bluuebunny/crossref_metadata_2025 huggingface dataset:
ULTRAVIOLET INACTIVATION OF PAPAIN*
Authors: Baugher J. F. , Grossweiner L. I.
Published: January 2008

Abstract— Flash photolysis transient spectra (Λ > 250 nm) of aqueous papain show that the initial products are the neutral tryptophan radical Tip (Λmax 510 nm), the tryptophan triplet state 3Trp (Λm., 460nm), the disulfide bridge electron adduct –ṠS‐— (Λmax 420nm) and the hydrated electron eaq‐. The –ṠS‐– yield was not altered by nitrous oxide or air, indicating that the formation of this product does not involve electrons in the external medium. The original papain preparation was activated by irradiating under nitrogen. The action spectrum supports previous work attributing the low initial activity to blocking of cysteinyl site 25 with a mixed disulfide. Flash lamp irradiation in nitrogen led to activation at low starting activities and inactivation at higher starting activities, while only inactivation at the same quantum yield was observed with air saturation. The results are consistent with photoionization of an essential tryptophyl residue as the key inactivating step.
PHOTODYNAMIC ALTERATIONS OF THE CELL ENVELOPE OF PROTEUS MIRABILIS AND THEIR REPAIR
Authors: Jacob Hans‐Egon , Hamann Marianne
Published: January 2008

Abstract— Photodynamic treatment of Proteus mirabilis gives rise to changes in the cell envelope as can be detected by the behaviour of cells during lysis: lysis of cells proceeds more readily than that of untreated cells, measured by the liberation of labelled DNA. After photodynamic treatment the cell envelope is restored to the control levels. This repair process takes place within 5 min in broth as well as in buffer solutions.
PHOTOELECTRON QUANTUM YIELDS AND PHOTOELECTRON MICROSCOPY OF CHLOROPHYLL AND CHLOROPHYLLIN
Authors: Dam Rudy J. , Kongslie Keith F. , Griffith O. Hayes
Published: January 2008

Abstract— The absolute PE quantum yield curves of chls a and b,.chin, and phytol were examined over the wavelength range 500‐180 nm. In the long wavelength region (500‐240 nm) quantum yields are below 5 × 10‐6 electrons per incident photon. Below 240 nm the quantum yields rise sharply. The chls and chin exhibit similar yield curves; measured yields were of order 5 × 10‐6 electrons per incident photon at 240 nm, 1 × 10‐4 at 220 nm, and 1 × 10‐3 at 180 nm. These yields are at least 2 orders of magnitude greater than those of the amino acids and more than three orders of magnitude greater than that of phytol over this wavelength region. Photoemission observed in chl thin films is due to the porphyrin moiety of the molecule. High contrast is obtained in PE micrographs of chin deposited on substrates of bovine serum albumin, dipalmitoyl phosphatidylcholine, or starch. Chl is expected to be the dominant photoemissive component of thylakoid membranes and accounts for the image contrast observed previously in PE micrographs of spinach chloroplasts.
THE EFFECT OF 9‐ETHYLADENINE ON THE PHOTODIMERIZATION OF 1‐CYCLOHEXYLTHYMINE
Authors: Nakata Toshio , Yamato Masayuki , Tasumi Mitsuo , Miyazawa Tatsuo
Published: January 2008

Abstract— The photodimerization of 1‐cyclohexylthymine (l‐CT).and the effect of adding 9‐ethyladenine (9‐EA) on this reaction were studied in chloroform and/or acetonitrile solutions. The photodimerization of 1‐CT is shown to occur through an excited triplet state. 9‐EA works as an inhibitor against this reaction by quenching the excited singlet state of 1‐CT. It is suggested that a singlet exciplex made up from the excited state 1‐CT and the ground state 9‐EA by hydrogen‐bonding may play an important role in the quenching process.
THE PHOTOSENSITIZED OXIDATION OF TYROSINE DERIVATIVES IN THE PRESENCE OF ALGINATE—II: REACTION UNDER HETEROGENEOUS CONDITIONS
Authors: Seely G. R. , Hart R. L.
Published: January 2008

Abstract—The thionine sensitized photooxidations of several tyrosine derivatives have been compared in a system in which the dye, bound to the anionic polysaccharide alginate, is separated by a dialysis membrane from a much larger external phase containing most of the substrate. Brown oxidation products appear both inside the bag and outside, but at considerably greater concentration inside. Oxidation products inside the bag retard the oxidation of the original substrate by competing with it for photooxidant. Substrates were divided into two groups, related to tyrosine and tyramine respectively, according to their rates of oxidation. The groups differ as to whether the prevailing phenolate form of the substrate is a zwitterion or an anion. In case of the latter, the Donnan equilibrium set up by the polyelectrolyte reduces its concentration in the polymer phase, and thereby the rate of oxidation. Titration and dialysis data support this interpretation.
SPECTROSCOPIC BEHAVIOUR OF RETINYL POLYENES IN SOLID FILMS
Authors: Hotchandani Surat , Leblanc Roger M.
Published: January 2008

Abstract— The absorption spectroscopic study of retinyl polyenes, i.e. all‐trans retinal, 9‐cis retinal, 13‐cis retinal, all‐trans retinol, 13‐cis retinol and all‐trans retinyl acetate in solid films is discussed. The spectra of the films with low surface coverages obtained from dilute solutions are red shifted relative to their solution spectra. This shift is interpreted as due to the weak interaction between the surface and polyene molecules. With increased surface coverages, i.e. the films obtained from concentrated solutions, the retinals show a large red shift whereas a blue shift is observed with the retinols. Chromophore–chromophore interactions in addition to the surface effects are believed to be responsible for such observations. Effect of surface causing permanent changes in molecule is also discussed.
ACTION SPECTRUM AND ELECTROPHYSIOLOGICAL RESPONSES CORRELATED WITH THE PHOTOPHOBIC RESPONSE OF STENTOR COERULEUS
Authors: Wood David C.
Published: January 2008

Abstract— The blue‐green ciliate. Stentor coeruleus, is found predominantly in shady places. This concentration occurs because stentor responds when swimming from a shaded area to a lighted area by reversing the direction of its ciliary beat and reorienting its swimming direction until it once again is in the shaded area. A graded receptor potential is recorded from microelectrodes in vacuoles of stentor when the animal is photically stimulated. For all but very weak stimuli this receptor potential is sufficient to elicit a regenerative transmembrane response of variable amplitude in a swimming animal. Suprathreshold electrical stimuli also elicit this regenerative response. In turn the regenerative response is coupled to ciliary reversal. Thus ciliary reversal appears to be produced whenever the photic receptor potential crosses the threshold for elicitation of the regenerative response.

Using the threshold for production of ciliary reversal as a criterion response, an action spectrum was obtained. This action spectrum correlates well with the absorption spectrum of the major pigment of S. coeruleus, stentorin. Stentor bleached of pigment also have an elevated threshold for ciliary reversal. Thus stentorin seems to be the photosensitive pigment in stentor responsible for its photophobic behavior.
SINGLET AND TRIPLET MECHANISMS IN PHOTOCHEMISTRY
Authors: Birks J. B.
Published: January 2008

A perturbation method is proposed for determining the photochemical quantum yields of the singlet and triplet mechanisms for an organic compound in solution. Some common fallacies about singlet and triplet mechanisms in the photochemical literature are discussed.
PHOTOLYSIS AND RADIOLYSIS OF THE BENZENE‐FUMARONITRILE SYSTEM
Authors: Schuler P. , Heusinger H.
Published: January 2008

Abstract— The photolytic and radiolytic product formation of the complex benzene‐fumaronitrile are compared. The equilibrium constants for the complexes of benzene‐fumaronitrile and benzene‐maleonitrile determined by UV and NMR spectroscopy are given. The products which were found in both photolysis and radiolysis of the system benzene‐fumaronitrile were biphenyl. phenylsuccinodinitrile and maleonitrile. The production of a 2:1 adduct of fumaronitrile and benzene in very small yields could only be confirmed in the case of photolysis. Additional products in radiolysis were phenylcyclohexadienes and benzonitrile. Experiments using filtered light proved that isomerisation of fumaronitrile to maleonitrile and production of phenylsuccinodinitrile proceed via the excited charge‐transfer complex. There are indications that the excited charge transfer complex is likewise an intermediate in the radiolytic formation of these nitriles. The addition of fumaronitrile to benzene reduces the yield of biphenyl in both photolysis and radiolysis.
DISTORTIONS IN AMPHIBIAN DEVELOPMENT INDUCED BY ULTRAVIOLET‐B ENHANCEMENT (290–315 NM) OF A SIMULATED SOLAR SPECTRUM
Authors: Worrest Robert C. , Kimeldorf Donald J.
Published: January 2008

Abstract— Effects of increased intensity of UV‐B radiation (290–315nm) on the systemic development and viability of boreal toad tadpoles were studied. When compared with animals exposed to UV‐B deficient radiation of similar irradiance, tadpoles exposed to UV‐B enhanced radiation displayed (1) abnormal development of the presumptive cornea, (2) areas of hyperplasia in the integument, (3) an anomalous, concave curvature of the spine, and (4) increased mortality. Daily exposure to photoreactivating radiation (> 315nm) following UV‐B insult mitigated the potentially lethal damage to the tadpole population.
THE PHOTOREDUCTION OF METHYLENE BLUE BY AMINES—I. A FLASH PHOTOLYSIS STUDY OF THE REACTION BETWEEN TRIPLET METHYLENE BLUE AND AMINES
Authors: Kayser R. H. , Young R. H.
Published: January 2008

Abstract— Flash photolysis was used to study the reduction of the triplet state of methylene blue by both alkyl‐ and aryl‐amines. The extent of the formation of the semireduced form of the dye yielded rate constants of interaction between the triplet state and the amine (k5). A correlation between log k5 and ionization potentials for alkylamines (slope = ‐1.75 eV‐1) was interpreted as evidence for the formation of a partial charge‐transfer intermediate. The rate constants (k5) calculated for aryl‐amines approached the rate of diffusion in many cases. A Hammett plot for a series of N, N‐dimethyl‐anilines yielded a moderately large p value (– 3.28) consistent with the formation of a charge‐transfer intermediate. It was concluded that reaction of amines with triplet methylene blue leads to the formation of a partial charge‐transfer intermediate which may undergo complete electron transfer to yield radicals, or undergo spin inversion and return to the ground state.
INTERACTION BETWEEN PROFLAVINE AND GUANOSINE 5‘‐PHOSPHATE: IMPORTANCE OF PHOTOEXCITATION
Authors: Badea M. G. , Georghiou S.
Published: January 2008

Abstract— The stoichiometry of the complex formed between the mutagenic drug proflavine and the nucleotide guanosine 5'‐phosphate has been demonstrated to be 1:1. Its association constant at room temperature is found to increase from 310 M‐1 when proflavine is in its ground electronic state, to 1550 M‐1, when proflavine is in its first excited singlet state. Thus, light absorbed by the drug alters its reactivity which, in turn, results in an appreciable increase in its ability to bind to the nucleotide. The enthalpy and the entropy of the ground state proflavine‐guanosine 5'‐phosphate complex formation are ‐12.6 kJ/mol (‐3 kcal/mol) and ‐6.7 J/mol/deg (‐1.6 cal/mol/deg), respectively. The implications of these findings concerning the proflavine‐DNA interaction as well as the possible importance of electronic excitaton in acridine mutagenesis are discussed. An appraisal of the methodology for analyzing fluorescence quenching data is also given.
ULTRAVIOLET RADIATION‐INDUCED MUTABILITY OF uvrD3 STRAINS OF ESCHERICHIA COLI B/r AND K‐12: A PROBLEM IN ANALYZING MUTAGENESIS DATA
Authors: Smith Kendric C.
Published: January 2008

Abstract— The involvement of the uvrD gene product in UV‐induced mutagenesis in Escherichia coli was studied by comparing wild‐type and uvrA or uvrB strains with their uvrD derivatives in B/r and K‐12(W3110) backgrounds. Mutations per survivor (reversions to prototrophy) were compared as a function of surviving fraction and of UV fluence. While recognizing that both methods are not without problems, arguments are presented for favoring the former rather than the latter method of presenting the data when survival is less than 100%. When UV‐induced mutation frequencies were plotted as a function of surviving fraction, the uvrD derivatives were less mutable than the corresponding parent strains. The B/r strains exhibited higher mutation frequencies than did the K‐12(W3110) strains. A uvrB mutation increased the mutation frequency of its parental K‐12 strain, but a uvrA mutation only increased the mutation frequency of its parental B/r strain at UV survivals greater than ˜ 80%. Both the uvrA and uvrB mutations increased the mutation frequencies of the uvrD strains in the B/r and K‐12 backgrounds, respectively. Rather different conclusions would be drawn if mutagenesis were considered as a function of UV fluence rather than of survival, a situation that calls for further work and discussion. Ideally mutation efficiencies should be compared as a function of the number of repair events per survivor, a number that is currently unobtainable.
SINGLE‐STRAND BREAKS IN THE DNA OF THE uvrA AND uvrB STRAINS OF ESCHERICHIA COLI K‐12 AFTER ULTRAVIOLET IRRADIATION
Authors: Youngs David A. , Smith Kendric C.
Published: January 2008

Abstract— DNA single‐strand breaks were produced in uvrA and uvrB strains of E. coli K‐12 after UV (254 nm) irradiation. These breaks appear to be produced both directly by photochemical events, and by a temperature‐dependent process. Cyclobutane‐type pyrimidine dimers are probably not the photoproducts that lead to the temperature‐dependent breaks, since photoreactivation had no detectable effect on the final yield of breaks. The DNA strand breaks appear to be repairable by a process that requires DNA polymerase I and polynucleotide ligase, but not the recA, recB, recF, lexA101 or uvrD gene products. We hypothesize that these temperature‐dependent breaks occur either as a result of breakdown of a thermolabile photoproduct, or as the initial endonucleolytic event of a uvrA, uvrB‐independent excision repair process that acts on a UV photoproduct other than the cyclobutane‐type pyrimidine dimer.
A SURVEY OF EPR INVESTIGATIONS OF BACTERIAL PHOTOSYNTHESIS
Authors: Corker G. A.
Published: January 2008

Abstract— Investigations in which EPR has been used as a probe of the mechanism of the primary quantum conversion reaction and/or electron transport reactions in bacterial photosynthesis are surveyed. These investigations include studies of whole cell organisms and simpler sub‐cellular preparations, chromatophores and bacteriochlorophyll‐protein complexes.

Electron paramagnetic resonance studies have successfully demonstrated that the primary donor of the photosynthetic, photochemical reaction involves a dimer of bacteriochlorophyll, generally referred to as P870. P870 is photochemically oxidized to a cation radical which exhibits a g= 2.0025 EPR signal. Comparative studies of the time behaviour of this signal in whole cells and in sub‐cellular preparations show that electron flow in the whole cells is substantially different than in the cell‐free systems.

The primary acceptor molecule of the photochemical reaction has not been conclusively identified. When it is photochemically reduced, it exhibits a broad EPR absorbance centered at g= 1.8 observable only at low temperatures. This signal involves an iron atom and a quinone molecule. Two possible identifications of the species responsible for the g= 1.8 signal are an iron‐quinone complex and an iron‐sulfur protein. The latter identification would require that one primary acceptor function for two primary donors and that the removal of a tightly held quinone alter the integrity of the system so as to inhibit the photochemistry.

When the primary acceptor is chemically reduced, a photo‐induced, polarized triplet EPR spectrum is detected. Both absorption and emission lines are, observed as if only one substate (m= 0) of the triplet manifold is populated. The zero field parameters of the triplet spectrum suggest that the triplet is formed through a decay of a biradical, not through an optical singlet to triplet transition.

Low temperature EPR studies of photosynthetic preparations which had been poised at room temperature by subjecting the preparations to different redox potentials and/or dark adaptation and illumination show the presence of a number of light‐influenced, EPR active components. The spectral characteristics of these components are indicative of iron‐heme (both low and high‐spin forms) and iron‐sulfur (both oxidized and reduced) proteins and at least one other organic free radical distinct from P870+. The spectra varied for different strains of bacteria. Also, some of the signals detected in the whole cell organism were not detected in cell free preparations and the kinetics of the light influenced signal amplitudes were different in the whole cells than in chromatophores.
AVERAGE LATITUDINAL VARIATION IN ULTRAVIOLET RADIATION AT THE EARTH'S SURFACE
Authors: Johnson Francis S. , Mo Tsan , Green Alex E. S.
Published: January 2008

Abstract— Tabulated values are presented for ultraviolet radiation at the earth's surface as a function of wavelength, latitude, and season, for clear sky and seasonally and latitudinally averaged ozone amounts. These tabulations can be combined with any biological sensitivity function in order to obtain the seasonal and latitudinal variation of the corresponding effective doses. The integrated dosages, based on the erythemal sensitivity curve and on the Robertson‐Berger sunburn‐meter sensitivity curve, have also been calculated, and these are found to vary with latitude and season in very nearly the same way as 307 and 314 nm radiation, respectively.
SIMILARITY IN DOSE RESPONSES, ACTION SPECTRA AND RED LIGHT RESPONSES BETWEEN PHOTOTROPISM AND PHOTOINHIBITION OF GROWTH*
Authors: Elliott W. M. , Shen‐Miller J.
Published: January 2008

Abstract— First positive phototropism and photoinhibition of growth of oat colcoptiles share similar dose response curves and action spectra. Both responses increase with increasing dosage of blue light (440 nm) up to 1013 photons cm‐2, then both decrease with increasing dosage. Action spectra for both responses have peaks at 360, 440, and 470 nm. When red light (660 nm) was given beforehand, the sensitivity of each response to blue light was lessened. These data indicate a close correlation between phototropism and photoinhibition of growth. Both phenomena can be explained as a result of photoinhibition of basipetal transport of auxin.
PHOTOSENSITIZING EFFECTS OF 8‐METHOXYPSORALEN ON THE SKIN OF HAIRLESS MICE—11. TRAIN AND SPECTRAL DIFFERENCES FOR TUMORIGENESIS
Authors: Grube D. D. , Ley R. D. , Fry R. J. M.
Published: January 2008

Abstract— The photosensitizing effects of 8‐methoxypsoralen on the skin of two strains of hairless mice were studied using fractionated exposure to UV Spectral dependent differences for tumorigenesis were studied by comparing the tumor responses to three different spectra; the exposure levels for each spectrum here adjusted in proportion to their relative efficiencies for tissue damage and cytokinetic responses. There were no strain differences in the spectral dependent induction of cutaneous damage or estimates of the photomediated interstrand cross‐linking of epidermal DNA by 8‐methoxypsoralen.

Squamous cell carcinomas were induced in the photosensitized skin of both strains of mice after fractionated exposures to emissions at principally 365 nm. Exposures to a broader spectrum of light resulted in the earlier appearance of tumors in the photosensitized skin of the SKH: hairless‐1 mice, but produced few or no tumors in the HRS/J/Anl strain. In a second series of experiments; mice were exposed to a fluorescent sun lamp prior to each combined treatment of psoralen and exposure at 365 nm to determine the influence of shorter wavelengths of UV on the tumor response. These treatments resulted in an enhanced expression of tumors in the SKH:hairless‐1 mice as compared to the HRS/J/Anl strain.

Under the conditions of the experiments, the marked strain and spectral dependent differences for tumorigenesis demonstrated that although treatments that induce psoralen photoadducts also induce tumors. there was no apparent quantitative correlation between the occurrence of DNA cross‐links and the incidence of tumors. The results also suggested, first, an interaction between UV (280–400 nm) induced photoproducts and psoralen photoadducts and secondly, a strain difference in the oncogenic effects of this interaction.
THE RELATIONSHIP BETWEEN CARCINOGENIC ACTIVITIES OF POLYCYCLIC AROMATIC HYDROCARBONS AND THEIR SINGLET, TRIPLET, AND SINGLET‐TRIPLET SPLITTING ENERGIES AND PHOSPHORESCENCE LIFETIMES
Authors: Morgan David D. , Warshawsky David , Atkinson Tom
Published: January 2008

Abstract— The energies of the lowest excited singlet, Es, and triplet, Et, states, and singlet‐triplet splitting energies, ΔEs,t, were determined on 18 carcinogenic and 31 noncarcinogenic polycyclic aromatics. A highly significant correlation was found between carcinogenic activity and the energy of the excited singlet state. Compounds with an Es < 312 kJ/mol were 4.8 times more likely to be carcinogens than those compounds with Es 312 kJ/mol (P= 0.015). Compounds whose singlet energies fell within the narrow range of 297 ≤Es≤ 310 kJ/mol were 22.8 times more likely to be carcinogens than those compounds which fell outside this range (P= 0.00006). A significant correlation between carcinogenic activity and Et energies was not found, while the correlation involving ΔEs,t energies was intermediate between the Es and Et correlations. The phosphorescence lifetimes, τp, of the 18 carcinogenic aromatics and 27 of the noncarcinogenic aromatip were determined, and were shown not to be correlated with carcinogenic activity. When either the Et or ΔEs,t energies were plotted as a function of Es it was found that the carcinogens tended to form in an elliptical cluster. Compounds whose Es and Et energies placed them within the ellipse were 9.7 times more likely to be carcinogens than those compounds which fell outside the ellipse (P= 0.002), while with the Es, ΔEs,t ellipse, compounds which fell inside were 20.6 times more likely to be carcinogens than those which fell outside (P= 0.0004). Es, Et, ΔEs,t and τp values were also determined on 12 carcinogenic and 4 noncarcinogenic alkyl substituted benz[a]anthracenes. There was no significant difference between the carcinogens and noncarcinogens and the “elliptical” correlation predicted both the carcinogens and noncarcinogens to be carcinogenic. The results suggest that either some property(ies) of the lowest excited singlet state, but not its energy, or some molecular property(ies) which runs parallel to singlet state energies may be important in determining carcinogenic activity in polycyclic aromatics.
THE EFFECT OF MOLECULAR POLARIZATION ON THE ELECTROCHROMISM OF CAROTENOIDS—I. THE INFLUENCE OF A CARBOXYLIC GROUP
Authors: Reich Roland , Sewe Kai‐Udo
Published: January 2008

Abstract—Electrochromism of oriented all‐trans‐β‐apo‐8′‐carotenoic acid is studied in thin capacitors. The linear electrochromism is very strong, in contrast to that of symmetrical carotenoids. It is proportional to the first derivative of the absorption spectrum. The quadratic electrochromism can be described as a superposition of fractions proportional to the first and second derivatives of the absorption spectrum. The permanent dipole moment difference between the ground state and the excited state of the carotenoic acid molecule is Δμ= 3.6 × 10‐29C·m (±20%) (10.7 Debyes). The polarizability difference parallel to the long axis of the molecule is Δα|| = 1.17 × 10‐37C·m2·V‐1(±20%) (1050 Å3). Furthermore, the relative permittivity of the solid carotenoic ethyl ester isr= 3.5 ± 0.2.

Δμ is due to the polarizing force of the carboxylic group. This force is equivalent to a mean local electric field ofFt≅3 × 106V/cm. Such a “local field” may also be exerted on a symmetrical carotenoid in the membrane of photosynthesis, e.g. by asymmetrical complex formation with a polarizing molecule. To obtain an effective permanent field ofFp≅ 2 × 106V/cm across the membrane, as postulated in photosynthesis, a local field ofFl≅ 5.5 × 105V/cm would be sufficient.Fpis shown to be directed from inside to outside of the thylakoid. To realize this, e.g. a positive polar (i.e. electron‐attracting) complex partner of the carotenoid, located more to the inside of the thylakoid, can be postulated.
PHOTOSYNTHETIC NITRITE REDUCTION BY DITHIOERYTHRITOL AND THE EFFECT OF NITRITE ON ELECTRON TRANSPORT IN ISOLATED CHLOROPLASTS
Authors: Spiller Hart , Böger Peter
Published: January 2008

Abstract. Photosynthetic reduction of nitrite to ammonia with type C chloroplasts from the heterocont alga Bumilleriopsis filiformis was investigated using 3,6‐diaminodurene/ascorbate and 3,6‐diaminodurene/dithioerythritol (DAD/DTE) as electron donor couple. Rates approach 6–10 μmol NO‐2 reduced/mg chlorophyll/h and are steady for up to 30 min. The presence of oxygen or NADP+ only slightly diminished the rates of nitrite reduction obtained with DAD/DTE. Illuminated chloroplasts reduce oxygen in the presence of DAD/DTE at 135 μmol/mg chlorophyll/h without acceptor supplied. Photosynthetic oxygen uptake by this system in the presence of ferredoxin and NO‐2, however, is inhibited to 42% by nitrite reductase with concurrent nitrite reduction. NO‐3 and NO‐2 have no effect on photosystem I‐mediated NADP+ reduction, NO‐2 (10 mM) inhibits ferricyanide‐mediated oxygen evolution to 72%. Also photosystem II reactions assayed e.g. with silicomolybdate are inhibited significantly by NO‐2 (1 mM), but only slightly by NO‐3. Nitrite reductase is inhibited by p‐chloromercuribenzoate (pCMB), and this inhibition is prevented by DTE. Results suggest that photosynthetic nitrite reduction can cope with low concentrations of either compound, provided relevant thiol groups are protected.
PATHWAYS FOR FORMATION OF HYDRATED ELECTRONS FROM EXCITED PHENOL AND RELATED COMPOUNDS
Authors: Grabner G. , Köhler G. , Zechner J. , Getoff N.
Published: January 2008

Abstract. The dependence of primary photophysical and photochemical processes, especially of electron photoejection, in phenol and related compounds in aqueous solution on excitation intensity and excitation energy is examined. Theoretical and experimental evidence is presented for the possibility of three pathways for electron ejection: (1) A monophotonic pathway via the fluorescent state, which most probably does not involve the lowest triplet state; (2) a monophotonic pathway requiring higher excitation energies, which takes place in competition with internal conversion to the fluorescent state; and (3) a consecutive biphotonic pathway in which the lowest triplet state absorbs the second photon, and which can become predominant at high intensities, e.g. under flash conditions. It is shown that this model reconciles apparently conflicting results published in the literature.
FLUORESCENCE QUENCHING OF INDOLES BY N,N‐DIMETHYLFORMAMIDE
Authors: Froehlich Peter M. , Gantt D. , Paramasigamani V.
Published: January 2008

Abstract. The quenching of the excited state of indoles by small polar molecules is believed to occur via the formation of excited state complexes. The rate of excited state complex formation of indoles with dimethylformamide is shown to be a function of the group appended to the indole ring at the 3‐ or 5‐position. Substituents which can strengthen the charge transfer character of the exciplex are observed to enhance the rate of fluorescence quenching. In contrast to other amides, dimethylformamide appears to be a moderately good quencher of indole fluorescence, and may be a useful probe for proteins.
REACTION OF SINGLET OXYGEN WITH CHOLESTEROL IN LIPOSOMAL MEMBRANES. EFFECT OF MEMBRANE FLUIDITY ON THE PHOTOOXIDATION OF CHOLESTEROL
Authors: Suwa Kunihiko , Kimura Tokuji , Schaap A. Paul
Published: January 2008

Abstract— The photosensitized oxygenation of cholesterol in liposomal membranes results in the formation of the characteristic singlet oxygen product, 3β‐hydroxy‐5α‐cholest‐6‐ene‐5‐hydroperoxide. The yield of this product was found to be strongly temperature dependent with 6‐ to 7‐fold increase above the transition temperature of the membrane using 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphorylcholine or 1.2‐dimyristoyl‐sn‐glycero‐3‐phosphorylcholine. In contrast, the formation of the radical autoxidation products of cholesterol was not significantly enhanced in these systems by higher temperatures. We conclude from the results that the oxidation of cholesterol by singlet oxygen in the artificial membranes is affected by both membrane fluidity and amount of hematoporphyrin incorporated into the membrane. The ratio of cholesterol to phospholipid which affects the morphology of membranes is a crucial factor in determining the yield of the singlet oxygen product.
METHYLENE BLUE SENSITIZED PHOTOINACTIVATION OF E. COLI RIBOSOMES: EFFECT ON THE RNA AND PROTEIN COMPONENTS†
Authors: Singh Harwant , Ewing Donald D.
Published: January 2008

Abstract— Methylene blue sensitizes photoinactivation of E. coli ribosomes. This photoinactivation shows dose‐dependent minor changes in the ribosome particles. The ribosomal RNA extracted from irradiated ribosomes also shows small changes. On gel electrophoresis the 23S ribosomal RNA band decreases in intensity at low doses with a corresponding increase in the minor band which moves slightly faster than the 23S band. The appearance of this minor band is dose‐dependent. The other major ribosomal component (16S ribosomal RNA) is relatively stable. The S6 protein is one of the first proteins to decrease in intensity at low doses followed by fairly marked changes in some of the other proteins, at high doses.
PHOTOOXIDATION OF A REFINED PETROLEUM OIL: INHIBITION BY β‐CAROTENE AND ROLE OF SINGLET OXYGEN
Authors: Larson Richard A. , Hunt Laura L.
Published: January 2008

Abstract— β‐Carotene, at concentrations 0.1 mM, inhibits the formation of hydroperoxides and other oxidation products in a refined petroleum oil exposed to Pyrex‐filtered UV. The effect appears to be due to 1O2 quenching. A mechanism incorporating 1O2 and radical processes is proposed as a model for environmental photooxidation of petroleum.
PHOTOCHEMISTRY OF cis‐POLYISOPRENE AND ITS SINGLET OXYGEN ADDUCT
Authors: Ng Howard C. , Guillet James E.
Published: January 2008

Abstract— Reaction of singlet oxygen (1Δg, 1O2) with cis‐polyisoprene yields an allylic hydroperoxide with an olefinic double bond shifted in the polymer chain. The photochemical decomposition of the resultant hydro‐peroxide and the subsequent polymer chain scission kinetics have been studied in the absence of oxygen. Quantum yields of hydroperoxide decomposition range from 3.1 to 8.4 in cyclohexane, depending on the initial amount of hydroperoxide in the polymer. On the other hand, the quantum yields for polymer chain scission are low, and vary with the frequency of the incident light. The ratio for number of polymer scissions per number of hydroperoxy groups decomposed is of the order of 10‐2. The polymer chain degradation is sensitized by the addition of ketones. Based on these data, a reaction mechanism for the overall photodegradation of the cis‐polyisoprene initiated by singlet oxygen is proposed.
USE OF A HIGH INTENSITY DYE LASER TO PRODUCE SINGLET OXYGEN*
Authors: Koroll Grant W. , Singh Ajit
Published: January 2008

Abstract— A coaxial, flashlamp‐pumped, dye laser is being used to directly excite ground state oxygen at high pressures (˜150atm, ˜15MPa), to singlet oxygen. The parameters of the laser beam are as follows: pulse width, ˜350ns; beam diameter, ˜18 mm; beam energy, ˜3J/pulse (at 590 nm using Rhodamine 6G in ethanol as the dye). The laser can be tuned to produce light beams at most of the wavelengths at which oxygen shows optical absorption. Singlet oxygen has been produced in solutions of oxygen (˜15 MPa) in Freon‐113 and CCl4 by irradiation at 477, 575 and 632 nm.
HO2 ELIMINATION FROM α‐HYDROXYALKYLPEROXYL RADICALS IN AQUEOUS SOLUTION
Authors: Bothe Eberhard , Schuchmann Man Nien , Schulte‐Frohlinde Dietrich , Sonntag Clemens von
Published: January 2008

Abstract— In aqueous solutions α‐hydroxyalkylperoxyl radicals undergo a spontaneous and a base catalysed HO2 elimination. From kinetic deuterium isotope effects, temperature dependence, and the influence of solvent polarity it was concluded that the spontaneous reaction occurs via an HO2 elimination followed by the dissociation of the latter into H+ and O2‐. The rate constant of the spontaneous HO2 elimination increases with increasing methyl substitution in α‐position (k(CH2(OH)O2) < 10s‐1k(CH3CH(OH)O2) = 52s‐1k((CH3)2C(OH)O2) = 665 s‐1). The OH‐ catalysed reaction is somewhat below diffusion controlled. The mixture of peroxyl radicals derived from polyhydric alcohols eliminate HO2 at two different rates. Possible reasons for this behaviour are discussed. The mixture of the six peroxyl radicals derived from d‐glucose are observed to eliminate HO2 with at least three different rates. The fastest rate is attributed to the HO2 elimination from the peroxyl radical at C‐l (k > 7000s‐1). Because of the HO2 eliminations the peroxyl radicals derived from d‐glucose do not undergo a chain reaction in contrast to peroxyl radicals not containing an α‐OH group. In competition with the first order elimination reactions the α‐hydroxylalkylperoxyl radicals undergo a bimolecular decay. These reactions are briefly discussed.
CHEMILUMINESCENCE FROM AUTOXIDIZING 6‐HYDROXYDOPAMINE: THE INVOLVEMENT OF ACTIVATED FORMS OF OXYGEN
Authors: Heikkila Richard E. , Cabbat Felicitas S.
Published: January 2008

Abstract—The autoxidation of the catecholamine neurotoxin 6‐hydroxydopamine (20 μM) gave rise to a chemiluminescence which was greatly stimulated by FeSO4(20 μM) or by hydrogen peroxide addition (20 μMto 2 mM). The luminescence of both 6‐hydroxydopamine alone or 6‐hydroxydopamine plus hydrogen peroxide was strongly inhibited by catalase and by superoxide dismutase (both at 10 μg/m/); bovine serum albumin at 10 μg/m/ had no inhibitory effect. The luminescence was also strongly inhibited by several potent hydroxyl radical trapping agents and also by low concentrations of the1O2quencher DABCO (l,4‐diazabicyclo‐2.2.2.‐octane). Chemiluminescence was greatly enhanced in D2O, a solvent in which1O2has a prolonged lifetime. These data demonstrate the involvement of hydrogen peroxide, the superoxide radical and the hydroxyl radical in the chemiluminescence. The data are also consistent with some role for1O2.
THE EFFECT OF IRON ON THE DISTRIBUTION OF SUPEROXIDE AND HYDROXYL RADICALS AS SEEN BY SPIN TRAPPING AND ON THE SUPEROXIDE DISMUTASE ASSAY
Authors: Buettner Garry R. , Oberley Larry W. , Leuthauser Susan W. H. Chan
Published: January 2008

Abstract— Using the spin trap 5,5‐dimethyl‐1‐pyrroline‐1‐oxide we have demonstrated the presence of OH in the xanthine‐xanthine oxidase system when iron and/or iron‐EDTA (ethylenediamine‐tetraacetic acid) is present. With increasing iron (or iron‐EDTA) concentration the intensity of the O2‐ spin adduct decreased while that of OH increased. However, use of diethylenetriaminepentaacetic acid (DETAPAC) as a metal chelator in the reaction mixture suppressed the OH spin adduct signal while maintaining the intensity of the signal from the O2‐ spin adduct.

Use of EDTA to eliminate the interfering effects of metal ions in the superoxide dismutase assay employing xanthine oxidase and nitroblue tetrazolium introduces an artifact from the iron present. The interference in the assay from metal ions, including iron, can be eliminated with use of DETAPAC as a metal chelator. Thus, it is possible to make comparisons of measured superoxide dismutase activities even when there are variations in the amount of iron present in the samples.
THE REACTION BETWEEN SUPEROXIDE ANION AND HYDROGEN PEROXIDE
Authors: Ferradini Christians , Foos Jacques , Houee Chantal , Pucheault Jacques
Published: January 2008

Abstract— In order to obtain a better understanding of the kinetics of the Haber‐Weiss reaction

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often proposed as a source of OH radicals, we have measured the decomposition rate of H2O2 in aqueous solutions by y rays and for different pH values. This decomposition proceeds by a chain reaction involving the preceding one as the propagating step.

The rate constant found is to be

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THE EFFECT OF 1,4‐DIAZABICYCLO[2.2.2]OCTANE ON THE RADIOSENSITIVITY OF BACTERIA
Authors: Anderson Robert F. , Patel Kantilal B.
Published: January 2008

Abstract— Hydroxyl radicals ('OH) are scavenged by 1,4‐diazabicyclo[2.2.2]octane (DABCO) at a diffusion‐controlled rate of 1.25 ± 0.1 × 109M‐1s‐1. Unlike other efficient 'OH scavengers which exhibit protection of bacteria against irradiation both in oxic and hypoxic conditions, DABCO has been shown to protect Serratia marcescens and various strains of Escherichia coli only in oxic conditions.

DABCO appears to eliminate a component of the sensitization afforded by oxygen in all strains of E. coli tested. The level of this protection increases from ∼15% in the wild type AB 1157 to ∼100% in the recA uvrA mutant AB 2480. It is suggested that DABCO protects against lethal events that can occur on macromolecules other than DNA such as the cell membrane.

Results with added glycerol, as well as work in D2O solution, indicate that DABCO is more likely to be acting by scavenging radicals rather than by quenching 1O2. If 1O2 is a component of the sensitization afforded by oxygen, then it is unlikely to be formed in a hydrophilic environment in the cell.
AFFINITY FOR OXYGEN IN PHOTOREDUCTION OF MOLECULAR OXYGEN AND SCAVENGING OF HYDROGEN PEROXIDE IN SPINACH CHLOROPLASTS
Authors: Asada Kozi , Nakano Yoshiyuki
Published: January 2008

Abstract— The apparent Km for O2 in the photoreduction of molecular oxygen by spinach class II chloroplasts and photosystem I subchloroplast fragments was determined. In both cases, a value of 2 ∼ 3 μM O2 was obtained. The reaction rate constant between O2 and P‐430, the primary electron acceptor of PS I, is estimated to be ∼ 1.5 × 107M‐1 s‐1 and the factors affecting the production of superoxide by the photoreduction of O2 in chloroplasts are discussed. Preliminary evidence is presented indicating the occurrence of an azide‐insensitive scavenging system for H2O2 in chloroplast stroma.
EFFECT OF LIGHT ON OSCILLATIONS OF ENZYME ACTIVITY DURING PHOTOMORPHOGENESIS IN CHENOPODIUM RUBRUM L.
Authors: Deitzer G. F. , Hopkins D. W. , Haertlé U. , Wagner E.
Published: January 2008

An approach to determine the photomorphogenic effect of light (white or continuous far‐red) on the development of rhythmic enzyme activity in Chenopodium rubrum L. is described. Previous results, obtained from mature seedlings grown in white light, demonstrated stable oscillations with periods ranging between 12 and 15 h for all of the enzymes tested. The present results, obtained during deetiolation, were complicated by the presence of a higher frequency component with a period of about 6 h. When the various oscillating components were defined, the analysis showed: (1) the enzymes of the Krebs cycle (malate and isocitrate dehydrogenase), the closely associated glutamate dehydrogen‐ase, and the glycolytic pathway ((NAD) glyceraldehyde‐3‐phosphate dehydrogenase) had a dominant period in the range of 12–15 h, (2) those of the oxidative pentose phosphate pathway were either weakly circadian (glucose‐6‐phosphate dehydrogenase) or apparently arhythmic (6‐phosphogluconate dehydrogenase), (3) the (NADP) glyceraldehyde‐3‐phosphate dehydrogenase from the Calvin cycle was circadian when kept in continuous darkness but becomes 15 h when placed in light, and (4) only the Calvin cycle enzyme is affected by light in the level of its activity and in its oscillatory behavior.
CHARACTERIZATION OF THE 32,000 DALTON MEMBRANE PROTEIN—I. EARLY SYNTHESIS DURING PHOTOINDUCED PLASTID DEVELOPMENT OF SPIRODELA
Authors: Reisfeld AVI , Gressel Jonathan , Jakob Karl M. , Edelman Marvin
Published: January 2008

The kinetics of 35S methionine incorporation into soluble and membrane proteins during the transition from steady state dark growth to greening was studied in Spirodela. A sharp increase in the rate of incorporation occurred at 3 h, which was several h before major increases in chlorophyll were apparent. Part of this enhanced incorporation was due to enhanced synthesis of a 32,000 dalton membrane protein. This synthesis was paralleled by a temporal increase in in uitro template capacity for this protein and an increase in 0.5 × 106 dalton plastid messenger RNA.
THE EFFECT OF LEVULINIC ACID ON THE LIGHT INDUCED DEVELOPMENT OF PHOTOSYSTEM I AND II ACTIVITIES IN GREENING MAIZE LEAVES*
Authors: Konis Y. , Klein S. , Ohad I.
Published: January 2008

Photosystem I and Photosystem II activities were measured in chloroplasts isolated after 0–20 h illumination from etiolated maize leaves in which chlorophyll synthesis was specifically inhibited by levulinic acid. In control leaves not treated with levulinic acid, Photosystem I activity/chlorophyll developed rapidly during the first 2h in light, then fell off, and reached a constant level after 6h of illumination. In levulinic acid treated leaves, in which chlorophyll accumulation was inhibited up to 60%, a similar initial rise in Photosystem I activity was observed. However, the decrease in activity was much slower and continued for at least 20 h. The development of Photosystem I activity calculated on a leaf fresh weight basis was similar for control leaves or leaves treated with levulinic acid. This indicates that development of Photosystem I activity may not be related to chlorophyll accumulation during greening.

Photosystem II activity/chlorophyll in leaves treated with or without levulinic acid increased similarly during the first 6h and then remained constant. Activity of Photosystem II per leaf fresh weight increased linearly, after the first h, for 20 h in the control leaves; in levulinic acid treated leaves this development was reduced by about 60%. Thus, development of Photosystem II activity can be related to chlorophyll accumulation. SDS gel electrophoresis of plastid membranes from control leaves illuminated for 12 h showed the presence of chlorophyll‐protein complex I as well as Chl‐protein 11; in the case of levulinic acid treated leaves only Chl‐protein complex I was detectable, while Chl‐protein complex II was markedly reduced.
TRIPLET EXCITED STATE OF FUROCOUMARINS: REACTION WITH NUCLEIC ACID BASES AND AMINO ACIDS
Authors: BEnsasson R. V. , Land E. J. , Salet C.
Published: January 2008

Abstract. The triplet‐triplet absorption spectra of psoralen, xanthotoxin, angelicin and bergapten have been determined using the technique of pulse radiolysis and laser flash photolysis in benzene and water. The extinction coefficients of the triplet transitions have been measured and used to determine the singlet → triplet intersystem crossing quantum yields for 353 nm excitation. These yields vary considerably in passing from benzene to water as solvent. The highest yields were obtained for psoralen and angelicin in water, being 0.45 and 0.33, respectively. Reaction rate constants of the psoralen and angelicin triplets with various pyrimidine and purine nucleic acid bases and amino acids have been measured. The high reactivities support the suggestion that the photosensitising properties of furocou‐marins are mediated by the corresponding furocoumarin triplet states. The similarly high S → T quantum yields, and triplet reactivities with pyrimidines of psoralen and angelicin, also support the suggestion that the observed differences in photosensitising properties of these two psoralens may be due to their differing geometries, which allow psoralen itself to intercalate DNA more easily than angelicin. The efficient reactions also found for psoralen and angelicin triplets with amino acids suggest that such triplets in vivo may also react with these components. Significant damage may thus be caused to protein as well as nucleic acid components of the cell.
DIFFERENTIAL EFFECTS OF TRYPTOPHAN PHOTOPRODUCTS AND H2O2 ON THE GROWTH OF MOUSE EMBRYONIC FIBROBLASTS*
Authors: Zigman S. , Hare J. D. , Yulo T. , Ennist D.
Published: January 2008

Abstract. Exposure of dilute solutions of L‐tryptophan in balanced salt mixtures to near‐ultraviolet light (ca. 320–390nm) yield several photoproducts capable of inhibiting the growth of cultured mouse embryonic fibroblasts. Recent literature suggested a need to test the possibility that the major toxic photoproduct is hydrogen peroxide, and therefore several lines of experimentation were pursued. On the basis of chemical and morphological studies and an analysis of the uptake of 3H‐thymidine by these cells and its incorporation into their DNA, it is concluded that sufficient hydrogen peroxide could not be generated without the addition of high concentrations of oxygen to influence the growth or DNA synthesis of mouse embryonic fibroblasts.
SIMILAR SPECTRA FOR THE INACTIVATION BY MONOCHROMATIC LIGHT OF TWO DISTINCT LEUCINE TRANSPORT SYSTEMS IN ESCHERICHIA COLI
Authors: Robb F. T. , Hauman J. H. , Peak M. J.
Published: January 2008

Abstract—Kinetics of inactivation of two separate leucine transport systems (leucine specific and LIV) in E. coli by seven wavelengths of monochromatic light have been studied. Loss of leucine uptake is not due to generalized membrane damage causing non‐specific leucine leakage. Inactivations are usually exponential but some wavelengths show shoulders at low doses. Two‐component spectra between 254 and 435 nm occur for both transport systems. Inactivation is most efficient at 290 nm and a second peak occurs at 365 nm. Both leucine transport systems are inactivated similarly.
DIRECT PHOTO‐AFFINITY LABELING WITH CYCLIC NUCLEOTIDES: ACTION SPECTRA
Authors: Antonoff Ross S. , Ferguson J. J.
Published: January 2008

Abstract— When [3H]‐cyclic adenosine 3′,5′‐monophosphate and [3H]‐cyclic guanosine 3′,5′‐monophos‐phate are irradiated at varying UV wavelengths in the presence of cyclic nucleotide receptor proteins, photo‐incorporation is maximal in the region of 280 nm. This suggests that covalent coupling occurs by means of photo‐activation of an entity other than the ligand cyclic nucleotide. The action spectra more closely resemble the absorbtion spectrum of the reacting protein, making it likely that absorhtion of radiant energy by components of the protein receptor leads to photo‐affinity labeling.
EFFECT OF PHOTIC STIMULATION ON THE HUMAN MENSTRUAL CYCLE
Authors: Dewan Edmond M. , Menkin Miriam F. , Rock John
Published: January 2008

Abstract— A theoretical rationale is presented to justify a study of the effect of light on the variability of the menstrual cycle. The experiment consisted of exposure to light all night for several consecutive nights of cycle days 14 through 17, day one being determined by the first day of menses. Our conclusion is that we have statistical evidence that this regimen of photic, stimulation can regularize the length of the menstrual cycle and can therefore presumably influence the time of ovulation. Further studies involving much larger samples and more sophisticated measurements are fully justified at this time.