blum Aleksander , Grossweiner Leonard I.
Published: January 2008

—The photosensitized inactivation of subtilisin BPN' by free hematoporphyrin (HP) followed exponential kinetics with positive mechanistic tests for the involvement of singlet oxygen (1O2) as the principal intermediate. The photoinactivation quantum yield was 0.029 at 390 nm in oxygen‐saturated, D2O buffer at pH 7.0. The effects of HP binding were investigated for tryptophan oxidation in bovine serum albumin (BSA) and human serum albumin (HSA) at high protein:HP concentration ratios where the HP was > 97% complexed. The reaction kinetics were non‐exponential and mimick a second‐order process in the initial stages. The rate of HP photobleaching was 30‐fold faster for complexed HP compared with free HP, which was shown to account for the observed kinetics. Mechanistic tests showed that 1O2 was the dominant photooxidizing intermediate of tryptophan residues and that it was not involved in the accompanying photobleaching of HP. The quantum yield for tryptophan oxidation in BSA was 0.11 at 390 nm in oxygen‐saturated, D2O buffer at pH 8.0. The reactivity of HSA was approximately 2‐fold lower than BSA for equivalent conditions. Estimates of the reaction cross sections led to 3 Å2 for the inactivation of subtilisin BPN' by 1O2 and 20 Å2 for the oxidation of tryptophan in BSA.
INTRODUCTION OF PYRIMIDINE DIMERS INTO DIFFERENT INTRACELLULAR FORMS OF SIMIAN VIRUS 40
Authors: Edenberg Howard J. , Roman Ann
Published: January 2008

We examined the production of pyrimidine dimers by UV radiation in different intracellular forms of simian virus 40 DNA. Virus and chromatin or previrions were selectively labeled with [l4C]‐thymidine and [3H]‐thymidine, respectively, in the same monolayer of infected cells. Viral DNA was extracted immediately after irradiation, and pyrimidine dimers were detected as sites sensitive to the UV‐endonuclease encoded by bacteriophage T4. No difference in the number of dimers introduced into chromatin, previrions. or virions was detected.
ARTIFICIAL PHOTOSYNTHESIS: QUANTUM CAPTURE and ENERGY STORAGE
Authors: Calvin Melvin
Published: January 2008

Organized systems are described to achieve separation of the charges produced by quantum absorption in a sensitizer, and their stabilization in separated chemical form. These systems involve phase boundary charge separation by both membranes and charged particles, in both cases simulating the natural system.
SINGLET AND TRIPLET ENERGY TRANSFER IN α‐DIKETONE DERIVATIVES OF URACIL and THYMINE
Authors: Lee Y.J. , Burr J. G.
Published: January 2008

Irradiation of 1‐(3,4‐dioxopentyl)uracil (UPD) and 1‐(3.4‐dioxopentyl)thymine (TPD) in acetonitrile solution at 25°C, at the wavelength (280 nm) where only the pyrimidine absorbs the light, sensitizes both fluorescence and phosphorescence of the diketone chromophore in the sidechain. From comparison of the intensity in the corrected excitation spectra with the absorption spectra in acetonitrile solution, it was estimated that the yield of singlet energy transfer in UPD was 0.17 and in TPD was 0.44. It was also observed that the ratio of phosphorescence to fluorescence was greater in the sensitized emission than in that from direct excitation of the diketone chromophore. The yield of triplet energy transfer thus measured corresponds to minimum values for the yields of intersystem crossing from singlet excited state to triplet excited state of 0.075 in the uracil chromophore of UPD and of 0.14 in the thymine chromophore of TPD. These are in agreement with other recent values for these quantities. The value of this type of system as an intramolecular triplet counter is discussed.
PHOTORECEPTIONS IN THE ECLOSION OF THE SILKWORM, Bombyx mort
Authors: Shimizu Isamu , Matsui Kei
Published: January 2008

When silkworms, Bombyx mori, were kept in a photoperiodic regime of LD 8:16 during pupal development, the moths showed overt bimodal eclosion rhythms with one peak in the dark period, and with the other peak at light‐on. When the developing pupae were transferred from the photoperiodic cycle to continuous darkness, the eclosion of the dark period persisted with a free‐running circadian rhythm, while the eclosion corresponding to the light‐on peak was not shown. Vitamin A‐deficiency. which brought about a loss of photoreceptive function in compound eyes, significantly reduced the light‐on peak, but did not influence the timing of eclosion in the dark period. Covering compound eyes with black wax also reduced the light‐on peak. These results show that the eclosion clock of the silkworm is most likely entrained by an extraretinal photoreceptor, but the eclosion at light‐on is evoked by an exogenous light effect that is mediated via compound eyes
A NEW REUSABLE CHEMICAL ACTINOMETER FOR UV IRRADIATION IN THE 248 ‐ 334 nm RANGE
Authors: Brauer H.‐D. , Schmidt R.
Published: January 2008

The highly reversible thermally stable photochromic system consisting of heterocoerdianthrone‐endoperoxide (HCDPO) and its parent compounds HCD and 02 is proposed as a new reusable liquid chemical actinometer in the UV region 248 ≤λ≤ 334 nm. The foremost advantageous features of this new system are: (1) high reproducibility and accuracy, (2) high sensitivity, (3) almost wavelength independent quantum yields, (4) no loss in accuracy even after 100 repeated actinometric cycles and (5) very easy handling and straightforward calculability of the radiation quantum flux.
PREPARATION AND PROPERTIES OF CHLOROPHYLL/WATER‐SOLUBLE MACROMOLECULAR COMPLEXES IN WATER. STABILIZATION OF CHLOROPHYLL AGGREGATES IN THE WATER‐SOLUBLE MACROMOLECULE
Authors: Inamura Isamu , Ochiai Hideo , Toki Kenzi , Watanabe Sachiko , Hikino Satomi , Araki Takeo
Published: January 2008

Abstract— As an artificial model compound of the chlorophyll‐protein complex in vivo, the chlorophyll/water‐soluble macromolecular complexes were prepared by using synthetic linear polymers of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG), and a natural polymer of bovine serum albumin (BSA). By the method described here, it is possible to prepare an aqueous chlorophyll (Chl)‐macromolecular complex solution of a desired Chi aggregate, such as: Chi a(670), Chi a(740) and Chi b; and with a desired relative content and concentration. These procedures for preparing such complexes will have wide applicability for technical use in Chi studies. For example, extremely diluted aqueous complex solutions of at least 1 × 10‐4% wt Chi a(670 or 740)‐macromolecular complex / wt can be obtained without changing the spectral features. From viscosity measurements, the structures of the complexes were inferred: (1) for a linear macromolecular (PVA or PVP) complex, a Chi species is tightly surrounded by a chain of the polymer causing shrinkage of the chain; (2) globular BSA molecules surround Chi species to form a large complex. The mechanism of stabilization of Chi aggregates in thylakoid membrane was discussed concerning an analogy to the complexes studied here.
ON THE TYROSINATE INVOLVEMENT IN THE SCHIFF BASE DEPROTONATION IN THE PROTON PUMP CYCLE OF BACTERIORHODOPSIN
Authors: FUKUMOTO JOSEPH M. , HANAMOTO JANE H. , EL‐SAYED M. A.
Published: January 2008

Abstract— The ultraviolet transient absorption assigned to the tyrosinate species in bacteriorhodopsin is followed in time and as a function of pH. Both its rise time and titration curve closely resemble those observed for the production of the M412 intermediate. These results may support a recently proposed mechanism that couples tyrosinate production to the Schiff base deprotonation in the proton pump of bacteriorhodopsin.
SPECTROSCOPIC PROPERTIES AND PHOTOREACTIVITY WITH DNA OF NEW MONOFUNCTIONAL PYRIDOPSORALENS
Authors: BLAIS J. , VIGNY P. , MORON J. , BISAGNI E.
Published: January 2008

Abstract— New psoralen derivatives have been synthesized in order to enhance their affinity towards DNA. The spectral properties (absorption, fluorescence emission, fluorescence quantum yield) and the photostability of pyrido[3,4‐c]psoralen are first reported. The drastic changes observed in the solubility and in the fluorescence emission when these compounds are added to native DNA give evidence of the formation of non covalent dark complexes. Upon UV irradiation (365 nm) of the complexes, a photobinding occurs. Heat denaturation and renaturation experiments of modified DNA show that only monoadducts are formed. From the analysis of their fluorescence properties the involvement of the 4′, 5′ double bond is assumed. The monofunctional character has also been established for psoralens having a fused pyridine ring in the 4′, 5′ site. On the opposite, a fused tetrahydropyrido group in the 4′, 5′ site is inefficient to inactivate this reactive site.
PHOTO‐ELECTRIC EFFECTS IN BILAYER MEMBRANES; ELECTROMETERS AND VOLTAGE CLAMPS COMPARED
Authors: HUEBNER JAY S. , ARRIETA RODOLFO T. , ARRIETA IRIS C. , PACHORI PAPPI M.
Published: January 2008

Abstract— Laser flash induced voltage transients recorded with high speed electrometers are compared to signals generated by voltage clamps, using chromophores which generate photo‐electric effects in membranes by different mechanisms and with time constants that varied from < 100 ns to > 1 s. The chromophores used were; (i) azo dye, 3,3‐bis‐(α‐(trimethylammonium)methyl) azobenzene‐bromide, (ii) cyanine dye, 3,3‐dimethyl‐2,2‐oxacarbocyanine‐chloride, (iii) xanthene dye, 2,4, 5, 7‐tetraiodofluorescein or erythrosin, and (iv) chlorophyll a. A scheme for classifying photo‐electric effects is presented. Voltage clamp signals are functions of both apparatus and photo‐current time constants. They vary with aqueous solution salt concentration, and usually mask kinetic information that may be obtained with electrometers.
THE PURPLE MEMBRANE PROTON PUMP: A MECHANISTIC PROPOSAL FOR THE SOURCE OF THE SECOND PROTON*
Authors: SELTZER STANLEY , EHRENSON STANTON
Published: January 2008

Abstract— A mechanistic proposal is presented to account for the observation that two protons are pumped for each turnover in the photocycle of bacteriorhodopsin. One of the protons pumped presumably arises from the deprotonation of the Schiff base as suggested by others. Photoexcitation of retinal is known to result in substantial positive charge development in the six membered ring of the chromophore. It is suggested that the other proton pumped comes from a proteinic Brönsted acid group located close to the cyclohexenyl ring of the bound chromophore. Calculations indicate that the acidity of such a suitably placed Brönsted acid can be increased 3 to 5.5 pK units by virtue of a purely electrostatic effect if 0.2 units of additional positive charge develops atC–5 of the chromophore in its excited state. Two other observations: (a) the bathochromic shift and (b) the deuterium isotope effect in the formation of the first intermediate (bR568→hv K610) are also shown to be consistent with this mechanistic proposal.
QUALITATIVE STUDIES OF THE LOW TEMPERATURE PHOTOCHEMISTRY OF RHODOPSIN AND RELATED PIGMENTS
Authors: WADDELL WALTER H. , LECOMTE JULIETTE , WEST JOHN L. , YOUNES USAMA E.
Published: January 2008

Abstract— Rhodopsin, the isomeric pigments formed from 9‐cis‐ and 9, 13‐dicis‐retinal, and the synthetic pigments formed from 9‐cis‐ and 11‐cis‐14‐methylretinal were irradiated with 490 nm light at ‐196C. Absorption spectral changes indicate that a distinguishable bathorhodopsin type intermediate may be formed for each pigment. The bathorhodopsin intermediates of the 9‐cis pigments have band maxima hypsochromically shifted by4–5 nm compared to their corresponding rhodopsins. The bathorhodopsin type intermediate formed upon irradiation of 9, 13‐dicis‐rhodopsin has an absorption that maximizes 6 nm shorter than that of rhodopsin. Band maxima of the bathorhodopsin intermediates of the 14‐methylrhodopsins are bathochromatically shifted ca. 8 nm compared to their corresponding rhodopsins.
SEARCH FOR SINGLET OXYGEN LUMINESCENCE IN THE DISPROPORTIONATION OF HO2/O2
Authors: Arudi Ravindra L. , Bielski Benon H. J. , Allen Augustine O.
Published: January 2008

Abstract— During the reaction HO2+ HO2 (or O2‐) = H2O2+ O2 in aqueous solution, no luminescence in the region 620–720 nm, expected if the product O2 were formed in a singlet state, could be detected. If any singlet O2 is formed, its yield must be less than 10%. Faint luminescence, sometimes found at shorter wavelengths, was shown to arise from reaction of HO2 with impurities in the reagents present.
EVIDENCE FOR THE PRODUCTION OF SINGLET OXYGEN BY PHOTOEXCITED ACRIDINE ORANGE
Authors: Decuyper J. , Houba‐Héin N. , Calberg‐Bacq C. M. , Van De Vorst A.
Published: January 2008

Abstract In contrast to previous results obtained with the nitroxide radical detection technique, generation of the specific 1O2 oxidation product of cholesterol shows that photoexcited acridine orange produces singlet oxygen.
THE REDUCTIVE PHOTOALKYLATION OF FLAVIN BY N‐ALLYLTHIOUREA
Authors: Ott Ulrich , Traber Rainer , Hemmerich Peter , Kramer Horst E. A.
Published: January 2008

Illumination of flavin in the presence of N‐allythiourea (ATU) inhibits catalytic turnover of flavin between its reduced and oxidized redox states by adduct formation, the adduct being no longer reoxidisable by oxygen. The first step in the mechanism of adduct formation is an electron transfer from ATU to flavin in the photoexcited triplet state. In further steps, the ATU radical cation deprotonates, electronic rearrangement occurs and radical combination with the flavosemiquinone follows, yielding a cyclic product in which ATU is added in the 4a‐ and 5‐position to the flavin chromophore.

Reaction rates and yields were determined by flash photolysis and continuous illumination. A photochemical study by variation of the molecular structure of ATU was undertaken to prove the proposed mechanism and to determine the structural requirements of flavin inactivators.
ASSOCIATION OF POLAR LIPIDS TO SPINACH SUBCHLOROPLAST FRACTIONS EVOLVING OXYGEN
Authors: Farineau N. , Guillot‐Salomon T. , Tuquet C. , Farineau J.
Published: January 2008

An O2‐evolving photosystem II (PSII) fraction was isolated from spinach chloroplasts using Triton X‐100. The distribution of polar lipids is different from that in thylakoids: the ratio monogalactosyldiacylglycerol/digalactosyldiacylglycerol being higher and the level of sulfoquinovosyldiacylglycerol being lower in the PSII fraction. A large amount of phosphatidylglycerol containing trans‐Δ3‐hexadecenoic remains associated to the PSII fraction. A possible role for molecules of phosphatidylglycerol containing trans‐Δ3‐hexadecenoic acid in the regulation of energy transfer between the two photosystems is suggested.
CHROMOPHORE OF A LONG‐LIVED PHOTOPRODUCT FORMED WITH METARHODOPSIN III IN THE ISOLATED FROG RETINA
Authors: Azuma Masami , Azuma Katsu
Published: January 2008

Abstract Long‐lived photoproducts of frog rhodopsin in isolated retina and digitonin solution have been investigated by spectrophotometry and their chromophores have been analyzed by high‐pressure liquid chromatography (HPLC). By irradiation (> 560 nm) at 3°C and pH 8.6, a product analogous to metarhodopsin III (MIII) is formed, whose absorption maximum is at about 450 nm. This product decays more slowly than MIII does. The results of HPLC analysis indicate that the chromophore of this photoproduct is 7‐cis retinal and that of MIII is all‐trans retinal. The product possessing 7‐cis retinal is called 7‐cis photoproduct. The amount of 7‐cis isomer in rhodopsin solution irradiated at various temperatures between 15°C and –82°C, has been determined. The results suggest that the 7‐cis photoproduct can be formed by the photoconversion of lumirhodopsin and metarhodopsin I.
EVALUATION OF THE COMPLEXITY OF CHARGE RECOMBINATION KINETICS IN PHOTOSYNTHETIC BACTERIA*
Authors: Woodle Martin C. , Bustamante Peggy L. , Zebrowski‐Morrison Karen E. , Loach Paul A.
Published: January 2008

Abstract Improvements in instrumentation and methodology have allowed us to collect data of high signal to noise and reliability on the kinetics of recovery of both light‐induced absorbance changes and ESR signals at 95 K. The results obtained by the two methods are identical and can not be fit with a single exponential curve. The decay kinetics can be fit well with three exponential components which represent 85, 9 and 6% of the total change with rate constants of 29 s−1, 69 s−1 and 2.3 s−1, respectively. An interesting effect by molecular oxygen on the relaxation time of the donor cation radical was found by ESR measurements at low temperatures and higher microwave power. This interaction with oxygen could be blocked by addition of small amounts (e.g. 0.05%) of organic solvents such as ethanol. A variety of systems were examined including R. rubrum whole cells and chromatophores prepared from R. rubrum and Rps. sphaeroides. R. rubrum chromatophore samples were examined at high and low light intensities, at pH values from 6 to 10, in the presence and absence of air and after equilibration in D2O media. In all cases, the same decay kinetics were observed. It seems possible that the observed complex decay may be a characteristic of phototraps of all photosynthetic material and reflect fundamental structural and functional features yet to be uncovered.
THE INFLUENCE OF LIGHT ON THE NON‐DIAPAUSE RELATED ASPECTS OF DEVELOPMENT AND REPRODUCTION IN INSECTS
Authors: J. R. Philogene Bernard , McNeil Jeremy N.
Published: January 2008

A literature review was undertaken to evaluate the effects of light on larval development and adult reproduction excluding diapause. Shortening or lengthening of larval developmental time, adult emergence, gametogenesis, fecundity and oviposition are all affected by both photoperiod and light quality.
EFFICIENCY OF REPAIR OF PYRIMIDINE DIMERS AND PSORALEN MONOADDUCTS IN NORMAL AND XERODERMA PIGMENTOSUM HUMAN CELLS
Authors: Cleaver James E. , Charles Wayne C. , Kong Seouk Hwan
Published: January 2008

Abstract —Repair of DNA damage produced by ultraviolet light or 5‐methylisopsoralen in normal and xeroderma pigmentosum human cells involves many similar steps. Aphidicolin and cytosine arabinoside block repair of both kinds of damage with similar efficiency, indicating that DNA polymerase a has a major role in repair for these lesions. In xeroderma pigmentosum cells of various complementation groups, the relative efficiency of excision repair for both ultraviolet‐ and 5‐methylisopsoralen‐induced damage was group A < C < D, indicating a close resemblance between both kinds of lesions in relation to the repair deficiencies in these groups. At high doses, the maximum rate of repair of damage by ultraviolet light was about twice that for methylisopsoralen damage, possibly because ultraviolet‐induced damage forms a substrate that is more readily recognized and excised than that of the psoralen adducts. Differences in the structural distortions to DNA caused by these kinds of damage could be detected using single strand specific nucleases which excised dimers but not 5‐MIP adducts from double strand DNA.
LOW AND MODERATE IRRADIANCES OF UVB AND UVC IRRADIATION ARE EQUALLY ERYTHEMOGENIC IN HUMAN SKIN*
Authors: Park Y. K. , Gange R. W. , Levins P. C. , Parrish J. A.
Published: January 2008

Abstract —The effect of irradiance on ultraviolet‐induced delayed erythema was studied in normal human skin. With both UVB and UVC radiation, the minimal erythema dose was the same whether exposure lasted several seconds or 5 h. A reciprocal relationship between exposure duration and irradiance has previously been shown to exist for exposures ranging from nanoseconds to minutes. The present study shows that even if exposures last over 4 h the minimal erythema dose is a function of exposure dose and not of irradiance or exposure duration.
ACTION SPECTRUM FOR ANTHRACENE‐INDUCED PHOTOSENSITIZATION OF HUMAN SKIN
Authors: KAIDBEY KAYS H. , NONAKA SHIGEO
Published: January 2008

Abstract— The action spectrum for photosensitization by topically applied anthracene was determined in human volunteers. Spectral reactivity was demonstrated in the range between 320 and 380 nm, with peak activity at around 360 nm. Three distinct inflammatory responses viz. immediate transient erythema, delayed erythema, and wealing were evoked following exposure to effective wavelengths. The action spectra for these responses were similar but the threshold doses were different. Prior treatment with a mast cell degranulating agent (codeine) abolished anthracene‐UVA induced wealing but did not influence the erythema response. These findings suggest that photosensitized damage to cutaneous mast cells may be partially responsible for some of the observed inflammatory responses, but other sites of photochemical injury are also involved.
VIDEO DATA ACQUISITION FOR MOVEMENT RESPONSES IN INDIVIDUAL ORGANISMS
Authors: LIPSON EDWARD D. , HÄDER DONAT‐P.
Published: January 2008

Abstract— We describe a simple approach for the semiautomatic acquisition of data from video recordings of movement responses of microorganisms. For a sessile microorganism like Phycomyces blakesleeanus, we describe an angle transducer consisting of a precision rolary potentiometer and a transparent ruler. This device is placed in front of a video monitor during playback from a time‐lapse video recorder. The experimenter maintains the ruler parallel to the image of the upper region of the bending sporangiophore; a voltage proportional to the bending angle is directed to a strip‐chart recorder. The chart provides a continuous and precise graph of the bending angle as a function of time, so that the latency, bending rate, and other parameters may be readily measured. For motile microorganisms, such as Euglena gracilis, paths from video recordings are traced onto acetate sheets during playback. A rotary and a linear potentiometer convert the angle and length of successive path elements into analog voltages which are transmitted by analog‐to‐digital converters to a microcomputer for subsequent statistical and mathematical treatment. The general approaches presented here should be applicable to the study of movement responses of many types of organisms.
A HIGHLY REACTIVE HETEROATOM ANALOG OF RETINAL AND ITS INTERACTION WITH BACTERIORHODOPSIN
Authors: Birnbaum Dov , Seltzer Stanley
Published: January 2008

Abstract

C18 formate ester (5) [2‐(6‐methyl‐8‐(2,6,6‐trimethyl‐1‐cyclohexen‐1‐yl)‐3E,5E,7E‐octatrienyl formate], a highly reactive analog of retinal, was synthesized and its interaction with bacterioopsin studied. The formate ester, in the absence of purple or bleached membrane, undergoes very rapid reaction (tl/2= 0.9 min) in neutral buffer but with membrane present it diffuses more rapidly into the membrane where it reacts slowly. Incorporation of 5 in the membrane results in a 38 nm (3900 cm‐1) red shift which remains after reconstitution with retinal. Similar experiments with the corresponding C18 alcohol (4) results in a red shift, but this absorption blue shifts upon reconstitution with retinal. Washing the formate ester‐treated membrane with bovine serum albumin or the corresponding lyophilized preparation with hexane, treatments that remove retinal oxime, fails to remove the UV‐visible absorption, suggesting that a covalent bond between the C18 moiety and a nucleophilic group of the protein has probably formed.
STUDIES ON HUMAN LENS: I. ORIGIN AND DEVELOPMENT OF FLUORESCENT PIGMENTS
Authors: Sen Asok C. , Ueno Norio , Chakrabarti Bireswar
Published: January 2008

Abstract

Fluorescence spectra of normal mature human lenses have been measured and at least eight species with distinct emission characteristics identified. To determine the specific photochemical and photophysical processes responsible for the origin and development of these fluorophores, emission behavior of the products generated by successive irradiation of young human lenses (3–6 y old) as well as of L‐tryptophan solution have been systematically monitored. Fluorescent products that resulted from this irradiation were comparable to many of the fluorophores detected in aged lenses, indicating that light plays a major role in the development of these pigments. In addition to photogenerated species, there are other compounds in human lenses, presumably advanced glycosylated end products, with marked fluorescence properties.

Several oxidation products of tryptophan including N‐formylkynurenine or its derivatives, β‐carboline or its derivatives, and anthranilic acid have been identified in the mature human lens. The development of several photoproducts also was attributed to endogenous ascorbate‐mediated Maillard reaction products, which undergo photoconversion by the visible light. Although some of these chromophores could act as photosensitaizers, the sensitizing efficiency of many are low. Conversely, the near‐UV filtering capability of these colored compounds conceivably could protect the vitreous and retina from development of any photochemical lesion.
PHTHALOCYANINE AND NAPHTHALOCYANINE PHOTOSENSITIZED OXIDATION OF 2′‐DEOXYGUANOSINE: DISTINCT TYPE I AND TYPE II PRODUCTS
Authors: Ravanat J.‐L. , Berger M. , Benard F. , Langlois R. , Ouellet R. , Lier J. E. van , Cadet J.
Published: January 2008

Abstract

The photodynamic properties of the di‐and tetrasulfonated zinc and aluminium phthalocyanines and a tetrasulfonated aluminium napththalocyanine were studied using 2′‐deoxyguanosine as a DNA model compound. The major photooxidation products of this nucleoside were identified and classified according to their formation through a radical mechanism (type I) or a singlet oxygen mediated mechanism (type II). The major type I product was obtained and identified as 2,2‐diamino [(2‐deoxy‐β‐d‐erythropentofuranosyl)‐4‐amino]‐5(2H)‐oxazolone. Two major type II products were characterized as the 4R* and 4S* diastereomers of 9‐(2‐deoxy‐β‐d‐erythropentofuranosyl)‐7,8‐dihydro‐4‐hydroxy‐8‐oxoguanine. In addition a third product, also resulting from a type II photooxidation, was identified as 8‐oxo‐7,8‐dihydro‐2′‐deoxyguanosine. Quantification of these products provided a means to estimate the contribution of type I and type II pathways during the phthalocyanine and naphthalocyanine mediated photooxidation of 2′‐deoxyguanosine, confirming the major role of singlet oxygen in these processes.
KINETICS OF DYNAMIC HOLOGRAM RECORDING IN POLYMER FILMS WITH IMMOBILIZED BACTERIORHODOPSIN
Authors: Zaitsev S. Yu. , Kozhevnikov N. M. , Barmenkov Yu. O. , Lipovskaya M. Yu.
Published: January 2008

Abstract

Polymer films with immobilized photosensitive membrane protein, bacteriorhodopsin (BR), were prepared and investigated. A sensitive holographic interferometer with phase modulated optical beams was used for investigation of kinetics of dynamic hologram recording in BR polymer films. It was found that phase hologram formation consisted of two quasi‐exponential stages demonstrating existence of a diffusive process in obtained films. It was shown that the kinetics of a phase hologram recording by high intensity beams do not correlate with the exponential law. The applicability of BR polymer films as reversible photorefractive materials for dynamic holography and real‐time interferometry was discussed.
MONOLAYER STUDIES OF 5‐(4‐CARBOXYPHENYL)‐10,15,20‐TRITOLYL‐PORPHYRIN–I. OPTICAL STUDIES OF FILMS AT THE AIR‐WATER INTERFACE and OF FILMS TRANSFERRED ONTO SOLID SUBSTRATES†
Authors: Bardwell Jennifer , Bolton James R.
Published: January 2008

Abstract— The title compound forms well‐behaved monomolecular films at the air‐water interface. The surface pressure‐molecular area isotherms change with the pH of the subphase in a manner which suggests that the carboxylic acid group acts as the hydrophylic portion of the molecule with a pKa of –7.3. In compressed monolayers the porphyrin ring appears to be oriented so that the plane of the ring is perpendicular to the surface.

Spectroscopic studies of single monolayer films transferred to quartz slides using the Langmuir‐Blodgett technique indicate that three distinct species are present in the films, with the amount of each phase depending on the pH of the subphase. One species, present at low pH, is assigned as a monomer on the basis of its optical and fluorescence spectra and its fluorescence lifetime. At low pH this monomer species co‐exists with another non‐fluorescent aggregated species. For films formed on subphases with pH > 7.3, these two species are converted to a single, weakly fluorescent species which exhibits an unusual absorption spectrum. We postulate that this third species is a constrained aggregate but rule out the possibility of a face‐to‐face dimer on spectroscopic grounds.

For films at the air‐water interface specular reflection, indicative of a smooth, highly absorbant film, is observed from monolayers of the title compound. Visual examination of this phenomenon proved to be very useful in assessing the completeness of spreading and the collapse point. Under certain conditions a distinct macroscopic structure is observed in the monolayer film. This structure is interpreted as evidence for the presence of two or more two‐dimensional crystalline phases. Support for this view comes from previous measurements of specular reflection on single crystals of tetraphenylporphyrin. There is no indication that variations in the macroscopic structure of the films have any significant effect on the microscopic properties such as the surface pressure‐area isotherms.
PROTONATED SCHIFFS BASE CHLOROPHYLL: A MODEL FOR P700?
Authors: Maggiora Linda L. , Maggiora Gerald M.
Published: January 2008

Abstract— A Schiff's base of the Ni(II) analog of pyrochlorophyll a (PChl a) has been synthesized which exhibits a reversible bathochromic shift relative to Ni‐PChl a of 504 cm‐1. The shift approaches that observed between Chi a and P700, the photoactive pigment of photosystem I in plants, and suggests that the protonated Schiff s base may be an appropriate model for P700.
TRYPTOPHANYL FLUORESCENCE QUENCHING OF UROCANASE FROM Pseudomonas putida BY ACRYLAMIDE, CESIUM, IODIDE, and IMIDAZOLEPROPIONATE
Authors: O'Donneix Peter S. , Hug Daniel H.
Published: January 2008

Abstract— Urocanase from Pseudomonas putida can be photoactivated by UV radiation. Because of the action spectrum peak at 280 nm, tryptophan has been implicated in the photoactivation by energy transfer. In these studies, tryptophan was determined, the exposure and environment of tryptophanyl residues were studied with collisional quenchers, and the involvement of tryptophanyl residues in the photoactivation of urocanase was investigated. There are sixteen tryptophanyl residues per urocanase molecule as measured by two methods. Fluorescence quenching with acrylamide, cesium, and iodide was used to describe the accessibility and environment of urocanase tryptophanyl residues. Quenching constants indicated there is little difference in the accessibility of tryptophanyl residues between active and inactive enzyme. Tryptophanyl residues of native enzyme were most accessible to acrylamide (fa, = 0.6–0.7), less accessible to iodide (fa= 0.4), and not accessible to cesium ion, suggesting that surface residues were in regions of positive charge. Stern‐Volmer plots indicated a heterogeneous population of tryptophanyl residues with different accessibilities. A competitive inhibitor, imidazolepropionate, quenched fluorescence; the quenching was used to determine the dissociation constant for the enzyme‐inhibitor complex (Kd= 0.20 mM). Kinetic data showed Ki= 0.25 mM. Mixed quencher experiments indicated that the tryptophanyl residues quenched by imidazolepropionate were more accessible to acrylamide and less accessible to iodide. These studies suggest that the residues involved in putative energy transfer during photoactivation are not fully exposed.
THE OCULAR DOSE OF ULTRAVIOLET RADIATION FROM SUNLIGHT EXPOSURE
Authors: Rosenthal Frank S. , Saf>ran Marc , Taylor Hugh R.
Published: January 2008

Abstract— The ocular toxicity of ultraviolet radiation has been demonstrated in acute photokeratitis and is suspected of contributing to cataractogenesis and senile macular degeneration. While previous studies have emphasized photochemical and epidemiologic aspects of ocular UV‐B irradiation, little is known about the extent of such exposure in human subjects. To determine levels of ocular UV‐B exposure from sunlight, four mannikin headforms were fitted with UV‐B sensitive film (polysulphone) and exposed on an unobstructed rooftop (Baltimore, Md.: latitude = 39.5 degrees) to four hours of sunlight (11 am‐3 pm local time) over a three month period (June‐August). Simultaneous measurements of ocular and ambient exposure revealed a ratio of 19.5 ± 2.9% that was independent of ambient level (P < 0.05). Measurements performed during earlier hours (8 am‐11 am) revealed a similar ratio. Mannikin headforms fitted with brimmed baseball caps showed a22–95% reduction in ocular exposure, depending on the angle of the hat brim to the forehead. Three sets of spectacles substantially reduced ocular UV‐B exposure,62–94% dependent on the absorption properties of the spectacle lenses. These anthropomorphic measurements indicate that a substantial percentage of ambient UV‐B light is incident upon the cornea and that personal factors, such as wearing a hat or spectacles, can markedly affect UV‐B exposure.
INDUCTION OF SEED GERMINATION IN Lactuca sativa L. BY NANOSECOND DYE LASER FLASHES*,†
Authors: Scheuerlein R. , Braslavsky S. E.
Published: January 2008

Abstract— A 15 ns, tunable dye laser was used to induce germination of the photoblastic seeds of Lactuca sativa. One red laser flash in the range from 620 to 690 nm was sufficient to increase germination significantly above the dark level. Repeated flashes, however, were necessary to saturate the physiological response.

The wavelength dependence for induction of germination differed for single and repetitive flashes. After saturating far‐red irradiation, the effect of single‐flash induction was a function primarily of the absorption spectrum of Pr. In addition, the establishment within the lifetime of a flash of a photochromic system between the red absorbing form of phytochrome (Pr) and the sum of photoreversible intermediate forms (ΣI700) contributes to this wavelength dependence at high fluence rates. This photochromic system is assumed to be shifted significantly toward Pr by wavelengths 660 nm. Similarly, a strong double‐flash effect, which is seen as an increase in effectiveness when a given total fluence is provided by two consecutive flashes rather than by one flash only, is restricted to those wavelengths that considerably shift the photochromic system Pr⇔ΣI700 toward Pr. Finally, the saturation level produced by a series of laser flashes depends, additionally, on absorption by Pfr.