bluuebunny/crossref_metadata_2025_split huggingface dataset:
INHIBITION AND UNCOUPLING OF ELECTRON TRANSPORT IN ISOLATED CHLOROPLASTS BY THE HERBICIDE 4,6‐DINITRO‐O‐CRESOL
Authors: Rensen J. J. S. van , van der Vet W. , Vliet W. P. A. van 
Published: January 2008

Abstract— Dinitrophenols are known to affect photosynthetic electron transfer. It is shown that the widely used herbicide 4,6‐dinitro‐o‐cresol is a potent inhibitor of the Hill reaction in isolated chloroplasts. By studying different parts of Photosystem II dependent electron transport it is indicated that this herbicide inhibits at the same site as 3‐(3.4‐dichlorophenyl)‐l,1‐dimethylurea.However, the Photosystem I dependent Mehler reaction ascorbate/dichlorophenolindophenol→ diquat is stimulated at higher concentrations of the herbicide. This stimulation does not occur when an uncoupler is added to the reaction medium. There is also no stimulation of the ascorbatep‐tetra‐methyl‐p‐phenylene diamine → diquat Mehler reaction. This suggests that 4,6‐dinitro‐o‐cresol uncouples electron transport in the Photosystem I dependent Mehler reaction, when added at higher
PHOTOSENSITIZED SPLITTING OF PYRIMIDINE DIMERS BY INDOLE DERIVATIVES AND BY TRYPTOPHAN‐CONTAINING OLIGOPEPTIDES AND PROTEINS
Authors: Hèléne Claude , Charlier Michel 
Published: January 2008

Abstract— Indole derivatives including tryptophan can be used as photosensitizers of the splitting of pyrimidine dimers. The reaction can take place in frozen aqueous solutions as well as in fluid medium. Electron transfer from the indole ring to the dimer appears to be involved in the photosensitized reaction. Solvated electrons produced by flash photolysis in the presence of indoles or by pulse radiolysis are also able to split thymine dimers.The splitting of pyrimidine dimers in DNA can be photosensitized by indole derivatives such as serotonin and by tryptophan‐containing oligopeptides. Several methods including fluorescence and nuclear magnetic resonance have been used to show that the indole ring of these oligopeptides is able to stack with bases in nucleic acids. These stacked complexes are involved in the photosensitized reaction.The splitting of pyrimidine dimers in DNA has also been photosensitized by the protein coded by gene 32 of phage T4 which binds strongly and cooperatively to single‐stranded DNA. The mechanism of the splitting reaction as well as the possible use of this reaction to investigate the role of tryptophan residues in the binding of proteins to nucleic acids are discussed.
SINGLET OXYGEN REACTIONS WITH 2,7‐DIMETHYL‐2,6‐OCTADIENE
Authors: Tanielian Charles , Chaineaux Jacques 
Published: January 2008

Abstract— Results concerning Rose Bengal sensitized photoxidation of 2,7‐dimethyl‐2,6‐octadiene (A) are discussed. This diolefin may be considered as a model molecule of polyisoprene of polymerization number two with 1,4‐4,1 addition mode.All the mono‐ and dihydroperoxides apt to occur are actually obtained. One of the occurring hydroperoxides, 2,7‐dimethyl‐dihydroperoxy‐3,5‐octadiene, which has the structure of a conjugated diene, does not lead to an endoperoxide. This is contrary to Kaplan and Kelleher's hypothesis. On the other hand, no trihydroperoxide forms as a result of further addition of singlet oxygen (1O2).A complete kinetic study has allowed us to determine the rate constants of all the reactions which take place. The reactivity of (A) is twice that of 2‐methyl‐2‐pentene and the addition of 1O2 to one of the double bonds of (A) induces deactivation of the remaining double bond.
THE PHOTOMORPHOGENETIC CONTROL OF THE DEVELOPMENT OF PLASTID GLYCERALDEHYDE‐PHOSPHATE DEHYDROGENASE AND PHOSPHORIBULOKINASE ACTIVITIES IN COTYLEDONS OF MUSTARD SEEDLINGS
Authors: Bradbeer J. W. , Hargrave D. F. , Langman L. 
Published: January 2008

AbstractThe plastid glyceraldehyde‐phosphate dehydrogenase and phosphoribulokinase of mustard cotyledon extracts were activated by preincubation with ATP and with ATP and dithiothreitol respectively. By in vitro activation prior to assay, it was possible to determine the potential activities, which appear to have been directly proportional to the amount of each enzyme protein present. In this way it was possible to deduce the net synthesis of these two enzymes. The induction of synthesis of glyceraldehyde‐phosphate dehydrogenase and phosphoribulokinase, by continuous far red or white light were similar hut net synthesis in continuous far red continued longer for glyceraldehyde‐phosphate dehydrogenase than for phosphoribulokinase. The kinetics of the development of the glyceraldehyde‐phosphate dehydrogenase potential activity were very close to those reported by Bruning et al. (1975) for this enzyme. The data do not permit elimination of either the single switch or multiple switches hypotheses for the action of phytochrome.Continuous white illumination gave results similar to those for continous far red for the net synthesis of the two enzymes but it was more effective than far‐red in bringing about enzyme activation in vivo.
SOLAR DOSIMETRY WITH REPAIR DEFICIENT BACTERIAL SPORES: ACTION SPECTRA, PHOTOPRODUCT MEASUREMENTS AND A COMPARISON WITH OTHER BIOLOGICAL SYSTEMS
Authors: Tyrrell Rex M. 
Published: January 2008

Abstract— Populations of radiation sensitive spores (Bacillus subtilis UVSSP), vegetative bacteria (E. coli K12‐AB2480) and bacteriophage (E. coli phage T4vx) have been considered as possible biological dosimeters to integrate DNA‐absorbed solar energy incident on the Earth's surface.Irradiation of spores of B. subtilis UVSSP with monochromatic far‐ and near‐UV radiation and solar radiation have indicated that these radiations have a similar efficiency in inducing spore photoproducts per lethal event. Action spectra for lethality taken with the three radiation sensitive biological systems show a similar pattern in each case with a broad shoulder in the 334–365 nm wavelength region. This finding indicates a relatively high susceptibility of the DNA to chemical alteration in this wavelength range. Although less sensitive to sunlight than the other biological systems tested, the B. subtilis UVSSP spore mutant has the advantage of temperature independence of inactivation, stability between irradiation and assay and a simple, reproducible irradiation and assay procedure. Field measurements have supported the utility of this mutant as a sunlight dosimeter.
RELATIONSHIP BETWEEN MUTAGENESIS AND CARCINOGENESIS*
Authors: Trosko James E. , Chang Chia‐cheng 
Published: January 2008

Abstract— Since the neoplastic condition is a phenotypic expression of the genome of the tumor cells, it is reasonable to assume that the neoplastic state can be the result of the alteration of gene activity by either mutagenesis or gene modulation. The review of the literature seems to support the hypothesis that both mutations and epigenetic processes are components to carcinogenesis. Consistent with the mutation theory of cancer are: (1) the clonal nature of tumors; (2) the mutagenicity of most (but not all) carcinogens; (3) correlation of high mutation frequencies in cells of cancer‐prone human fibro‐ blasts lacking DNA repair enzymes; (4) correlation of in vitro DNA damage, in vitro mutation and transformation frequencies with in vivo tumorigenesis; (5) age‐related incidences of various hereditary tumors; and (6) the correlation between photoreactivation of DNA damage and the biological amelioration of UV‐induced neoplasms. Supporting the epigenetic theory of carcinogenesis is the reversion of certain types of neoplastic cells to a state allowing normal development. These latter studies demonstrate the totipotency of the genes in some types of malignant cells.An integrative theory of carcinogenesis is presented that synthesizes the mutation and epigenetic theories with Comings' general theory of carcinogenesis and the 2‐stage theory of carcinogenesis. Data are presented that test the predictions of the 2‐stage theory of carcinogenesis, and that support the hypothesis that mutagenesis plays a major role in carcinogenesis (initiation phase) and that gene modulation of repressed mutations is responsible for tumor promotion.
PROTOPORPHYRIN‐SENSITIZED PHOTODYNAMIC MODIFICATION OF PROTEINS IN ISOLATED HUMAN RED BLOOD CELL MEMBRANES
Authors: Dubbelman T. M. A. R. , Goeij A. F. P. M. de , Steveninck J. van 
Published: January 2008

Abstract— The photodynamic action of protoporphyrin on red cell ghosts is reflected by extensive cross‐linking of membrane proteins to very high molecular weight protein aggregates. This process was studied with sepharose gel chromatography and sodium dodecyl sulphate polyacrylamide gel electrophoresis.Most sensitive to this photodynamic effect are spectrin and band 2. 1, 2. 2, 2.3 and 4.1. polypeptides, which are cross‐linked after very brief illumination periods, with a concomitant loss of spectrin‐associated ATPase activity. Band 6 protein, representing the monomeric form of glyceraldehyde‐3‐phosphate dehydrogenase, is also very sensitive to protoporphyrin‐induced cross‐linking. The enzymatic activity decreased even faster than the amount of band 6 polypeptides, suggesting that modification(s) of the enzyme other than cross‐linking, possibly by rapid photooxidation of a thiol group, may be responsible for inactivation.Extracted and purified spectrin was cross‐linked with about the same velocity as membrane‐bound spectrin, reinforcing our previously drawn conclusion that membrane lipids are not involved in the cross‐linking reaction. Eluted band 6 polypeptides on the other hand exhibited a relatively fast photo‐oxidative modification but a much slower cross‐linking to dimers and tetramers. This suggests that the membrane structure, e.g. the spectrin matrix may play an essential role in the incorporation of membrane‐bound band 6 polypeptides in the high molecular weight cross‐linked complex.
LOCAL ELECTRIC FIELD EFFECT ON THE CHLOROPHYLL FLUORESCENCE
Authors: Frackowiak D. 
Published: January 2008

Abstract. Polarized absorption and fluorescence of chlorophyll a and bacteriochlorophyll solutions in nematic liquid crystal mixtures have been studied in the presence of an external electric field.The electric field caused a reorientation of the pigment molecules as concluded from changes in the polarized absorption. However, no correlation was found between the change in the polarized absorption and the change in the polarized fluorescence as a function of the field strength. The field influence was much stronger than expected only from the molecular orientation. The fluorescence polarized parallel to the direction of the liquid crystal was found to increase, whereas the similarly polarized absorption decreases. As a whole, the fluorescence yield significantly increased. It is suggested that the additional electric field is reinforced by a local field, most probably due to a protonation of the liquid crystal molecules.Charged solvent molecules are reoriented in an external electric field which changes the local electric field acting on chlorophylls. Similar changes in CHI fluorescence yield due to local electric field can be created in vivo by the shift of charged molecules present in surrounding pigments. Such effects can be at least partially responsible for slow induction of fluorescence phenomena.
PROPERTIES OF CHLOROPH'YLL‐LECITHIN VESICLES: ULTRACENTRIFUGATION, ABSORBANCE, EMISSION AND PHOTOBLEACHING
Authors: Dijkmans H. , Leblanc R. M. , Cogniaux F. , Aghion J. 
Published: January 2008

Abstract— Egg lecithin vesicles (liposomes) containing up to one Chl a per 11 lecithin molecules were prepared without sonication. Their absorbance and emission properties indicate that Chl is dispersed in the lecithin, that the vesicles are dispersed in the medium and that there is a strong quenching of fluorescence.Their photobleaching and chemical bleaching show that there is a negligible amount of colloidal Chl present. In vesicles with a Chl:lecithin molar ratio higher than 0.05, there are probably some small aggregates of Chl a in the bilayer.The ultracentrifugation of such vesicles shows that their sedimentation constant increases, though not regularly, with their relative Chl content
KINETICS OF TRIPLET OXIDATION OF METALLO‐PORPHYRIN COMPOUNDS TO THEIR CORRESPONDING RADICAL CATIONS
Authors: Potter W. , Levin G. 
Published: January 2008

Abstract— The kinetics of photooxidation of triplets of metalloporphyrin compounds to their corresponding radical cations was investigated. Zn‐tetraphenyl porphyrin (ZnTPP) and Mg‐tetraphenylpor‐phyrin (MgTPP) triplets were oxidized by europium salt with rate constants of 4.8 × 105M‐1s‐1 and 2.1 × 106M‐1s‐1, respectively. The high rate constant of oxidation of MgTPP triplet might be related to the ground state oxidation potential, being 0.54 V (SCE) for the Mg complex and 0.71 (SCE) for the Zn complex.The rate constant of oxidation of ZnTPP excited singlet is in the order of diffusion control, i.e. ˜ 1010M ‐1 s‐1. Excitation of ferric, cupric, cobaltic, and vanadyl tetraphenylporphyrin did not result in a long‐lived triplet state that would allow oxidation studies using flash photolysis.
THE ASSOCIATION OF THE 5‐METHYLPHENAZINIUM CATION AND THE 5‐METHYL‐10‐HYDRO‐PHENAZINIUM RADICAL CATION WITH MICELLES*
Authors: Evans C. Anderson , Bolton Jms R. 
Published: January 2008

Abstract— 5‐Methylphenazinium (MP+) cation salts are known to stimulate photophosphorylation in photosynthetic systems. The mechanism is thought to involve the translocation of protons across the thylakoid membrane although few details are known concerning the mechanism and the identity of the proton carrier. As there is some indication that the semireduced species, the 5‐methyl‐10‐hydro‐phenazinium (MPH+) cation radical, may be the proton carrier, we have studied the interaction of MPH+ with micelles as a model system for aqueouslipid interactions in a membrane. In this study we have used the techniques of NMR and EPR.In the presence of sodium dodecyl sulfate (NaLS) micelles the EPR spectrum of MPH + is broadened indicating specific binding of MPH+ to the micelle. A binding constant of ‐105M‐1 was obtained. The 220 MHz NMR spectrum of a micellar solution with added MPH! shows specific broadening of the alkyl protons. The use of model paramagnetic adducts has allowed us to infer from the NMR results that the MPH+ ion penetrates the hydrocarbon part of the micelle to a considerable extent. This would indicate to us that MPH+ can indeed function as a proton carrier as it should be able to penetrate deeply into the lipid layer of the membrane.From these results, we conclude that:

Both MP+ and MPH+ interact strongly with NaLS micelles. MPH+ interacts more weakly with neutral Triton X‐100 micelles while in this case, no evidence of interaction is seen for MP+. No binding of either MP+ or MPH+ is observed with cationic micelles from CTAB.
MP+ is adsorbed to NaLS micelles in a very hydrophilic region, probably In the Stern layer. MPH+, however, is much less hydrophilic than MP+ and appears to reside in the Palisade layer a few angstroms below the head groups.

On the basis of these results, we make the following proposals:

MPH+ is sufficiently hydrophobic to be a candidate for the reduced MP+ species which actually carries the proton across the thylakoid membrane.
The site at which MP+ is reduced by X must be anionic in nature in order for MP+ to be bound strongly.
THE PHOTOREDUCTION OF FLAVINS BY AMINO ACIDS AND EDTA. A CONTINUOUS AND FLASH PHOTOLYSIS STUDY
Authors: Heelis P. F. , Parsons B. J. , Phillips G. O. , McKellar J. F. 
Published: January 2008

Abstract— Primary and secondary photochemical processes in oxygen‐free aqueous solution have been characterised for FMN alone and in the presence of EDTA and four amino acids using nanosecond and microsecond flash photolysis and continuous photolysis techniques. The relative contributions of oneelectron and two‐electron (group or hydride transfer) reactions to the deactivation of the triplet has been determined by comparing the radical concentration (560 nm) with the bleaching of the ground state (446 nm). It was concluded that one‐electron reactions (hydrogen atom or electron abstraction) are the major mode of reactivity of the flavin triplet state with all the suhstrates studied.The nature of the reactions of the flavin semiquinone radical have been studied quantitatively by microsecond flash photolysis. These secondary reactions consist of either a ‘back reaction’ between the flavin and substrate radicals (tryptophan or glycyl‐tyrosine) or the transfer of a second electron (or hydrogen atom) from the substrate radical to the flavin radical (EDTA, methionine and possibly cysteine) to form reduced flavin and oxidised substrate. From a comparison of the quantum yields of formation of reduced flavin using ‘flash’ and continuous irradiation, an additional pathway for the decay of the flavin radical is suggested to occur at low light intensities in the presence of glycyl‐tyrosine or histidine.
HORMONAL AND DIM LIGHT EFFECTS IN RETINAL PHOTODAMAGE*
Authors: O'Steen W. Keith 
Published: January 2008

Abstract—Exposure of albino rats to continuous visible dim light results in the rapid. but graded. loss of photoreceptor cells. The age at which albino rats are exposed to light influences the degree of photoreceptor damage. The severity of cell destruction per unit exposure time gradually increases in rats exposed at different ages from postweaning to adulthood, and by 8 weeks of age, reduction in the thickness of the outer nuclear layer (photoreceptor cell nuclei) is highly significant. The period of increasing susceptibility to light damage is coincident with the occurrence of sexual maturation, which suggests a relationship between photoreceptor destruction and the maturation of the pituitary gland‐gonadal axis. To determine whether the absence of the pituitary gland and ovarian hormones influences photoreceptor damage, animals were either hypophysectomized or ovariectomized and exposed to continuous illumination for up to 45 days. The degree of photoreceptor destruction is significantly reduced in operated, as compared with sham‐operated control, rats exposed to an identical light regimen. Small, physiologic doses of estradiol reverse the protective effects of ovariectomy, but larger, pharmacologic doses do not. Retinal damage is significantly enhanced by injection of pituitary homogenates during the light‐exposure period and by transplantation of pituitary glands under the kidney capsule of rats in which the pituitary has been removed. Pituitary glands transplanted in this location produce high levels of prolactin, while other pituitary hormones are found at unusually low, and sometimes nonfunctional, levels. Prolactin administration to rats during the light exposure period effectively reverses the protection afforded by removal of the pituitary gland.Pituitary gland hormones as well as hormones from some of the pituitary target organs, appear to have a regulatory influence on the severity of light‐induced photoreceptor damage in this species.
HERPES VIRUS PRODUCTION IN MONKEY KIDNEY AND HUMAN SKIN CELLS TREATED WITH ANGELICIN OR 8‐METHOXYPSORALEN PLUS 365 nm LIGHT
Authors: Coppey J. , Averbeck D. , Moreno G. 
Published: January 2008

Abstract—At an cquimolar concentration of 50 μM the bifunctional furocoumarin, 8‐methoxypsoralen (8‐MOP), is about 36 times more efficient in inhibiting the colony forming ability of CV‐I monkey kidney cells than the monofunctional furocoumarin angelicin. In contrast 8‐MOP is only 7.5 times more efficient than angelicin for the inhibition of herpes simplex virus (HSV) production in CV‐1 cells. This latter factor seems to reflect differences in photoreactivity of the two compounds with host cell DNA.A substantial recovery of HSV production was seen when cells were infected at different time intervals after treatment with angelicin‐plus‐light, whereas recovery was very limited after 8‐MOP plus light treatment. The recovery process was slow as compared to that observed after UV (254 nm)‐irradiation.The repair capacities of treated normal and xeroderma pigmentosum (group A) skin fibroblasts were estimated by measuring HSV production and unscheduled DNA synthesis. XP‐A cells repaired angelicin induced damage less efficiently than did normal cells. Neither cell type showed any repair activity after 8‐MOP plus light treatment.
CHEMICAL REACTION RATES OF AMINO ACIDS WITH SINGLET OXYGEN
Authors: Matheson I. B. C. , Lee John 
Published: January 2008

Abstract— The chemical reactions of amino acids with singlet oxygen have been measured in D2O solution where the singlet oxygen was generated directly by irradiation of the oxygen 3∑g‐→1δg+ lv electronic transaction with the 1.06 μm output of an Nd‐Yag laser. Chemical reaction was measured as amino acid loss by an amino acid analyzer or by fluorescence in the cases of tryptophan and tyrosine.The chemical rate constants, in units of 107M‐1s‐1, are histidine 10, tryptophan 3, methionine 1.7, tyrosine 0.8 and alanine 0.2, In the cases of histidine, methionine and alanine the interaction appears to be entirely chemical, i.e. there is no evidence for physical quenching in addition to the chemical reaction. The histidine chemical reaction rate constant shows an increase with pD with a pK of 6.9.
VISIBLE LIGHT IRRADIATION OF HUMAN AND BOVINE SERUM ALBUMIN‐BILIRUBIN COMPLEX*
Authors: Rubaltelli Firmino F. , Jori Giulio 
Published: January 2008

Abstract— The UV absorption and the fluorescence emission spectra of both bovine (BSA) and human (HSA) serum albumin underwent noticeable changes upon irradiation of their 1:1 complexes with bilirubin; both these phenomena are suggestive of the photosensitized modification of aromatic amino acid residues. Amino acid analysis showed that after relatively short irradiation times of both albumins, only histidyl and tryptophyl residues appeared to be affected to a significant extent. After 60min of irradiation, some decrease in the tyrosine content was also observed, especially for HSA.Conformational studies, obtained by exposing unirradiated and irradiated BSA and HSA to denaturing agents, showed that the three‐dimensional organization of the 15 min irradiated samples was slightly different from that of the native proteins. On the other hand, after 15 min of irradiation, the association constant of the bilirubin‐albumin complexes decreased from 2.07 to 0.54×108M‐1 for HSA and from 2.16 to 0.87×107M‐1 for BSA.These data indicate that the histidyl residues are relatively unimportant for maintaining the native tertiary structure of BSA and HSA, but they are critical for determining the binding capacity of the albumins. Our data also imply that the tertiary structure of the BSA molecule is more labile than that of HSA.
COMPLEX FORMATION BETWEEN PYRENE AND THE NUCLEOTIDES GMP, CMP, TMP AND AMP
Authors: Lianos P. , Georghiou S. 
Published: January 2008

Abstract—Pyrene has been found to form ground and excited electronic state complexes of 1:1 stoichi‐ometry with GMP, CMP, TMP and AMP. The values of their ground state association constants are 45 M‐1, 13M‐1, 14 M‐1, and 52 M‐1 respectively. The fluorescence of pyrene is strongly quenched by GMP, CMP, and TMP but only slightly by AMP. Fluorescence quenching analysis has yielded the values 87M‐1, 73 M‐1, and 154 M‐1 for the excited state association constants with GMP, CMP, and TMP, respectively. The corresponding values for the excited state second‐order rate constant for complex formation are: 3.3 times 109M‐1 s‐1 4.1 times 109M‐1 s‐1, and 4.0 times 109M‐1 s‐1. The probabilities of complex formation per collision between an excited pyrene molecule and a nucleotide are: 0.52, 0.64, and 0.63. The values for the excited state rate constant for dissociation of the complex are: 3.8 times 107s‐1 5.6 times 107s‐1, and 2.6 times 107s‐1. The possibility is discussed that partial transfer of charge from pyrene to nucleotide may be playing a role in the complex formation process.