bluuebunny/crossref_metadata_2025_split huggingface dataset:
PHOTOREACTIVATION OF KILLING IN STREPTOMYCES: ACTION SPECTRA AND KINETIC STUDIES*
Authors: JAGGER JOHN , TAKEBE HIRAKU , SNOW JEANNE M. 
Published: January 2008

Abstract— An action spectrum was obtained for photoreactivation of killing (PR) of Streptomyces griseus conidia. This spectrum shows a major peak around 436 nm, originally observed by A. Kelner, and a secondary peak at 313 nm not previously reported. The rate of PR shows a strong dependence upon temperature and dose rate of the PR light at 436 nm, but this decreases to only a slight dependence upon these parameters at 313 nm. These findings suggested that PR at 436 nm in this organism is of the usual photoenzymatic type, but that PR at 313 nm might be of a different kind.A mutant (PHR‐1) of S. griseus was found that shows only a narrow range of PR (roughly 310–400 nm) with a single peak at 313 nm. The PR efficiency was lower than for wild type and the PR sector not greater than one‐half that of wild type. This PR shows no temperature dependence. Essentially similar behavior was observed with wild‐type Streptomyces coelicolor. These findings show that at least some of the PR at 313 nm is a separable phenomenon. It is therefore unlikely to involve a mechanism identical to that at 436 nm.The nature of PR at 313 nm in Streptomyces is not known. If it is enzymatic, it is remarkable in having little or no dependence upon temperature and dose rate. Absence of photoprotection and liquid‐holding recovery indicate that it is not indirect PR. Some of it (that part exhibited by S. griseus PHR‐1 and S. coelicolor) might result from a direct photochemical action on DNA.
PHOTOPRODUCTS OF BROMOURACIL‐LABELED DNA AND THE STRUCTURE OF 5‐BROMODEOXYURIDYLYL‐(3' → 5')‐THYMIDINE PHOTOPRODUCT
Authors: PETER HEINRICH H. , DREWER ROBERT J. 
Published: January 2008

Abstract— –An attempt was made to identify some of the ultraviolet (u.v.) photoproducts of 5‐bromouracil‐labeled DNA (BrU‐DNA). Two synthetic dinucleotides, 5‐bromodeoxyuridylyl‐(3' →5 ')‐thymidine (BrdUpT) and 5‐bromodeoxyuridylyl‐(3' → 5')‐deoxycytidine (BrdUpdC), were prepared. Each gave a single u.v. photoproduct which in turn gave a single acid hydrolysis product. 2‐14C‐BrU‐DNA. prepared from E. coli B3, was irradiated (275–280 nm), hydrolyzed, and paper chromatographed in four systems. Comparison with the two synthetic photoproducts showed that if present at all, BrdUpT and BrdUpdC photoproducts could account for no more than 10 and 3.5 per cent respectively of the total photoproducts. At 55 per cent conversion of BrU into photoproducts, the major 14C‐photoproduct was uracil (78 per cent); the remaining 22 per cent was made up of at least six products, three of which were reversed by 232 nm irradiation.The debrominated cyclobutane structure proposed by Haug for BrdUpT photoproduct has been shown to be incorrect. It was found to contain one atom of bromine per molecule. On the basis of nuclear magnetic resonance and u.v. spectra, two possible structures are proposed for the photoproduct, each containing an eight‐membered ring.
EPR STUDY OF WOOL IRRADIATED WITH BLUE LIGHT
Authors: SHATKAY A. , MICHAELI I. 
Published: January 2008

Abstract— Wool fibres were exposed to visible light in the blue range. The free radicals created by the illumination were studied using electron paramagnetic resonance. It is shown that by control of the light intensity and frequency it is possible to get considerable insight into the mechanism of the creation and the decay of the free radicals. The radical population under the above conditions appears to consist of an initial stable radical insensitive to radiation, and three other radicals, two of which follow decay kinetics considerably different from that of the remaining free radical. All the latter three radicals are probably caused by N–H or C–H bond scission.The kinetics of radicals in irradiated proteins is discussed. It is shown that the mechanisms previously suggested in the literature are inadequate to account for the form of the experimental curve describing the number of radicals vs. time in irradiated protein. A new mechanism is suggested in which the decayed radicals form sites immune to further irradiation. Such a mechanism is shown to be consistent with the experimental curves. The kinetics of the decay of radicals after the cessation of illumination is examined in detail. It is found that in the case of irradiated keratin the mechanisms assuming first order decay are inconsistent with the experimental results, while the assumption of second order decay for two different species of radicals yields results consistent with the experimental evidence.
THE NATURE OF ULTRAVIOLET LIGHT‐INDUCED STRAND BREAKAGE IN DNA CONTAINING BROMOURACIL
Authors: DODSON M. L. , HEWITT R. , MANDEL M. 
Published: January 2008

Abstract— Single‐strand breaks are produced in the phosphodiester backbone of ultraviolet‐light‐irradiated 5–bromodeoxyuridine‐containing DNA (BU‐DNA) after treatment with alkali. No radiation dependent breakage is observed in thymine‐containing DNA (thy‐DNA). The relative yields of breaks terminated by 5′‐hydroxyl and 5′‐phosphate groups was determined by measuring the rate of phosphorylation achieved with polynucleotide kinase in BU‐DNA single strands before and after treatment with alkaline phosphatase. The ratio of 5′‐phosphate to 5′ hydroxyl groups ranged from 2.3 to 2.9 in different experiments. When cysteamine was present during irradiation no new end groups were produced.In order to identify the nucleoside(s) at the 5′‐termini, phosphate groups were removed with alkaline phosphatase and the 5′‐hydroxyl groups were phosphorylated with polynucleotide kinase. Electrophoresis of enzymatic digests showed a single 32P‐labeled component migrating more rapidly than any of the four usual 5′‐mononucleotides. Upon column chromatography this component resolved into a major peak coincident with 5′‐dUMP and a lesser unidentified constituent. No 5′‐dBUM32P was observed among these nucleotides.
PHOTOREACTION OF FMN‐TRICINE AND ITS PARTICIPATION IN PHOTOPHOSPHORYLATION*
Authors: NELSON N. , NELSON H. , RACKER E. 
Published: January 2008

Abstract— In the presence of light, Tricine efficiently reduced flavin. Under aerobic conditions, oxygen uptake was observed. Inhibition studies with superoxide dismutase, with cytochrome c as electron acceptor, suggested that about 50% of the reduced oxygen was superoxide anion. Oxygen uptake by this system was markedly inhibited by 2.5 mM phenol or salicyl aldehyde.A rapid and convenient assay for superoxide dismutase was developed based on the light‐induced reduction of cytochrome c by flavin mononucleotide (FMN) and Tricine.Reduction of cytochrome c in chloroplasts without addition of ferredoxin appears to be mediated by superoxide anions, as indicated by inhibition of this reaction by superoxide dismutase.Loss of photophosphorylation by sonication of chloroplasts could be partially prevented by the presence of Tricine and FMN during sonication. Phosphorylation under these conditions was dependent on white light, but no evidence for the participation of superoxide anion could be obtained with internal or external superoxide dismutase.
A STUDY OF THE METHYLENE BLUE‐SENSITIZED OXIDATION OF AMINO ACIDS
Authors: KNOWLES A. , GURNANI S. 
Published: January 2008

Abstract— A study has been made of the effects of eight amino acids and a group of compounds related to tryptophan upon the photofading of methylene blue under anaerobic conditions and upon the excited species generated by flash photolysis of the dye. These effects are discussed in relation to the ease of sensitized photooxidation of the amino acids by methylene blue, in order to test the hydrogen‐abstraction mechanism proposed for this reaction.In general, amino acids susceptible to sensitized oxidation also act as reducing agents in the photoreduction of methylene blue, while the insensitive compounds do not reduce the light‐excited dye molecule. Methionine, histidine and tyrosine are exceptions, but this is probably due to our choice of pH for the photofading experiments.The flash‐photolysis experiments give no clear‐cut evidence for a reaction between amino acid and dye triplet excited state leading to an enhanced yield of the semi‐reduced radical, thought to be an intermediate of the photofading reaction. The lifetime of the semi‐oxidized radical is reduced by many of the amino acids, and this may be the reactive intermediate in their oxidation.
MEASUREMENT OF THE TEMPERATURE DEPENDENCE OF THE FLUORESCENCE QUANTUM YIELD OF ORGANIC MOLECULES IN SOLUTION
Authors: MANTULIN W. W. , HUBER J. R. 
Published: January 2008

A DETAILED investigation of the temperature dependence of the fluorescence quantum yield φf can yield–directly or indirectly–significant information about behavior of excited states of organic molecules, such as the temperature effect on radiationless transitions and on photochemical reactivity. Variation of the temperature changes the viscosity of the solvent and, in conjunction with measurements of φf(T), allows investigations of diffusion‐controlled processes. For example, energy transfer and quenching processes as well as excimer or exciplex formation fall into this category. Recent review articles by Weller (1962) and Birks (1970) deal with this topic. Moreover, Huber and Mantulin (1972) have suggested that restraints placed upon geometric modifications of the excited molecule by temperature‐induced changes in the solvent cage (variation of site structure) are reflected in a varying φf.The purpose of this note is to describe and verify a simple procedure, accurate to about ± 5%, for measuring the relative fluorescence quantum yield as a function of temperature. A quantum yield study of 9,10‐diphenylanthracene between room temperature and 77°K is employed to demonstrate the capabilities of this method. In addition, we consider an example of diffusion‐controlled quenching by oxygen measured over a wide temperature range.
ROLE OF THE TRYPTOPHAN FLUORESCENT STATE IN THE ULTRAVIOLET‐INDUCED INACTIVATION OF β‐TRYPSIN*
Authors: Sellers D. R. , Ghiron C. A. 
Published: January 2008

Abstract— Stern‐Volmer quenching constants for β‐trypsin at pH 3 were determined for fluorescence quenching by histidine, acrylamide, and nitrate ion. A modified Stern‐Volmer plot (Lehrer, 1971) was employed to show that all of the fluorescent tryptophanyl residues of β‐trypsin were equally susceptible to quenching by acrylamide at pH 3 when the enzyme was either in its native conformation or denatured in 6 M guanidine hydrochloride (GuHCl). Fluorescence lifetime measurements indicated that acrylamide quenched β‐trypsin fluorescence by a purely collisional mechanism. Solvation of tryptophanyl residues of the protein was maximal at 2.5 M GuHCl, as monitored by fluorescence emission wavelength.Investigations of the ultraviolet‐induced inactivation of β‐trypsin at 295 nm were performed in the presence of acrylamide at pH 3. The quantum yields for enzyme inactivation and indole destruction (determined using the PDAB reagent) were unchanged upon depopulation of the fluorescent state by 65 per cent, whether the enzyme was in its native conformation or denatured by 6 M GuHCl. It is concluded that the fluorescent state of tryptophanyl residues of β‐trypsin is not involved in enzyme inactivation or tryptophan destruction.
COMPARISON OF PHOTOTRAP COMPLEXES FROM CHROMATOPHORES OF RHODOSPIRILLUM RUBRUM, RHODOPSEUDOMONAS SPHEROIDES, AND THE R‐26 MUTANT OF RHODOPSEUDOMONAS SPHEROIDES*
Authors: HALL R. L. , Kung M. Chu , Fu M. , Hales B. J. , Loach P. A. 
Published: January 2008

Abstract— After dissolution of the membrane structure of chromatophores from Rhodospirillum rubrum, Rhodopseudomonas spheroides, and the R‐26 mutant of Rhodopseudomonas spheroides, active phototrap complexes from each have been purified by a column electrophoresis procedure. Phospholipids and transition metals were well separated from the phototrap complex in all three systems. The purified R. rubrum phototrap complex retained a full complement of antenna bacteriochlorophyll and carotenoid pigments which had nearly the same absorbance spectra as in the intact cell, and which delivered absorbed light energy to the phototrap with just as high efficiency as in the intact cell. Sodium dodecyl sulfate (SDS) disc gel electrophoresis using Tris buffer showed that these preparations often contained only two prominent polypeptides of 30,000 ± 2000 and 12,000 ± 4000 mol. wt., and a lesser amount of a third polypeptide of 21,000 ± 2000 mol. wt.The phototrap complexes prepared from the wild type and the R‐26 mutant of R. spheroides were similar, in that a partial separation from antenna pigments occurred during column electrophoresis. Both complexes had prominent polypeptides of 24,000 ± 2000 and 21,000 ± 2000 mol. wt., but no polypeptide of 30,000 mol. wt remained after electrophoresis. A third major polypeptide occurred with a mol. wt. of about 12,000 but seemed identifiable with an incompletely separated antenna pigment fraction. The phototrap complex prepared from the R‐26 mutant had a typical reaction center spectrum.In the case of wild type R. spheroides purification, two distinct protein‐pigment complexes separated. Although the absorbance of the bacteriochlorophyll and carotenoid pigments were little changed from those of the in vivo system, different polypeptides in the two fractions were observed by SDS disc gel electrophoresis; only one fraction seemed to be intimately related with the phototrap complex.
PHOTOFRAGMENTATION OF HYDROXYACETONE, 1.3‐DIHYDROXYACETONE, AND 1.3‐DICARBOXYACETONE IN AQUEOUS SOLUTION. AN EPR STUDY
Authors: Steenken S. , Jaenicke‐Zauner W. , Schulte‐Frohlinde D. 
Published: January 2008

Abstract—On photoexcitation, hydroxyacetone undergoes a Norrish‐type‐1 fragmentation to yield CH3CO and CH2OH. CH2OH is identified by its EPR spectrum. The existence of CH3CO is inferred from the presence of diacetyl and acetaldehyde in irradiated solutions. Above pH 5, in addition to CH2OH, the cis and trans forms of the hydroxyacetone enediol radical anion, CH3C(O‐)=C(O***)H, are detected. 1.3‐Dihydroxyacetone is photodecomposed to HOCH2C̀O and C̀H2OH. The former radical decarbonylates to yield CH2OH and CO. At 254 nm the overall quantum yield of CO production is 0.75. Above pH 5, in addition to CH2OH, the cis and trans forms of the 1.3‐dihydroxyacetone enediol radical anion, HOCH2C(O‐)C(O***)H, are observed.Electronically excited hydroxyacetone and 1.3‐dihydroxyacetone react exclusively by C‐C fragmentation, and no H‐abstraction from H‐donors is observed. In contrast, electronically excited 1.3‐dicarboxyacetone shows H‐abstraction from H‐donors in competition with C‐C fragmentation. In the absence of H‐donors, fragmentation resulting in CH2CO2‐ and ‐O2CCH2C̀O occurs followed by decarbonylation of ‐O2H2C̀O. At 254 nm the quantum yield of CO production is 0.02. In the presence of H‐donors, H‐abstraction, yielding HO2CCH2C(OH)CH2CO2, predominates.
THERMOLUMINESCENCE STUDIES ON SPINACH LEAVES AND EUGLENA
Authors: Desai T. S. , Sane P. V. , Tatake V. G. 
Published: January 2008

Abstract— Spinach leaves and Euglena cells when frozen in light to 77 K emit light during slow warming in the dark to give 6 peaks. The peak appearing at 118 K is observed even after DCMU or heat treatment and also in aged chloroplasts that are inactive in electron transport.The data indicate that peaks appearing at 261 and 321 K are due to back reactions of primary acceptors of PS II and PS I respectively with oxidized chlorophylls. The DCMU sensitivity of Tl peaks at 283 and 298 K suggests that they are associated with the flow of electrons between PS II and PS I. Evidence has been presented to show that the PS 1 chlorophylls are involved in part of the luminescence observed during the temperature rise.A mechanism involving the return of the thermally detrapped electrons to the ground state of chlorophylls through their excited states has been proposed to explain some of the Tl peaks.
INTER‐ AND INTRAMOLECULAR EFFECTS OF TYROSYL RESIDUES ON FLAVIN TRIPLETS AND RADICALS AS INVESTIGATED BY FLASH PHOTOLYSIS*
Authors: McCormick Donald B. , Falk Michael C. , Rizzuto Frank , Tollin Gordon 
Published: January 2008

Abstract— Addition of tyrosine or derivatives to aqueous solutions of flavins does not significantly impede either formation of the flavin triplet or the rate of O2 oxidation of the flavin radical generated by reaction of triplet with the phenol. However, the rate of radical decay is decreased.There is only a modest effect that results from altering the nature of the group on alkyl side chains of the flavin when the substituent, e.g. phenylalanine, does not complex avidly with the isoalloxazine system. However, when a tyrosyl or O‐methyltyrosyl residue is covalently attached to an alkyl side chain at the N10‐position of the flavin, the considerable intramolecular complexing that results markedly decreases the formation of flavin triplet and, therefore, the radical yield. The rate of triplet decay is not much different than for noninternally complexed flavins, but extensive intramolecular radical decay occurs, and the rate of 02 oxidation of radical is decreased. A shorter alkyl chain is more effective than a longer one for decreasing triplet production, but the greater proximity of a photooxidiz‐able tyrosyl residue to the flavin nucleus within the former allows a slightly higher intramolecular radical yield. Attachment of a tyrosyl residue by a short chain from the N3‐position of the flavin has only a modest effect on the production of flavin triplet and its decay. There is less radical production from internal than from external tyrosyl residues, and the rate of O2 oxidation of the flavin radical generated by such intermolecular photoreductants as N‐acetyl tyrosine ethyl ester or EDTA is somewhat decreased.The tyrosyl residue within the active‐site peptide of mitochondrial monoamine oxidase is not so susceptible to photooxidation by the 8α‐(S‐L‐cysteinyl)flavin involved, since the thioether linkage at this position severely reduces triplet production. Upon oxidation of the thioether to sulfone, however, the triplet yield is partially restored. Some flavin radical can then be generated from either the intra‐ or an intermolecular tyrosyl residue.Taken together, these results demonstrate that tyrosyl residues near the flavin‐binding sites of flavo‐proteins can become oxidized by the flavin triplet that is light‐generated unless the proximity and steric disposition of the interactants is such as to allow dissipation of much of the energy as radiationless decay within a tight complex or unless an 8α‐thioether linkage to the flavin coenzyme is involved. Also, flavin radicals, whether generated photochemically or by biochemical oxidation of substrate, are readily oxidized by O2 in the presence of tyrosyl functions unless tight complexing occurs. More remarkable, though, is the decreased rate of radical decay conferred by the association with a tyrosyl residue. This stabilization of reactive flavin radicals may have considerable consequence in the catalytic mechanism of such enzymes.
EXTRARETINAL PHOTORECEPTION IN LIZARDS
Authors: Underwood Herbert , Menaker Michael 
Published: January 2008

Abstract— In lizards both photoperiodic photoreception and entrainment (synchronization) of the biological clock by environmental light cycles can be accomplished by extraretinal photoreceptors. Testicular size and spermatogenic activity in the green anole, Anolis carolinensis, is maintained under long (14 h) photoperiods in the summer in both sighted and blinded lizards whereas short days (6h) cause testicular regression. In the fall, long photoperiods cause testicular recrudescence and maturation in blinded and blinded‐parietalectomized anoles as well as in sighted anoles.Extraretinal photoreceptors can mediate entrainment of the circadian locomotor rhythm in every lizard species examined to date (8 species). The photosensory pineal complex in lizards (pineal organ and parietal eye) may not be involved in entrainment; in any case, its removal does not prevent entrainment of blinded lizards. Localization experiments have shown that the brain is the site of the extraretinal receptors mediating entrainment. The lateral eyes can also contribute to entrainment. In some species, but not all, blinding alters the pattern of the entrained activity rhythm. The free‐running activity rhythms of two species of lizards exposed to continuous illumination respond very differently to blinding; these experiments yield insight into the mechanisms of entrainment in the two species as well as showing that caution must be observed when generalizing about the role of retinal and extraretinal receptors not only among different vertebrate classes but also among species of the same class.
PHOTOCHEMISTRY OF POLYURIDYLATE‐TERBIUM(III) COMPLEX
Authors: Formoso Carl 
Published: January 2008

SummaryUpon irradiation with 240–300nm light a photochemical reaction occurs in Tb3+ complexes of polyuridylate and oligouridylate. The reaction is monitored by the appearance of a fluorescence excitation band which does not exist in non‐irradiated samples. The photochemical reaction is not observed in uridine nucleotides, dinucleoside phosphates, or when polyuridylate forms a double stranded helix with polyadenylate.
THE EFFECT OF OXIDANT INJURY ON THE LYMPHOBLASTIC TRANSFORMATION OF HUMAN LYMPHOCYTES*
Authors: Jr Arthur L. Sagone , Ramps Susan , Campbell Robert 
Published: January 2008

Abstract— We have studied the effect of oxidant injury on the lymphoblastic transformation and glucose metabolism of human lymphocytes. Lymphocyte cultures were incubated with xanthine oxidase and xanthine, an enzyme system known to generate several highly reactive oxygen compounds. Lymphoblastic transformation to phytohemagglutinin was quantitated by the stimulation of DNA synthesis as indicated by the 3H‐thymidine uptake of the cultures at 3 days.The lymphoblastic transformation of cultures incubated with the enzyme system was significantly impaired compared to controls. These cultures also failed to demonstrate the burst of glucose metabolism characteristic of transforming cells. To firmly establish that the effect of the enzyme system on lymphoblastic transformation was related to reactive oxygen molecules, the effect of several scavengers was studied. Cultures supplemented with catalase were almost completely protected against the effect of the enzyme system. In contrast, cultures supplemented with superoxide dismutase, mannitol and azide. scavengers of superoxide, hydroxyl radicals, and singlet oxygen, respectively, were not protected. These data indicate that the functional capacity of human lymphocytes can be impaired in vitro by exposure to hydrogen peroxide.
BLUE‐LIGHT INDUCED DEVELOPMENT OF CHLOROPLASTS IN ISOLATED SEEDLING ROOTS. PREFERENTIAL SYNTHESIS OF CHLOROPLAST RIBOSOMAL RNA SPECIES
Authors: Richter Gerhard , Dirks Werner 
Published: January 2008

AbstractExcised roots of pea seedlings (Pisum sativum var. “Alaska”) cultured in a synthetic medium under sterile conditions exhibit differentiation of functional chloroplasts from leucoplasts when irradiated with blue light (350–550 nm). This transition is a relatively slow process; nevertheless, the chloroplasts formed in blue light compare very well to leaf chloroplasts as far as microstructure and photosyn‐thetic activities are concerned.Apparently certain activities of the apical meristem are mandatory in bringing about a transition from leucoplasts to chloroplasts in blue light. After short‐time labelling with [jH]uridine the synthesis of plastid ribosomal RNA (rRNA) was studied either during irradiation with blue and red light (600–700 nm), respectively, or in darkness. Polyacrylamide gel electrophoresis revealed that in blue light the synthesis of specific chloroplast rRNA species with molecular weights of 1.1 × 106 and 0.56 × 106 daltons is markedly stimulated. In contrast, in dark cultured roots these RNA species were synthesized to a limited extent only whereas the cytoplasmic rRNA species of 1.3 × 106 and 0.7 × 106 daltons molecular weight were preferentially formed. The same holds true for roots irradiated with red light.