bluuebunny/crossref_metadata_2025 huggingface dataset:
MEDIATION OF LIGHT‐INDUCED CHANGES IN PINEAL RECEPTOR AND SUPPORTING CELL NUCLEI AND NUCLEOLI IN STEELHEAD TROUT (SALMO GAIRDNERI)
Authors: Hafeez M. A. , Wagner H. H. , Quay W. B.
Published: January 2008

Abstract— Mediation of the chronic effects of differences in environmental illumination on pineal photoreceptor and adjacent supporting cells was studied in two experiments using larval trout. Experiment 1 had 7 groups exposed to controlled lighting conditions for 14 months: (1) constant darkness (DD); (2) natural photocycles (LD) followed by constant light (LL); (3) natural photocycles (LD); (4) LD fluorescent light; (5) LD blue (400–525nm) light; (6) LD green (500–612nm) light; and (7) LD red (600–750 nm) light. In Experiment II the fish were exposed to LL for 27–28 days, following 10 months in DD and one of five surgical manipulations: (1) pineal masked; (2) pineal sham‐masked; (3) blinded; (4) blinded + pineal masked; (5) blinded + pineal sham masked.

Nuclei and nucleoli of pineal receptor and supporting cells were largest in fish raised in DD. LL or LD cycles, and light of either narrow or broad spectral range, were not notably different in their chronic effects on receptor cell nuclei and nucleoli. However, supporting cell nuclei and nucleoli were smallest in LL. Blinding and pineal masking demonstrated that: (1) pineal receptor cell nuclei and nucleoli were affected by chronic incident light in the pineal region but not by photic or visual influences via the lateral eyes; and conversely, (2) pineal supporting cell nuclei and nucleoli were affected by chronic photic input only via the lateral eyes. The results suggest the possible presence of a cellular comparator system in which photic inputs from lateral eyes and pineal affect separately and respectively the adjacent supporting and receptor cells of the pineal organ.
EPR STUDIES ON SINGLET OXYGEN PRODUCTION BY PORPHYRINS
Authors: Cannistraro Salvatore , van de Vorst Albert , Jori Giulio
Published: January 2008

Abstract— EPR studies of the porphyrin‐sensitized photooxidation of 2, 2, 6,6‐tetramethyl‐piperidine to the nitroxide demonstrate that all the porphyrins examined are able to generate 1O2, although the efficiency of the photoprocess is dependent on the nature of the side chains. Incorporation of metal ions into the porphyrin molecule depresses or even inhibits the formation of 1O2. Comparison of these results with previously obtained kinetic data points out that the efficiency of porphyrins as photosensitizes is controlled by the lifetime of their lowest triplet state.
TIME RESOLUTION OF A BACK PHOTOREACTION IN BACTERIORHODOPSIN
Authors: Kalisky Ofra , Lachish Uri , Ottolenghi Michael
Published: January 2008

Abstract— The back photoreaction from the M(412nm) intermediate in the photocycle of light‐adapted bacteriorhodopsin, BRLA(570 nm), is studied using pulsed laser excitation. The decay of a primarily produced species, MP, regenerates BRLA(570nm) in a process characterized by a half life of 200 ns at 25°C. The absorption maximum of MP is blue shifted (Λmax≃ 395 nm) relative to that of M(412nm). The primary photochemical step, M(412nm) → MP, is attributed to a conformational change in the polyene residue. The energy and entropy of activation of the subsequent MP→ BRLA (570 nm) relaxation are reported and discussed.
BIOLUMINESCENCE: PHYSIOLOGICAL CONTROL AND REGULATION AT THE MOLECULAR LEVEL
Authors: Henry J. P. , Michelson A. M.
Published: January 2008

Abstract— Three different classes of bioluminescence have been critically reviewed with special reference to the molecular physiology of control and regulation of light emission in its various forms.
SEDIMENTATION ANALYSIS OF DNA PHOTOOXIDIZED IN THE PRESENCE OF THIOPYRONINE
Authors: Triebel H. , Bär H. , Jacob H‐E. , Sarfert E. , Berg H.
Published: January 2008

Abstract. Illumination of single‐stranded φ×174 phage DNA with visible lightλ > 500 nm) in the presence of the sensitizer thiopyronine results in both chain scissions detectable by velocity sedimentation in neutral medium and in alkali‐labile bonds which yield secondary strand breaks after alkaline treatment. Compared with the generation of primary strand breaks, the formation of alkali‐labile sites seems to be the predominant reaction.

Photodynamic treatment of homogeneous double‐stranded Ta, phage DNA leads to changes in the overall conformation of DNA as revealed by an initial increase of the sedimentation coefficient. The simultaneous occurrence of different effects (decrease of molecular weight, increase of effective DNA flexibility) is particularly evident from changes in the sedimentation coefficient distribution. The fact that both processes influence the sedimentation behaviour questions the common procedure of calculating double‐strand break numbers from sedimentation coefficient distributions on the basis of s#‐M relations which are valid for intact DNA only.

Photooxidized double‐stranded DNA exhibits an increased sensitivity against shear forces.
A STUDY OF THE UNSENSITIZED PHOTOOXIDATION OF TETRACYCLONE BY 18O LABELLING
Authors: Chaney Brian D. , Brown Stanley B.
Published: January 2008

Abstract. The photooxidation of tetracyclone yielding dibenzoyl stilbene was studied by means of an 18O labelling method recently used to study heme catabolism. Unlike heme degrading systems, the photooxidation of tetracyclone was found to proceed by a one‐molecule mechanism whereby both oxygen atoms in dibenzoyl stilbene are derived from the same molecule of molecular oxygen. This is evidence for a dioxobridged intermediate.
SKIN CANCER AND ULTRAVIOLET RADIATION
Authors: Rundel R. D. , Nachtwey D. S.
Published: January 2008

Abstract. A new model is presented for the calculation of the increased incidence of non‐melanoma skin cancer in Caucasians resulting from ozone reduction. The model postulates that the probability of first incidence of such skin cancer is distributed log‐normally as a function of total accumulated lifetime dose of harmful ultraviolet radiation. The effect on skin cancer incidence of an increase in harmful ultraviolet radiation due to ozone reduction can then be calculated directly from the extent to which each individual's lifetime accumulated dose is thereby increased. The result of such a perturbation, on average, would be to cause skin cancer to appear at a slightly earlier age. Since skin cancer is predominantly a disease of the elderly, this shift to younger ages has the effect, when integrated over the entire population, of increasing the overall total incidence of skin cancer.
PHYTOCHROME‐MEDIATED LOSS OF POLYRIBOSOMES IN ETIOLATED MUSTARD HYPOCOTYLS
Authors: Acton G. John
Published: January 2008

Abstract. Continuous far‐red light operating through phytochrome reduces the rate of hypocotyl lengthening by a factor of 8. Consonant with this was a reduction of up to 12% in the proportion of total cytoplasmic ribosomes present as polysomes. A 2% reduction was elicited by brief red light. Evidence is presented which argues against these changes arising from a change in extractability or nucleolytic activity. The speed of the response (1.5 h) is much slower than that for inhibition of lengthening (15 min). The data therefore indicate that phytochrome is unlikely to act by controlling the general rate of translation in this instance.
SIGNIFICANCE OF FLUENCE‐RESPONSE DATA IN PHYTOCHROME‐INITIATED SEED GERMINATION
Authors: Duke Stephen O.
Published: January 2008

Abstract. A model was developed to describe changes in fluence‐response kinetics in terms of total phytochrome level (Ptot), level of the factor X interacting with active phytochrome (Pfr), PfrX equilibrium constant, seed sensitivity to Pfr‐X interaction, and variation in phytochrome sensitivity within the seed population. Under conditions of stable X levels and stable population variation, the model predicted that a change in any of the other components will result in a parallel fluence‐response curve on a probit‐logarithmic plot. The linearity of the subsaturation plot is dependent on the ratio of Ptot to X concentrations. The model showed that changes in threshold response fluences can result from many causes other than changes in total phytochrome [Ptot>]. Changes in response‐saturating fluences when maximal germination is less than 100% are predicted to be due to limiting levels of X. Changes in slope of fluence‐response curves can be explained by changes in seed population variation by this model. Rumex crispus L. fluence‐response data for germination is best explained by this model in terms of neither changes in Ptot nor X levels altering kinetics.
A NOVEL PHOTO‐OXETANE FROM 6‐ACETYLURACIL
Authors: Sarpotdar Arvind , Burr John G.
Published: January 2008

Abstract. Photolysis of 6‐acetyluracil (λ>300nm) in aqueous solutions produced a single major photoproduct, arising from a singlet excited state. This photoproduct has been isolated and characterized as a novel oxetane‐type dimer.
CHARGE TRANSFER COMPLEXES BETWEEN POLYENES AND AROMATIC ACCEPTORS
Authors: Barboy N. , Feitelson J.
Published: January 2008

Abstract. Both the cone pair electron donating ability of a polyene Schiff base and the strength of the bond formed indicate a weakening of the complex formed with increase in the conjugated double bond system.
PICOSECOND FLUORESCENCE STUDIES OF EXCITON MIGRATION AND ANNIHILATION IN PHOTOSYNTHETIC SYSTEMS. A REVIEW*
Authors: Campillo A. J. , Shapiro S. L.
Published: January 2008

Abstract. In this paper we review picosecond fluorescence studies of exciton dynamics in photosynthesis. We discuss some of the exciton interactions that led to artifacts in early picosecond data and outline procedures for avoiding their presence. In the case of high intensity single pulse excitation (> 1013 photons cm2), the dominant mechanism is singlet‐singlet fusion, manifesting itself by a decrease in the observed lifetime and quantum efficiency of fluorescence. The manner in which excitons interact in vivo provides an indicator of the topology of the photosynthetic unit (PSU). The shape of the fluorescence quenching curve, as a function of intensity, in particular, can be used to test various models. In addition to fluorescence quenching curves, we also report the results of fluorescence decay following ps laser flashes, using an ultrafast streak camera in four types of systems: (1) organic crystal anologues, (2) chromatophores of various mutants of the photosynthetic bacteria, Rhodopseudomonas sphaeroides, (3) intact cells of the green alga, Chlorella and (4) chloroplasts of higher plants (e.g. spinach).
INTERACTIONS AMONG PHOTOSYNTHETIC ANTENNA EXCITED STATES
Authors: Devault Don , Kung Mayfair Chu
Published: January 2008

Abstract. The data of Kung and DeVault (1978) showing high‐order fluorescence from chromatophores of photosynthetic bacteria are analyzed in relation to other data on first‐order fluorescence of photosynthetic systems, particularly that of Monger and Parson (1977). The wavelengths of emission observed (down to 445 nm) require energy equivalent to two lowest singlet‐excited states. The dependence on excitation intensity is best explained by any of the following third‐order processes: (a) 3S1→3S0; (b) 2S1+T, → 2S0+T1; (c) S1+ 2T1→ 3S0. However, (c) is ruled out because it predicts heavy T1‐destruction which is not observed. Contribution from the second order process: 2 S1→S0 is probable, but even the data of Monger and Parson show that it is insufficient by itself. Two‐photon absorption: S0+hv1→S1; S1+hv1→Sn; SnS0+hv2 could also account for the high‐order fluorescence and its dependence on excitation intensity. [S0, S1Sn are ground, first excited and a higher excited singlet states, respectively, of antenna bacteriochlorophyll, Tt is the lowest triplet state, c/v, is the exciting wavelength (694 or 868 nm) and c/v2 the wavelength of the high‐order fluorescence (445, 535. or 600 nm), where c= velocity of light.] Maximum values are estimated for some of the rate constants.
UV‐INDUCED FREE RADICALS IN ORIENTED DNA†
Authors: Gräslund A. , Ehrenberg A. , Rupprecht A. , Ström G.
Published: January 2008

Abstract— Samples of oriented DNA containing 30% water were UV‐irradiated at 77 K and investigated by electron paramagnetic resonance (EPR). The EPR spectra recorded in directions parallel and perpendicular to the DNA fibre direction showed that at low UV doses the induced free radicals are very similar to those induced by γ‐irradiation at the same temperature. The γ‐induced free radicals have previously been analysed and found to consist mainly of anionic free radicals on thymine and cationic free radicals on guanine. At higher UV doses or by suitable annealing of the samples given a low UV dose, significant amounts of hydrogen‐addition radicals on thymine were observed. The quantum yield of free radical formation for irradiation at 300nm ± 10nm was estimated to 10‐‐4. We also made a quantitative determination of the UV‐induced free radicals inside an optically effective volume of the sample. The following free radical induction frequencies at 77 K were estimated: γ‐rays: 2 × 10‐‐12 free radicals per rad per dalton and UV (300nm): 6 × 10‐‐12 free radicals per J/m2 per dalton.
BIPHASIC ENERGY CONVERSION KINETICS AND ABSORBANCE DIFFERENCE SPECTRA OF PHOTOSYSTEM II OF CHLOROPLASTS. EVIDENCE FOR TWO DIFFERENT PHOTOSYSTEM II REACTION CENTERS
Authors: Melis A. , Duysens L. N. M.
Published: January 2008

Abstract— The continuous illumination induced kinetics of photochemical energy conversion at system II have been measured with isolated and 3‐(3, 4‐dichlorophenyl)‐l, l‐dimethylurea (DCMU) poisoned chloroplasts by means of absorbance difference spectroscopy in the UV and by the area growth over the fluorescence induction curve at room temperature. An optimal set of conditions was found in order to isolate absorbance changes caused by the reduction of the primary electron acceptor Q of PS II by suppressing other electron transfer processes. The light induced kinetics of Q‐ accumulation in the absorbance change measurements were found to be biphasic and strictly correlated with the kinetics of the area growth measured under the same conditions. From the resolution of the biphasic kinetics at different wavelengths in the UV region of the spectrum, it was found that both kinetic components in the system II photochemistry involve the reduction of a plastoquinone molecule to its plastosemiquinone anion. From the two kinetic components one was fast and non‐exponential and the other relatively slow with an exponential time course. The initial rate difference in the kinetics of the two components was by a factor of approximately 3. A difference by a factor of about three was also found in the flash saturation curves of the two kinetic components.

The results are explained by the hypothesis that in higher plant chloroplasts there are system II reaction centers embedded in a large pigment matrix with statistical energy transfer, and system II reaction centers embedded in separate, in terms of excitation energy transfer, units. The effective absorption cross section per reaction center for the centers in the statistical pigment bed is approximately 3 times larger than that of the reaction centers in the separate system II units. The two types of system II reaction centers have different yields of excitation trapping and charge stabilization properties.
BIOLUMINESCENCE FROM THE REACTION OF FMN, H2O2 AND LONG CHAIN ALDEHYDE WITH BACTERIAL LUCIFERASE
Authors: Hastings J. W. , Tu Shiao‐Chun , Becvar James E. , Presswood Robert P.
Published: January 2008

Abstract— The bioluminescent oxidation of reduced flavin mononucleotide by bacterial luciferase involves a long‐lived flavoenzyme intermediate whose chromophore has been postulated to be the 4a‐sub‐stituted peroxy anion of reduced flavin. Reaction of long chain aldehyde with this intermediate results in light emission and formation of the corresponding acid. These experiments show that the typical aldehyde‐dependent, luciferase‐catalyzed bioluminescence can also be obtained starting with FMN and H2O2 instead of FMNH2 and O2. We postulate that the 4a‐peroxy anion intermediate is formed directly by attack of H2O2 on FMN. The latter may be bound to luciferase. An enzyme bound intermediate is formed which by kinetic analysis, flavin specificity for luminescence, aldehyde dependence, and bioluminescent emission spectrum appears to be identical with the species generated by reaction of FMNH, and O2 with luciferase. The quantum yield of the H2O2‐‐ and FMN‐initiated biolumlnescence is low but can be enhanced by certain metal ions, which also stimulate a chemiluminescent reaction of oxidized flavin with H2O2. The peak of this chemiluminescence. however, appears to be at a shorter wavelength than that (490 nm) of the bioluminescence.
QUANTUM YIELDS OF TRIPLET FORMATION OF SOME DERIVATIVES OF ANTHRAQUINONE
Authors: McVie James , Sinclair Roy S. , Truscott T. George
Published: January 2008

Abstract— Quantum yields of triplet formation for five amino substituted anthraquinones have been determined by the comparative actinometer method using laser flash photolysis. Substitution reduces the yields to values of ˜10‐‐2. and the requirement of low laser intensities required high sensitivity of detection of triplet absorption. The øT values are compared with the quantum efficiencies of fluorescence and decomposition for the compounds, and the criteria for light stability discussed.
EXTERNAL HEAVY ATOM EFFECTS ON THE S1 AND T1 ELECTRONIC STATES OF INDOLE
Authors: Lessard Ginette , Durocher Gilles
Published: January 2008

Abstract— The absorption, fluorescence and phosphorescence spectra along with the phosphorescence decay function of indole perturbed by various amounts of halocarbons have been studied in a 1:1 ethanol‐ether glass at 77 K. For carbon tetrachloride. chloroform, halothane and methylene chloride used as quenchers. the biexponential nature of the phosphorescence decay prompted us to assume the existence of a triplet state complex (exciplex) between indole and the halocarbons. On the other hand. propyl bromide gives rise to a non‐exponential decay and to an increase in the phosphorescence intensity suggesting the occurrence of a normal external spin‐orbital coupling interaction between indole and the propyl bromide molecule.
A SIMPLE MODIFICATION OF THE SPECTROPHOTOMETER FOR RAPID PHYTOCHROME ASSAY
Authors: Jung Jin , Song Pill‐Soon
Published: January 2008

Abstract— A simple, low cost modification of a conventional single wavelength spectrophotometer (e.g. Cary 118C) enables one to quantitate phytochrome in crude extracts and purified phytochrome preparations without the use of a dual‐wavelength ratio spectrophotometer.
ORD OF RETINAL AND RETINYLIDENE PHOSPHORYL ETHANOLAMINE IN A MICELLE
Authors: Rabinovitch B. , Yamakawa M.
Published: January 2008

Abstract— In the course of observing the formation of Schif bases of phosphatidyl ethanolamine and phosphoryl ethanolamine with all‐trans retinal in a detergent micelle, we have studied their spectroscopic behavior and ORD properties. In so doing, we have demonstrated that all‐rruns retinal itself, although having no intrinsic chirality at the aldehyde group, gives a marked Cotton effect, when dispersed in a CTAB micelle, at the absorption peak of the nπ* transition. This extrinsic chirality is attributed to the markedly asymmetric environment of the Stern layer of the micelle, and its significance is related to the ORD behavior of rod outer segments.
DETERMINATION OF THE KINETICS OF THE BACK REACTION OF PHOTOSYSTEM II IN THE PRESENCE OF 3–(3,4‐DICHLORPHENYL)‐1,1‐DIMETHYLUREA FROM LUMINESCENCE MEASUREMENTS
Authors: Vierke Gerhard
Published: January 2008

Abstract— An alternative method to that used by Mar and Roy (1974) for the determination of the kinetics of the back reaction of photosystem II from the luminescence decay curve in the presence of 3–(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) has been suggested. The new theory relies upon two hypotheses: the well‐known recombination hypothesis of luminescence and the assumption that the luminescence yield in the seconds region is given by the variable part of the live fluorescence yield. The second hypothesis was introduced since assuming a constant luminescence yield results in kinetic data that are not consistent with measurements of the kinetics of the back reaction by the restoration of the area over the fluorescence rise curve. The dependence of the live fluorescence yield from the concentration of closed PS II traps was assumed to be represented by Delosme's expression originally derived for the rise curve of the fluorescence yield in the presence of DCMU.

The theory is based on the fact that then the partial and total light sums of luminescence are simple functions of the concentration of the primary electron acceptor Q‐ of PS II. Thus, after integrating the luminescence decay curve the theory permits a convenient evaluation of the kinetics of the back reaction [Q‐](t) in terms of the partial and total light sum.

This method was applied in order to determine the kinetics of the back reaction in Chlorella fusca in the presence of DCMU. It is shown that the kinetics of deactivation of the S, state can be described using the expression for the kinetics of the back reaction derived by Mar and Roy. As an alternative explanation, a biphasic first order decay of S2 is proposed.
MODIFICATION OF LETHAL INTERACTIONS BETWEEN NEAR‐ULTRAVIOLET (365 nm) RADIATION AND DNA‐DAMAGING AGENTS
Authors: Tyrrell Rex M. , Correia Ivanosca S.
Published: January 2008

Abstract— The modification of the lethal interaction between near‐UV (365 nm) radiation and a second DNA‐damaging agent by incubation between treatments in either a minimal salts medium or complete growth medium has been studied in the wild‐type bacterial strain Escherichia coli K12 AB 1157. The results indicate that the lethal interaction may be separated into at least two distinct processes whose evaluation may help in classifying DNA‐damaging agents in terms of the repairability of the DNA lesions induced. An observation of changes when methyl methane sulphonate is given prior to the irradiation treatment indicates that this chemical irreversibly damages repair enzymes.
FORMATION AND CHEMILUMINESCENT DECOMPOSITION OF DIOXETANES IN THE GAS PHASE
Authors: Bogan Denis J. , Durant Joseph L. , Sheinson Ronald S. , Williams Frederick W.
Published: January 2008

Abstract— High resolution chemiluminescence spectra have been obtained of the singlet electronically excited products of O2(1Δ) plus alkene, dioxetane forming, reactions. The experiments were conducted in a flow apparatus at pressures of 1–5 torr. The spectra are a measure of the unrelaxed initial distribution of energy in the excited product. Results are reported for ethylene, 1, 1‐difluoroethylene. methyl vinyl ether, ethyl vinyl ether, n‐butyl vinyl ether, ketene, ketene‐d2, allene, unsymdimethyl allene, dimethyl ketene, 2‐methoxy propene, 1‐ethoxy propene, 2‐bromo propene, and N, N‐dimethyl isobutenyl amine. Chemiluminescence activation energies, representing the cycloaddition process, and absolute quantum yields for singlet excited product, ranging from 10‐‐4 to 2.5 × 10‐‐2. are reported for 10 alkenes. Several of the reactions, 1,1‐difluoroethylene, ketene, ethylene and allene give formaldehyde 1nπ* product with excess vibrational‐rotational energy and a higher quantum yield than reactions not displaying this phenomenon. This is an indication of at least partially statistical partitioning of the energy in excess of that needed to electronically excite the formaldehyde. The experiments with ketene and ketene‐d2 provide the first evidence for the existence of unsubstituted 1,2‐dioxetanone. The results from several of the experiments, particularly those with 2‐methoxy propene and I‐ethoxy propene are consistent with the mechanism of Goddard, which predicts regioselective and stereoselective attack of O2(1Δ) upon alkoxy substituted alkenes having allylic hydrogen.
CHEMICAL MECHANISMS OF CHEMI‐ AND BIOLUMINESCENCE. REACTIONS OF HIGH ENERGY CONTENT ORGANIC COMPOUNDS
Authors: Schuster Gary B. , Dixon Brian , Koo Ja‐Young , Schmidt Steven P. , Smith J. P.
Published: January 2008

Abstract— The chemistry of high energy content molecules was investigated. In particular, the mechanisms by which these compounds rearrange to generate electronically excited states was probed. A mechanism for chemiexcitation involving chemically initiated electron transfer is described. It is concluded this mechanism is applicable to many chemi‐ and bioluminescent processes.
PEROXIDASE CATALYZED GENERATION OF TRIPLET ACETONE
Authors: Bechara Etelvino J. H. , Oliveira Olga M. M. Faria , Duran Nelson , Baptista Roberto Casadei de , Cilento Giuseppe
Published: January 2008

Abstract— Triplet acetone generated in the isobutanal/horseradish peroxidase/O, system is quenched by collisional agents of the diene type. A Stern‐Volmer analysis indicates that collision is considerably impeded, the barrier being largely entropic. Triplet‐triplet energy transfer to biacetyl is also observed. Quenching of triplet acetone by energy transfer to 9,10‐dibromoanthracene‐2‐sulfonate (DBAS) is a much faster process than energy transfer to these collisional agents, in accordance with the earlier inference that transfer to DBAS is a long‐range triplet‐singlet transfer process. The fraction of the triplet acetone which undergoes reduction to isopropanol is not interceptable by quenchers.

Absorption and circular dichroism studies suggest that peroxidase shuttles between Compound II and I when generating the precursor hydroperoxide.
KYNURENIC ACID — I. SPECTROSCOPIC PROPERTIES
Authors: Pileni M. P. , Giraud M. , Santus R.
Published: January 2008

Abstract— The presence of different ground state species in ionic and/or keto s enol equilibrium has been demonstrated by studying NMR, IR and UV spectroscopic properties of kynurenic acid and related quinoline derivatives. The optical and emission properties of kynurenic acid and related compounds are thus very sensitive to pH conditions. Fluorescence and intersystem crossing (ISC) quantum yields have been measured in various solvents. The first excited singlet state is probably very short‐lived in neutral aqueous solution. The triplet state is long‐lived (10 μs) as shown by 353 nm laser flash spectroscopy. A high ISC quantum yield and a large molar extinction coefficient make it easy to detect the T1→ Tn transient (Δmax≃ 570 nm).
ORIENTATION OF AROMATIC RESIDUES IN RHODOPSIN. ROTATION OF ONE TRYPTOPHAN UPON THE META I→META II TRANSITION AFTER ILLUMINATION
Authors: Chabre Marc , BReton Jacques
Published: January 2008

Abstract— Linear dichroism measurements have been performed in the visible and the UV on suspensions of intact retinal rod outer segments, isolated from frog and from cattle retinas and oriented by a magnetic field. In the UV a sharp double peaked signal is observed around 290 nm. It is characteristic of a tryptophan residue having its 1Lb transition oriented preferentially perpendicular to the membrane plane. Only one tryptophan residue per rhodopsin molecule seems to be involved, and this is insufficient to account for the diamagnetic anisotropy of the rods which causes their orientation. Upon bleaching one observes a rotation of this tryptophan coupled to the Meta I →Meta II transition, and the rotation is reversed in the next step Meta II → Meta III. The correlation with other spectral changes suggests that this tryptophan is in close relation with the retinal chromophore.
AN ACTION SPECTRUM FOR LIGHT AVOIDANCE BY PHYSARUM NUDUM PLASMODIA
Authors: Bialczyk J.
Published: January 2008

Abstract— Plasmodia of the myxomycete Physarum nudum, grown on agar in darkness, avoided a lighted field. The percentage of plasmodia migrating out at the lighted field was found to be dependent on light intensity. An action spectrum for this response has two maxima at 452 and 375 nm.
PHOTOCHEMISTRY OF DNA CONTAINING IODINATED CYTOSINE*
Authors: Rahn R. O. , Stafford R. S.
Published: January 2008

Abstract— –Irradiation at 313 nm of compounds containing iodinated cytosine moieties results in the photolysis of iodine. Photolysis occurs with a quantum yield of 0·0224·024 for 5‐iododeoxycytidine and 5‐iododeoxycytidine monophosphate, and 0·004–0·008 for iodinated DNA as well as for iodinated polycytidylate. Photodegradation of the cytosine moiety occurs when air is present during irradiation, presumably due to the reaction of oxygen with the cytosyl radical formed when iodine is lost. This oxygen promoted photodegradation destroys the cytosine chromophore and is complete in the monomers but occurs to only a limited extent in the polymers. In the absence of oxygen or in the presence of ethanol, photodegradation is prevented and the loss of iodine leads exclusively to the formation of the cytosine chromophore. In DNA, the loss of iodine is accompanied by the formation of sugar damage and/or chain breaks. As measured by sedimentation in alkaline sucrose gradients, approximately one break is made for every six iodinqs lost in denatured DNA. The frequency of chain breakage per iodine photolyzed is reduced 2‐fold in renatured DNA. Analysis in neutral gradients suggests that half of the breaks observed in alkali are alkali‐labile bonds. Both ethanol and cysteamine reduce the number of chain breaks observed in alkali by ˜ 3‐fold.
A PREVIOUSLY UNREPORTED INTENSE ABSORPTION BAND AND THE pK, OF PROTONATED TRIPLET METHYLENE BLUE
Authors: Ohno T. , Osif T. L. , Lichtin N. N.
Published: January 2008

Abstract— Excitation by a Q‐switched giant ruby laser (1.2 J output at 694 nm ˜50 ns flash) of 2–10 µM solutions of methylene blue in water, 30% ethanol in water or 50 v/v% water‐CH3CN at pH values in the range 2.0–9.3 converted the dye essentially completely to its T1 state. The absorption spectrum of T1 dye was measured in different media at pH 2.0 and 8.2 by kinetic spectrophotometry. Previously reported T‐T absorption in the violet in acidic and alkaline solutions and in the near infrared in alkaline solution was confirmed. Values found for these absorptions in the present work with 30% ethanol in water as solvent are λmax ‐ 370nm, εmax, ‐ 13,200 M‐1 cm‐1 at pH 2 and λmax,˜420nm, εmax 9000 M‐1 cm‐1, λmax, ‐ 840 nm, εmax ‐ 20,000 m‐1 cm‐1 at pH 8.2. Long‐wavelength T‐T absorption in acidic solution is reported here for the first time: λmax, ˜ 680 nm, emax˜ 19,000 M cm‐1 in 30% ethanol in water at pH 2. Observation of a pH‐independent isobestic point ˜ 720 nm confirms that the long‐wavelength absorptions are due to different protonated states of the same species, MB+(T1) and MBH2+(T1). The pKa of MBH2+(T1) in water was determined from the dependence on pH of absorption at 700 and 825 nm to be 7.14± 0.1 and from the kinetics of decay of triplet absorption to be 7.2. The specific rate of protonation of MB+(T1) by H2PO4 in water at pH 4.4 was found to be 4.5 ± 0.4 times 108M‐1s‐1.
PHOTOBIOLOGICAL ACTIVITY IN YEAST OF DERIVATIVES OF PSORALEN SUBSTITUTED AT THE 3,4 AND/OR THE 4',5' REACTION SITE
Authors: Averbeck D. , Bisagni E. , Marquet J. P. , Vigny P. , Gaboriau F.
Published: January 2008

Abstract— Derivatives of psoralen substituted at the position 3 and/or 5′ with various substituents (CN, CO‐R or COO‐R) have been newly synthesized. Their photobiological reactivity was determined by measuring the effects on survival and the induction of cytoplasmic ‘petite’ mutations (rho‐) in the haploid yeast Saccharomyces cereuisiae after treatment with 365‐nm irradiation in the presence of the different compounds. The effects were compared to those of known mono‐functional compounds such as angelicin, 3‐carbethoxypsoralen and 5,7‐dimethoxycoumarin and bi‐functional compounds such as psoralen and 8‐methoxypsoralen for which the photoaffinity to DNA is well known. The derivative carrying a CN group in position 3 of the psoralen molecule exhibited effects comparable to those of the bi‐functional agent 8‐methoxypsoralen. Three derivatives substituted at position 3 showed a biological activity comparable to those of the mono‐functional agent 3‐carbethoxypsoralen. Two compounds substituted at position 5′ by COOH or COOCH3‐groups were much less photobiologically active than the corresponding derivatives substituted in position 3. This suggested that the furanic site of the psoralen molecule may be photobiologically more active than the 3,4 site. Four newly synthesized angular derivatives, i.e. furo (2,3 f, g) coumarins, were found to be two to three times less active than angelicin.

At the dose rate of 365‐nm irradiation used the measure of survival and rho‐ induction per viable cell allowed the classification of some of the compounds as mono‐ and some as bi‐functional agents in analogy to known mono‐ and bi‐functional compounds.
CAROTENOID TRIPLET STATE AND CHLOROPHYLL FLUORESCENCE QUENCHING IN CHLOROPLASTS AND SUBCHLOROPLAST PARTICLES
Authors: Mathis P. , Butler W. L. , Satoh K.
Published: January 2008

Abstract— Absorption changes attributed to the triplet state of carotenoids and to primary electron donors (P‐700. P‐680): and fluorescence quenching at several wavelengths have been measured with a single apparatus. following flash excitation with a dye or a ruby laser. Spinach chloroplasts as well as subchloroplast particles enriched in Photosystem‐1 (F1), Photosystem‐2 (F1) or the light‐harvesting Chl a/h (FIII) have been examined at temperatures varying between 5 and 294 K.

The triplet state of carotenoids has been identified on the basis of its difference spectrum (having a peak at 515 nm) and decay kinetics (⋍ 7 µs at low temperature; accelerated by O2 at 294 K). It is formed in all of the materials studied. The quantum yield of carotenoid triplet formation in chloroplasts increases at low temperature, but less than the fluorescence yield.

In most cases the fluorescence quenching recovers approximately with the same kinetics as the decay of the carotenoid triplets. The fluorescence recovery is, however, significantly faster for chloroplasts at 730 nm. Fluorescence quenching occurs in all types of materials. The ratio of fluorescence quenching to the concentration of carotenoid triplets varies with the material, being maximum in chloroplasts and minimum in Fm particles.

We conclude that the formation of the carotenoid triplet state is not limited to a few sites in the chloroplast and that a carotenoid triplet is a quencher of chlorophyll fluorescence. A detailed comparison of carotenoid triplets and fluorescence quenching gives some information concerning the organization of the pigments in the photosynthetic apparatus.
PROTOCHLOROPHYLL(IDE)630 PHOTOSENSITIZES ACTIVE Ca2+ ACCUMULATION IN MICROSOMAL AND MITOCHONDRIAL FRACTIONS ISOLATED FROM PLANTS
Authors: Gross Joachim , Ayadi Abdelkader , Marmé Dieter
Published: January 2008

Abstract— White light irradiation of a microsomal fraction from etiolated plants affects their ATP‐dependent Ca2+ accumulation by inhibiting active uptake and enhancing passive efflux. The succinate‐dependent mitochondrial Ca2+ accumulation as well is decreased by light. The wavelength dependence of these light effects as well as their low quantum yield suggest non‐phototransformable protochloro‐phyll(ide) [PChl(ide)] to be the photoreceptor. PChlide has been isolated from corn leaves pretreated with 5‐amino levulinic acid. Addition of Pchlide causes photosensitization of an otherwise light insensitive microsomal Ca2+ accumulation. The observed light effect may be due to contamination of the mitochondrial as well as the microsomal fractions with PChl(ide)‡ containing particles. Irradiation of the intact tissue leads to the almost complete disappearance of the light effect on the in vitro Ca2+ accumulation.
FLUOROMETRIC STUDY OF TRYPTOPHAN PHOTOLYSIS
Authors: Roshchupkin D. I. , Talitsky V. V. , Pelenitsyn A. B.
Published: January 2008

Abstract— Measurements of fluorescence spectra and fluorescence intensity for tryptophan solutions at different pH show an effective decarboxylation and deamination of tryptophan molecules under UV irradiation. The nonexponential dose‐relationship of decrease in total fluorescence of tryptophan solutions is due to the formation of the products retaining indole ring in the course of these reactions. Dose‐relationships and quantum yields of indole ring photolysis, deamination and decarboxylation are determined for tryptophan at 254 nm irradiation. Indole ring destruction accounts for about 60% of the total photolysis of tryptophan. Decarboxylation of tryptophan is two times more effective than its deamination. In the absence of oxygen quantum yield of indole photolysis in tryptophan and in the products of decarboxylation and deamination is reduced by a factor of two and by approximately an order of magnitude, respectively. Tryptophan photolysis products which, when excited at 365 nm. fluoresce in the visible region are formed from an intermediate product of indole ring destruction.
PHOTOSENSITIZED REDUCTION OF PYRIMIDINE BASES BY TRYPTOPHAN*
Authors: Reeve A. E. , Hopkins T. R.
Published: January 2008

Abstract— Thymine and uracil were chemically altered when irradiated with UV light in aqueous solution containing tryptophan as a photosensitizer. The reaction is inhibited by oxygen and is therefore not an example of photodynamic action. Unlike the pyrimidine bases, purine bases were not altered under similar reaction conditions. Two major photoproducts were identified. One of the products was identified as the reduced base, dihydrouracil or dihydrothymine. The quantum yield for formation of dihydrouracil was 0.24 times 10‐‐4 to 13.6 times 10‐‐4, depending upon the concentrations of uracil and the reaction temperature. Radical scavengers such as cysteine and nitrous oxide decreased the rate of dihydrouracil formation. Other indole compounds also sensitized the photoreduction of uracil, their quantum yields ranging from <1 × 10‐‐5 for tryptamine to 1.3 times 10‐‐3 for indole‐3‐acetic acid. A reaction mechanism is presented whereby the pyrimidines are reduced by electron transfer from a metastable charge transfer complex originating from the first excited singlet state of tryptophan.
CHROMOSOMAL ABERRATIONS RESULTING FROM UV EXPOSURES TO G1XENOPUS CELLS*
Authors: Griggs H. Gaston , Orr Troy V.
Published: January 2008

Abstract— The dose dependence of chromosomal aberration frequencies induced by UV light in G1Xenopus cells has been examined. Total aberration frequencies did not exceed control levels until a dose of approximately 7.5 Jm‐2 was administered. Chromatid type aberrations were prevalent throughout the dose range 7.5–25.0 Jm‐2. Chromosome type aberration frequencies were comparatively low but exceeded control levels throughout the range 10.0–25.0 Jm‐2, Results of supporting experiments suggested that most of the chromosome type aberrations observed were in the second mitosis following exposures and were derived from aberrations which normally appear as chromatid types at the first mitosis following exposures.
PRODUCTION OF BREAKS IN SINGLE‐ AND DOUBLE‐STRANDED FORMS OF BACTERIOPHAGE øx174 DNA BY PROFLAVINE AND LIGHT TREATMENT
Authors: Piette J. , Calberg‐Bacq C. M. , Van de Vorst A.
Published: January 2008

Abstract— Irradiation at 440 + 360 nm and a fluence rate of 3.8 kJm‐2 min‐1, of both complexes previously formed between proflavine and either øX circular single‐stranded (ss) DNA or øX supercoiled duplex (RFI)DNA, induces single‐strand scissions in the two DNAs under consideration. Linear øXSS DNA molecules are detected by sedimentation through alkaline sucrose gradients. After treatment of the øXRFI DNA, however, the degree of degradation is the same whether it is measured under neutral or alkaline conditions, indicating that alkaline‐labile bonds are not created; moreover, double‐strand breaks can only be detected after accumulation of single‐strand breaks.

In addition to the amount of proflavine bound to the DNA and the duration of irradiation, the following factors are shown to influence the nicking activity of the treatment: (1) the DNA structure (the øXRFI DNA is much more sensitive than the øXss DNA); (2) the ionic strength of the medium during irradiation (a high value of 0.5 leads to a markedly increased efficiency); (3) the addition of cysteamine (this latter compound decreases the reaction rate) and (4) the irradiation wavelength (after irradiation at 440 nm alone, the reaction occurs at a reduced rate and is sensitive to NaN3).

The kinetics of the nicking reaction does not follow a single‐hit curve showing that at least one primary lesion occurs prior to strand breakage. On the other hand, strand scission cannot be detected after irradiation of the proflavine‐DNA complexes at the low fluence rate causing a decrease in the infectivity of both øXSS and øXRFI DNAs. Similarly. the sedimentation pattern of the DNA extracted from treated øx174 phages 99.9% inactivated, is identical to that of the control ss DNA, although more drastic treatments are susceptible to induce single strand breaks inside the phage head. Finally, the unknown lesion (s) that is biologically important does not prevent the treated DNAs from penetrating into the hostcells.
INACTIVATION OF THE LACTOSE PERMEASE OF ESCHERICHIA COLI BY MONOCHROMATIC ULTRAVIOLET LIGHT
Authors: Robb F. T. , Peak M. J.
Published: January 2008

Abstract— The lactose permease of E. coli is inactivated exponentially by seven wavelengths of monochromatic UV light. An action spectrum reveals that the shorter wavelengths (243, 290 and 313 nm) are much more efficient than longer wavelengths. Inactivation at 290 nm is most efficient and is not due to generalized membrane damage. The rate of counterflux of intracellular β‐galactoside in response to externally added β‐galactoside was slowed by 290 nm irradiation, indicating destruction of the facilitated diffusion mechanism. The induction of β‐galactosidase and β‐galactoside permease was co‐ordinate both with and without pre‐irradiation by 290 nm light. The β‐galactosidase is approximately 26‐fold more resistant to 290 nm than the permease. These results are discussed in terms of a greater sensitivity of membrane proteins to 290 nm light, which may be due to the role of aromatic amino acids in conferring stability to the permease in the membrane.
INFRARED AND RAMAN STUDIES ON SOME IMINES AND THEIR PICRATES. RELATION TO THE PROBLEM OF PROTONATION IN VISUAL PIGMENTS
Authors: Favrot J. , Vocelle D. , Sandorfy C.
Published: January 2008

Abstract— Picrates of conjugated Schiff bases have C=N stretching frequencies similar to those of the respective free bases. This raises the question if the frequency of this vibration can provide proof for the protonation of the retinylidene Schiff base occurring in visual pigments.
EVIDENCE FOR A MAGNESIUM DEPENDENT ATPase IN BOVINE ROD OUTER SEGMENT DISK MEMBRANES*†
Authors: Uhl Rainer , Borys Tom , Abrahamson Edwin W.
Published: January 2008

Abstract—In the presence of Mg2+ and adenosine triphosphate (ATP), a rapid. light‐induced, light‐scattering transient is observed from bovine rod outer segments (ROS). This light‐scattering transient we have labelled ‘A’. Ca2+ cannot replace Mg2+. nor can guanosine triphosphate (GTP) replace ATP. ‘A’ is observed at ATP concentrations as low as a few μM.

The half‐time of ‘A’, 60 ms at 20° and 20 ms at 37°, is consistent with a process possibly involved in visual transduction.

‘A’ has the action spectrum of rhodopsin bleaching and its amplitude is strictly proportional to the fraction of rhodopsin bleached per flash. ‘A’ can be regenerated by 11‐cis retinal.

Inhibition studics with ATP analogues, which cannot be hydrolysed and fail to evoke an ‘A’ response, reveal that an ATP hydrolysis process has to precede illumination in order for ‘A’ to occur.

On the basis of the above findings. it is proposed that there is a Mg2+ dependent ATPase in ROS that allows the disk membrane to assume a new membrane state which, upon illumination, is altered. giving rise to the structural phenomenon monitored as light‐scattering transient ‘A’.
SENSITIVITY OF THE RETINA TO RADIATION DAMAGE AS A FUNCTION OF WAVELENGTH*
Authors: Ham William T. , Mueller Harold A. , Ruffolo John J. , Clarke A. M.
Published: January 2008

Abstract—Exposure of the retina of the rhesus monkey to visible and infrared radiation from CW optical sources like the Sun, xenon lamps, etc. produces small lesions or scotomata which may be classified as thermal or photochemical, depending on the wavelength and duration of exposure. The action spectrum for the production of retinal lesions has been determined for eight monochromatic laser wavelengths extending from 1064 to 441 nm. The corneal power required to produce a lesion decreases by three orders of magnitude in going from 1064 to 441 nm. Exposure to 1064 nm radiation for 1000 s produces a typical thermal lesion at elevated retinal temperatures. whereas a 1000 s exposure to 441 nm light produces a photochemical lesion at power levels too low to raise the retinal temperature by an appreciable amount (<0.1°). The two types of lesion have entirely different characteristics as will be discussed in some detail. The photopathology of thc photochemical lesion has been studied at postexposure times ranging from 1 h to 90 days and will be demonstrated in a number of histological slides. Moreover, this photopathology correlates well with monocular visual acuity tests in the rhesus monkey as defined by the Landolt ring technique.

To further elucidate the differential effects on the retina of short vs long wavelength CW radiation, we have divided a simulated solar spectrum at sea level into two spectral bands. 400–800 nm and 700–1400 nm, and determined the radiant exposures required to produce very mild lcsions on the rhesus retina for exposure times of 1, 10, 100 and 1000 s. To correlate our data with solar retinitis and eclipse blindness the image diameter or spot size on the retina was 159 μm, corresponding to the image size of the Sun on the human retina. Exposure to the 400–800 nm spectrum for durations of 10 s or greater required approximately 400 J/cm2 to produce a mild photochemical lesion. Reciprocity is maintained over the exposure range 10–1000 s. Radiant exposure to the 700–1400 nm spectrum, on the other hand, required roughly 69,100 J/cm2 for a 1000 s exposure. This was a mild thermal lesion. We were unable to produce a lesion for exposure times less than 1000 s. We interpret these data to mean that solar retinitis and eclipse blindness are primarily photochemical events produced by the short wavelength component of the solar spectrum, and that the infrared component of the solar spectrum plays only a minor role in these retinal pathologies.
ON THE LUMINESCENCE OF α‐DIKETONES OF THE STEROID SERIES
Authors: Weinreb A. , Werner A. , Lebovitz Z.
Published: January 2008

Abstract—The absorption and luminescent properties of two steroids [16‐ketoestrone (I), 5α‐androstane‐3β‐ol‐16,17‐dione (II)] are compared. The behaviour of these compounds which differ only in their A‐ring is significantly different with regard to solvent dependence. The transfer of excitation energy in compound (I) from the phenolic to the diketonic chromophore is studied and compared with data from analogous estrogens. The results obtained in this study indicate a significant long range (presumably conformational) influence of the steroid A and D rings on each other.