bluuebunny/crossref_metadata_2025_split huggingface dataset:
ELECTROCHEMICAL LUMINESCENCE WITH N(5)‐ETHYL‐4a‐HYDROXY‐3‐METHYL‐4a, 5‐DIHYDROLUMIFLAVIN. THE MECHANISM OF BACTERIAL LUCIFERASE
Authors: Kaaret Thomas W. , Bruice Thomas C. 
Published: January 2008

AbstractIt has been proposed in the literature that the chemiluminescence of the flavoenzyme of bacterial luciferase is caused by a chemically initiated electron‐exchange luminescence mechanism which provides an excited 4a‐hydroxy‐4a,5‐dihydroflavin ([4a‐FlHOH]*) as product of le− reduction of the radical 4a‐FlHOHt. Electrochemical/photon counting experiments were performed to assess the feasibility of this proposal. Potentials for step‐wise oxidation of N(5)‐ethyl‐4a‐hydroxy‐4a,5‐dihydroluminfiavin (4a‐FlEtOH) have been determined in dry N,N‐dimethylformamide (DMF). Photon counting was carried out during the le− reduction of 4a‐FlEtOH+ in both DMF and acetonitrile by use of an apparatus consisting of a photocell mounted below a Pt ring‐disk electrode. By use of the ring‐disk electrode a steady state concentration of [4a‐FlEtOH]* could be maintained by continuous le oxidation of 4a‐FlEtOH +→ 4a‐FlEtOH+ and le− reduction of 4a‐FlEtOH+→ 4a‐FlEtOH. A maximum of 14% collection (theoretical maximum is 18%) of FlEtOH+ at the ring electrode was obtained below 5000 rotations per minute. Calibration of the apparatus using 9,10‐diphenylanthracene allowed approximation of the quantum yield for le− reductive capture of 4a‐FlEtOrP as lO−6 to 10−4 in DMF and 10−7 to 10−5 in acetonitrile. No fluorescence for 4a‐FlEtOH in DMF could be observed; if fluorescent, the efficiency of 4a‐FlEtOH can be no greater than − 3 × 10−5. No electrogenerated chemiluminescence is observed on the electrochemical recycling of FlEt+→ FlEt2+ and FlEt2+→ FlEt+.
STUDIES ON THE MECHANISM OF THE HEMATOPORPHYRIN‐SENSITIZED PHOTOOXIDATION OF 1,3‐DIPHENYLISOBENZOFURAN IN ETHANOL and UNILAMELLAR LIPOSOMES
Authors: Reddi Elena , Valduga Giuliana , Rodgers Michael A. J. , Jori Giulio 
Published: January 2008

AbstractThe 5μM hematoporphyrin‐sensitized photooxidation of 1,3‐diphenylisobenzofuran (DPBF) was studied in homogeneous ethanolic solutions and in aqueous dispersions of unilamellar liposomes of dipalmitoylphosphatidylcholine; both the porphyrin and DPBF are embedded in the phospholipid bilayer. The rate and quantum yield of DPBF photooxidation were found to increase upon increasing the substrate concentration and were higher in the liposome system, while they were unaffected by the fluidity of the phospholipid bilayer. Time‐resolved spectroscopic measurements showed that the photooxidation of DPBF in ethanol solution proceeds by a type II O2(1Δg)‐involving mechanism. In the liposomal vesicles the high local concentration of hematoporphyrin (Hp) and DPBF in the phospholipid bilayer (ca 2000‐fold higher than the stoichiometric concentration) enhances the probability of energy transfer from triplet Hp to DPBF with generation of triplet DPBF; hence O2(1Δg) formation can be promoted by both triplet Hp and triplet DPBF. A minor fraction of triplet DPBF quenchings appears to generate radical species which propagate DPBF damage by chain reaction.
LONG PERSISTENCE OF MONOFUNCTIONAL 8‐METHOXYPSORALEN‐DNA ADDUCTS IN HUMAN SKIN in vivo
Authors: Ortel Bernhard , Maytum Daniel J. , Gange Richard W. 
Published: January 2008

AbstractHuman skin can be persistently photosensitized by topical application of aqueous 8‐methoxypsoralen plus immediate irradiation with a non‐erythemogenic dose of wavelengths above 380 nm. Re‐exposure of skin thus sensitized to broadband UV‐A produces phototoxic erythema72–120 h later. The persistence of the photosensitization was demonstrated by phototoxic erythema after re‐exposure up to 15 days after the first sensitizing irradiation. According to the concept that the first exposure induces primarily psoralen monoadducts, we consider this an investigation of psoralen monoadduct persistence. In contrast to several earlier studies, this sensitive method indicates that psoralen monoadducts may remain in human skin in vivo for more than 2 weeks after formation.
FERROUS ION RELEASE FROM FERRITIN BY ULTRAVIOLET‐A RADIATIONS
Authors: Aubailly M. , Santus R. , Salmon S. 
Published: January 2008

AbstractFerritin is the principal protein of iron storage (in the Fe(III) state). The UV‐A irradiation of 0.25 μM ferritin solutions (from horse spleen) loaded with 530 μM Fe(III) induces Fe2+ release in the medium. The initial quantum yield is wavelength dependent (φ(365 nm) − 2 times 10−3) but pH and oxygen independent. The Fe2+ release reaches a plateau which strongly depends on pH and oxygen. The amino acid composition of the apoprotein is not altered by the UV irradiation. Addition of formate ions enhances the Fe2+ production, suggesting that the ferritin photoreduction involves an electron transfer from an OH− ligand. The possible importance of this phenomenon in skin photo‐biology is discussed.
DYNAMIC LINEAR DICHROISM IN CHROMOPROTEINS
Authors: LYLE PAUL A. , STRUVE WALTER S. 
Published: January 2008

Abstract—The time‐dependent polarized fluorescence and optical density transients arising from electronic excitation transport are derived for solutions of randomly oriented chromoproteins in which the chromophore transition moments have well‐defined orientations with respect to the protein. The treatment is extended to oriented monolayers of chromoproteins, in which the molecules are aligned with a particular protein‐fixed axis perpendicular to the surface plane and with random azimuthal angles about the surface normal. The initial ratio of parallel to perpendicular transients is invariably 3:1, irrespective of system dimensionality and chromophore organization. The residual anisotropy observed at long times is directly related to the relative orientations of the donor and acceptor chromophores. These calculations form a basis for detailed interpretation of ultrafast fluoresence and pump‐probe linear dichroism studies in photosynthetic systems, for which 3‐dimensional structures are becoming increasingly available.
PROPERTIES OF CREMOPHOR EL MICELLES PROBED BY FLUORESCENCE
Authors: Kessel David 
Published: January 2008

Abstract—Using 1‐anilino,8‐naphthalenesulfonic acid (ANS) as a probe, we examined properties of micelles of Cremophor EL, an amphipathic agent which can solubilize hydrophobic photosensitizing agents and promote their distribution to plasma lipoprotein. In aqueous solution, Cremophor micelles persisted for several hours after dilution below the critical micellar concentration (CMC). After equilibrium was reached, we found a CMC of 0.009% (wt/vol). Fluorescence data suggest that the micellar environment of ANS binding has a dielectric constant of approximately 27. Cremophor also reverses examples of multi‐drug resistance associated with impaired accumulation of anti‐tumor agents, e.g. daunorubicin. Although the latter drug is relatively hydrophilic, fluorescence spectroscopy and anisotropy studies indicate an association with Cremophor. Moreover, resistance reversal occurred only at Cremophor concentrations above the CMC.
EXTENSION GROWTH AND ANTHOCYANIN RESPONSES OF PHOTOMORPHOGENIC TOMATO MUTANTS TO CHANGES IN THE PHYTOCHROME: PHOTOEQUILIBRIUM DURING THE DAILY PHOTOPERIOD
Authors: Kerckhoffs L. H. J. , Kendrick R. E. , Whitelam G. C. , Smith H. 
Published: January 2008

Abstract—Four genotypes of tomato (Lycopersicon esculentum Mill.) in the genetic background ‘Aha Craig’ were used: an aurea (au) mutant, deficient in the bulk light‐labile phytochrome pool; a high pigment (hp) mutant, showing exaggerated phytochrome responses at the time of de‐etiolation; the au,hp double mutant and the isogenic wild type (WT). A dramatic increase in plant height resulting from an increase in the length of all internodes for each of the genotypes studied was observed upon reduction of the red light: far‐red light photon ratio (R:FR) from 6.90 to 0.13 by addition of FR for the whole photoperiod. A concomitant increase in leaf length was also observed. Since au and au,hp mutants, deficient in the bulk light‐labile phytochrome pool, respond to this reduction in the R:FR these data demonstrate that the phytochrome pool that mediates this response is present and fully functional. Anthocyanin was detectable in the comparably developed young growing leaves of the WT and hp mutant under the high R:FR, but not in the au and au,hp mutants, suggesting that the potential for anthocyanin synthesis is correlated with the presence of the bulk light‐labile phytochrome pool. The kinetics of anthocyanin decrease in the young growing leaves were investigated in the hp mutant and the results suggest a very rapid cessation of flavonoid biosynthesis upon reduction of the R:FR. The functions of different phytochrome types are discussed.
PHOTOMORPHOGENIC RESPONSES TO UV RADIATION. II: A COMPARATIVE STUDY OF UV EFFECTS ON HYPOCOTYL ELONGATION IN A WILD‐TYPE AND AN aurea MUTANT OF TOMATO (Lycopersicon esculentum Mill.)
Authors: Lercari Bartolomeo , Sodi Francesco 
Published: January 2008

Abstract—Hypocotyl growth in etiolated seedlings of wild‐type and an aurea mutant of tomato (Lycopersicon esculenturn Mill.), that appears to be deficient in labile phytochrome, is strongly inhibited by UV radiation in the region of 300–400 nm. The role of phytochrome in the UV‐mediated inhibition of hypocotyl growth was studied using different experimental approaches: (1) by comparing the effectiveness of treatments of increasing duration of exposure to 692 nm and UV radiation; (2) by modifying the UV spectral range with specific cut‐off filters. The experimental results suggest that the UV‐induced inhibition of growth in wild‐type tomato is mediated to a large extent by the longer wavelengths of the UV‐A region and is mediated mainly by phytochrome. In contrast, at wavelengths < 305 nm a strong UV‐B effect was found in the aurea mutant, suggesting a preeminent action of a specific UV‐B absorbing photoreceptor that displays less action in the wild‐type.
PHOTODYNAMIC INACTIVATION OF AN ION CHANNEL: GRAMICIDIN A
Authors: Sträszle M. , Stark G. 
Published: January 2008

Abstract— The ion channel formed by the peptide gramicidin A in planar lipid membranes is inactivated by visible light in the presence of the photosensitizer Rose Bengal. This is concluded from the strong decrease of the membrane conductance by more than two orders of magnitude.Experiments performed at different oxygen concentrations, in the presence of the singlet oxygen quenchers β‐carotene or α‐tocopherol indicate, that presumably a type I process between the dye Rose Bengal and the tryptophan residues of the gramicidin channel with a subsequent oxidation of the tryptophans is responsible for the loss of the conductance properties of the channel.
FREE RADICALS AND EXCITED SPECIES IN THE METABOLISM OF INDOLE‐3‐ACETIC ACID AND ITS ETHYL ESTER BY HORSERADISH PEROXIDASE AND BY NEUTROPHILS
Authors: Escobar Jorge A. , Vásquez‐Vivar Jeannette , Cilento Giuseppe 
Published: January 2008

Abstract— The peroxidative metabolization of indole‐3‐acetic acid, a biologically important process, has been followed by EPR spectroscopy with the aim of obtaining information on the mechanism of generation of electronically excited species.The skatole‐3‐methylene radical detected during oxidation by horseradish peroxidase, does not appear to be involved in a major oxygen consuming process or in the generation of singlet oxygen. The chemiluminescence spectrum exhibits several maxima, which are also observed when the ethyl ester of indole‐3‐acetic acid is metabolized by horseradish peroxidase or by myeloperoxidase in neutrophils. When the ester is metabolically activated in either of these systems, the EPR spectrum indicates a tertiary carbon‐centered radical. This radical centered on the carbon in the 3‐position participates in a chemiexcitation/emissive route. Within the cell, this emissive process is responsible for a large part of the oxygen consumed. Some of the emitters originate in the cleavage of the 2,3 double bond.The ester, which is capable of penetrating into the cells, also emits with other myeloperoxidase‐containing cells. This compound may have useful applications as an intracellular chemiluminescent probe for the presence of myeloperoxidase.
A PHYTOCHROME PHOTOTRANSFORMATION STUDY USING TWO‐LASER/TWO‐COLOR FLASH PHOTOLYSIS: ANALYSIS OF THE DECAY MECHANISM OF I700*
Authors: Scurlock Rodger D. , Evans Christopher H. , Braslavsky Silvia E. , Schaffner Kurt 
Published: January 2008

AbstractThe mechanism of I700 decay, representing an early event in the phytochrome Pr→ Pfr phototransformation, was reanalyzed in the microsecond range by conventional laser flash photolysis as well as by two‐laser/two‐color flash photolysis. Three kinetic models that might describe the I700 decay mechanism following Pr excitation were considered: a parallel, a sequential, and an equilibrium model. These models were used to mathematically simulate both the one‐ and two‐laser flash experiments in an effort to select the model best describing the I700 decay. The sequential model could be excluded already on the basis of the one‐laser flash photolysis results alone. Discussion of the two‐laser/two‐color flash rcsults in the context of the equilibrium and the parallel models is presented.
STRUCTURAL AND FUNCTIONAL INTEGRITY OF THE PHOTOSYSTEM II REACTION CENTER ON SILVER ELECTRODES: FLUORESCENCE AND REDOX PROBES
Authors: Chumanov George , Picorel Rafael , Toon Stephen , Seibert Michael , Cotton Therese M. 
Published: January 2008

AbstractTwo simple and sensitive methods have been developed to assess the structural and functional integrity of isolated photosystem II reaction centers deposited on a roughened Ag electrode. Surface‐enhanced resonance Raman scattering (SERRS) spectra useful for ascertaining structural information can be obtained from biological materials with this technique. The first method presented is based on observing differences in the fluorescence emission properties of reaction centers; these depend on the activity of the material. The second is based on the observation of changes in Raman bands that are sensitive to the redox state of cytochrome b559 present in the reaction center complex. It is concluded that the conditions used here to obtain SERRS spectra do not affect the structural or functional integrity of the isolated photosystem II reaction center complex. In principle these approaches also could be used with other chromoproteins.
PHOTOSENSITIZATION OF SUPERCOILED DNA DAMAGE BY 5,6‐DIHYDROXYINDOLE‐2‐CARBOXYLIC ACID, A PRECURSOR OF EUMELANIN
Authors: Routaboul C. , Serpentini C.‐L. , Msika P. , Cesarini J.‐P. , Paillous N. 
Published: January 2008

Abstract—The photosensitizing or photoprotecting action of 5,6‐dihydroxyindole‐2‐carboxylic acid (DICA), an intermediate in the biosynthesis of eumelanins, was investigated. Under irradiation at 313 nm, aqueous buffered solutions of DICA (22.5 μW) photosensitized the cleavage of phage φX174 DNA. The number of single strand breaks (SSB) depended on the dose of irradiation and was more important in the absence than in the presence of oxygen. In the presence of oxygen, the quantum yield of SSB was around 6′10 7 (ΦSSB) The influence of specific scavengers, such as mannitol, sodium azide or superoxide dismutase, indicated that hydroxyl radicals, superoxide anions and perhaps singlet oxygen were involved in these processes. The increase in SSB in D2O was also indicative of the participation of singlet oxygen. Comparative experiments performed with indole‐2‐carboxylic acid (IC), a dehydrox‐ylated analog of DICA, showed that this compound, although lacking a phenol group, also photosensitized DNA cleavage via a mechanism involving hydroxyl radicals. Various sources of these radicals were envisioned. Furthermore, under our conditions, DICA was not found to photoinduce the formation of DNA dimers: No increase in SSB was observed in DNA irradiated in the presence of DICA, after treatment by phage T4 endonuclease V (an enzyme that selectively cuts DNA at dimer sites), whereas, in contrast, a significant increase in SSB was detected after treatment of DNA irradiated alone. So it appears that DICA may both photosensitize DNA cleavage and reduce UV‐induced DNA dimer formation.
INTERCONVERSION OF BACTERIOCHLOROPHYLL c AGGREGATES IN SOLID FILMS UPON ORGANIC VAPOR TREATMENT
Authors: Uehara Kaku , Tachibana Taro , Tsunooka Masahiro , Ozaki Yukihiro 
Published: January 2008

Abstract—Bacteriochlorophyll c (BChl c) solid films were prepared from a carbon tetrachloride solution on CaF2 plates as artificial aggregates. Effects of organic vapor such as acetone and tetrahydrofuran (THF) on the BChl c films were studied by absorption and Fourier‐transform infrared spectroscopy. Two major homologs (R[E,E]BChl cF and R[P,E]BChl cF) and one minor homolog (S[I,E]BChl c) isolated from the green photosynthetic bacterium Chlorobium limicola strain 6230 were examined for the experiments. The BChl c polymeric aggregates absorbing at739–753 nm similar to those in the chlorosome were induced for all homologs upon the treatment of BChl c solid film with acetone vapor. The 131‐keto C=O stretching band in the R[E,E]BChl cF solid film showed a downward shift from 1651 cm−1to 1643 cm−1 with a concomitant shift of the 31‐OH stretching bands from 3337 and 3238 cm−1 to 3163 cm−1. It was suggested that the lower aggregates brought about by Mg…O=C(131) and (31)O…O=C(131) bonds were transformed into the higher aggregates strongly hydrogen‐bonded in a Mg…(31)O‐H…O=C(13l) interaction. They were transformed to a monomer‐like form absorbing at 667 nm upon exposure to THF vapor and were reversibly converted to the higher aggregates upon removal of THF molecules in vacuo.
REDISTRIBUTION AND VIRUS INACTIVATION EFFICACY OF A SILICON PHTHALOCYANINE IN RED BLOOD CELL CONCENTRATES AS A FUNCTION OF DELIVERY VEHICLE
Authors: Ben‐Hur E. , Zuk M. M. , Chin S. , Banerjee D. , Kenney M. E. , Horowitz B. 
Published: January 2008

Abstract—The silicon phthalocyanine, HOSiPcOSi(CH3)2(CH2)3N(CH3)2 (Pc 4), is a new photosensi‐tizer that can inactivate lipid‐enveloped viruses in red blood cell concentrates (RBCC) upon exposure to red light. Because Pc 4 is insoluble in water, it was delivered either as an emulsion in saline and cremophor EL (CRM) or as a solution in dimethyl sulfoxide (DMSO). In RBCC, Pc 4 added in either vehicle distributed between the plasma and red blood cells (RBC) in a ratio of 4:6, similar to the ratio of these components in RBCC 3:7 (i.e. a hematocrit of 70%). Light exposure did not affect this distribution and caused only marginal degradation of Pc 4 at a light dose that inactivates >5 log,0 vesicular stomatitis virus (VSV). Among human plasma proteins, Pc 4 bound mainly (about 70%) to lipoproteins and to a lesser extent to albumin and lower molecular weight proteins when delivered in DMSO. When delivered in CRM, distribution between lipoproteins and albumin became more even. Among the lipoproteins Pc 4 bound almost exclusively to very low‐density lipoproteins (VLDL) when delivered in DMSO and to both VLDL and low‐density lipoproteins when added in CRM. The rate of VSV inacti‐vation was independent of the delivery vehicle but there was less RBC damage, as measured by hemolysis during storage, when Pc 4 was added in CRM. These results indicate that using CRM as emulsifier can enhance the specificity of Pc 4‐induced photochemical decontamination of RBCC for transfusion.
REACTIVITY OF SINGLET OXYGEN TOWARD LARGE PEPTIDES
Authors: Michaeli Albert , Feitelson Jehuda 
Published: January 2008

Abstract— The reactions of singlet oxygen, 1O2, with amino acids and their derivatives have been studied previously. It was found that only five amino acid residues interact readily with 1O2. Here we describe its reactions with the large peptides melittin, neuropeptide Y (NPY) and insulin in their native and in their denatured forms. The singlet oxygen quenching by a polypeptide was compared with that of a solution at the same concentration as those of its constituent amino acids, which are known to react efficiently with 1O2. It was found that the quenching rate by such a mixture exceeded that of the polypeptides in their native form. The ratio of the rate constants for NPY to that of the corresponding amino acid mixture in solution was 0.75. For melittin in its monomeric form it was 0.83 and for a tetramer of melittin (at high ionic strength) it was 0.70. For native insulin the ratio of the rate constants was 0.55. For oxidized insulin with its ‐S‐S‐ bridges opened the figure became 0.80. However, the quenching by all the polypeptides in their fully denatured form (in the presence of 6 M urea) equalled that of the corresponding amino acid mixtures. Although polypeptides are generally supposed not to possess a stable secondary structure in solution the effects are explained by shielding of some of the reactive amino acid residues in the chain by temporary folding or incipient secondary structures of the native polypeptide.It is shown that the kinetics for a homogeneous solution of quenchers applies also to measurements in a polypeptide solution where the quenchers are localized along the polypeptide backbone and thus form clusters in solution.
Preservation of Immunoreactivity in the Photolabeling of the B72.3 Human Antibody
Authors: Pandurangl Raghoottama S. , Karra Srinivasa R. , Kuntz Robert R. , Volkert Wynn A. 
Published: January 2008

AbstractA versatile photochemical method of labeling human antibodies is described. Labeling is achieved by photolyzing 4‐azido‐2, 3, 5, 6‐tetrafluoro‐14C‐methylbenzoate and the B72.3 human antibody in a buffer at physiological pH. The photochemically produced nitrene presumably inserts into bonds in the hydrophobic part of the antibody resulting in >75% attachment of the photoprobe. An immunoassay of B72.3 with mucin (B72.3 antigen) reveals >97% retention of immunoreactivity and suggests that photochemical labeling is a viable alternative for the conjugation of biomolecules.
Plant Canopy Shape and the Influences on UV Exposures to the Canopy
Authors: Parisi A. V. , Wong J. C. F. 
Published: January 2008

AbstractThe solar spectra at selected sites over hemispherical, conical and pinnacle plant canopy models has been evaluated with a dosimetric technique. The irradiance at the sites varies by up to a factor of 0.31 compared to the irradiance on a horizontal plane. The biologically effective (UVBE) exposures evaluated with the dosimetric technique at sites over the plant canopy are up to 19% of that on a horizontal plane. Compared to a spectroradiometer, the technique provides a more practicable method of measuring the UVBE exposures at multiple sites over a plant canopy. Usage of a dosimeter at one site to provide the exposures at that site for different sun angles introduces an error of more than 50%. Knowledge of the spectra allowed the UV and UVBE exposures to be calculated at each site along with the exposures to the entire canopies. These were dependent on the sun angle and the canopy shape. For plant damage, the UVBE was a maximum of about 1.4 mJ cm 2 min−1. Compared to the hemispherical canopy, the UVBE exposure for generalized plant damage was 45% less for the pinnacle canopy and 23% less for the conical canopy. The canopy exposures could not be determined from measurements of the ambient exposure.