bluuebunny/crossref_metadata_2025 huggingface dataset:
EFFECT OF IONIZING RADIATION UPON TOTAL DIFFUSE SPECTRAL REFLECTANCE OF ULTRAVIOLET LIGHT BY SKIN
Authors: Aglin J. H.
Published: January 2008

Abstract— Irradiation of guinea‐pig skin with X rays and beta particles resulted in decreased total diffuse reflectance (DSR) of 330–400 nm light. Qualitatively, this response resembled that seen after irradiation of the skin of normal guinea‐pigs with ultraviolet (UV) radiation of wavelength shorter than 300 nm or that of photosensitized guinea pigs with UV wavelengths longer than 300 nm. We postulate that the transformations which depress the DSR result from energy‐transfer processes, independent of the class of radiation. Moreover, they are intimately related to subsequent changes in vascular permeabilities (delayed erythema) which occur after the same radiation exposures that lower the 330–400 nm DSR of skin surfaces.
PHOTO‐OXIDATION OF LYSOZYME IN THE PRESENCE OF METHYLENE BLUE: A PROBABLE MECHANISM
Authors: Churakova N. I. , Kravchenko N. A. , Serebryakov E. P. , Lavrov I. A. , Kaversneva E. D.
Published: January 2008

Abstract— In order to elucidate the mechanism of the photo‐oxidation of lysozyme sensitized by methylene blue this enzyme was oxidized by singlet oxygen generated by a high–frequency discharge in gaseous oxygen. The action of singlet oxygen on lysozyme gives products identical with those obtained upon dye‐sensitized oxidation with respect to their affinity to chitin, their amino acid content, their UV spectra and their enzymic activity. It is concluded that photo‐oxidation of lysozyme in the presence of methylene blue proceeds according to the singlet‐oxygen mechanism.
A CORRELATION OF EPR SPINS WITH P700 IN SPINACH SUBCHLOROPLAST PARTICLES
Authors: Baker Robert A. , Weaver Ellen C.
Published: January 2008

Abstract— The ratio of the concentrations of P700, as measured by oxidized‐minus‐reduced (also light‐minus‐dark) spectroscopy, and electron paramagnetic resonance (EPR) signal I, as measured by EPR spectroscopy, were determined on aliquots of photosystem I spinach subchloroplast particles. The results substantiated a 1:1 ratio with a precision of ±25%. This constitutes correlative evidence that P700 is the molecular source of the EPR signal I.
DEPTH RESOLUTION IN PHOTOELECTRON MICROSCOPY OF ORGANIC SURFACES. THE PHOTOELECTRIC EFFECT OF PHTHALOCYANINE THIN FILMS
Authors: Burke C. A. , Birrell G. B. , Lesch G. H. , Griffith O. H.
Published: January 2008

Abstract— The application of photoelectron microscopy as a general method of imaging organic and biological surfaces requires a knowledge of the photoelectric effect of very thin organic films. In this study, low magnification images of a 7 Å thick pattern of copper phthalocyanine were obtained, demonstrating that it is possible to visualize a monolayer of organic compound in photoelectron microscopy. Relative photoelectron currents were measured for a series of copper phthalocyanine films ranging in thickness up to 1900 Å. The relative photoelectron currents were independent of temperature (90–298°K), suggesting that electron‐electron and not electron‐phonon scattering is the dominant mechanism. The photoelectric properties measured are determined primarily by the large organic ring structure and not the central metal atom, as evidenced by the fact that substitution of metal‐free phthalocyanine for copper phthalocyanine did not substantially alter the values of observed photoelectron currents. An analysis of the data indicates the depth resolution is 15 Å± 5 Å, and equals the electron mean free path. This very good depth resolution is a result of the low kinetic energy associated with electrons released by irradiation near the photoemission threshold.
INHIBITION OF THE extra GENE‐DEPENDENT BRANCH OF THE DNA EXCISION REPAIR SYSTEM IN ESCHERICHIA COLI K‐12 BY 2, 4‐DINITROPHENOL
Authors: Schueren Emmanuel Van der , Smith Kendric C.
Published: January 2008

Abstract— Ultraviolet (UV)‐irradiated E. coli K‐12 wild‐type cells were sensitized by a post‐irradiation treatment with 10‐2M 2, 4‐dinitrophenol (DNP). This effect was not seen in strains carrying a uvr mutation, suggesting that DN P interferes with the excision repair process. The polA strain was sensitized to the same extent as the wild‐type strain, while the exrA strain was not affected by DNP treatment.

Recombination deficient strains (recA, recB and recA recB) were protected by DNP treatment after UV irradiation. This protection was abolished by the addition of a uvr mutation (i.e., in strains recA uvrB and recB uvrB).

Alkaline sucrose gradient sedimentation studies showed that DNP treatment interfered with the rejoining of DNA single‐strand breaks induced by the excision repair process. This interference was apparently specific for the exr gene‐dependent branch of the uvr gene‐dependent excision repair process, since the uvr and exr strains were not sensitized while the wild‐type and polA strains were sensitized.
EFFECTS OF NON‐IONIZING AND IONIZING RADIATIONS ON THE TRANSFORMING ABILITY OF E. COLI DNA
Authors: Ranade S. S. , Avadhani N. G. , Rege D. V.
Published: January 2008

Abstract— A transformation system in Escherichia coli was employed to verify the extent of the lesions caused by ultraviolet (UV) and ionizing radiations. DNA inactivated at 280 nm could be reactivated to some extent by exposing the transforming DNA solutions at 240 nm. This reactivation has been tested using more than one strain of E. coli as recipient. Transforming DNA inactivated by ionizing radiations (90Sr beta rays and 60Co gamma rays) was not reactivable. Low doses of beta rays, however, reactivated the DNA inactivated by 280 nm UV to a slight but significant extent.
CHLOROPHYLL ONE‐ELECTRON PHOTOCHEMISTRY‐II. PHOTOSENSITIZATION BY CHLOROPHYLL, PHEOPHYTIN AND BACTERIOCHLOROPHYLL OF A ONE‐ELECTRON TRANSFER REACTION BETWEEN ETHANOL AND QUINONE*
Authors: Harbour John R. , Tollin Gordon
Published: January 2008

Abstract— Chlorophyll, pheophytin and bacteriochlorophyll sensitize a one‐electron transfer in the presence of quinones in ethanol, to produce a ternary complex of ground state porphyrin analog, alcohol cation radical and semiquinone anion radical as the primary photo‐product at low temperature. A similar photo‐oxidation of alcohol to produce a binary complex is caused by direct excitation of quin‐one in the absence of chlorophyll. The mechanisms of these reactions and their implications for photosynthesis are discussed.
LIQUID HOLDING RECOVERY OF PHOTODYNAMIC DAMAGE IN E. COLI
Authors: Das Jyotirmoy , Bagchi B. , Chaudhuri U.
Published: January 2008

Escherichia coli cells lose viability when irradiated with visible light in the presence of acridine dyes. There has been some controversy about whether such photodynamic damage can be repaired. Several investigations on different E. coli strains failed to reveal any significant difference in the sensitivity to photodynamic damage between radiation‐resistant E. coli B/r and radiation‐sensitive E. coli Bs‐1 strains (Uretz, 1964; Janovska et al., 1970) suggesting the absence of repair. On the contrary, other investigators (Rupp, 1966; Harm, 1968) strongly predicted the existence of a dark‐repair mechanism for such damage. No systematic study of liquid‐holding recovery of photodynamic damage has yet been reported and knowledge of repair capacity for photodynamic damage is still incomplete. In the present communication, liquid‐holding‐repair capability of E. coli B/r and Bs‐1 for photodynamic inactivation in the presence of acridine orange or acriflavine has been investigated. These studies show that B/r can repair photodynamic damage while Bs‐1 is deficient in this ability.
EXCITATION SPECTROSCOPY OF RETINAL AND RELATED POLYENES†
Authors: Christensen Ronald L. , Kohler Bryan E.
Published: January 2008

Abstract— Fluorescence excitation spectra of all‐trans retinal and the related polyene hydrocarbons anhydrovitamin A and diphenyloctatetraene show that only retinal has a wavelength‐dependent fluorescence quantum yield. Three possibilities for the unusual quantum yield behavior of retinal are considered. We conclude that competition between a fast radiationless process (perhaps of photochemical origin) and internal conversion between 1ππ* states and a low‐lying 1nπ* state provides the best rationalization for the data now in hand.
KINETICS OF THE PHOTO‐INDUCED EPR SIGNAL IN WHOLE‐CELL RHODOSPIRILLUM RUBRUM: EFFECTS OF LIGHT INTENSITY, DARK ADAPTATION, TEMPERATURE, AND MICROWAVE POWER
Authors: Corker G. A. , Sharpe S. A.
Published: January 2008

Abstract— Kinetics of the bacteriochlorophyll (P870+) electron paramagnetic resonance signal photo‐induced at room temperature in whole‐cell Rhodospirillum rubrum exhibit transients which are strongly dependent upon the light‐dark history of the cells. This paper reports a study of these kinetics as a function of actinic light intensity, light‐dark history, temperature and applied microwave power. The simplest interpretation of the observed complexities in the kinetic curves is that the rate of formation and the rate of decay of P870+ are controlled by slow dark reactions of the electron‐transport chain, and that the rate‐controlling reaction is variable during the transition from a dark‐adapted to a steady state in the light. With this interpretation, it is possible to measure or to infer order‐of‐magnitude estimates of the lifetimes of some of the slow reactions.
PHOTOREACTIONS OF 5‐BROMOURACIL IN THE PRESENCE OF CYSTEINE AND GLUTATHIONE
Authors: Varghese A. J.
Published: January 2008

Abstract—Sulfhydryl compounds such as cysteine and glutathione enhance the photochemical reactivity of 5‐bromouracil irradiated in aqueous solution with ultraviolet light (Λ > 240 nm). Production of uracil and addition of the sulfhydryl compound to the 5‐bromouracil residue are the major photoreactions.
KINETICS OF 4‐THIOURIDYLATE‐SENSITIZED PHOTOINACTIVATION OF RIBONUCLEASE A
Authors: Sawada Fumio
Published: January 2008

Abstract—An action spectrum for the inactivation of ribonuclease A photosensitized with 4‐thiouridylic acid follows the shape of the absorption spectrum of an RNase‐thiouridylate complex or of the unbound nucleotide. The quantum yield is 3.3 times 10‐3. Statistical analysis of the data suggests that only the bound nucleotide participates in the photoinactivation. An Arrhenius plot for the first‐order rate constants of inactivation gives a straight line in the range 0–40d̀C and an apparent activation energy of photoinactivation of 5.7 kcal/mol. The 4‐thiouridylate‐sensitized photoinactivation of ribonuclease A is regarded as a kind of photodynamic action in which the substrate analogue plays the role of photosensitizer.
AN EPR STUDY OF THE SPECIES PRODUCED DURING THE UV PHOTOLYSIS OF HETEROCYCLIC COMPOUNDS IN METHYLTETRAHYDROFURAN AT 77 K
Authors: Arce R. , Ramirez L.
Published: January 2008

Abstract—The ultraviolet irradiation (290 nm ≤Λ≤ 390 nm) of indole, purine, indazole, acridine and quinoline in 2‐methyltetrahydrofuran glass at 77 K produces trapped radicals. Two electron‐paramagnetic‐resonance (EPR) signals are found at 77 K during illumination, one at high magnetic field (3–25 times 10‐1 T) assigned to the matrix radical and the other at low field (1.3 times 10‐1 to 1–5 times 10‐1 T) attributed to the lowest triplet state of the heterocyclic molecule. Quantum yields for triplet production at 77 K are 0–34 for indole, 0.51 for purine, 0.55 for indazole, 0.15 for acridine, and 0.94 for quinoline. The rate of formation of matrix radicals varies as the nRth power of the incident light intensity, I0nR, where 1.6 ≤nR=≤ 2. Solvent radical yields, which depend on the light intensity, have been determined. Under the experimental conditions, no signals attributable to trapped electrons or cations have been observed. The dependence of the reciprocal value of the rise lifetime of the low field EPR signal as a function of the intensity of exposure is in accordance with a biphotonic mechanism.
PHOTOPROTECTION OF E. COLI B/r: RESPIRATION, GROWTH, MACROMOLECULAR SYNTHESIS AND REPAIR OF DNA*
Authors: Swenson P. A. , Ives J. E. , Schenley R. L.
Published: January 2008

Abstract— Photoprotecting effects of near UV radiations (300–400 nm, maximum at 360 nm) against far UV radiations (primarily 254 nm) have been studied in Escherichia coli B/r cells in minimal medium with glycerol as a carbon source. Near UV light (105 Jm‐2) has a negligible effect on survival, but causes transitory inhibition of respiration, growth, DNA, RNA, and protein syntheses and cell division. Far UV (52 J m‐2) reduces survival to about 0.5 per cent; respiration, growth and RNA and protein syntheses proceed for about 60 min, after which they nearly cease for several hours. Near UV given before this fluence of far UV increases survival 10‐fold and the above processes resume at times and with kinetics characteristic of those produced by lower fluences of far UV. Single‐strand breaks appear in the DNA of both unprotected and photoprotected cells; repair of the breaks is essentially complete in protected but not unprotected cells. The viability kinetics for far‐UV‐irradiated cells with and without photoprotecting treatment are identical except that the curve for the latter is displaced upward about 1 log; exponential increases (cell division) begin at 120 min in each case. The data suggest that, in B/r cells grown under our particular conditions, namely in minimal medium with glycerol, photoprotection is not the result of growth or division delays, but reflects an increased repair capability due to continued respiration.
LIGHT‐INDUCED EFFECTS ON A FLAVOPROTEIN, D‐AMINO‐ACID OXIDASE
Authors: Colombetti G. , Lenci F. , Mckellar J. F. , Phillips G. O.
Published: January 2008

Abstract— Upon irradiation of D‐amino‐acid oxidase‐benzoate complex with monochromatic light, an increase is observed in fluorescence emission and in transient absorption, whilst no variation is detected in optical absorption. The phenomenon is discussed in terms of a flavin‐adenine‐dinucleotide release from the apoprotein, possibly followed by chromophore photodegradation.
PHOTOREACTIVITY OF HYDROXYPSORALENS AND THEIR PHOTOBIOLOGICAL EFFECTS IN BACILLUS SUBTILIS*
Authors: Song Pill‐Soon , Mantulin William W. , Mcinturff Dyna , Felkner Ira C. , Harter Marian L.
Published: January 2008

Abstract— Although psoralen and many substituted psoralens are potent skin‐photosensitizing agents, hydroxypsoralens are not. A satisfactory molecular interpretation of this structural specificity has been given in terms of dissociation of the hydroxyl group of 5‐ and 8‐hydroxypsoralens in their excited states. The dissociation process in the S1 state effectively competes with S1→T1 intersystem crossing, thus reducing the photoreactive T1 population. The T1 states of the anions are more delocalized than those of neutral psoralens so that they are less reactive toward photocycloaddition with pyrimidine bases of DNA. The lack of significant phosphorescence of hydroxypsoralens in ionizing solvent or in the presence of base at low temperatures (14–77 K.) indicates ineffective S1→T1 and/or effective T1→S0 intersystem crossing. These factors make hydroxypsoralens unreactive, electronically and kinetically, as skin photosensitizers, which are known to react with DNA. In correlation with the hydroxypsoralens' spectroscopic characterization, they are also found to be ineffective or less effective photosensitizers in Bacillus subtilis.
THE ORIGIN OF BIOLUMINESCENCE*
Authors: Seliger H. H.
Published: January 2008

Abstract— Primitive luciferases evolved in order to utilize oxygen directly as an electron acceptor at the low oxygen concentrations of the primitive atmosphere. This provided a major selective advantage in the ability to metabolize aromatic molecules and n‐alkanes. These strongly exergonic reactions produce product molecules in electronically excited states, from which light emission is possible. The low‐level luminescence observed from microsomal extracts, from the action of leukocytes on phagocytized bacteria and from rapidly growing tissues is ascribed to these same exergonic hydroxylase reactions, or to the release during these reactions of superoxide radicals which can initiate chemiluminescent reactions. Bioluminescence is a later secondary adaptation of this oxygenase reaction to signaling for sex, food or escape. The similarity of the reaction pathways is shown in the three bioluminescent systems from which the substrates and products have been identified.
ON THE ELECTRONIC SPECTRUM OF PURINE
Authors: Robey M. J. , Ross I. G.
Published: January 2008

Abstract— Sharp absorption and emission spectra are reported for crystalline purine at 4 K. Molecular orbital calculations and correlations with pyrimidine, indene and aza‐substituted indenes are used to interpret the pattern of the excited singlet states.
PHOTOCHEMISTRY OF BIOLOGICAL MOLECULES‐V. A MECHANISTIC STUDY OF THE PHOTOLYSIS OF CYCLOALANYLALANINE IN THE SOLID STATE
Authors: Johns R. B. , MCGregor J. W.
Published: January 2008

Abstract— Earlier studies of the photodamage induced by 254 nm irradiation of linear alanine peptides in the solid state have been supplemented by an investigation into the gaseous photoproducts from the cyclic dipeptide, 3,6‐dimethyl‐2,5‐diketopiperazine. The trans and cis isomers have been prepared and the photoproducts compared with those from the DL‐mixture. The conformation of the molecule does influence the yield of gaseous products. CO was produced by peptide bond rupture with concomitant release of hydrogen. CO2 was also produced. The use of N‐ and C‐deuterated analogues together with relevant crystallographic and EPR data has enabled a detailed study of the mechanism of photode‐gradation to be made, from which it is concluded that the methyl protons are not inert but rather are the major source of the hydrogen observed on photolysis.
A LINEAR DICHROISM STUDY USING CHLOROPLASTS OF VARIOUS STRUCTURE and PIGMENT COMPOSITION
Authors: Faludi‐Dániel ÁGnes , Breton Jacques
Published: January 2008

Abstract— The orientation of pigments was studied in maize chloroplasts of different granum content and pigment composition. Comparison of the linear dichroism (LD)t of granal and agranal chloroplasts exhibited differences in the chl a forms, Ca 670 and Ca 691. The chl b content of the chloroplasts appeared to have little effect on the LD spectra.

In the LD spectra of carotenoid deficient mutant chloroplasts, the red band corresponding to oriented Ca 678 was considerably smaller than in those of normal chloroplasts. LD spectra of lycopenic chloroplasts revealed a band at 740 nm not present in the spectra of normal chloroplasts. Various signals of carotenoids observed in the LD spectra of carotenoid deficient mutant chloroplasts imply that the different carotenoids can be oriented in a different manner in the photosynthetic membrane.
STUDIES ON HOOK‐OPENING IN PHASEOLUS VULGARIS L. BY SELECTIVE R/FR PRETREATMENTS OF EMBRYONIC AXIS and PRIMARY LEAVES*
Authors: Caubergs R. , Greet J. A. De
Published: January 2008

Abstract— Hook‐opening of etiolated bean seedlings was studied by inductive light pretreatments, selectively applied to the embryonic axis and to the primary leaves. Statistical analysis of the experimental results substantiated that hook unbending in intact plants is mutually influenced by both organs. When the leaves were excised immediately after their selective preirradiation, hook opening was the same as in the intact control series.

Far red light could only fully reverse a red inductive effect when both light qualities were administered to the intact plant.

When the cotyledons were removed prior to the light treatments the results did not change qualitatively. Our data indicate that a very precise, highly ordered biophysical recognition system of light signals exists in plants. The transmission of these signals between different organs is very rapid and phytochrome‐mediated.
LIGHT‐INDUCED LEAKAGE OF SPIN LABEL MARKER FROM LIPOSOMES IN THE PRESENCE OF PHOTOTOXIC PHENOTHIAZINES
Authors: Copeland Edmund S. , Alving Carl R. , Grenan Marie M.
Published: January 2008

Abstract— Liposomes prepared from dipalmitoyl lecithin, cholesterol and dicetyl phosphate and containing a trapped spin label marker were exposed to long wavelength UV light in the presence of a series of phenothiazine tranquilizers. EPR spectroscopy was used to detect spin label marker released from liposomes, taking advantage of the disappearance of line broadening from electron spin exchange which occurred on spin label release. The minimum effective phototoxic dose in mice of these phenothiazines was also determined. Kinetic studies of light‐induced spin label release from phenothiazine‐sensitized liposomes showed that membrane damage was rapidly induced and that the damaging species were short‐lived. The damage process was oxygen dependent and could be temporarily prevented by cysteamine or α‐tocopherol added immediately before irradiation. Only those phenothiazines which mediated light‐dependent liposomal membrane damage had phototoxic activity in mice and the degree of photosensitization was parallel in the two systems. In both photosensitization phenomena, the nature of the substituent at the phenothiazine 2‐position was more important than the phenothiazine side chain.
CHEMILUMINESCENCE FROM THE OXIDATION OF AUXIN DERIVATIVES
Authors: Durán Nelson , Zinner Klaus , Baptista Roberto Casadei de , Vidigal Carmen C. C. , Cilento Giuseppe
Published: January 2008

Abstract— The thiophenyl ester of indole‐3‐acetic acid and indole‐3‐acetonitrile produce chemiluminescence in aerated dimethylsulfoxide in the presence of potassium t‐butoxide. The emitter is the aromatic aldehyde. In the case of acetonitrile, the other product expected from the cleavage of an intermediate dioxetane, cyanate/isocyanate, has also been identified. Other auxins also chemiluminesce under similar conditions, but the emitters have not been properly identified.

These systems are models for the peroxidase catalyzed oxidation of indole‐3‐acetic acid to indole‐3‐carboxaldehyde and as such support the earlier inference (Vidigal et al, 1975) that the excited aldehyde is generated in the enzymic process.

An additional result is the observation of an exciplex between excited indole‐3‐carboxaldehyde and the thiophenylester of indole‐3‐acetic acid. This appears to be the first case of chemical generation of an exciplex by a route other than radical ion reaction, presumably by the dioxetane route.
A NEW FLUORESCENT PHOTOPRODUCT OF TRYPTOPHAN EVIDENCED BY LONG WAVELENGTH EXCITATION OF FLUORESCENCE
Authors: Tatischeff I. , Klein R. , Duquesne M.
Published: January 2008

Abstract— Besides the normal tryptophan (Trp) fluorescence in aqueous solution (emission maximum at 350 nm), a new emission, peaking around 380 nm, appears by long wavelength excitation. Its fluorescence yield (φs 0.24) is higher than that of tryptophan (φTrp= 0.13). The growth of this emission is observed under different experimental conditions, mainly under UV anaerobic irradiation. To explain this observation, the formation of a C3‐hydroxylated derivative is tentatively suggested.
EVENTS SURROUNDING THE EARLY DEVELOPMENT OF EUGLENA CHLOROPLASTS—XI PROTOCHLOROPHYLL(IDE) AND ITS PHOTOCONVERSION*
Authors: Cohen Charles E. , Schiff Jerome A.
Published: January 2008

Abstract— The small amounts of chlorophyll precursors in dark‐grown cells of Euglena gracilis Klebs var. bacillaris Pringsheim and the presence of contaminants which interfere with their purification have made their isolation and characterization difficult. We now extract cells with acetone: 0.1 M NH4OH (9:1 v/v). Protochlorophyll is obtained by extracting this solution with petroleum ether (30–50° b.p.) and extracting this petroleum ether fraction with 80% acetone to remove substances which interfere with subsequent chromatography. Protochlorophyllide remaining in the original acetone: NH4OH fraction is extractable into diethyl ether after adjusting the pH to approximately 5.5. Both pigments are verified and further purified by chromatography on Whatmann 3 MM paper using benzene:petroleum ether:acetone (30:10:1) or cellulose MN 300 thin layers with methanol:methylene chloride:water (100:18:20). These pigments resemble their well‐described barley counterparts in solubility properties, spectral absorption maxima in ether (432, 530, 571 and 623 nm) and chromatographic behavior. Substantial amounts of protopheophytin and protopheophoribide are also found along with the Mg2+— containing pigments in cell extracts even when precautions are taken to avoid loss of Mg2+ during extractions and purification.

Using heated cells before and chilled solvents after illumination to preclude enzymatic modification of pigments, chlorophyll and very small amounts of chlorophyllide are found as products of the photo‐conversion of the protopigments suggesting that both protochlorophyll and, to a much smaller extent, protochlorophyllide are photoconvertible in these organisms. These properties join several others which suggest that the Euglena chorophyll‐forming system more closely resembles that found in young bean leaves rather than the chlorophyll‐forming system of the older leaf material usually studied.
EFFECTS OF PIGMENT HETEROGENEITY ON FLUORESCENCE IN PHOTOSYNTHETIC UNITS
Authors: Swenberg C. E. , Dominijanni R. , Geacintov N. E.
Published: January 2008

A computer solution of the Pauli Master Equation is used to study the fluorescence quantum yield of a two‐dimensional random host‐trap‐anti‐trap system. Calculations predict that both the quantum yield and prompt fluorescence lifetime from photosynthetic units increase as pigment heterogeneity increases. From the temperature dependent action spectrum of fluorescence the pairwise Forster transfer rate is predicted to decrease with decreasing temperature.
PHOTOCHEMISTRY OF MODIFIED PROTEINS BENZOPHENONE‐CONTAINING BOVINE SERUM ALBUMIN
Authors: Mariano Patrick S. , Glover George I. , Wilkinson Timothy J.
Published: January 2008

Abstract— The results of exploratory and mechanistic studies of the photochemistry of poly‐p‐benzoyl‐acetimido‐bovine serum albumin, a modified protein containing photoreactive and photosensitizing groups, are reported. Specifically described are our recent findings concerning (1) the synthesis and characterization of a modified bovine serum albumin that contains benzophenone‐like moieties, (2) the photochemistry of this modified protein which appears to involve photoreductive coupling of the benzophenone chromophores to the protein backbone, and (3) triplet energy transfer from modified bovine serum albumin to small molecule acceptors resulting in quenching of the photoreaction.
THE MECHANISM OF ENERGY TRANSFER FROM POLY‐p‐BENZOYLPHENYLACETIMIDO‐BOVINE SERUM ALBUMIN TO SMALL‐MOLECULE QUENCHERS
Authors: Mariano Patrick S. , Glover George I. , Wilkinson Timothy J.
Published: January 2008

Abstract— Results of a quantitative photochemical study of poly‐p‐benzoylphenylacetimido‐bovine serum albumin in the presence of small‐molecule triplet quenchers are reported. The efficiency of quenching by organic salts containing low triplet energy chromophores is shown to be qualitatively dependent on their predicted association constants to the modified protein. In addition, quenching is inhibited by salts of organic acids which possess high binding affinities for the protein but do not contain chromophores of low triplet energy. Quantitative treatment of the quenching and inhibition data yields results which strongly support the operation of an ‘affinity controlled’ mechanism for triplet energy transfer from the benzophenone moieties of the modified‐bovine serum albumin to quenchers such as α‐naphthylacetate and trans‐cinnamate.
PHOTOREDUCTION OF PORPHYRINS TO CHLORINS BY TERTIARY AMINES IN THE VISIBLE SPECTRAL RANGE. OPTICAL AND EPR STUDIES
Authors: Harel Yaacov , Manassen Joost , Levanon Haim
Published: January 2008

Abstract— The photoreduction of free base porphyrins by tertiary amines in the visible spectral range leads to the formation of chlorin. The increase of the apparent first order rates to yield chlorin is correlated with the inductive effect on the nitrogen of the amine used. A mechanism involving a charge transfer interaction between the photoexcited singlet of the prophyrin and the amine is proposed. The porphyrin radicals formed recombine to form a light sensitive dimer which disproportionates in the dark to yield chlorin and porphyrin. The mechanism is elucidated by the use of EPR, laser and flash photolysis.
SIMULTANEOUS MEASUREMENT OF ACTION SPECTRA FOR PHOTOREACTIONS I AND II OF PHOTOSYNTHESIS
Authors: Wang Richard T. , Myers Jack
Published: January 2008

Abstract— We have devised a method of obtaining simultaneous action spectra for photoreactions I and II by analysis of direct and indirect effects involved in enhancement. The method requires previous determination of the neutral wavelength which gives maximum quantum yield by virtue of equal fractions of open reaction centers (p and q) for each photoreaction. A sufficient intensity of the neutral wavelength is used as a constant background. Upon addition of a weak modulated measuring light of intensity Im and wavelength λm two amperometric signals are obtained for rate of oxygen evolution. A modulated signal (AC¯) isolates the direct effect of Im and gives action of photoreaction II as AC/Im. An increment in total rate (ΔDC) also includes an indirect effect of Im in perturbing reaction center conditions (p and q). From analysis of interaction of the two photoreactions, action for photoreaction I can be estimated as (2 ΔDC‐AC)/Im. The method is applicable to whole cells, properly scales the two action spectra to each other, and removes contribution of the State 1‐State 2 phenomena. Action spectra were obtained for Chlorella.
EXCITED STATE PROCESSES AND SOLUTION CONFORMATION OF DIPYRIMIDINE ADDUCTS*
Authors: Hauswirth William , Wang Shih Yi
Published: January 2008

Abstract— The absorption and emission properties of the photochemically produced dipyrimidine adducts are analyzed at 300 and 77K. Those adducts which have a saturated C(5)—C(6) bond in the pyrimidin‐2,4‐dione (Pyr) ring and a pyrimidin‐2‐one (Pyo) ring behave spectroscopically as a substituted Pyo. However, those consisting of one Pyr and one Pyo moiety can be considered as bichromophoric molecules and their spectral properties can be understood in terms of the relative torsional angle between the two rings. The adduct with the most bulky substituents ortho to the torsional bond bears the largest torsional angle and exhibits relatively independent absorption and emission phenomenon. At the other extreme, those adducts with no substituents at this position exist as almost planar molecules and exhibit considerable overlap of absorption bands as well as room temperature fluorescence which, in certain cases, is characteristic of intramolecular exciplex interaction. Using inter‐ring torsional angles of ortho‐substituted biphenyl molecules as a basis for comparative calculation, quantitative estimates of the torsional angles in dipyrimidine adducts at 300K have been made.
LIGHT‐INDUCED ABSORBANCE CHANGES IN PHYCOMYCES PHOTOMUTANTS
Authors: Lipson Edward D. , Presti David
Published: January 2008

Abstract— Blue‐light‐induced absorbance changes indicating the reduction of a b‐type cytochrome by a flavin photoreceptor have been reported elsewhere for Dictyostelium, Neurospora, and Phycomyces. On the basis of action spectra alone these absorbance changes were associated with the blue‐light physiological photoresponses in the latter two organisms. We have investigated phototropically abnormal mutants of Phycomyces in order to determine if there were common defects in blue‐light‐induced absorbance changes and photophysiology. However, mutants representing four genes, madA, madB, madC, and madE, the first two of which are associated with early steps in the sensory pathway, showed blue‐light‐induced absorbance changes identical to those in a phototropically normal strain. A pigment kinetics model, which was used to interpret dose‐response data, indicated a rather low quantum yield of 0.015 for the light‐induced absorbance changes. Similar blue‐light induced absorbance changes were observed in HeLa cells. These cells are derived from a human cervical carcinoma and are thus very unlikely to possess any natural photophysiology. Our results question the relevance of these blue‐light‐induced absorbance changes regarding the blue‐light receptor for physiological responses in various organisms.
PHOTOCHEMISTRY OF KETONES IN SOLUTION‐49* A STUDY OF PHOTOSENSITIZED SPLITTING OF DIMETHYLTHYMINE DIMERS
Authors: Schuster David I. , Gupta A. B.
Published: January 2008

Abstract— Several high energy ketone triplet sensitizers, e.g. carvone, camphor, 3‐methylcyclohexanone, benzoin and 3‐methylindanone, were studied as photosensitizers for the splitting of dimethylthymine dimers. The absence of splitting in all cases and the lack of quenching of benzoin and 3‐methylindanone triplets by the trans‐anti dimer of dimethylthymine strongly suggests that cleavage of dimethylthymine dimers cannot be achieved by a triplet mechanism on irradiation at Λ> 300 nm. The absence of optical rotation in the recovered chiral cis‐anti dimethylthymine dimer after sensitized photolysis (12% splitting) in the presence of (—)‐tryptophan suggests that. in highly polar solvents, such as methanol, where reaction probably takes place according to an electron transfer mechanism involving ion‐pair intermediates, close approach of the sensitizer and substrate does not occur. To the extent that these results can be extrapolated to sensitized cleavage of cis‐syn pyrimidine dimers in DNA brought about by action of photoreactivating enzyme or conventional photosensitizers, a mechanism involving dimer triplet states appears highly unlikely.
PHOTOSENSITIZING EFFECTS OF 8‐METHOXYPSORALEN ON THE SKIN OF HAIRLESS MICE—I. FORMATION OF INTERSTRAND CROSS‐LINKS IN EPIDERMAL DNA
Authors: Ley R. D. , Grube D. D. , Fry R. J. M.
Published: January 2008

Abstract— The photomediated induction of interstrand cross‐links by 8‐methoxypsoralen has been measured in the epidermal DNA of hairless mice. Equivalent efficiencies for cross‐link induction were determined for HRS/J/Anl and SKH: hairless‐1 mice. A wavelength dependence on the relative efficiency of cross‐link induction was observed; a broad spectrum light source, 300–400 nm, was approximately 5 times more effective in cross‐link formation than a 365 nm light source. Repeated exposure to 8‐methoxypsoralen followed by ultraviolet light, 5 times a week for 6 weeks, altered epidermal thickness and resulted in a decreased efficiency for DNA cross‐link formation.
STUDIES ON THYMINE‐DERIVED UV PHOTO‐PRODUCTS IN DNA—II. A COMPARATIVE ANALYSIS OF DAMAGE CAUSED BY 254 NM IRRADIATION AND TRIPLET‐STATE PHOTOSENSITIZATION
Authors: Patrick Michael H. , Snow Jeanne M.
Published: January 2008

Abstract— From the rates of cyclobutyl dipyrimidine (Pyr < > Pyr) formation and the ratio of inactivation of transforming or phage DNA caused by direct (254 nm) or sensitized (1.0 M acetone, 313 nm; 0.02 M acetophenone, 334 nm) irradiation, we conclude that Thy < > Pyr and Cyt < > Pyr are equally lethal, and that they are repaired with equal efficiency by the host cell. Not all the damage formed by photosensitized irradlation can be photoenzymatically repaired, especially when acetone is the sensitizer. We found no compelling evidence for photosensitized interstrand cross‐links or sensitizer‐DNA addition products for the fluence range used in these studies (< 106 Jm‐2); moreover, strand breakage can account for only a part of the non‐photorepairable damage. We suggest that a fraction of the damage may be due to Pyr < > Pyr isomers other than the cis, syn type usually formed in native DNA by far‐UV light.
PHOTOCHEMISTRY OF POLYENES—XI. FLASH PHOTOLYTIC STUDIES OF HINDERED ISOMERS OF RETINAL
Authors: Harriman Anthony , Liu Robert S. H.
Published: January 2008

Abstract— The μs transient absorption spectra of benzene solutions of 7‐cis, 7,9‐dicis, 11‐cis and all‐trans isomers of retinal were recorded both by direct and sensitized excitation. The spectra are indistinguishable, as are the transient decay rates. The results are consistent with the notion of rapid isomerization of the 7‐cis triplets and possibly equilibration of all retinal triplets.
EFFECT OF PHOTOCROSSLINKING ON ESCHERICHIA COLI tRNA STRUCTURE
Authors: Bolton P. H. , Wong K. L. , Kearns D. R.
Published: January 2008

Abstract— The effect of photocrosslinking s4U8 with C13 on the structure of E. coli tRNA has been examined by high resolution NMR. Photocrosslinking affects both the structure and the enzymatic acylation of tRNA. The NMR measurements demonstrate that except for the s4U8.A14 base pair, there is no evidence that photocrosslinking perturbs any of the common tertiary structure interactions. However, this modification does perturb several resonances which are assigned to the secondary structure base pairs of the hU stem and the terminal base pair of the acceptor stem. The variable effect of photocrosslinking on the extent and rate of enzymatic acylation of different tRNA is attributed to different recognition sites for tRNA by the cognate synthetases.
FLUORESCENCE SPECTRA OF CHLOROPHYLL‐a AND CHLOROPHYLL‐b FROM SITE SELECTION SPECTROSCOPY
Authors: Fünfschilling J. , Williams D. F.
Published: January 2008

Abstract— …Highly resolved fluorescence spectra of chlorophyll‐a and ‐b have been measured in ethanol and methyltetrahydrofuran glasses at ˜4K. The vibrational frequencies measured are independent of solvent and were highly reproducible, ±1cm‐1 or less. A possible use of this experimental technique as an analytical tool is discussed.
REPAIR OF UV DAMAGE IN ESCHERICHIA COLI UNDER NON‐GROWTH CONDITIONS
Authors: Tang Moon‐shong , Patrick Michael H.
Published: January 2008

Abstract. –A large difference in survival occurs between buffered suspensions of E. coli irradiated with UV radiation at a low fluence rate and those irradiated at a high fluence rate. For sufficiently large fluences, the extent of this fluence rate dependent recovery (FRR) is about two orders of magnitude greater than that which can be brought about by liquid holding recovery (LHR) following high fluence rate irradiation in most of the E. coli strains studied. LHR and FRR occur in excision resynthesis repair proficient (ERR+) but not ERR‐ strains of E. coli, although its observation can be masked in strains with complete repair potential upon subsequent growth on nutrient plates. Accumulation of DNA strand interruptions and excision of cyclobutyl dipyrimidine occur during LHR and FRR but are more extensive for the latter. Our data suggest mat events beyond incision and excision occur during LHR and FRR, but differences in the extent of ERR during LHR and FRR cannot account for the difference in cell survival between these two phenomena.
THE ROLE OF DNA POLYMERASE I IN LIQUID HOLDING RECOVERY OF UV‐IRRADIATED ESCHERICHIA COLI
Authors: Tang Moon‐Shong , Patrick Michael H.
Published: January 2008

Abstract. –Excision of cyclobutyl dipyrimidines from, and accumulation of strand interruptions in, DNA of different strains of E. coli K12 were determined during liquid holding recovery after UV irradiation. The extent of Pyr <> Pyr excision was the same (20–25%) for both a polA mutant (E. coli P3478) and its parental wild type strain (E. coli W3110); however, single strand interruptions accumulate during liquid holding of polA cells, but not in the parental strain. In contrast, excision was greatly reduced in a mutant (KMBL 1789) which is defective in the 5′→3′ exonucleolytic function of DNA polymerase I. These data suggest that excision and resynthesis during liquid holding are carried out primarily, if not entirely, by DNA polymerase I. We further conclude that excision alone is both a necessary and sufficient condition to elicit liquid holding recovery, and that this excision requires a functional polymerase I 5′→ 3′ exonuclease.
FORMATION OF PHOTOPRODUCTS LETHAL FOR HUMAN CELLS IN CULTURE BY DAYLIGHT FLUORESCENT LIGHT AND BILIRUBIN LIGHT
Authors: Nixon B. Tracy , Wang Richard J.
Published: January 2008

Abstract. Irradiation of Dulbecco's modified Eagle's tissue culture medium with “Daylight,”“Special Blue,” or “Bilirubin” fluorescent light produces photoproducts lethal to human cells. Killing is abolished when (1) riboflavin, (2) tryptophan and tyrosine, or (3) riboflavin, tryptophan and tyrosine are deleted from medium prior to irradiation with any of the above fluorescent lamps. Toxic photoproducts are also formed when buffered salt solutions containing (a) riboflavin and tryptophan, (b) riboflavin and tyrosine, or (c) riboflavin, tryptophan and tyrosine are exposed to any of these light sources.
A SINGLE PULSE PICOSECOND LASER STUDY OF EXCITON DYNAMICS IN CHLOROPLASTS
Authors: Geacintov Nicholas E. , Breton Jacques , Swenberg Charles E. , Paillotin Guy
Published: January 2008

Abstract. Using single picosecond laser pulses at 610 nm, the fluorescence yield (φ) of spinach chloroplasts as a function of intensity (I) (1012‐1016 photons/pulse/cm2) was studied in the range of 21–300 K. The quantum yield decreases with increasing intensity and the φ vs I curves are identical at the emission maxima of 685 and 735 nm. This result is interpreted in terms of singlet exciton‐exciton annihilation on the level of the light‐harvesting pigments which occurs before energy is transferred to the Photosystem I pigments which emit at 735 nm.

The yield φ is decreased by factors of 12 and 43 at 300 and 21 K, respectively. The shapes of the φ vs I curves are not well accounted for in terms of a model which is based on a Poisson distribution of photon hits in separate photosynthetic units, but can be satisfactorily described using a one‐parameter fit and an exciton‐exciton annihilation model. The bimolecular annihilation rate constant is found to be γ= (5–15) times 10‐9cm3s‐1 and to exhibit only a minor temperature dependence. Lower bound values of the singlet exciton diffusion coefficient (≥ 10‐3cm2s‐1), diffusion length (≥ 2 times 10‐6cm) and Förster energy transfer rates (≥ 3 ≥ 1010s‐1) are estimated from γ using the appropriate theoretical relationships.
NEAR ULTRAVIOLET AND POSTIRRADIATION DNA DEGRADATION: EFFECTS ON THE INDUCIBLE INHIBITOR OF IONIZING RADIATION‐INDUCED DNA DEGRADATION
Authors: Coetzee W. F. , Pollard E. C.
Published: January 2008

Abstract— Possible effects of near ultraviolet radiation (near UV) on DNA degradation were examined. Postirradiation DNA degradation induced by ionizing radiation in strain Bs‐l (uur‐, lex‐) is shown to be inhibited by carbon monoxide (CO) and potassium cyanide (KCN) if the cells are grown on glycerol. Presumably the blockage of respiration by these agents lowers the amount of ATP in the cell. 50 kJ/m2 near UV did not simulate the action of CO and KCN, indicating that at this Ruence the supply of ATP remains adequate for postirradiation DNA degradation. Near UV did not, itself, produce DNA degradation. In a strain (B/r) in which an inhibitor of postirradiation DNA degradation can be induced by both UV and ionizing radiation, near UV affects the inhibitor formation, whether administered before or after induction.
FERRIC ION AS PHOTORECEPTOR OF PHOTO‐ PHOBOTAXIS IN NON‐PIGMENTED RHODOSPIRILLUM RUBRUM
Authors: Harayama Shigeaki , Iino Tmsuo
Published: January 2008

Abstract— Rhodospirillum rubrum cultivated aerobically and containing no detectable bacteriochloro‐phyll assembled in their phobotactic response into a spot of blue and near UV light. The shape of the action spectrum for the phenomenon was similar to that of the absorption spectrum of ferric ion in aqueous solution. The photophobotactic response was not observed in media containing no ferric ion. Increasing concentration of the ion in the media resulted in an increasing degree of their photophobotactic response. Ferrous ion could not be substituted for ferric ion unless its autooxidation in medium was allowed.

In addition to ferric ion, existence of appropriate anion, by which photoreduction of ferric ion took place efficiently, was necessary to induce an appreciable photophobotactic response. This suggested that the apparent photophobotaxis was, strictly speaking, chemophobotaxis induced by a photochemical product of ferric complex in medium.
PHOTOREACTIVATING ENZYME FROM ESCHERICHIA COLI
Authors: Snapka R. M. , Fuselier C. O.
Published: January 2008

Abstract— Escherichia coli photoreactivating enzyme (PRE) has been purified in large amounts from an E. coli strain lysogenic for a defective Λ bacteriophage carrying the phr gene. The resulting enzyme has a pH optimum of 7.2 and an ionic strength optimum of 0.18. It consists of an apoprotein and cofactor, both of which are necessary for catalytic activity. The apoprotein has a monomer molecular weight of35,200 and shows stable aggregates under denaturing conditions. The amino acid analysis of the E. coli enzyme is very similar to that of the photoreactivating enzyme from orchid seedlings (Cattelya aurantiuca). Both have arginine at the amino terminus. The cofactor, like the holoenzyme, shows absorption, magnetic circular dichroism, and emission properties indicative of an adenine moiety. Although the isolated enzyme has an action spectrum which peaks at about 360 nm, neither the cofactor, apoenzyme nor holoenzyme shows any detectable absorption between 300 and 400 nm.
PHOTOPHYSICS AND PHOTOCHEMISTRY OF PHOTOREACTIVATION
Authors: Sutherland John Clark
Published: January 2008

Abstract— Photoreactivating enzyme (PRE) monomerizes cyclobutyl pyrimidine dimers formed in DNA by UV light (Λ < 300 nm). The enzyme requires near UV and visible wavelengths (300 < Λ < 600 nm) for activity. Possible mechanisms of action of the PRE are suggested by non‐enzymatic processes in which pyrimidine dimers are monomerized by UV and visible light. Two such non‐enzymatic processes are (a) photolysis of dimers resulting from direct absorption of UV, and (b) sensitized monomerization involving charge transfer complexes. Several lines of evidence suggest that the mechanism of action of the PRE more closely resembles (b) than (a). Recent experiments on the PRE from E. coli reveal the presence of new long wavelength absorption which may indicate the presence of a ground state complex. The known ability of PRE to monomerize dimers of thymine, cytosine and uracil suggests that the carbonyl groups at 2 position of the pyrimidine ring may be important in the interaction between enzyme and dimer.
THE EFFECT OF 8α‐SUBSTITUTION ON FLAVIN TRIPLET STATE AND SEMIQUINONE PROPERTIES AS INVESTIGATED BY FLASH PHOTOLYSIS*
Authors: Edmondson Dale E. , Rizzuto Frank , Tollin Gordon
Published: January 2008

Abstract— Flash photolysis techniques have been used to study the effect of 8α‐substitution on flavin triplet state formation and decay and on the properties of neutral and anionic serniquinones. Compared with riboflavin, the N(1) and N(3) isomers of 8α‐histidylriboflavin show a lower triplet yield (˜10%) and a faster rate of decay (˜ 4‐Cfold). Acetylation of the histidyl a‐amino groups and of the flavin ribityl side chain results in a 2‐fold increase in triplet yield and a 2‐fold slower rate of decay.

The yield of neutral 8α‐substituted flavin semiquinones upon flash photolysis in the presence of EDTA was approximately 50% that given by riboflavin. These substituted flavin neutral semiquinones dismutated at a rate 2–3 times slower than the corresponding unsubstituted form, although the anionic semiquinones dismutated at approximately the same rate.

In the presence of oxygen, the kinetics of semiquinone decay changed from second order to pseudo‐first order upon raising the pH, thus showing anionic semiquinone oxidation as seen previously with unsnbstituted flavins. The pK values for the ionization of the neutral 8α‐substituted Aavin semiquinones are 1–1.5 units lower than the unsubstituted form. The anionic 8α‐substituted flavin semiquinones react with oxygen at a rate 2–10 times more slowly than does the riboflavin form. Such alterations in properties probably reflect the electron‐withdrawing effect of the 8α‐substituents on the flavin ring system.