bluuebunny/crossref_metadata_2025 huggingface dataset:
THE COMPLEXITY OF THE FLUORESCENCE OF CHLORELLA PYRENOIDOSA
Authors: WILLIAMS W. P. , MURTY N. R. , RABINOWITCH E.
Published: January 2008

Abstract— The complexity of the room‐temperature emission spectrum of Chlorella was investigated by a matrix analysis method. This approach revealed the presence of two independently fluorescent components in the short‐wave region of the spectrum. These components, maximal at about 687 and 695 nm, appeared to correspond to the fluorescence of the bulk pigments of PS II and PS I respectively. The analysis was insensitive to the individual species within the photosystems. As such, other minor fluorescent species, usually observed at low temperatures, which presumably correspond to fluorescence from the trapping centres, did not appreciably complicate the analysis. The absorption spectra of the two photosystems were calculated from the fluorescence data. The results were similar to those that have been obtained by other workers from oxygen evolution and DCMU poisoning data but differed from those obtained by computer analysis of the absorption spectrum. Addition of reduced DCPIP was observed to reverse the increase in fluorescence yield and changes in the spectral distribution of emission taking place on poisoning the algae. The correlation between this and the catalysis of photophos‐phorylation in aged or poisoned chloroplasts was noted. This correlation was tentatively interpreted as evidence for a direct interaction between the donor system and the photochemical apparatus associated with PS II, rather than with a member of the electron transport chain as is normally assumed.
PHOTOCHEMISTRY OF TOBACCO MOSAIC VIRUS RNA. EFFECT OF HCN*
Authors: EVANS NEIL A. , SAVIGE W. E. , McLAREN A. D.
Published: January 2008

Abstract— In attempting to sort out possible mechanisms of photoreactivation of tobacco mosaic virus RNA (TMV‐RNA) inactivated by ultraviolet radiation (u.v.) in buffer of ionic strength 0.25, we have investigated the effect of HCN on the quantum yield for u.v. inactivation of TMV‐RNA and on the percent photoreactivation of inactivated TMV‐RNA. Some photo‐products produced by irradiation of model substances, polyuridylic acid (poly U) and polycytidylic acid (poly C), in the presence of HCN have also been studied.

The ratio of the quantum yield for inactivation of TMV‐RNA in the presence of HCN to that in the absence of HCN is 1.5, under non‐photoreactivating conditions. By comparison, the ratio of the initial rates of loss of uracil residues in poly U under comparable conditions is 1.6; by contrast, the rate of loss of cytosine residues in poly C is unaffected by HCN. This similarity of ratios between poly U and TMV‐RNA suggests that two of the mechanisms of u.v. inactivation of TMV‐RNA at high ionic strength are akin to known reactions of uracil residues in poly U, i.e. hydrate and dimer formation.

The photohydration reaction in poly U, as measured by the heat reversal of hydrated residues to uracil residues, is almost abolished by HCN, and the rate of dimerization, as measured by the appearance of dimer containing oligonucleotides following enzymatic hydrolysis of irradiated poly U, is reduced to half by HCN. HCN does not affect the rate of hydration of cytosine residues in poly C. Since photoreactivation of RNA inactivated in presence of HCN is only 60 per cent of that in absence of HCN it is suggested that uracil dimers are somehow involved in photoreactivation of TMV‐RNA inactivated at high ionic strength.
STRUCTURE OF UROCANIC ACID PHOTODIMERS
Authors: ANGLIN. J. H. , BATTEN W. H.
Published: January 2008

Abstract— U.V. irradiation of trans‐urocanic acid frozen in an ice matrix results in trans, trans, trans‐2,4‐di‐imidazolyl‐1,3‐cyclobutanedicarboxylic acid from pH 8.0 solutions; or cis, trans, cis‐3, 4‐di‐imidazolyl‐1, 2‐cyclobutanedicarboxylic acid from pH 5.9 solutions.
PHOTOREACTIVATION OF ESCHERICHIA COLI Bs‐3 AFTER IN ACTIVATION BY 313 nm RADIATION IN THE PRESENCE OF ACETONE
Authors: MENNIGMANN HORST‐DIETER , WACKER ADOLF
Published: January 2008

Abstract— The colony‐forming ability of E. coli Bs‐3 can be inactivated by light of 313 nm wavelength in an acetone‐sensitized photochemical reaction. This ability can subsequently be restored quantitatively by illumination with photoreactivating light. A small fraction of the population cannot be inactivated; this is assumed to be due to a complete dark repair of the lesions, whatever the dose of radiation has been. Thus, such triplet energy‐transfer experiments can successfully be applied to whole cells. Since thymine dimers are formed almost exclusively, this suggests a new way of studying these lesions in relation to the biologically observable effects.
A STUDY OF THE RELATIONSHIP BETWEEN SURVIVAL AND REPAIR SYNTHESIS‘ OF DNA AFTER ULTRAVIOLET LIGHT EXPOSURE
Authors: SEDLIAKOVÁ M. , BILLEN D. , BRUNS L.
Published: January 2008

Abstract— The influence of amino acid prestarvation on both the resistance to u.v. and the postirradiation repair synthesis of E. coli 15 T‐ 555‐7 thy meth arg trp and E. coli B/r (HCR+) was followed. Prestarvation increased the number of survivors about 30–100 fold in both strains at doses 600‐1200ergs/mm2. In contrast to survival no increase in repair synthesis was observed. Thus, the increase in survival has to be brought about by a mechanism which seems to be independent of additional repair synthesis.
PHOTOELECTRONIC EFFECTS IN ORGANIC MATERIALS–II. VARIATION OF PHOTOVOLTAGE WITH pH IN CHLOROPHYLL‐QUINONE SOLUTIONS
Authors: SIMPSON W. H. , FREEMAN R. A. , REUCROFT P. J.
Published: January 2008

Abstract— The photovoltaic effect in ethanolic solutions of chlorophyll a with benzoquinone or hydroquinone has been measured as a function of pH. In acidic media, stable, fast‐rising photovoltaic signals of positive sign are obtained. In neutral and basic media, less stable, slower rising photovoltaic signals of negative sign are found. The results in acid media are explained in terms of a photochemical interaction between chlorophyll and either the benzoquinone or hydroquinone producing protons which can then act as the electrode active agent. In basic media, negatively charged radical species, such as the benzoquinone radical‐anion, are considered to be the most likely electrode‐active species.
A SEQUENTIAL REPAIR MODEL OF PHOTOREACTIVATION IN BACTERIA*
Authors: DAVIES D. J. G. , TYLER SYLVANUS A. , WEBB R. B.
Published: January 2008

Abstract— Kinetics of photoreactivation were studied in E. coli WP2 hcr‐, a strain deficient in dark repair. Cells in aqueous suspension were subjected to u.v.‐irradiation, then exposed to photoreactivating light for different periods. Survival curves, with samples at a minimum of six u.v. doses, were obtained at several periods of photoreactivation ranging from zero to maximum. The surviving fractions do not conform to a dose‐reduction model, but instead, they fit a ‘sequential repair’ model that assumes as a limiting condition that the number of active enzyme molecules is small. The model used assumed: (1) a single enzyme molecule is active at any one time; and (2) inactivating events are nullified consecutively around the DNA molecule. The mathematics of the model are derived and presented. Photoreactivation is attributed to the action of two processes. (1) A photochemical process, that is rate limiting below 1000 ergs mnr‐2 sec‐1, was measured at a photoreactivating irradiance of 60 ergs mm‐2 sec‐1. This has a rate constant of 5 × 10‐5‘events’ erg‐1 mm2. (2) A dark process, measured at photoreactivating irradiances of 4000 and 6000 ergs mm‐2 sec‐1, has a rate constant of 2.2 ‘events’ min‐1.
MIGRATION OF EXCITATION ENERGY FROM THIONINE TO METHYLENE BLUE IN MICELLES
Authors: SINGHAL G. S. , RABINOWITCH E. , HEVESI J. , SRINIVASAN V.
Published: January 2008

Abstract— The main absorption bands of thionine (Th+) and methylene blue (MB+) in aqueous solution lie at 598 nm and 664 nm, respectively. This position permits excitation energy transfer from Th+ to MB+, but not vice versa. We describe here studies of such transfer between these molecules adsorbed on micelles of sodium lauryl sulfate (SLS), imitating, at least to some extent, the state of pigments in chloroplasts.

The SLS concentration was varied from 3.0 to 11 × 10‐3M. In the presence of dye, aggregation to micelles, each containing 70–100 detergent molecules, begins at about 3.0 × 10‐3M SLS. Practically all dye ions are adsorbed on these micelles as soon as their formation begins.

Energy transfer from adsorbed Th+ ions to adsorbed MB+ ions can be demonstrated by observing the quenching of the fluorescence of thionine and the sensitization of that of methylene blue.

At [Th+] = [MB+] = 1 × 10‐5M, the most efficient energy transfer (82 per cent efficiency, as derived from measurements of the quenching of Th+ fluorescence, or 90 per cent, as derived from sensitization of MB+ fluorescence) is observed at the lowest SLS‐concentration (3.0 × 10‐3M), when the only micelles present are those formed by aggregation of dye‐carrying low molecular complexes of SLS with dye cations. Each micelle carries, under these conditions, 10–14 molecules of the two dyes, and the distance between two closest dye ions is about 16 A. Transfer becomes less efficient as the SLS‐concentration increases, causing pigment molecules to distribute themselves among a greater number of micelles.
PHOTOLYSIS OF ETHYL CHLOROACETATE IN LIQUID PHASE AT 2537 A°R
Authors: WOJTCZAK JAN , MATUSZEWSKI BOGDAN
Published: January 2008

Abstract— Results on the photolysis of ethyl chloroacetate, CICH2COOC2H5, at A°≅ 254 nm in liquid phase are presented. GLC and i.r. methods revealed as products: hydrogen chloride and ethyl acetate; in smaller quantities–ethyl succinate and ethyl oxalate; in traces–ethyl malonate, CO2, CO and CH3CI; yet other, unidentified products with higher boiling points. Quantum yields are determined for some products. Similar studies were performed in the presence of I2 as a radical scavenger. In the present case, ethyl iodoacetate I – CH2COOC2H5 was found to arise in the system. The following primary process may be written on the basis of the experimental data:

CICH2COOC2H5← CI + CH2COOC2H5

Attempts to explain the production of these compounds are based mainly on the properties of the CH2COOC2H5 radical.
LIGHT INDUCED SYNCHRONIZATION OF ALGAL SPECIES THAT DIVIDE PREFERENTIALLY IN DARKNESS*
Authors: CARROLL JACK W. , THOMAS JERRY , DUNAWAY CHARLES , O'KELLEY JOSEPH C.
Published: January 2008

Abstract— Three algal species (Protosiphon botryoides, Chlorella pyrenoidosa and Chlamy‐domonas gymnogama) which divide preferentially at night during natural or simulated day‐night conditions are shown to have cell division inhibited by light in the blue region of the visible spectrum (400–500 nm) and stimulated by the remainder of this spectrum (500–730 nm). Synchronous division has been established in cultures of these organisms on a circadian or longer period by alternating fluorescent cool‐white light and cool‐white with the blue component removed. This procedure is suggested as potentially superior to other methods for synchronizing cultures of algae that prefer, in nature, to undergo cell division at night. Where this procedure does not work it is recommended that an action spectrum for cell division be obtained, since this may provide information for achieving optimal synchrony through the use of other specific wavelength regimes.
PROFLAVINE‐SENSITIZED PHOTOOXIDATION OF METHIONINE
Authors: JORI GIULIO , CAUZZO GIULIO
Published: January 2008

Abstract— A study was made of the kinetics of the proflavine‐sensitized photooxidation of methionine to methionine sulfoxide. The reaction is inhibited by the paramagnetic ions Cu2+ and Mn2+, which suggests that the triplet state of the sensitizer is an intermediate. A mechanism is proposed in which methionine reacts with the first singlet state of oxygen, produced by energy transfer from the triplet sensitizer. The decrease in the rate of photooxidation with increasing proflavine concentration is ascribed to self‐quenching of the excited singlet state of the dye.
INACTIVATION BY ULTRAVIOLET RADIATION AT DIFFERENT WAVELENGTHS OF THE RNA ISOLATED FROM POTATO VIRUS X
Authors: GOVIER D. A. , KLECZKOWSKI A.
Published: January 2008

Abstract— –The action spectra and quantum yields for photoreactivable, non‐photoreactivable and total damage caused by u.v. in the RNA isolated from potato virus X differ from those for similar types of damage in the whole virus. The differences result from the virus protein partly protecting the RNA from damage, and the degree of protection depends on the wavelength of u.v. and on the salt concentration of the irradiated solution. The action spectra for the different types of damage in the RNA all resemble the absorption spectrum of the RNA, but do not exactly parallel it. The photoreactivable sectors of the RNA and of the whole virus are greater at 290 nm than at 230 nm but, whereas that of the virus increases rectilinearly, that of the RNA has a pronounced minimum at about 250 nm. At wavelengths longer than 240 nm, the photoreactivable sector of the virus exceeds that of the RNA, because, at these wavelengths, the virus protein protects the RNA more against non‐photoreactivable damage than against photoreactivable damage.
ON THE POSSIBILITY OF INFRARED LASER‐INDUCED CHEMISTRY*
Authors: GOODMAN MYRON F. , SELIGER H. H. , MINKOWSKI JAN M.
Published: January 2008

Abstract— –We examine whether chemical reactions can be selectively stimulated by the absorption of infrared photons which individually do not satisfy activation energy requirements. By a modification of available rate theory we demonstrate that a non‐thermal enhancement of a chemical reaction is in principle possible, and is primarily dependent upon the extent to which a molecular mode can be coherently driven. An assumed coherent response to laser radiation leading to a minimally detectable rate enhancement places realistic constraints on the allowable magnitudes of vibrational and phase relaxation times for the mode. The inclusion of anharmonic limitations on the amount of energy stored in the mode results in the placement of more stringent though not impossible limitations on the relaxation times. A non‐linear reaction rate dependence on light intensity suggests that a Q‐spoiled laser be used. Optimum experimental conditions should involve the use of liquids at a temperature where thermal rates are just beneath the level of detection.
PHOTOSENSITIZED CONVERSION OF ETHIONINE TO ETHYLENE BY FLAVIN MONONUCLEOTIDE*
Authors: YANG S. F.
Published: January 2008

When methionine or one of several analogues (ethionine, homocystine, homocysteine, 2‐hydroxy‐4‐methylthiobutyric acid or 4‐methylthio‐2‐oxo‐butyric acid) was irradiated by visible light in the presence of flavin mononucleotide (FMN), ethylene was produced in good yield [1,2]. The ethylene was derived from carbons 3 and 4 of methionine. Later Shimokawa and Kasai [3] reported that the ethyl moiety of ethionine could also be converted to ethylene by FMN and light, but these authors did not show the proportion of the ethylene derived from the ethyl moiety of ethionine. Under the optimal conditions, I have found that the ethylene derived from the ethyl moiety of ethionine represents less than 1 per cent of the total ethylene produced. The present paper describes the characteristics of ethylene production from the ethyl moiety and from carbons 3 and 4 of ethionine, and presents a mechanism to explain these reactions.
CHANGES IN FLUORESCENCE SPECTRA OF CHLOROPLASTS INDUCED BY A NATURALLY‐OCCURRING FACTOR
Authors: NATHANSON B. , BRODY M.
Published: January 2008

Abstract— –Fluorescence emission changes (measured at – 196°C) of Ricinus chloroplasts incubated in isolation medium, and of chloroplasts from algae and higher plants incubated in Ricinus leaf extract, are described. Such incubation results in a transformation of the three‐banded emission spectrum (F735, F698, F685) into a virtually one‐banded spectrum, with maximum at 698 nm. That these changes are a consequence of the conversion (deaggregation) of the form of chlorophyll giving rise to F735 into a form contributing to fluorescence at 698 nm is suggested on the basis of room temperature absorption and low temperature fluorescence excitation studies, made concomitantly with the low temperature emission studies.
TRIPLET STATES OF POLYCYCLIC AROMATIC HYDROCARBONS IN FLUID SOLUTION AND IN THE SOLID STATE
Authors: SLIFKIN M. A. , WALMSLEY R. H.
Published: January 2008

Abstract— –Triplet states of several large polycyclic aromatic hydrocarbons together with their lifetimes have been determined both in fluid solution and in the solid state using a spectrophoto‐metric technique.

Excited states and lifetimes of some solid charge transfer complexes between the hydrocarbons and chloranil have been examined.

The assignment of the 1Bb states of some of the hydrocarbons have been made from the energies of the triplet states.
DELAYED FLUORESCENCE FROM CHLORELLA PYRENOIDOSA: EFFECT OF BACKGROUND ILLUMINATION*
Authors: RUBY R. H.
Published: January 2008

Abstract— –With background illumination the delayed fluorescence intensity from Chlorella pyrenoidosa observed at 1 msec following a flash of light is greatly increased. It is shown that the background illumination makes a photosystem II product that increases the delayed fluorescence yield and decays in the dark with second order kinetics. The delayed fluorescence observed at 1 msec appears to be more closely related to the primary energy conversion act than delayed fluorescence observed at longer times which is more indicative of electron transport chemical activity.
PHOTODYNAMIC RESPONSES IN RHODOTORULA GLUTINIS IN THE ABSENCE OF ADDED SENSITIZERS*
Authors: MAXWELL W. A. , CHICHESTER C. O.
Published: January 2008

Abstract— –The lethal effect of a continuous spectrum of light at wavelengths longer than 300 nm has been examined for the yeast Rhodotorula glutinis. A survival curve consisting of a shoulder, an exponential phase of death, and a “tailing off” phase was shown to occur when cells were irradiated in the absence of a sensitizing dye. An action spectrum showed that the portion of the light used for irradiation which is lethal to the cells lies between 310 and 430 nm. It was found that carotenoid pigments were not able to provide any protection against this endogenously photosensitized oxidation. Exponentially growing cells were the most sensitive to killing and, as cells approached and entered into the stationary phase of growth, they became more resistant until a constant level of sensitivity was reached. A primary temperature effect on the length of the shoulder prior to the death of the cell has been observed. The sensitivity was greatest at low temperatures with an optimum resistance occurring at 22.5°C and an increasing sensitivity occurring at higher temperatures. Various sites have been examined for cellular damage which might lead to the death of the cell. Damage was found to impair the function of the plasma‐lemma, the glycolytic and respiratory system, the nucleus, and to be observable cytologically.
ETUDE PAR RESONANCE PARAMAGNETIQUE ELECTRONIQUE DE LA PHOTOSENSIBILISATION DES ACIDES AMINES PAR LA PROFLAVINE
Authors: VORST ALBERT VAN DE
Published: January 2008

Abstract— –The photosensitization of amino acids by proflavine is studied using the technique of electron spin resonance spectroscopy. The analysis of the line shape as a function of the incident microwave power (both in the presence and absence of oxygen) and the dependence of the numbers of free radicals on the intensity of the incident light allow one to suggest that two types of radicals are formed. One is formed by a biphotonic process, the nature of the radicals being the same as in the case of ionising radiation, while the other is probably the RO2 radical formed as a result of photodynamic action.
A FLASH PHOTOLYSIS STUDY OF THE TRIPLET STATE OF ACRIDINE ORANGE IN BASIC SOLVENTS
Authors: KELLMANN A.
Published: January 2008

Abstract— Photochemical reactions of acridine orange (AO) in basic aqueous and ethanolic solutions were studied using the flash photolysis technique. The absorption spectrum of AO was determined in detail (230–900 nm) and extinction coefficients were obtained. The decay of the triplet state is the result of a first order process, a triplet‐triplet annihilation process and a quenching by the dye in the ground state. The main part of the triplet decays to the ground state; however the observation of semi‐reduced AO shows that the decay is partly due to chemical reactions.

An efficient reversible reaction is observed on flashing aqueous solutions of AO containing tetramethyl‐p‐phenylenediamine: semi‐reduced AO is formed in high yield by reaction between the triplet dye and the diamine. In addition, irreversible reactions of AO occur; these are shown to be due to the triplet state by the method of triplet energy transfer.
INDOLE N—H BOND FISSION DURING THE PHOTOLYSIS OF TRYPTOPHAN
Authors: PAILTHORPE M. T. , NICHOLLS C. H.
Published: January 2008

Abstract— By comparing the photochemical behaviour of tryptophan and N'‐methyl tryptophan, both in the free state and protein bound, evidence has been obtained which indicates that indole N—H bond fission is a primary photochemical reaction during the photolysis of tryptophan with 300–360 nm radiation. ESR evidence suggests that immediately following N—H bond fission, rearrangement of the indole nucleus occurs to form the 3‐indolyl free radical. This radical was found to be quite stable in a frozen matrix at 150°K, but has a lifetime of only 50 μsec at 25°C.
THE CORRELATION BETWEEN THE ABSORPTION AND THE FLUORESCENCE ENERGY SPECTRA, AND THE QUANTUM YIELD OF CHLOROPHYLL a IN DIFFERENT SOLVENTS†
Authors: SINGHAL G. S. , HEVESI J.
Published: January 2008

Abstract— The applicability of Stepanov's relation to solutions of chlorophyll a in 17 solvents was determined. The value of T* (the local temperature of the excited molecules calculated by the relation) was higher than T (the ambient temperature) in 7 solvents and lower in one. The relative quantum yield determined by comparing the fluorescence spectrum with the thermal emission spectrum was fairly constant (˜ 1.0) up to 690 nm in dioxane, methylene chloride and dimethylformamide. In other solvents its value at 690 nm varied between 0.2 and 067. It is suggested that existence of a solute‐solute or solute‐solvent interaction in some solvents could possibly cause such a drop in the quantum yield.
AN ACTION SPECTRUM FOR ULTRAVIOLET‐INDUCED SPORULATION IN THE FUNGUS STEMPHYLIUM SOLANI WEBER
Authors: SPROSTON T.
Published: January 2008

Abstract— An action spectrum for conidial (spore) production in the fungus Stemphylium solani Weber is presented. The response is in the far‐ultraviolet region (far u.v.). The spectrum shows a single peak at 280 nm, a shoulder at 260 nm, a trough at 250 nm, followed by a rise which is still rising at 230 nm, the shortest wavelength studied. The u.v. induced spore stimulation can be interrupted temporarily by irradiation in the visible region within 4 hr after induction.
PHOTOTACTIC AND PHOTOKINETIC ACTION SPECTRA OF THE DIATOM NITZSCHIA COMMUNIS
Authors: NULTSCH W.
Published: January 2008

Abstract— Three different types of photomotion reactions, photokinesis, photo‐topotaxis and photo‐phobotaxis, have been investigated in the diatom Nitzschia communis. In photokinesis the active light appears to be absorbed by the photosynthetic pigments. Apparently, the acceleration of movement by light is due to an additional ATP supply from photosynthetic phosphorylation, as it is the case in the blue‐green algae of the genus Phormidium. On the other hand, no correlations exist between photo‐phobotaxis and photosynthesis, because red light does not induce photo‐phobotactic responses in N. communis. The phobotactic action spectrum resembles that one of photo‐topotaxis. In the visible region only violet, blue and blue‐green light is active in both the reactions. However, it is not yet clear whether or not the stimuli are mediated by the same photoreceptor, mainly because of the different sensitivity of both the reactions to u.v.
THERMOLUMINESCENCE OF NUCLEIC ACID CONSTITUENTS IN SOLUTION AFTER U.V.‐IRRADIATION
Authors: BRYNDA E.
Published: January 2008

Abstract— The thermoluminescence of purines and pyrimidines has been studied in ethylene glycol (EG)/water (2:1) glass matrices after ultraviolet (u.v.) irradiation at 77°K. An investigation of the mechanism of thennoluminescence has been made for adenine. The thermoluminescence involved biphotonic ionisation and recombination. The thermoluminescence depended on the square of the excitation light intensity, and the observed lifetime of the second photonabsorbing intermediate was the same as the phosphorescence lifetime. The emission spectrum lay in the same wavelength region as the phosphorescence spectrum. It was possible to bleach the thennoluminescence with visible light.
HIGH RESOLUTION SCINTILLATION SPECTRA OBTAINED WITH NANOSECOND PULSES OF 3 MeV ELECTRONS*
Authors: HORROCKS D. L.
Published: January 2008

In studies involving an energy transfer process it is important to have definite knowledge of the excited state of the solute which is responsible for the emitted fluorescence that is measured. When solutions with low solute concentration are irradiated with ionizing particles, the initial excitations are produced in the solvent molecules (excited molecules or ions). The excited solvent molecules and ions can transfer energy to the solute producing excited solute molecules. The measured scintillations are the result of the return of the solute molecules to the ground state.
FLASH PHOTOLYSIS STUDIES OF PROTEINS AND INDOLE DERIVATIVES IN SOLUTION
Authors: SUBRAMANYAN V. , TOLLIN G.
Published: January 2008

Abstract— Transients obtained upon flash photolysis of a number of proteins in aqueous solution appear to derive from electron ejection from tryptophyl residue side chains. These decay by a second order process. Oxygen is an effective quencher for the protein transients but is less so for the flash‐induced signals obtained from simple indole derivatives. Experiments using other quenchers indicate that the signals are not due to an indole triplet state, but that the triplet state may be a precursor of the flash‐induced metastabie species. Compounds which bind to the active site of chymotrypsin were found to exert only non‐specific effects on the flash‐induced signals.
OLIGONUCLEOTIDE PHOTOPRODUCTS FORMED BY PHOTOLYSIS OF POLYRIBOBROMOURIDYLIC ACID
Authors: EHRLICH MELANIE , RILEY MONICA
Published: January 2008

Abstract— Polyribobromouridylic acid was irradiated with 313 nm light at an exposure of ˜ 190 pE/cm*. Oligonucleotides found after RNase hydrolysis of the photolysed poly‐rBrU were isolated by DEAE‐cellulose chromatography and partially characterized. The dmucleo‐tide fraction, found in highest amounts, was not susceptible to hydrolysis by KOH or snake venom phosphodiesterase and may contain a coupled photoproduct. The properties of the dinucleotide were not those of a molecule containing a cyclobutane‐type dimer, but were compatible with the properties of a coupled product similar to 5–5′‐diuracil. The trinucleotide fraction probably consisted of more than one component. One component may contain a dimeric photoproduct. The tetranucleotide material was sensitive to cleavage into fragments by KOH, and could consist of adjacent photoproducts of the types found in the di‐ and trinucleotide fractions. The photoproducts formed over a range of lower doses of light were found to have properties similar to those found at high doses.
OBITUARY
Authors: ROE Dr. EDNA M. F. , KNOWLES AUBREY
Published: January 2008

Edna Roe died on 31 July, 1971, in London after a long illness borne cheerfully and with great courage. This was typical of Edna, who had often given courage and hope to others in similar situations.

Edna Margaret Frances Roe was born and educated in London and worked there for most of her life. Soon after graduating she joined the staff of the Research Institute of the Royal Cancer Hospital to work with W. V. Mayneord on the absorption spectra of carcinogenic hydrocarbons. This work included a study of the fluorescence of these molecules and this encounter with the excited state led to a sustained interest in the photochemistry of biologically active molecules, particularly in the fields of photodynamic action and the UV degradation of nucleic acids.
PROFLAVIN‐SENSITIZED PHOTOOXIDATION OF 3‐METHYL INDOLE TO 2‐METHYL‐2‐METHOXY‐1, 4‐BENZOXAZINE
Authors: ESKINS K.
Published: January 2008

Abstract— The dye‐sensitized photochemical oxidation of 3‐methyl indole was studied as a model for the photooxidation of the indole amino acid, tryptophan. The major product formed by proflavin‐sensitized photooxidation is 2‐methyl‐2‐methoxy‐1,4‐benzoxazine. The compound was isolated by preparative gas chromatography and identified by a combination of NMR, u.v., i.r., and mass spectroscopy on the photoproduct and its derivatives.
THE DESTRUCTION OF TRYPTOPHANYL RESIDUES IN TRYPSIN BY 280‐nm RADIATION
Authors: VOLKERT W. A. , GHIRON C. A.
Published: January 2008

Abstract— The destruction of tryptophanyl residues in trypsin by 280‐nm radiation was studied in relation to enzyme inactivation. Quantum yields for destruction of this residue (determined using the pDAB reagent) and for the inactivation of trypsin were measured when the enzyme was exposed to different environmental perturbations. The conformational modifications of trypsin induced in 6 M guanidine‐HCl did not alter the rates of tryptophan destruction and enzyme inactivation. However, an enhanced destruction of the tryptophanyl residues was observed when trypsin solutions were irradiated at 60°C in the presence of air. The increased rate of tryptophan destruction at this temperature was not accompanied by a corresponding increase in the inactivation quantum yield. It was concluded that any photochemically induced reactions of this chromophore that are sensitive to conformational modifications or that result in the destruction of the indole ring are not important in the inactivation mechanism of trypsin.
ISOLATION OF PHOTOCHEMICAL REACTION CENTERS FROM A CAROTENOIDLESS MUTANT OF RHODOSPIRILLUM RUBRUM*
Authors: WANG RICHARD T. , CLAYTON RODERICK K.
Published: January 2008

Lauryl dimethyl amine oxide was used to isolate reaction centers from a carotenoid‐less mutant, strain G‐9, of Rhodospirillum rubrum. These reaction centers have absorption spectra and light or chemically induced difference spectra very similar to those obtained from Rhodopseudomonas spheroides, strain R‐26. But, unlike those from Rps. spheroides, they are more labile to higher detergent concentrations and to ammonium sulfate. The cytochrome content was estimated to be less than one per 10 P870.
PHOTOALKYLATION OF PURINES IN DNA
Authors: BEN‐ISHAI R. , GREEN M. , GRAFF E. , ELAD D. , STEINMAUS H. , SALOMON J.
Published: January 2008

Abstract— Ultraviolet light irradiation of DNA in the presence of alcohols such as 2‐propanol leads to hydroxyalkylation of the purine bases. The purine photoproducts were identified as C‐8 hydroxyalkyl derivatives of adenine and guanine by chromatographic mobility, co‐crystallization with authentic samples, and by photoreversal to the original purines. Experiments are reported which demonstrate that the photoalkylation reaction is dependent upon secondary structural alterations in DNA. It is suggested that the photoalkylation of purines proceeds through free‐radical intermediates.

The presence of alcohols during irradiation considerably decreases pyrimidine‐dimer formation.
THE PHOTOLYSIS OF TRYPTOPHAN IN THE PRESENCE OF OXYGEN
Authors: PAILTHORPE M. T. , BONJOUR J. P. , NICHOLLS C. H.
Published: January 2008

Abstract— Quantum yields for the destruction of tryptophan by a single 500 J flash in aqueous solution have been determined over the pH range 1–13 in both air‐equilibrated and nitrogen‐saturated conditions. When these quantum yields are compared with the quantum yields for radical formation and photoejection of electrons, it is found that there is good agreement only for the nitrogen‐saturated case. In air‐equilibrated solutions of tryptophan, there is a large disparity between the measured degradation quantum yields and those for photoejection of electrons and radical formation. Oxygen, therefore, is playing a major role in the photochemical decomposition and it is proposed that the major reaction which occurs, under normal atmospheric conditions, is the reaction of the lowest triplet excited state of tryptophan with oxygen.

Preliminary photolysis‐product distributions against pH are discussed, and indicate that a total of nine major products are formed in the presence of oxygen.
SENSITIVITY OF THE ELECTRON TRANSPORT CHAIN OF PIGMENTED AND NON‐PIGMENTED SARCINA MEMBRANES TO PHOTODYNAMIC ACTION
Authors: PREBBLE J. , HUDA A. S.
Published: January 2008

Abstract— With malate as substrate, the respiratory system of Sarcina lutea is subject to photodynamic action when toluidine blue is added as a photosensitiser. Both whole cells and isolated cell membranes show similar photoinactivation. Cell and membrane suspensions of a carotenoid‐containing strain are significantly less sensitive than those from a non‐pigmented mutant prepared from the pigmented strain. Addition of histidine also provides photoprotection. Attempts to locate the site of photoinactivation within the respiratory system lead to the conclusion that several sites are affected. Short periods of illumination do not result in permanent damage since activity is recovered in these suspensions when incubated in the dark subsequent to illumination. The significance of these results and the possible mechanisms involved are discussed.
THE PHOTOADDITION OF NUCLEOPHILES TO URACIL
Authors: SUMMERS W. A. , ENWALL C. , BURR J. G. , LETSINGER R. L.
Published: January 2008

Abstract— Quantum yields for 254 nm ultraviolet photoaddition of the nucleophiles hydrazine, HCN, HSO3‐, methyl amine, and BH4‐ to uracil have been measured; the quantum yields for hydrazine, HCN, and HSO3‐ additions are pH‐dependent. The nucleophiles sulfide, azide, chloride, bromide, iodide, nitrite and thiocyanate failed to photo–add under similar conditions. These reactions are interpreted as 1,4‐additions to the conjugated enone system of the anti‐aromatic compound, uracil; as suggested by S. Y. Wang (Wang and Nnadi, 1968). The nuclear magnetic resonance (NMR) spectrum of the photohydrate of uracil‐5‐d‐showed that the proton was added to the 5‐position in a stereochemically random manner. The photoaddition of HSO3‐ takes place at much lower concentrations than required for the thermal addition of this anion and is also stereochemically random.
EARLY CHANGES IN LIGHT‐IRRADIATED SOLUTIONS OF BILIRUBIN: A SPECTROPHOTOMETRIC ANALYSIS
Authors: DAVIES RONALD E. , KEOHANE SONJA J.
Published: January 2008

Abstract— Early changes in irradiated solutions of bilirubin were evaluated by spectrophotometric techniques. By absorbance difference (AD) spectroscopy, the photoproducts formed in solutions of bilirubin combined with human serum albumin were found to differ from those formed in naturally or artificially jaundiced rat serum, bovine serum albumin solutions, or chloroform or carbon tetrachloride solutions.

With a technique based on variable path‐length compensation for bilirubin loss (compensated absorbance difference or CAD spectroscopy) the approximate shapes of photoproduct absorption spectra could be evaluated. Chloroform and bovine serum albumin solutions produced single‐peaked products absorbing at slightly shorter wavelengths than bilirubin. Human serum albumin solutions produced a twin‐peaked chromophore absorbing most strongly near 490 nm.
CHARGE ACCUMULATION IN THE REACTION CENTER OF PHOTOSYSTEM 2
Authors: GORKOM H. J. VAN , DONZE M.
Published: January 2008

Abstract— The significance of the accumulation of positive charge in the reaction center of the oxygen‐evolving system of photosynthesis is discussed. Many experiments on delayed and prompt fluorescence are explained by the electric field caused by positive charges on the various components at the oxidizing side of the photosystem 2 reaction center. A molecular model for this reaction center is proposed.
ENERGY TRANSFER FROM CAROTENOIDS TO CHLOROPHYLL a IN BLACK LIPID MEMBRANES
Authors: STRAUSS G. , TIEN H. TI
Published: January 2008

Abstract— Black lipid membranes (BLM) were prepared from extracts of Chlorella and spinach chloroplasts. Excitation spectra of the 730 nm fluorescence of chlorophyll a in the BLM contained peaks identified as due to carotenoids and which therefore indicate sensitization of the chlorophyll fluorescence by them. The efficiency of this energy transfer was evaluated by comparison of the actual excitation spectra with those corresponding to 0 and 100 per cent transfer efficiency. Efficiencies were of the order of 40–50 per cent in BLM, but only 10 per cent in pigment solutions, when the mean distance between pigment molecules was 23 Å in both systems. The fluorescence quantum yield of chlorophyll a in such solutions was only 2 per cent of that found in BLM. Enhancement of energy transfer in BLM is considered to be mainly due to suppression of competing deactivation processes of excited carotenoid states, such as diffusional quenching by ground‐state molecules and internal conversion. Favorable orientation of pigment molecules in the BLM constitutes a further enhancement factor.
PHYTOCHROME INTERMEDIATES IN VIVO– III KINETIC ANALYSIS OF INTERMEDIATE REACTIONS AT LOW TEMPERATURE
Authors: Kendrick R. E. , Spruit C. J. P.
Published: January 2008

Abstract— Kinetic experiments have provided evidence for a series of light and dark reactions of phytochrome intermediates at low temperature in Pisum epicotyl tissue. A photoequilibrium exists between Pr and P698, and between Pfr and P650. A dark reversion of P698Pr and P650pfr at –70°C has been demonstrated. When cooled to 70°C under incandescent light, most of the phytochrome in the tissue is driven into photochemically unreactive intermediates. About 2% of the phytochrome remains as weakly absorbing intermediates that form Pr and Pfr in darkness. A scheme is presented for phytochrome phototransformation in vivo.
SUBSTRATE SPECIFICITY OF A BACTERIAL UV ENDONUCLEASE AND THE OVERLAP WITH IN VITRO PHOTOENZYMATIC REPAIR
Authors: Patrick M. H. , Harm Helga
Published: January 2008

Abstract— The action of an endonuclease from Micrococcus luteus, that operates on ultraviolet (UV) radiation damage, overlaps greatly with that of the yeast photoreactivating enzyme: homo and hetero cyclobutyl pyrimidine dimers in DNA are substrate for both enzymes, but pyrimidine adducts or the ‘spore photoproduct’ in DNA are not.

As expected from this overlap, the action of the two enzymes is mutually interfering: single‐strand nicks introduced by the endonuclease effectively preclude photoreactivation; conversely, formation of a photoreactivating enzyme‐dimer complex can prevent nicking by the UV endonuclease. While complex formation between photoreactivating enzyme and dimers in UV‐endonuclease‐treated DNA is apparently normal, the light‐dependent repair step either fails to occur or proceeds at a very low rate. Hence, besides the requirement of a minimum chain length for the function of the photoreactivating enzyme, there is the additional restriction on the position of the dimer in a polynucleotide strand.

Finally, rough approximations of the rate constants, k1 and k2, for the UV endonuclease indicate that the in vitro UV‐endonuclease‐dimer complex is relatively unstable, with dissociation of the complex being more probable than hydrolysis of the phosphodiester bond.
LUMINESCENCE AND PHOTOCHEMISTRY OF 4‐THIOURIDINE IN AQUEOUS SOLUTION
Authors: Favre Alain
Published: January 2008

Abstract— In bidistilled water, 4‐thiouridine (4TU) exhibits a weak unusual luminescence, the quantum yield of which is 3 × 10‐4 at 25°C. The excitation spectrum corresponds well to the 4TU absorption spectrum. The emission lies at longer wavelengths (Λmax 550 nm) than the 4TU phosphorescence observed at 77 K (Λmax, 470–480 nm). From the emission signal obtained after an excitation flash of 3 ns half‐width, an “apparent” rate constant for the radiative deactivation process, shorter than 5 × 106 s, can be inferred. The 300 K emission is efficiently quenched by halides and by oxygen: quenching involves a long‐lived intermediate (⋍ 200 ns).

Clearly the emissive state X is populated through the S0‐S1 electronic transition π→π* of 4TU. The nature of X cannot be unambiguously determined: it cannot be an excimer but can be either the 4TU triplet state or another chemical state distinct from the 4TU excited singlet or triplet states.

An interesting finding is that the 300 K emission and the ability of 4TU to photoreact are related: they are quenched with the same efficiency by halide anions. This indicates that quenching occurs at the same long‐lived intermediate species, which is either a precursor of the emitter or the emitter itself.
MECHANISM OF PHOTOREDUCTION OF THIAZINE DYES BY EDTA STUDIED BY FLASH PHOTOLYSIS‐II. pH DEPENDENCE OF ELECTRON ABSTRACTION RATE CONSTANT OF THE DYES IN THEIR TRIPLET STATE
Authors: Bonneau Roland , Violet Philippe Fornier de , Joussot‐Dubien Jacques
Published: January 2008

Abstract— The pH dependence of the apparent reactivity of thiazine dyes in their triplet states has been studied in aqueous solutions, using as electron donor HY‐3, the trianionic species of ethylene diamine tetraacetic acid (EDTA), in the pH range 4–8. The pH dependence is found to be related to a change in the degree of protonation of the triplet excited dye. The apparent reactivity and lifetime of two differently protonated forms of thionine, azur B and methylene blue were determined by classical and dye‐laser flash techniques, making it possible to evaluate the rate constant for electron abstraction of these molecules in their triplet states. It is found that: (a) protonation on the ring nitrogen increases the electron‐abstraction rate constant of the triplet‐state species about twenty‐fold, and (b) methylation on the side amino groups decreases it.
YEAST DEOXYRIBODIPYRIMIDINE PHOTOLYASE (PHOTOREACTIVATING ENZYME): OPTIMUM CONDITIONS FOR ACTIVITY AND COMPETITIVE INHIBITION*
Authors: Cook John S. , Proctor William R.
Published: January 2008

Abstract— Using flash photolytic techniques and direct chemical measurements of the conversion of the substrate (conversion of thymine dimers in DNA to monomeric thymine), we have determined photolyase concentrations in partially purified preparations of soluble proteins from yeast and have determined under continuous intense light the forward rate constant k1 for binding of the enzyme and its substrate under a variety of conditions. The ionic requirements and the sharp peak of ionic strength dependence are independent of the species of uni‐univalent salts used in the assay. At infinite dilution, the k1 for denatured DNA, and its ionic strength dependence, both appear identical to the values for native DNA. Both unirradiated denatured and unirradiated native DNA inhibit binding, denatured DNA being 10‐ to 20‐fold more effective. These combined factors have been taken into account to devise a sensitive assay for photoreactivable lesions in unlabeled DNA by competition in a flash photoreactivation reaction. The assay is used to measure dark repair in Micrococcus luteus in complete medium. After a dose of 100 J/m2 the wild type of this organism removes photoreactivable lesions (pyrimidine dimers) from its DNA with a half‐time of 7 min at 35°C.
SENSITIZATION OF ULTRAVIOLET‐IRRADIATED Escherichia coli K‐12 BY DIFFERENT AGARS: INHIBITION OF A rec AND exr GENE‐DEPENDENT BRANCH OF THE uvr GENE‐DEPENDENT EXCISION‐REPAIR PROCESS
Authors: Schueren Emmanuel van der , Youngs David A. , Smith Kendric C.
Published: January 2008

Abstract—E. coli K‐12 wild‐type cells plated immediately after UV irradiation had a much lower survival on minimal medium solidified with agar‐agar No. 3 (Oxoid), purified agar (Difco) or ionagar (Colab) than on plates solidified with laboratory‐washed Noble agar (Difco). An intermediate survival was obtained on plates solidified with unwashed Noble agar (Difco). When irradiated cells were incubated in liquid minimal medium for various times before subsequent plating on agar‐agar No. 3, their survival increased rapidly and became identical to the survival of cells plated on washed Noble agar. The same phenomenon was found with polA 1 cells, but no differences in survival on the different agars were observed with uvrB, exrA, recA or recB cells. These‐ data suggest that a repair process dependent on the uvrB, recA, recB and exrA (but not the polA) gene products is inhibited when UV irradiated E. coli K‐12 cells are plated on minimal medium solidified with agar‐agar No. 3, purified agar or ionagar. This implies that the uvr gene‐dependent excision‐repair process consists of at least two branches, one controlled by the polA gene and a second controlled by the recA, recB and exrA genes and inhibitable by a substance present in certain agars. For maximum sensitivity, experiments designed to study chemical inhibitors of repair should use agar plates that do not themselves inhibit repair.
BLUE AND GREEN LIGHT EFFECTS, AND THEIR PHOTOREVERSIBILITY, UPON ZOOSPORE PRODUCTION AND THE SYNCHRONIZED CYCLE IN PROTOSIPHON BOTRYOIDES KLEBS*
Authors: O'Kelley Joseph C. , Durant Jennie P. , Stockdale Dennis L.
Published: January 2008

Abstract—The synchronized asexual cycle in Protosiphon botryoides Klebs is described. A blue light (430 nm) inhibition of zoospore production can be photoreversed by green light (550 nm). Similarly, a green light (550 nm) stimulation of zoospore production can be photoreversed by blue (430 nm) light. 430 nm light also shortens the period of zoospore motility, and 550 nm light lengthens this period.
ELECTRON PARAMAGNETIC RESONANCE SIGNAL II IN SPINACH CHLOROPLASTS—II. INFLUENCE OF PHOSPHORYLATION AND ELECTRON‐TRANSPORT INHIBITORS
Authors: Esser Alfred F.
Published: January 2008

Abstract—The influence of several groups of inhibitors on the electron paramagnetic resonance Signal II of spinach chloroplasts was investigated. It was found that phosphorylation uncouplers that do not inhibit electron transport (gramicidin, valinomycin) have no effect. Likewise, inhibitors that block electron transport between the two photosystems are ineffective. However, reagents that can inhibit electron transport and also uncouple phosphorylation, such as phenylhydrazones (FCCP) or anilino‐thiophenes (ANT 2p), will completely abolish Signal II in the dark. The signal is regenerated by red light and also by far‐red light, but in the latter case only if cyclic electron transport is possible. These agents, in addition to discharging the water‐splitting enzyme [ADRY effect, G. Renger, Biochim. Biophys. Acta (1972) 256, 428] were also found to inhibit cyclic electron flow. Light activation of Signal II in ANT 2p‐ or FCCP‐treated chloroplasts by either red or far‐red light can be suppressed by simazine or dichlorophenyl dimethylurea (DCMU) but not by other inhibitors that also inhibit linear electron flow. Evidence is provided which indicates that one functioning electron‐transport system, either linear or cyclic, is necessary and sufficient for the enhancement of Signal II. The requirement for Signal II activation seems to be the reduction of plastoquinone. In ANT 2p‐ and FCCP‐treated chloroplasts, a link probably exists between the water‐splitting enzyme and the plastoquinone pool, bypassing Photosystem II; the unknown substance giving rise to Signal II may be located on such a sidepath.