bluuebunny/crossref_metadata_2025_split huggingface dataset:
SOLVENT AND ACIDITY DEPENDENCE OF THE ABSORPTION AND FLUORESCENCE OF COUMESTROL*
Authors: Wolfbeis Otto S. , Schaffner Kurt 
Published: January 2008

Abstract—The UV absorption and fluorescence of the plant estrogen coumestrol (1) are markedly dependent on solvent and acidity. In neutral non‐aqueous solvents, emission occurs from the uncharged first excited singlet state. In aqueous solutions of 1, five species—the neutral form, the mono‐ and dianions, and the mono‐ and dications—were found and characterized by their UV absorptions, fluorescence (including lifetimes and quantum yields), and pK's of the ground and excited singlet states. The assignments are based on absorption, fluorescence and pK(*) data of coumestrol dimethyl ether (2), 3‐phenyl‐7‐hydroxy coumarin (3), 34′‐hydroxyphenyl coumarin (4), and appropriate model compounds from the literature. Variations in øF and, consequently, τF values are ascribed to excited state proton transfer processes. Fluorescence quantum yields as high as ca. 0.7 in most organic solvents and in certain pH ranges should render fluorimetry a suitable method for quantitative assays of this estrogen which is responsible for ‘clover disease’ in sheep.
THE PHOTOLYSIS RATES OF SOME DI‐ AND TRIPEPTIDES OF TRYPTOPHAN
Authors: Tassin J. D. , Borkman R. F. 
Published: January 2008

Abstract—We have measured the relative rates of photolysis of free tryptophan (trp), the dipeptides Gly‐Trp, Trp‐Gly, Leu‐Trp, and Trp‐Leu, and the tripeptides Gly‐Trp‐Gly and Leu‐Trp‐Leu. The photolyses were performed in neutral 0.1 mM aqueous solutions at 25°C using monochromatic 290 nm Xe arc radiation. Tryptophan loss was monitored by absorption, fluorescence and phosphorescence spectroscopy. The rate of tryptophan fluorescence loss was found to be different in the di‐and tripeptides than in tryptophan monomer. These rate differences depended on both the identity of the neighboring amino acid (gly or leu) and on the nature of the linkage, e.g., the rate of Gly‐Trp photolysis was more than 10 times greater than the rate of Trp‐Gly photolysis. Degassing was found to markedly reduce (factor of 8) the photolysis rates of Trp, Trp‐Gly, and Trp‐Leu, but degassing only slightly reduced (less than a factor of 2) the photolysis rates of the other di‐and tri‐peptides. Photochemical product structures were not determined, but absorption and fluorescence spectra were obtained and products could be inferred in some cases by comparison with data of previous workers. The products appeared to differ greatly among the various peptides studied; Trp, Trp‐Gly, and Trp‐Leu gave oxidation products, while Gly‐Trp and Leu‐Trp apparently gave ring closure products, not requiring oxygen.
EFFECTS OF ACRIDINE PLUS NEAR ULTRAVIOLET LIGHT ON ESCHERICHIA COLI MEMBRANES AND DNA IN VIVO
Authors: Wagner Stephen , Taylor William D. , Keith Alec , Snipes Wallace 
Published: January 2008

Abstract—Results from a variety of experiments indicate that photodynamic damage to E. coli treated with the hydrophobic photosensitizer acridine plus near‐UV light involves both cell membranes and DNA. Split‐dose survival experiments with various E. coli mutants reveal that cells defective in rec A, uvr A, or pol A functions are all capable of recovery from photodynamic damage. Alkaline sucrose gradient analysis of DNA from control and treated cells revealed that acridine plus near‐UV light treatment converts normal DNA into a more slowly sedimenting form. However, the normal DNA sedimentation properties are not restored under conditions where split‐dose recovery is effective. Several lines of evidence suggest that membrane damage may be important in the inactivation of cells by acridine plus near‐UV light. These include (a) a strong dependence of sensitivity on the fatty acid composition of the membranes; (b) a strong dependence of sensitivity on the osmolarity of the external medium; and (c) the extreme sensitivity of an E. coli mutant having a defect in its outer membrane barrier properties. Direct evidence that acridine plus near‐UV light damages cell membranes was provided by the observations that (a) the plasma membrane becomes permeable to o‐nitrophenyl‐ß‐D‐galactopyranoside and (b) the outer membrane becomes permeable to lysozyme after treatment. A notable result was that cells previously sensitized to lysozyme by exposure to acridine plus near‐UV light lose that sensitivity upon subsequent incubation. This strongly suggests that E. coli cells are capable of repairing damage localized in the outer membrane.
STRUCTURAL STUDIES OF BROWN MEMBRANE BY X‐RAY DIFFRACTION, CIRCULAR DICHROISM AND ABSORPTION SPECTRA
Authors: Hiraki Kenji , Hamanaka Toshiaki , Mitsui Toshio , Kito Yuji 
Published: January 2008

Abstract— Time course of formation and crystallization of bacteriorhodopsin upon the addition of retinal to brown apo‐membrane has been studied by X‐ray diffraction, circular dichroism (CD) spectra and absorption spectra. The rate of formation of bacteriorhodopsin decreases markedly at low pH (4.8) and low temperature (5°C). Furthermore, the formation of bacteriorhodopsin does not proceed in fully dried membranes. The half‐time of the increase of exciton CD band is about 70s at 17°C and pH 7.0, and is comparable to that of the formation of bacteriorhodopsins (∼48s). The crystallization of bacteriorhodopsin proceeds to a large extent within 30 min at pH 7.0 and 5°C.The bilobed CD band of the brown holo‐membrane attributed to exciton coupling of bacteriorhodopsin molecules becomes negligibly small at pH 4.8, even though X‐ray diffraction pattern indicates the lattice structure to be similar to that of the native purple membrane.
INHIBITION OF RESPIRATION AND LOSS OF MEMBRANE INTEGRITY BY SINGLET OXYGEN GENERATED BY A PHOTOSENSITIZED REACTION IN NEUROSPORA CRASSA CONIDIA
Authors: Shimizu‐Takahama Michiko , Egashira Takeshi , Takahama Umeo 
Published: January 2008

Abstract— It was found that killing of Neurospora crassa conidia by singlet molecular oxygen generated by a photosensitized reaction in the presence of toluidine blue O, accompanied inhibition of respiration and uptake of the photosensitizing dye by conidia. Both the inactivation of respiration and the uptake of toluidine blue O were stimulated by deuterium oxide and suppressed by azide. Mitochondria of irradiated conidia were swollen and showed matrix of low density under an electron microscope.These results suggest that singlet molecular oxygen induces the inhibition of respiration and the loss of membrane integrity of Neurospora conidia.
THE EFFECT OF COORDINATING LIGANDS ON THE TRIPLET STATE OF CHLOROPHYLL
Authors: Clarke R. H. , Hotchandani S. , Jagannathan S. P. , Leblanc R. M. 
Published: January 2008

AbstractUnder laser excitation at 457.9 and 514.5 nm, a frozen solution of chlorophyll a in n‐octane displays fluorescence peak maxima at 2K that may be assigned to two distinct monomeric chlorophyll species. Using zero‐field fluorescence‐detected magnetic resonance the triplet state properties of the two chlorophyll species have been assigned to the monoligated and biligated chlorophyll monomer in which water serves as the ligand coordinated to the magnesium metal center. These triplet state properties for chlorophyll in solution are then utilized in interpreting triplet state results for in vivo chlorophylls associated with the light harvesting chlorophyll protein complex. It is shown that the triplet state data are consistent with attachment of the chlorophyll molecule to the protein site with a single ligand coordinated to the chlorophyll metal center.
QUANTITATIVE MICROPHOTOMETRY AT THE CELLULAR LEVEL: A SIMPLE TECHNIQUE FOR MEASURING CHLOROPLAST MOVEMENTS IN VIVO*
Authors: Blairt Michael R. , Briggs Winslow R. 
Published: January 2008

Abstract— A recording microphotometer was developed to permit quantitative analysis of light‐induced chloroplast aggregation in single filaments of the alga Vaucheria. Optical fibers were used both to irradiate the cells and to collect the transmitted light. Light transmittance was examined as a function of time at a fixed point along an algal filament. The photoresponse was stimulated by combining an additional actinic beam with the measuring beams such that both actinic and measuring beams followed the same optical path. The quasi‐opalescent properties of the optical fibers and dual‐wavelength measurements compensated for light scattering and variations in sample geometry.Chloroplast aggregation, marked by a passive accumulation of organelles in the irradiated region of the cell, resulted in a decline of cell transmittance to 675 and 743 nm light. During stimulation with moderate intensities of actinic, 473 nm light the relative transmittance to 675 nm light (corrected for scattering, measured at 743 nm) fell below 0.1 within 5 min. The exponential form of this transmittance change as a function of time was consistent with changes in optical geometry of the aggregate during the photoresponse. It follows that the decay in algal transmittance can provide a measure of the rate of chloroplast accumulation in the light path.
REGULATION OF PROTOCHLOROPHYLL(IDE) LEVELS IN DARK‐GROWN NON‐DIVIDING Euglena—II. INFLUENCE OF UTILIZABLE SUBSTRATES AND INHIBITORS OF PROTEIN SYNTHESIS*
Authors: Alhadeff Myriam , Schiff Jerome A. 
Published: January 2008

Abstract—Dark‐grown cells of Euglena gracilis var. bacillaris incubated on resting medium for 7 days lose half of their extractable and phototransformable protochlorophyll(ide) [Pchl(ide)]. The readily‐utilized substrates glutamate and malate bring about a regeneration of both pools of Pchl(ide) to the levels found in growing cells, without causing cell division during the period of regeneration. Light does not cause a regeneration of total extractable Pchl(ide) to the levels found in growing cells, and the complete regeneration of phototransformable Pchl(ide) seen probably results from conversion of non‐transformable Pchl(ide) to transformable Pchl(ide). Optimal glutamate, malate, and light in any combination are no better in causing phototransformable Pchl(ide) regeneration than any one treatment alone, indicating that the Pchl(ide) pool size is limited by other factors. The regeneration of phototransformable Pchl(ide) induced by light or substrates is insensitive to inhibitors of protein synthesis on 80 S cytoplasmic ribosomes (cycloheximide) or on 70 S chloroplast ribosomes (streptomycin). Cycloheximide, however, induces the regeneration of phototransformable Pchl(ide) in darkness in the absencc of externally‐added substrates. Since cycloheximide is known to induce paramylum breakdown under the same conditions, it is likely that this process can provide internal substrates and/or reducing power for phototransformable Pchl(ide) regeneration. Possible mechanisms of regulation of formation of Pchl(ide)635 in Euglena are discussed and compared with regulation of Pchl(ide)650 in higher plants.
QUENCHING OF CHEMICALLY and ENZYMICALLY‐GENERATED TRIPLET ACETONE BY TYROSINE and 3,5‐DIHALOGENODERIVATIVES
Authors: Rivas‐Suárez Edy , Catalani Luiz H. , J. Etelvino , Bechara H , Cilento Giuseppe 
Published: January 2008

AbstractTyrosine and especially its 3,5‐dihalogenoderivatives quench acetone triplets. When the excited acetone is generated free in solution, the Stern‐Volmer plots for the quenching by these species, monitored via the sensitized emission of the 9,10‐dibromoanthracene‐2‐sulfonate ion, are linear. When triplet acetone is generated enzymically by the peroxidase‐catalyzed aerobic oxidation of isobutyral‐dehyde, the Stern‐Volmer plots for the quenching of the acetone phosphorescence curve upwards in the case of 3,5‐dibromotyrosine and even more markedly with 3,5‐diiodotyrosine. Quenching appears likely to occur by triplet‐triplet energy transfer and especially in the case of the phenoxide form, also by electron transfer. The curvature denotes a static contribution to quenching favoured by the enzyme.
BINDING OF RIBOFLAVIN TO LYSOZYME PROMOTED BY PEROXIDASE‐GENERATED TRIPLET ACETONE
Authors: Durán Nelson , Haun Marcela , De Toledo Sonia M. , Cilento Giuseppe , Silva Eduardo 
Published: January 2008

AbstractWhen riboflavin and lysozyme are added to the 2‐methylpropanal/peroxidase/O2 system, which generates triplet acetone, an adduct is formed to a small extent. The adduct can be separated by gel filtration and is similar to that prepared by irradiating riboflavin in the presence of lysozyme.
PROBING PHOTODYNAMIC DAMAGE IN NUCLEIC ACIDS WITH A DAMAGE‐SPECIFIC DNA BINDING PROTEIN: A COMPARISON OF THE B and Z DNA CONFORMATIONS
Authors: Feldberg Ross S. , Brown Caroline , Carew Josephine A. , Lucas Judith L. 
Published: January 2008

Abstract—We have employed a damage‐specific DNA binding protein from human cells as a probe for base damage in polymers irradiated with white light in the presence of methylene blue. Protein‐recognizable damage is introduced only into guanine‐containing polymers and quenching of damage introduction by H2O and sodium azide suggest the involvement of a singlet oxygen mechanism. Using poly d(G‐m5C), we have demonstrated that the left‐handed double helical Z conformation is much less susceptible to guanine photooxidation than is the usual B conformation. We speculate that this difference in reactivity may reflect steric hindrance at the purine C‐4 position and could provide some insight into the initial steps of the reaction between singlet oxygen and guanine in nucleic acid polymers.
A DIURNAL RHYTHM IN THE RATE OF LIGHT‐INDUCED ELECTRON FLOW IN MAIZE BUNDLE SHEATH STRIPS
Authors: LONERGAN THOMAS A. 
Published: January 2008

Abstract— A technique for the rapid mechanical isolation of bundle sheath strips from Zea mays was used to study the rate of light‐induced electron flow as a function of time of day. Seedlings were raised for 10 days in light/dark cycles and then exposed to various intensities of light. The rate of light‐induced electron flow was measured five times during the 24‐h cycle using a whole cell, H2O to methyl viologen assay in the presence of gramicidin. The uncoupled rate of electron flow reached a maximum at midday and then decreased for the remainder of the cycle.If at the end of the 14‐h dark period plants were either maintained in darkness, or exposed to very low irradiance white light. then no rhythmicity was observed. If continuous light at higher irradiance was used, then only one additional peak of activity was observed. The minimal light irradiance necessary to allow the continued expression of the rhythm in light/dark cycles is in the range between 11 to 54 W m‐2. A 15‐min bright‐light (54 W m‐2) pulse administered at dawn is not sufficient to stimulate the expression of the rhythm indicating that the light during the light/dark cycle is doing more than just acting as a “light‐on” synchronizing signal. An imposed dark period is also necessary if the rhythm is to be expressed for more than one cycle.
UV‐LYSOGENIC INDUCTION OF Λ PHAGE IN lexA1 MUTANTS OF Escherichia coli: KINETICS OF THE PROCESS
Authors: Carvalho R. E. S. , Leitāo A. C. 
Published: January 2008

Abstract— Although the lex gene has been described until recently as being required for lysogenic induction, both our work and the work of others have reported Λ prophage induction in some lexA mutants. However, the characteristics of the process were not defined. We describe UV induction of prophage in a lexA1 mutant at a slightly lower level and requiring 2 times longer than the wild type. As demonstrated in some work, in cells treated with low levels of rifampicin (RIF) no new synthesis of RecA protein is needed for the prophage induction although the onset of lysis is delayed. We suggest that the lysogenic induction in lexA cells is due to the same mechanism that induces prophage in the wild type cells treated with RIF. That is, the induction is due to the cleavage of Λ represser by the basal RecA protease in the DNA‐single‐strand gap, since RecA protease and monomer represser both have high affinity for this type of DNA. So, LexA protein need not be cleaved for the prophage induction.No Weigle‐reactivation (WR) was detected in the lex mutant even after a long post‐irradiation incubation, suggesting that unlike prophage induction, WR requires LexA protein cleavage.
P‐AMINOBENZOIC ACID CAN SENSITIZE THE FORMATION OF PYRIMIDINE DIMERS IN DNA: DIRECT CHEMICAL EVIDENCE
Authors: Sutherland John Clark , Griffin Kathleen Pietruszka 
Published: January 2008

AbstractThymine‐containing photoproducts with chromatographic properties similar to those of cyclobutyl pyrimidine dimers can be formed in [3H]‐thymine‐labeled DNA in solution by 313 nm ultraviolet radiation in the presence of para‐aminobenzoic acid (PABA), a compound used in sunscreen preparations. In the absence of PABA, similar fluences of 313 nm radiation do not produce significant numbers of these photoproducts. The thymine‐containing photoproducts can be reversed by 254 nm radiation so that the tritium label migrates with the mobility of thymine monomer, a behavior characteristic of thymine‐containing cyclobutyl pyrimidine dimers. This result supports previous, but less direct, data from other laboratories indicating that PABA can sensitize dimer formation in the DNA of bacterial and mammalian cells.
INTERACTION OF HUMAN SERUM LOW DENSITY LIPOPROTEINS WITH PORPHYRINS: A SPECTROSCOPIC AND PHOTOCHEMICAL STUDY
Authors: REYFTMANN J. P. , MORLIERE P. , GOLDSTEIN S. , SANTUS R. , DUBERTRET L. , LAGRANGE D. 
Published: January 2008

AbstractThe incorporation of proto‐, uro‐ and hematoporphyrin in low density lipoproteins (LDL) of human blood has been studied by equilibrium dialysis, fluorescence and absorption spectroscopy. The lipoproteins may efficiently compete with albumin in the binding of protoporphyrin to human blood proteins in patients suffering from protoporphyria. It can be concluded that hydrophobic porphyrins bind to blood proteins.The complexation of hydrophobic porphyrins in LDL is responsible not only for efficient photodynamic effect at the lipoprotein level, but also for photoinduced lipid peroxidation and for consumption of β‐carotene incorporated into LDL which are one of their natural carriers. The water‐soluble uroporphyrin, although an efficient photosensitizer for the LDL apoprotein photoinactivation, is much less efficient for lipid peroxidation and β‐carotene bleaching. The 353 nm laser flash photolysis shows that porphyrin triplet states are not affected by the physiological β‐carotene content of LDL but are fully accessible to oxygen.
CLEARANCE TIMES OF PORPHYRIN DERIVATIVES FROM MICE AS MEASURED BY in vivo FLUORESCENCE SPECTROSCOPY
Authors: Kennedy J. C. , Nadeau P. , Petryka Z. J. , Porrier R. H. , Weagle G. 
Published: January 2008

AbstractThe clearance times of 17 different porphyrin derivatives from SKH:HR‐1 mice have been measured using the technique of in vivo fluorescence spectroscopy. This technique monitors the in vivo porphyrin fluorescence observed from the external skin surface. Most hydrophilic porphyrin derivatives show relatively short clearance times, in the order of 2.5–6 h. The dicarboxylic acid porphyrins, proto‐, hydroxyethylvinyldeutero‐and hematoporphyrin IX have clearance times of 7.8, 12.2 and 14.7 h respectively. The mixture hematoporphyrin derivative has an intermediate clearance time of 12.6 h. N‐methylated porphyrins show clearance times in the vicinity of 15–22 h. Monoaspartyl chlorin e6 shows the longest clearance time of all porphyrin derivatives measured (30.3 h).
OXYGEN DEPENDENCE OF HYPERICIN‐INDUCED PHOTOTOXICITY TO EMT6 MOUSE MAMMARY CARCINOMA CELLS
Authors: Thomas Carin , Pardini Ronald S. 
Published: January 2008

AbstractThe photodynamic effect of hypericin on EMT6 mouse mammary carcinoma cells was investigated in vitro under aerobic and hypoxic conditions. Under aerobic conditions, hypericin‐induced photocytotoxicity was dose dependent within a 1–50 μM range. Under hypoxic conditions, cells were resistant to hypericin‐induced phototoxicity. In the dark, no cytotoxicity was observed at any hypericin concentration tested either aerobically or hypoxically. Cellular accumulation of hypericin, examined by chemical extraction and spectroscopy, occurred under both hypoxic and aerobic conditions. Fluorescence photomicrographs of cells exposed to hypericin corroborate drug uptake in the plasma membrane and subcellular regions. Our results demonstrate that hypericin cytotoxicity to EMT6 mouse mammary carcinoma cells in vitro is both light and oxygen‐dependent. These results suggest that EMT6 cell kill caused by photoactivated hypericin is mediated by an oxygen‐dependent mechanism, rather than by a type I oxygen‐independent mechanism.
INHIBITION OF PHOTOTAXIS IN Volvox aureus BY NATURAL AND SIMULATED SOLAR ULTRAVIOLET LIGHT
Authors: Blakefield Mary K. , Calkins John 
Published: January 2008

AbstractExposure to artificial UV wavelengths and the UV component of sunlight delays positive phototaxis in the green alga Volvox aureus. Broad band wavelength filters were used to modify the output from UV‐B sources (280–320 nm) and natural sunlight. The delay in phototaxis by artificial UV is increased with exposure to shorter UV‐B wavelengths. Natural sunlight experiments were performed with exposure to full sunlight and to its UV component only. The UV component present in summer sunlight produced long periods of inhibition in phototaxis and even lethality, while exposure to the total spectrum of sunlight had no significant effects on movement or survival. The data indicate that although this species of alga is well equipped to deal with present levels of UV exposure, increases in the short UV‐B wavelengths in sunlight may force an alteration in patterns of photomovement.
IN VIVO PROTECTIVE EFFECT OF β‐CAROTENE AGAINST PSORALEN PHOTOTOXICITY
Authors: Giles Albert , Wamer Wayne , Kornhauser Andrija 
Published: January 2008

Abstract—The protective effect of β‐carotene against PUVA‐ and UVB‐induced erythema was determined in groups of albino female Osborne Mendel rats fed standard, placebo or β‐carotene‐fortified diets. After 13 weeks, the backs of selected animals were clipped and the animals received 8MOP orally, 20 mg/kg in corn oil, followed by 5 J/cm2 UVA irradiation 2 h after dose. A significant β‐carotene protective effect was observed against phototoxicity induced by 8MOP, as measured by erythema production. A correlation was noted between the observed protective effect and β‐carotene serum and skin levels, determined by HPLC. No protective effect against erythema induced by UVB (0.7 J/cm2) was observed in animals fed the β‐carotene‐fortified diet. This report represents the first in vivo demonstration of a protective effect of dietary p‐carotene against psoraten‐induced phototoxicity. Possible mechanisms for the observed β‐carotene‐protective effect are discussed.