bluuebunny/crossref_metadata_2025_split huggingface dataset:
FLAVIN SENSITIZED PHOTOOXIDATION OF (POLY)AMINO ACIDS: FATE OF THE PHOTOSUBSTRATE
Authors: Armstrong Jacqueline S. , Hemmerich Peter , Traber Rainer 
Published: January 2008

Abstract—With respect to literature data, which seemed to be contradictory, we examined the fate of ethylenediaminetetraacetate (EDTA) and nitrilotriacetate (NTA) in flavin‐sensitized photooxidation reactions by quantitation of all possible products, i.e. CO2by acidimetric titration, CH2O by colometry and glyoxylate enzymatically; N‐methyl groups were quantified by1H‐NMR.Nitrilotriacetate yields 100% oxidative photodecarboxylation with CH2O formation, while EDTA behaves quite differently, yielding quantitative amounts of CO2and glyoxylate, but no CH2O. The electron balance in this reaction is found to be maintained by co‐formation of one equivalent >N‐CH3. From these data it is concluded that the photooxidation of the structural element >NCH2C02containing a tertiary nitrogen atom, occurs by electron transfer, followed by decarboxylation. The neutral radical that is formed is reductant and will give off an electron equivalent to yield the easily hydrolysed structural element >N+= CH2.With EDTA, containing the fragment –O2CCH2>NCH2CH2N< CH2CO2–, the electron transfer towards flavin is strongly favoured by stabilisation of a cisoid mesomeric radical cation (02cch2>+NCH2CH2NCH2CO2o2cch2>NCH2CH2N+CH2CO2), which, after loss of CO2undergoes internal 1,6‐hydrogen shift to yield the more stable radical:CH2>CH2CH2N CH2CO2CH2lt NCH2CH2NHCO2. The latter radical will easily be oxidized to the iminium ion >N*= CH‐C02‐. which in turn hydrolyses to glyoxylate.Chelation of EDTA by metal cations prevents the 1,6‐hydrogen shift, and leads to the product pattern obtained in the NTA photoreaction.
THE EFFECT OF CYTOKININS ON GROWTH and PIGMENT ACCUMULATION OF RADISH SEEDLINGS (RAPHANUS SATIVUS L.) GROWN IN THE DARK and AT DIFFERENT LIGHT QUANTA FLUENCE RATES*
Authors: Buschmann Claus , Lichtenthaler Hartmut K. 
Published: January 2008

Abstract— The dependency of cytokinin effects upon irradiance was studied with radish seedlings (Raphanus sativus L. cv. Saxa Treib). Kinetin (6‐furfurylamino‐purine) or BAP (6‐benzylamino‐purine) were applied via the roots of plants growing either in continuous darkness or under high (90 Wm‐2) or low intensity white light (10Wm‐2). Apart from the different development of plants at low and high fluence rates, the following cytokinin effects were found:(1) Both cytokinins acted in a similar manner on growth characteristics and pigment accumulation at high and low light conditions, BAP being in many cases more effective than kinetin.(2) When compared with the control, the cytokinins suppressed hypocotyl and root lengthening in the dark and light‐grown plants. In darkness they led to increased cotyledon areas, whereas in the light the leaf expansion was suppressed.(3) In the etiolated and low light grown plants, the anthocyanin content of the hypocotyls was enhanced due to the action of cytokinins, whereas under high light the anthocyanin accumulation was decreased.(4) In the cotyledons of etiolated plants, more phototransformable protochlorophyll(ide) and more carotenoids were formed when cytokinins were present. In green leaves the carotenoid content was diminished due to the action of cytokinins, particularly in plants grown in strong light. The chlorophyll a/b ratio was increased in the cytokinin‐treated plants in most cases.The results suggest a light dependency of the cytokinin effects. It is believed that the response of a plant towards exogenously applied cytokinins is similar to that with high intensity light.
PHOTOINACTIVATION OF ENZYMES BY LINEAR AND ANGULAR FUROCOUMARINS
Authors: Veronese F. M. , Schiavon O. , Bevilacqua R. , Bordin F. , Rodighiero G. 
Published: January 2008

Abstract Furocoumarins with linear (psoralen, 8‐methylpsoralen, 8‐methoxypsoralen and 3‐carbethox‐ypsoralen) and angular molecular structures (angelicin and 4,5'‐dimethylangelicin) were found to inactivate enzymes to different extents through UV‐A irradiation. Moreover, enzymes with different structures (glutamate dehydrogenase, lysozyme, 6‐phosphogluconate dehydrogenase, enolase, thermoly‐sine and ribonuclease) are inactivated to different extents by the same furocoumarin. UV‐A irradiation produces both covalent incorporation of the furocoumarins into the protein molecule and photodegra‐dation of amino acid residues; the latter phenomenon seems to be mainly responsible for the photoinactivation process. A close correlation was found between the capacity of the furocoumarins to photoinactivate enzymes and their capacity to modify free amino acids.A study of the effects of quenchers of various forms of activated oxygen on the photoinactivation of glutamate dehydrogenase, used as a model enzyme, and psoralen and 8‐methylpsoralen as a reference for furocoumarins, showed that singlet oxygen is the species most involved in the photoinactivation process.
STUDIES ON THE CAPACITY OF pR IN VITRO TO PHOTOCONVERT TO THE LONG‐WVELENGTH Ffr‐FORM. A SURVEY FO TEN PLANT SPECIES*
Authors: Baron O. , Epel B. L. 
Published: January 2008

AbstractStudies on the capacity of Pr in uitro to photoconvert to the long wavelength in uioo‐like Pfr form were performed with extracts from 10 species. Red irradiation, immediately after extraction of crude extracts from 9 species, photoconverted Pr to long‐wavelength Pfr with an absorbance maximum around 735 nm. Red irradiation of soybean extracts, however, photoconverted Pr to short‐wavelength Pfr, with an absorbance maximum at 725 nm. Red irradiation given later than 1.5‐2 h after extraction, to extracts of oats, pea, cucumber, radish, sunflower and soybean, photoconverted Pr to a short‐wavelength Pfr species with an absorbance maximum around 725 nm. In crude extracts of barley, corn, wheat and zucchini, red irradiation, even after a long dark‐incubation period at 4°C of up to 48 h, photoconverted Pr to long‐wavelength Pfr with an absorbance maximum around 735 nm. After incubation at 25°C for 3 h, however, Pr from barley also photoconverted to the short‐wavelength form. It is suggested that in the group exemplified by oats, Pr rapidly undergoes an alteration following extraction, which results in the loss of the capacity of Pr to photoconvert to long‐wavelength Pfr. In contrast, in extracts from the group exemplified by barley, Pr is much more stable and retains the capacity to photoconvert to long‐wavelength Pfr for much longer periods.
LETHALITY AND THE INDUCTION AND REPAIR OF DNA DAMAGE IN FAR, MID OR NEAR UV‐IRRADIATED HUMAN FIBROBLASTS: COMPARISON OF EFFECTS IN NORMAL, XERODERMA PIGMENTOSUM AND BLOOM'S SYNDROME CELLS
Authors: Smith P. J. , Paterson M. C. 
Published: January 2008

Abstract Using normal human fibroblasts we have determined the ability of far (254 nm), mid (310 nm) or near (365 nm) UV radiation to: (i) induce pyrimidine dimers (detected as UV endonuclease sensitive sites) and DNA single‐strand breaks (detected in alkali); (ii) elicit excision repair, monitored as unscheduled DNA synthesis (UDS); and (iii) reduce colony‐forming ability. Unscheduled DNA synthesis studies were also performed on dimer excision‐defective xeroderma pigmentosum (XP) cells, and the survival studies were extended to include XP and Bloom's syndrome (BS) strains. UV‐induced cell killing in normal, BS and XP cells was found to relate to an equivalent dimer load per genome after 254 or 310 nm exposure, whereas at 365 nm the lethal effects of non‐dimer damage appeared to predominate. Lethality could not be correlated with DNA strand breakage at any wavelength. The two XP strains examined showed the same relative UDS repair deficiency at the two shorter wavelengths in keeping with a predominant role for pyrimidine dimer repair in the expression of UDS. However, UDS was not detected in 365 nm UV‐irradiated normal and XP cells despite dimer induction; this effect was due to the inhibition of DNA repair functions since 365 nm UV‐irradiated normal cells showed reduced capacity to perform UDS subsequent to challenge with 254 nm UV radiation.In short, the near UV component of sunlight apparently induces biologically important non‐dimer damage in human cells and inhibits DNA repair processes, two actions which should be considered when assessing the deleterious actions of solar UV.
EFFECT OF CHRONIC UV EXPOSURE ON EPIDERMAL TRANSMISSION IN MICE*
Authors: Gruul F. R. de , Leun J. C. vander 
Published: January 2008

AbstractIn connection with an investigation on UV‐tumorigenesis in hairless mice, the question arose in what way the epidermal transmission changes under chronic UV exposure. At regular time intervals, epidermal sheets of these mice were optically probed, i.e. the specimen was irradiated perpendicularly to its surface with a collimated monochromatic beam of 313, 302 or 297 nm and the transmission was measured in forward direction and a small angle around it. The optical probe measurement was sensitive to epidermal changes and easy to perform; it correlated well with thickness and total transmission of the epidermal sheet.As a result it was found that over the dose range investigated the logarithm of the epidermal transmission at 297 nm was a simple linear function of the daily UV dose and the time of treatment. Calculations, in which this result is combined with data on UV‐tumorigenesis over the same dose range, show that the change in epidermal transmission is sufficiently large to have an important bearing on the dose‐response relationship for tumorigenesis by chronic UV exposure.
QUANTUM EFFICIENCY AND PHOTOSENSITIVITY OF THE RHODOPSIN ⇌ METARHODOPSIN CONVERSION IN CRAYFISH PHOTORECEPTORS
Authors: Cronin Thomas W. , Goldsmith Timothy H. 
Published: January 2008

AbstractPhotosensitivity (Kλ) of a visual pigment is the product of the molecular absorption coefficient (αλ) and the quantum efficiency for photoconversion (γ). Among the invertebrates, many visual pigments are stable not only in the rhodopsin (R) conformation but also as the photoproduct, metarhodopsin (M), We here employ a method for determining the photosensitivities of the two stable pigments of a rhodopsin‐metarhodopsin pair, using kinetic analysis of fluorescence from metarhodopsin combined with measurements of spectral absorption made before and after saturation at the isosbestic wavelength of the pigment pair. A curve fitting technique, in which a theoretical function is scaled for best fit to the measured absorption spectrum of the photosteady‐state mixture, yields values for the photosensitivity of rhodopsin at λ.max, the ratio of quantum efficiencies for rhodopsin—metarhodopsin interconversion, and the fractional composition of the steady‐state mixture. With knowledge of the molecular extinction coefficient, the absolute values of quantum efficiency can be calculated. For crayfish (Orconectes, Procambarus) rhodopsin, measured in isolated rhabdoms, Kmax= 1.05 x 10‐16 cm2 at 535 nm with >7λR→M0.69. These values are similar to the photosensitivity and quantum efficiency of bleaching of vertebrate rhodopsins in digitonin solution (Dartnall, 1972). For the metarhodopsin, Kmax= 1.02 x 10‐16 cm2 at 510 nm, and λM‐R= 0.49.
PHOTOKINETIC ASPECTS OF SPECIFIC HYDROGEN BONDING IN ALL‐TRANS RETINAL AT ROOM TEMPERATURE
Authors: Das P. K. , Hug G. L. 
Published: January 2008

AbstractRoom‐temperature hydrogen‐bonding of all‐trans retinal (ATR) with 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) in cyclohexane results in fluorescence enhancement and triplet yield quenching; these effects, as well as the associated absorption spectral changes in both ground and triplet states and the kinetics of H‐bonding in the triplet state, have been studied by steady‐state absorption‐emission and laser flash‐photolytic transient measurements. The fluorescence enhancement is predominantly controlled by the H‐bonding in the ground state (static interaction) and gives a value of 440 M‐1 for the corresponding equilibrium constant which is very similar to the value (420 M‐1) obtained from the analysis of absorption spectral data as a function of [HFIP˜. The quantum yield of triplet occupation (øT) of the H‐bonded complex, ATR‐HFIP, in cyclohexane is non‐negligible and is about one‐third of øT of free ATR. The kinetic data of H‐bonding equilibration in the triplet state, observable on a nanosecond time scale, indicate that the triplet ATR is a stronger base than the ground state as far as H‐bonding with HFIP is concerned.
PICOSECOND TIME RESOLVED ENERGY TRANSFER IN ISOLATED PHYCOBILISOMES FROM RHODELLA VIOLACEA (RHODOPHYCEAE)*
Authors: Holzwarth Alfred R. , Wendler Joachim , Wehrmeyer Werner 
Published: January 2008

AbstractEnergy‐transfer kinetics in isolated phycobilisomes (PBS) of the red algaRhodella violaceahave been measured by detecting both ground state recovery and fluorescene rise or decay using a synchronously pumped cavity‐dumped dye laser as excitation source. For the first time the constituent phycobiliproteins of PBS have been excited selectively, thus allowing the kinetics of both directly and indirectly excited pigments to be followed. Energy‐transfer between the phyeobiliproteins, which was found to proceed extremely fast, is governed by nonexponential kinetics at low excitation intensities. When analyzed in a biexponential model, the main components of the fluorescence of B‐phycoerythrin (B‐PE) and C‐phycocyanin (C‐PC) decay with τ= 34 ps and τ= 25 ps, respectively. Evidence is presented that transfer between the biliprotein pigments is close to a single‐step process with some contribution of homotransfer. Fluorescence quantum yields of PBS have been determined as a function of the excitation wavelength and were found to reflect a dissociation equilibrium involving ca. 10% dissociated PBS at the concentrations studied.
OBSERVATION OF C‐S BOND CLEAVAGE IN THE PHOTOLYSIS OF A 2‐AMINO‐Δ2‐THIAZOLINE DERIVATIVE
Authors: CORVAL A. , Gaude D. , Jardon P. , Gautron R. 
Published: January 2008

AbstractPhotoirradiation of 2‐benzoylamino‐Δ2‐thiazoline in outgassed toluene and cyclohexane solutions leads to N‐ethyl‐N'‐benzoyl thiourea after a C‐S bond cleavage in the thiazohne group. This photoreaction occurs from the first excited triplet state of the 2‐amino‐Δ2‐thiazoline derivative.
EFFECTS OF SOLVENT ON THE FLUORESCENCE PROPERTIES OF BACTERIOCHLOROPHYLL a
Authors: Connolly John S. , Samuel Edward B. , Janzen A. Frederick 
Published: January 2008

AbstractFluorescence lifetimes (τf) of bacteriochlorophyll a (BChl a) have been measured by the method of time‐correlated single‐photon counting on dilute (1 μM) solutions of the pigment in 15 solvents. There is a pronounced dependence of τf on the nature of the solvent. Specifically, τf, is longer when the central magnesium is hexacoordinated than when pentacoordinated and shorter when the macrocycle is hydrogen‐bonded than when it is not, but the latter effect is more pronounced. Both trends were confirmed by parallel studies on bacteriopheophytin a (BPheo a). Because of the short lifetimes (˜ 2.2–3.6 ns), quenching of fluorescence by molecular oxygen is not a significant factor in aerated solutions of the bacterial pigments. However, reabsorption artifacts are non‐negligible, which necessitates studies on dilute solutions. Fluorescence quantum yields (øf) have been estimated for BChl a in 13 solvents by comparing the observed fluorescence lifetimes with the radiative lifetimes calculated from the integrated absorption spectra.
COMPUTER‐CONTROLLED LIGHT MEASUREMENTS FOR PHOTOMORPHOGENESIS
Authors: Gaba V. , Ryall M. D. , Chapman J. M. 
Published: January 2008

AbstractA computer‐controlled spectroradiometer system is described that comprises a commercial spectroradiometer, a low‐cost microcomputer and a purpose‐built interface. The system is used in establishing controlled light environments for the study of plant growth. The method used to link the computer and spectroradiometer is described and an outline of the required control software is given. A set of application programs has been developed to convert the raw spectral data into meaningful physiological/photomorphogenic quantities. This obviates the large volume of manual measurements and calculations that were previously necessary.
CHLOROPHYLL PHOTOSENSITIZED ELECTRON TRANSFER IN PHOSPHOLIPID VESICLE BILAYERS: INSIDEVSOUTSIDE ASYMMETRY*
Authors: Ford William E. , Tollin Gordon 
Published: January 2008

Abstract—We have determined triplet quenching efficiencies. radical yields and radical recombination kinetics in mixed chlorophyll (Chl)‐egg phosphatidylcholine vesicle suspensions in the presence of electrically‐charged electron acceptors located either in the external. continuous aqueous phase or within the internal aqueous volume of the vesicles. There was a marked asymmetry between these processes as to whether they occurred at the outer or inner bilayer‐water interfaces.With methyl viologen (MV2+) as acceptor, 52 ± 4% of the total Chl triplet could be quenched from the inside. whereas only 16 ± 2% was quenchable from the outside. Approximately 35% of the triplet population was inacccssible to quenching by MV2+from either inside or outside. Ouenching rate constants were higher from the outside than from the inside (2 × 106M−lS‐Ivs1 × 106M−Is−1). A similar pattern was obtained when anthraquinone disulfonate or ferricyanide were used as acceptors.Radical yields and recombination kinetics also displayed asymmetric behaviour. From the inside. only 4 ± 2% of the quenched triplets gave rise to separated radicals using MV2+as acceptor, whereas from the outside the conversion yield was 32 ± 2%. The halftime for the Chl+MV+reaction was approximately 100 times longer at the outer surface than at the inner surface.We conclude the following: (a) Chl is distributed asymmetrically within the bilayer such that more triplet Chl is located within quenching distance of the interface at the inner surface than at the outer surface. Furthermore, an appreciable fraction of the triplet Chl is located sufficiently far from either interface so that quenching is not possible. (b) The mobility of Chl and quencher molecules is greater at the outer surface of the vesicles than at the inner surface.
LIGHT‐INDUCED ELECTRON TRANSFER REACTIONS BETWEEN CHLOROPHYLL AND QUINONE IN LIPOSOMES: RADICAL FORMATION AND DECAY IN NEGATIVELY AND POSITIVELY CHARGED VESICLES*
Authors: Fang Yifei , Tollin Gordon 
Published: January 2008

Abstract— The incorporation of relatively small amounts (≤ 20 mol%) of a negatively charged surfactant into otherwise electrically neutral phosphatidylcholine vesicles containing chlorophyll in the presence of benzoquinone has been shown to produce large effects on radical formation and decay as measured by laser flash photolysis. When salt ions are present in the aqueous phase, increasing the level of negative surfactant leads to a small increase in radical yield, followed by a larger decrease in radical yield. When the salt concentration is low, increasing the negative surfactant concentration leads to a suppression of the fast radical recombination process, an increase in slow radical decay and, at the highest surfactant concentration, an approximately 35% increase in total radical yield. An analysis of these effects is given in terms of the influence of a negative electrostatic field on radical pair stabilization and recombination, radical pair separation and expulsion of the acceptor radical anion from the vesicle.The incorporation of relatively small amounts (≤ 20 mol%) of a positively charged surfactant into egg phosphatidylcholine (EPC) vesicles containing chlorophyll and benzoquinone also produces large effects on radical formation and decay. When the electrolyte concentration in the suspending aqueous medium is high, radical yields are decreased as the surfactant concentration is increased, without any appreciable effect on decay kinetics. When deionized water is used, the slow recombination component of the decay is specifically suppressed by the presence of the positive surfactant, whereas the fast decay component decreased and then increased in amount as the surfactant concentration is increased. In all cases, however, the total radical yield is less than in pure EPC vesicles. These results can be understood in terms of the influence of a positive electrostatic field on radical pair separation and acceptor radical anion mobility. When equimolar amounts of both positively and negatively charged surfactants are incorporated into EPC vesicles, the radical yields and decay kinetics are relatively unaffected, but a large effect is observed on the radical difference spectrum. This may be a consequence of clustering of oppositely charged molecules within the bilayer surface.
ENERGY TRANSFER FROM ENZYMICALLY‐GENERATED TRIPLET SPECIES TO ACCEPTORS IN MICELLES
Authors: Brunetti Iguatemy L. , Cilento Giuseppe , Nassi Lilian 
Published: January 2008

Abstract— Electronically excited triplet species generated during the peroxidase catalyzed aerobic oxidation of appropriate substrates efficiently elicit fluorescence from acceptors in micelles, as shown with 9, 10‐dibromoanthracene and chlorophyll solubilized by various surfactants. In the case of 9, 10‐dibromoanthracene excited by triplet acetone, phosphorescence also can be detected near O2 depletion.The significant implications of this study are that micelle‐solubilized chlorophyll is an excellent detector of enzyme‐generated triplet carbonyl species, as confirmed with several systems, and that the use of micelles make it possible to extend ‘photobiochemistry without light’ to other photobiologically important, yet water insoluble acceptors.
THE ACTION OF ULTRAVIOLET RADIATION ON THE CELL PROLIFERATION OF TWO‐CELL MOUSE EMBRYOS
Authors: Endoh H. , Domon M. 
Published: January 2008

Abstract— The two‐cell mouse embryo has a unique cell cycle of a short DNA synthesis (S) phase and an extremely long post‐DNA synthesis (G2) phase. An attempt was made to investigate the radiation biology of the long G2 phase using UV radiation as a probe. Two cell mouse embryos, at various positions in the cell cycle, were UV‐irradiated in phosphate‐buffered saline. The embryos were cultured for a few hours to 3 days to assay for their cell proliferative characteristics. The embryos were most sensitive to the killing action of UV radiation in the late G2 phase. The embryos divided more than two times after low UV fluences before dying and experienced G2 phase delays.These results can be contrasted to the situation in somatic cells, in which the action of UV radiation is S phase selective. One possibility is that the target for the action of UV radiation is different in two‐cell mouse embryos from that in somatic cells and that the target is similar to that for X‐ray effects.
TRIPLET STATE PROPERTIES OF POLYCYCLIC AROMATIC HYDROCARBON‐DNA and PORPHYRIN‐DNA COMPLEXES DETERMINED BY OPTICALLY DETECTED ZERO FIELD MAGNETIC RESONANCE
Authors: Clarke R. H. , Harris G. , R. A. Mushlint N. Lasserand 
Published: January 2008

AbstractThe photoexcited triplet states of the physically bound (intercalated) complexes of benzanthracene, pyrene, and free base porphin with DNA have been examined at 77 and 2 K. Measurements of triplet lifetimes, zero field splittings, and individual triplet sublevel intcrsystem crossing rates were obtained by optically detected zero field magnetic resonance (ODMR) for the benzan‐thracene‐DNA and free base porphin‐DNA complexes. The triplet lifetime was measured for the pyrene‐DNA complex. No ODMR was observable in the pyrene‐DNA system. Comparison of triplet state data with new and previous results for the benzo(a)pyrene‐DN A complex is discussed in an attempt to characterize the interactions experienced by polycyclic aromatic hydrocarbons and porphyrins within the DNA environment.