bluuebunny/crossref_metadata_2025 huggingface dataset:
QUANTITATIVE CORRELATION BETWEEN SPECTROPHOTOMETRIC PHYTOCHROME ASSAY AND PHYSIOLOGICAL RESPONSE
Authors: Oelze‐Karow H. , Mohr H.
Published: January 2008

Abstract— Apparent synthesis* of the enzyme lipoxygenase in the cotyledons of the mustard seedling (Sinapis alba L.) is controlled by phytochrome (Pfr ground state)† through a threshold (all‐or‐none) mechanism. This response was used to determine physiologically the photostationary states, Λ that is, the [Pfr]/[Ptot] ratios established by different wavelengths in the red and far‐red range of the spectrum, including the standard red and far‐red sources used in this laboratory (Mohr, 1966). Under the premises (for which justification has been given on previous occasions) that the [Pfr]/[Ptot] ratio for standard red light is 0.8, and that the decay of Pfr is a first‐order process with a half‐life of 45 min, the [Pfr]/[Ptot] ratios determined physiologically by means of the lipoxygenase response agree with the [Pfr]/[Ptot] ratios determined spectrophotometrically by Hartmann and Spruit (cf. Fig. 9 in Hanke et al., 1969) in hypocotyl hooks of mustard seedlings. In the hook the fr, that is, the [Pfr]/[Ptot] ratio for standard far‐red, is found to be 0.023. In the cotyledons, this ratio is several times higher (Schafer et al., 1972). The conclusion that apparent lipoxygenase synthesis in the cotyledons is controlled by phytochrome located in the hook has been substantiated by further spectrophotometric (Schäfer et al., 1973) and physiological experiments (H. Oelze‐Karow and H. Mohr, in preparation). The minimum steepness of the threshold was determined. An increase of the Pfr level from 118 (relative units) to 130 leads to an instantaneous and total suppression of apparent lipoxygenase synthesis; a corresponding decrease from 130 (relative units) to 118 leads to an immediate resumption of apparent LOG synthesis at full speed. It is concluded that an explanation of the experimental facts requires a cooperative effect on the level of Pfr, a high degree of synchrony on the cellular and organismic level and rapid communication between the hypocotyl hook and the cotyledons.

*The term ‘apparent synthesis’ is used operationally in the present paper to denote any increase of enzyme activity, although de novo synthesis of lipoxygenase has not so far been rigorously demonstrated. The usual inhibitor experiments (cf. Oelze‐Karow et al., 1970) have led to the conclusion that intact RNA and protein synthesis is required for an increase of lipoxygenase activity.
EFFECTS OF PHOTODYNAMIC PROCESSES AND ULTRAVIOLET LIGHT ON DUCK AND HEN EGG‐WHITE LYSOZYMES
Authors: Risi S. , Silva E. , Dose K.
Published: January 2008

Abstract— The photochemical yields for inactivation and amino acid destruction in hen and duck egg‐white lysozyme are presented. Duck lysozyme II is devoid of histidine but it has two more tyrosine residues than does hen lysozyme. The data indicate that sensitized oxidation of the single histidine residue of hen lysozyme is of no significance for the inactivation of this lysozyme. The ultraviolet destruction of tryptophan and cystine residues appears to be equally related with the loss in enzymatic activity of hen lysozyme. In the case of duck lysozyme, however, the ultraviolet inactivation appears to be predominantly governed by the destruction of cystine residues.
A TWOFOLD ACTION OF PHYTOCHROME IN CONTROLLING CHLOROPHYLL a ACCUMULATION
Authors: Kasemir H. , Oberdorfer U. , Mohr H.
Published: January 2008

Abstract— A pretreatment with light prior to continuous illumination with high intensity white light eliminates the lag phase in chlorophyll a accumulation and increases the steady‐state rate of chlorophyll a accumulation. In mustard seedlings (Sinapis alba L.) the effect of a pretreatment can be fully attributed to phytochrome. The effect of phytochrome on chlorophyll a accumulation is twofold. It is possible to separate the effect on the lag phase from the effect on the steady‐state rate of accumulation. While the effect on the lag phase is a relatively fast process (occurring within less than 3 h) the effect on the rate requires a considerable period of time (at least 12 h) to become manifest.
THE ROLE OF HYDRATION IN THE PHOTOTRANSFORMATION OF PHYTOCHROME
Authors: Tobin Elaine M. , Briggs Winslow R. , Brown Paul K.
Published: January 2008

Abstract— Changes in the visible absorption spectrum and in phototransformation of phytochrome have been found to be associated with dehydration and rehydration. These spectral properties explain the previously reported rapid appearance of phytochrome in imbibing seeds. No evidence was found for the orientation of the phytochrome chromophore in gelatin films or in preparations subjected to a shearing force.
INCREASED QUANTUM YIELD OF PHOTOREDUCTION OF DYES (A CATALYTIC EFFECT)
Authors: Steiner U. , Hafner M. , Schreiner S. , Kramer H. E. A.
Published: January 2008

Abstract— While studying the photoreduction of some dyes (D) by reducing agents (R), it was observed that the quantum yield of the photoreduction increases considerably upon addition of a third substance (C), whereas it is very small when the dye is photoreduced by C alone (catalytic effect), (see Table 1).

The system thionine (D), allylthiourea (R), and azulene (C) was investigated in detail using both flash photolysis and continuous illumination. On photolysis, thionine is converted into its photo‐reduced form, leucothionine. Azulene reacts with the basic form of the thionine triplet 3TH+ to produce the semithionine radical. In the system thionine and azulene, most of these radicals revert back to thionine. When ATU (˜ 102‐M) is added to thionine and azulene (3 × 10‐4M), the semithionine radicals are reduced to leucothionine; the quantum yield of this reduction is considerably higher than in the system thionine and allylthiourea. Flash experiments demonstrate that allylthiourea does not react with the semithionine radicals.

At very high ATU concentrations (≥ 10‐1M), however, the primary reaction is between thionine triplet and allylthiourea; under these conditions the quantum yield is not influenced by azulene (3 × 10‐4M).
INTERORGAN CORRELATION IN A PHYTOCHROME‐MEDIATED RESPONSE IN THE MUSTARD SEEDLING
Authors: Oelze‐Karow H. , Mohr H.
Published: January 2008

Abstract—Phytochrome (Pfr)‐mediated threshold control of apparent lipoxygenase (LOG) synthesis in the cotyledons of the mustard seedling depends on the presence of the hypocotylar hook. With isolated cotyledons, no suppression by light of apparent LOG synthesis can be detected. As soon as the cotyledons are separated from the hook, the control of apparent LOG synthesis by Pfr is completely lost. The data are consistent with the hypothesis advanced in a previous paper [Oelze‐Karow, H. and H. Mohr (1973) Photochem. Photobiol.18, 319–330] that apparent LOG synthesis in the cotyledons is controlled by phytochrome located in the hypocotylar hook. The data support the concept [De Greef, J. A. and R. Caubergs (1972) Arch. Int. Physiol. Biochim.80, 959–960] that a very precise and highly ordered biophysical recognition and transmission system of light signals exists in plants.
LONG‐LIVED AFTERGLOW OF PHOTOSYNTHETIC PIGMENTS IN SOLUTION: PHOTOCHEMILUMINESCENCE
Authors: Krasnovsky A. A. , Litvin F. F.
Published: January 2008

Abstract—Our recent research on photochemiluminescence (PCL) of pigments in solutions is reviewed. PCL was observed in the course of photooxidation by oxygen of chlorophyll a, bacteriochlorophyll, protochlorophyll, their analogs, synthetic dyes and aromatic hydrocarbons. The PCL of chlorophyll was studied in detail. It depends on oxygen concentration, intensity of exciting light, pH, nature of pigments, solvents etc. The thermochemiluminescence was observed after illumination of liquid and solid pigment solutions at low temperature (down to ‐ 170d̀C). The excitation spectra of PCL coincide with the pigment absorption spectra. The PCL emission spectra in most cases differ from those of pigment fluorescence. Electron acceptors, electron donors, radical inhibitors and β‐carotene quench PCL. The quenching efficiency of electron acceptors is similar to their action on the chlorophyll triplet state. The quenching effect of radical inhibitors and β‐carotene correlates with their activity in reaction with singlet oxygen. The effect of quenchers on the chlorophyll fluorescence, photobleaching and pigment sensitized oxygenation was studied. Analysis of experimental data allowed the assumption that chemiluminescence accompanies the decomposition of labile pigment peroxides. The accumulation of peroxides is probably due to the reaction in the complex of pigment and singlet oxygen, formed as a result of energy transfer from photoexcited (triplet) pigment molecules to oxygen. The terminal chemiluminescence emission proceeds from the singlet excited states of molecules of pigments and products of their oxidation.
SPECTRAL CHARACTERISTICS OF THE PHOTORECEPTOR PIGMENT OF PHOTOTAXIS IN DICTYOSTELIUM DISCOIDEUM*
Authors: Poff Kenneth L. , Butler W. L.
Published: January 2008

Abstract—A photoresponsive pigment, described previously as the photoreceptor pigment for phototaxis in Dictyostelium discoideum, was examined by low‐temperature spectroscopy. The absorption spectrum of the purified pigment frozen in darkness indicates the reduced form of a high‐spin heme protein, and the spectrum of the pigment frozen during irradiation (to freeze in the photoproduct) indicates the oxidized form of the heme protein. The light‐induced absorbance changes measured at room temperature also indicate photooxidation of a heme pigment. The action spectrum for the light‐induced absorbance change shows a primary peak at about 430 nm and a broad, less active maximum in the 550–580 nm region. The absorption spectrum of the reduced pigment and the action spectrum for its photooxidation are both similar to the action spectrum for phototaxis of the pseudoplasmodia of D. discoideum.
SPECTRAL CHARACTERIZATION OF HIGH‐MOLECULAR‐WEIGHT PHYTOCHROME*
Authors: Pratt Lee H. , Cundiff Susan C.
Published: January 2008

Abstract— Previous information about the spectral and photochemical properties of phytochrome in vitro has apparently been determined in large part with chromopeptides derived from the native molecule by proteolysis. Characterization of high‐mol‐wt phytochrome in vitro has led to the observation that the far‐red‐absorbing form (Pfr) may undergo relatively large and reversible changes in far‐red extinction. Phytochrome preparations which exhibit reduced far‐red extinction as Pfr also exhibit a rapid reappearance of red absorbance after discontinuing the red illumination used to establish photostationary equilibrium. This rapid change in the red spectral region is not accompanied by any equivalent absorbance change in the far‐red. The molecular basis for these newly reported spectral properties is not known. However, both properties may be eliminated by the addition of either 2‐mercaptoethanol or ethylenediaminetetraacetic acid.
LAMP/FILTER SYSTEMS FOR SIMULATION OF SOLAR UV IRRADIANCE UNDER REDUCED ATMOSPHERIC OZONE*
Authors: Sisson William B. , Caldwell Martyn M.
Published: January 2008

Abstract— Lamp/filter systems for simulation of solar ultraviolet irradiance corresponding to various degrees of stratospheric ozone decrease are described for use in field and growth‐chamber biological experiments. In growth‐chamber applications, a constant ultraviolet enhancement simulation can be achieved with a 6000 W xenon arc with glass filters. For field applications, Westinghouse FS‐40 ‘sun lamps’ filtered with plastic films provide an ultraviolet supplement for use when solar altitudes exceed 40°.
PHOTOFRAGMENTATION OF α‐OXOCARBOXYLIC ACIDS IN AQUEOUS SOLUTION. AN EPR STUDY. FORMATION OF SEMIDIONE RADICALS BY DECARBOXYLATIVE SUBSTITUTION OF α‐OXOCARBOXYLIC ACIDS BY ACYL RADICALS–II. OXALOACETIC ACID (OXOSUCCINIC ACID)*
Authors: Steenken S.
Published: January 2008

Abstract— –On in situ photolysis (Λ= 250–400 nm) of aqueous oxaloacetic acid solutions, between pH 5 and 10, the radicals ‐O2CCH2C(O‐>=C(O+)CH2CO2‐ and ‐O2CCH2C(OH)CO2 are identified. With acetone present, CH2CO2, CH3C(OH)CO‐2, CH3C(O‐)=C(O)CH2CO2 and ‐O2CCHCOCO2 are also observed. CO2 and CO are identified as reaction products. The experimental results are explained in terms of α‐cleavage of the electronically excited keto‐isomer dianion of oxaloacetic acid to yield O2CCH2CO and CO2‐. ‐O2CCH2CO adds to the keto‐isomer of oxaloacetic acid and to pyruvic acid, which is formed from oxaloacetic acid by thermal decarboxylation, to yield ‐O2CCH2C(O‐)= C(O‐)CH2C0‐ and CH3C(O‐)=C(O)CH2CO‐2, respectively, via a decarboxylase substitution reaction. CH2CO2 is derived from ‐O2CCH2CO by decarbonylation. CO2‐ is scavenged by oxaloacetic acid and pyruvic acid to yield O2CCH2C(OH)CO2 and CH3C(OH)CO2‐, respectively.
EFFECT OF THE PHYSICAL STATE OF PHOSPHOLIPID ON RHODOPSIN REGENERATION FROM RETINYLIDENE PHOSPHOLIPID
Authors: Shichi Hitoshi , Somers Robert L.
Published: January 2008

Abstract— Rhodopsin regeneration in rod membranes involves reactions of all‐trans retinal (released from bleached pigment) with phosphatidylethanolamine, photic isomerization of retinal, and binding of 11‐cis retinal to opsin. This investigation demonstrated that formation of retinylidene phospholipid and retinal binding to opsin were both affected by the physical state of phospholipid. A fluid membraneous environment provided by the acyl chains of phospholipid was essential for these reactions to proceed efficiently. The retinal moiety of retinylidene phospholipid appeared to be directly transferred to opsin by transimination.
ON THE NATURE OF INTERACTION BETWEEN PROFLAVINE and DNA
Authors: Georghiou S.
Published: January 2008

Abstract— The fluorescence decay of the mutagenic drug proflavine (PF) bound to DNA at a phosphate‐to‐drug ratio of 420 is found to be a non‐exponential function of time. The deviation from exponentiality is shown to increase with increasing GC content of DNA. Thus, heterogeneity in the high affinity binding sites is clearly demonstrated. The nucleotides guanosine‐5‘‐monophosphate (GMP) and cyti‐dine‐5’‐monophosphate (CMP) are shown to form complexes with PF in 10‐3M sodium cacodylate buffer at pH 6.6. In addition, GMP quenches substantially the fluorescence of PF while CMP enhances it slightly. The fluorescence decay curves for 5 × I0‐6M PF in the presence of GMP concentrations greater than 10‐2M exhibit a deviation from exponentiality which parallels that exhibited by the fluorescence decay curves for PF bound to DNA of increasing GC content. It is inferred that (a) guanine is responsible for the quenching of the fluorescence of PF on binding to DNA; and (b) the forces involved in the interaction between PF and DNA are specific in nature. The implications of these findings concerning the mutagenic properties of acridine derivatives are discussed. Nanosecond depolarization studies reveal a quite fast depolarization of the fluorescence of bound PF; for the PF‐Cl. perfringens DNA complex the rotational correlation time is about 26 ns. Time‐resolved emission spectroscopy in the nanosecond scale demonstrates that, despite the change in the orientation of the drug, the electronic structure of the PF‐DNA complex is not substantially altered during the lifetime of the excited singlet electronic state of the drug.
PHOTOPRODUCTION OF IONS FROM CHLOROPHYLL α IN SOLUTION STUDIED BY FLASH PHOTOLYSIS and PHOTOCONDUCTIVITY
Authors: Imura Takeshi , Furutsuka Takashi , Kawabe Kazuo
Published: January 2008

Abstract— Ionic species were detected electrically on flash excitation of chlorophyll α following rapid production of the triplet state of the pigment. The action spectrum of photocurrent agreed well with the absorption bands of the pigment in the visible region; the threshold for the formation of ionic species in acetonitrile was 1.8 eV. Oxygen gas introduced into the solution completely prevented the appearance of the triplet and ionic species. The latter are suggested to result from electron‐transfer between the triplet pigments. Decay processes of the ionic species varied markedly with changes in the solvent polarity. Direct photo‐ionization of the pigment could be observed by UV excitation in some non‐polar solvents.
FLAVIN‐MEDIATED PHOTOREACTIONS IN ARTIFICIAL SYSTEMS: A POSSIBLE MODEL FOR THE BLUE‐LIGHT PHOTORECEPTOR PIGMENT IN LIVING SYSTEMS*
Authors: Schmidt W. , Butler W. L.
Published: January 2008

Abstract— The photoreduction of cytochrome c and the photostimulation of oxygen uptake were studied in solutions of flavin and cytochrome as a possible model system for similar photoreactions which have been observed in vivo. Light causes the photoreduction of the flavin. Under aerobic conditions the photoreduced flavin reacts with oxygen to form the superoxide anion which in turn can reduce cytochrome c. Dismutation of the superoxide anions forms hydrogen peroxide which mediates the dark oxidation of the photoreduced cytochrome. Superoxide formation and dismutation also account for the light‐induced oxygen uptake. Action spectra confirm the role of flavin in the photoreduction of cytochrome c and the photostimulation of oxygen uptake. Under anaerobic conditions the photoreduced flavin reduces cytochrome c directly. In the presence of an electron donor only catalytic amounts of flavin are required. In the absence of an added electron donor flavin itself can act as the electron donor if substrate amounts are present. Azide inhibits all of these flavin‐mediated photoresponses. Azide also inhibits the photoreduction of cytochrome b which occurs in the mycelium of Newospora.
LASER FLASH PHOTOLYSIS OF EOSIN AND ITS COMPLEX WITH LYSOZYME
Authors: Fisher Gordon J. , Lewis Colin , Madill David
Published: January 2008

Abstract— The transient absorption spectra of aqueous solutions of eosin and of the lysozyme‐eosin complex have been examined after excitation with a Q‐switched frequency‐doubled (347 nm) ruby laser pulse. Eosin itself gives three broad, intense short‐lived absorption bands with maxima at wavelengths of 410, 460 and 580 nm, which other workers have identified with the semi‐reduced and semi‐oxidized radicals and the triplet state of the dye, respectively. In the complex with lysozyme, the yield and lifetime of the eosin triplet are greatly reduced in comparison with the free dye. It is suggested that excited eosin, when bound to lysozyme, decays mainly from the singlet state by pathways such as charge transfer which are not available to the free molecule.
EVALUATING THE STABILITY AND REACTIVITY OF A LIGHT‐SENSITIVE PROBE BY ENZYME ANALYSIS
Authors: Tometsko Andrew M. , Turula Jon
Published: January 2008

Abstract— Enzymes can provide well defined functional targets for determining the availability and reaction characteristics of light sensitive probes. Trypsin and chymotrypsin are inhibited by flash photolysis with a photoprobe, 4‐fluoro‐3‐nitrophenylazide (FNPA). Inhibition is competitive in the dark, and non‐competitive (irreversible) following photolysis of the FNPA enzyme solution. Photoinactivation is dependent upon the concentration of FNPA, the flash rate, and the time of photolysis. The enzymes can be protected from photolytic inactivation with FNPA if photolysis is carried out in the presence of 2,4‐dinitrophenol or 4‐fluoro‐3‐nitroaniline which compete with FNPA for binding sites. The photo‐probe is effective over a wide pH range (i.e. pH 2–11), and provides a sensitive tool for probing conformational and charge adjustments which increase or decrease the affinity of the binding site. Chymotrypsinogen was also sensitive to photolysis, indicating that FNPA binding sites are present in the zymogen structure.
THE SUPEROXIDE ANION AS ELECTRON DONOR TO THE MITOCHONDRIAL ELECTRON TRANSPORT CHAIN
Authors: Ninnemann H. , Strasser R. J. , Butler W. L.
Published: January 2008

Abstract— In isolated respiratory multienzyme complexes of beef heart mitochondria the b‐type cytochromes can be photoreduced in presence of flavin via the superoxide anion. O‐2 does not reduce cytochrome c1. In an anaerobic system, FMNH2 formed by irradiation with blue light in presence of EDTA reduces cytochromes b and c1 The possible implication of O‐2 in the electron transfer from flavin/flavoprotein to cytochrome b in blue light‐controlled biological processes is discussed.
METHYLMERCURY: PHOTOCHEMICAL TRANSFORMATION OF MERCURIC SULFIDE INTO METHYLMERCURY IN AQUEOUS SOLUTIONS1
Authors: Akagi Hirokatsu , Fujita Yuzaburo , Takabatake Eigo
Published: January 2008

Abstract. The photochemical reaction of mercuric sulfide was studied in aqueous solutions. The photo‐solubilization of mercuric sulfide occurred under irradiation with light of ≤650nm and was enhanced in the presence of oxygen and electrolytes. The resultant mercuric ions were easily methylated in the presence of acetate ions via the photosensitized reaction by the simultaneously produced “photo‐sulfur” under irradiation with light of ≤420nm. The photoelectrochemical studies of mercuric sulfide electrode revealed that black mercuric sulfide was an n‐type semiconductor and the photo‐current due to the dissolution as mercuric ions was observed on anodic polarization. The photo‐solubilization of mercuric sulfide may be interpreted in terms of the local‐cell mechanism.
PHOTOKILLING OF MICROCOCCUS ROSEUS
Authors: Dieringer S. M. , Singer J. T. , Cooney J. J.
Published: January 2008

Abstract. Previous work showed that the bacterium Micrococcus roseus is killed by photodynamic action when an exogenous photosensitizer is present, but when a photosensitizer is not added the organism survives long exposure to high intensity (22,000ft‐c, 348 J/s/m2) white light. Experiments designed to demonstrate the presence of a mechanism to repair damage caused by photodynamic action failed to reveal such a mechanism. However, the organism was killed by light of a very high intensity (32,000ft‐c, 506 J/s/m2) in the absence of added photosensitizer, indicating that cells have an effective endogenous photosensitizer(s). Two carotenoid‐deficient mutants were killed via photodynamic action more rapidly than the fully pigmented wild‐type in the presence or absence of an exogenous photosensitizer. Thus, resistance of M. roseus to photodynamic action is not due to a repair mechanism, nor to lack of an effective endogenous photosensitizer, but to the protective action of carotenoid pigments.
COMPARATIVE ANALYSES OF ACTION SPECTRA OF GLYCOLATE EXCRETION (“PHOTORESPIRATION”) AND PHOTOSYNTHESIS IN THE BLUE‐GREEN ALGA AN ACYSTIS NIDULANS
Authors: Sörensen Leonard , Halldal Per
Published: January 2008

Abstract. The action spectra were determined by measuring photosynthetic H14CO‐3‐fixation and 14C‐glycolate excretion to the medium during 15 min exposure to light at 15 different wavelengths in the visible region using interference filters and a 2500 W high pressure Xe lamp at a constant photon flux of about 1.51 × 1019 quanta m‐2.s‐1 at all wavelengths.

When plotted on relative scales the action spectrum of glycolate excretion lies below that of photosynthesis at all wavelengths shorter than 517 nm. As glycolate excretion had an exponential relationship to photosynthetic rates, different methods were used to analyze for a specific blue light effect which demonstrated that the relative amount of glycolate excretion was depressed by blue light compared with that by green and red. The greatest difference was observed around 460–480 nm. However, on statistical grounds it is not permitted to draw a difference spectrum which might indicate the absorption characteristics of pigment(s) involved.

A hypothesis is discussed assuming that some glycolate is consumed in an oxidation process for supply of electrons to Photosystem I when Photosystem II is poorly excited in the blue region of the spectrum, which was the case for Anacystis used in the present investigation.
PHOTOCHEMICAL FORMATION OF METASTABLE SPECIES FROM 1,3‐DIPHENYLISOBENZOFURAN*
Authors: Singh Ajit , McIntyre Neil R. , Koroll Grant W.
Published: January 2008

Abstract— Photochemical formation of metastable species from 1,3‐diphenylisobenzofuran (DPBF) in solutions has been investigated. On irradiation at 410 nm, in the presence of oxygen, DPBF is bleached. The bleached solutions show two fluorescence bands, one at ˜380nm and the other at ˜420nm. None of these fluorescence bands are due to o‐dibenzoylbenzene, which is the main stable product formed on photo‐bleaching of DPBF in the presence of O2. The species showing fluorescence at ˜380nm and ˜420nm are also formed on reaction of DPBF with 1O2 and undergo further reactions with light as well with 1O2; the resulting products do not all show fluorescence. After the photo‐bleached solutions have stood for some time in the dark, or are warmed, regeneration of DPBF seems to occur. The triplet energy of DPBF has been estimated by energy transfer studies to be between 22 and 29 kcal/mol (between 92 and 121 kJ mol‐1).
THE HABER‐WEISS CYCLE
Authors: Koppenol Willem H. , Butler John , Leeuwen Johan W. van
Published: January 2008

Abstract— The Haber‐Weiss cycle:

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was investigated at low pH by radiolysis of oxygen or nitrogen saturated solutions of hydrogen peroxide. It was found that reaction 2 has a low rate constant: k2= 3.0 ± 0.6 M‐1 s‐1 (pH 2.3, 22°C). The rate determining step of reaction 2 is most probably the transfer of an electron from a π8* orbital of HO2 to the empty s̀u* orbital of H2O2. Overlap between these two orbitals is hindered by the filled π8* orbitals of H2O2. Fe(HI)EDTA catalyses reaction 2.
ASPECTS OF CHEMICAL DAMAGE IN RADIATION AND PHOTO‐BIOLOGY
Authors: Bisby R. H. , Cundall R. B. , Davies A. K.
Published: January 2008

Abstract— The reactions of oxidizing free radicals produced by the action of ionizing radiation on aqueous solutions with molecules of biological interest are discussed. In particular the reactions of inorganic radical anions with proteins are considered and their use as selective probes described by example.
PHOTOINDUCTION OF PHARBITIS FLOWERING: RELATIONSHIP TO RNA SYNTHESIS AND OTHER METABOLIC EVENTS
Authors: Gressel J. , Zilberstein A. , Strausbauch L. , Arzee T.
Published: January 2008

We have previously shown that a wave of enhanced uridine incorporation into RNA occurs in the more vegetative parts of the plumule at the end of the single dark period that evokes flowering in Pharbitis nil. We demonstrate here that a light break that suppresses flowering suppresses this wave as well. It does not shift the kinetics of the wave of uridine incorporation to a different time. The enhanced incorporation is into all RNA fractions.

It had been concluded from excision experiments that the floral stimulus reaches the apex much after photoinduction. There is a metabolic shock caused by such excision of the cotyledons or surgical removal of the plumule that can suppress flowering if it is performed near the end of the inductive dark period. The terminal bud is more affected by this shock than lateral buds. Excision of the cotyledons enhances the rate of incorporation of exogenous uridine into the plumule. We propose that the “floral stimulus” stimulating incorporation into RNA reaches the plumule immediately after the end of the critical dark period.
PHOTOELECTRON QUANTUM YIELD SPECTRUM AND PHOTOELECTRON MICROSCOPY OF β‐CAROTENE
Authors: Brown Hugh M. , Kingzett Paul C. , Griffith O. Hayes
Published: January 2008

Abstract—The absolute photoelectron quantum yield spectrum for β‐carotene in the wavelength range 180–230 nm is reported. β‐Carotene is very photoemissive over this wavelength region with photoelectron quantum yields on the order of 2 × 10‐‐3 electrons per incident photon at 180 nm, 4 × 10‐‐4 at 210 nm, and 3 × 10‐‐5 at 230 nm. At wavelengths longer than 240 nm, β‐carotene photoemission dropped off monotonically with increasing wavelength. The photoelectron quantum yield spectrum of β‐carotene is very similar to that of chlorophyll a. A photoelectron micrograph of β‐carotene deposited on a thin layer of the fatty acid arachidic acid demonstrates the marked photoemission contrast between β‐carotene and membrane lipid. Photoelectron micrographs of samples with β‐carotene and Chl a in the same field show that prolonged (1 h) illumination in vacuo causes β‐carotene to markedly fade while leaving the Chl a photoemissive. This differential bleaching of β‐carotene may allow it to be distinguished from Chl in high magnification photoelectron micrographs of photosynthetic membranes.
THERMODYNAMICS OF THE PRIMARY REACTIONS OF PHOTOSYNTHESIS
Authors: Parson William W.
Published: January 2008

Abstract. It appears to be widely believed that fundamental thermodynamic limitations prevent the products of the primary electron transfer reactions of photosynthesis from exceeding the reactants in energy by more than about 0.7 hv0 where v0 is the frequency of the lowest energy absorption band of the reaction center. Specifically, in photosynthetic bacteria, where hv0? 1.34 eV, it is often said that the midpoint redox potentials of the primary electron donor and acceptor cannot differ by more than about 0.9 eV. This is incorrect. A simple expression is developed for δμ, the increase in the partial molecular free energy of an absorber under illumination. The magnitude of δμ gives one no information about the nature of the photochemical reactions that can result from excitation of the absorber. It puts no limits on the midpoint redox potentials of the reactants. However, knowing δμ does allow one to calculate the concentrations of the products if the system comes to equilibrium during illumination.
ACTION SPECTRA FOR OXYGEN‐DEPENDENT AND INDEPENDENT INACTIVATION OF ESCHERZCHZA COLZ WP2s FROM 254 TO 460 NM*
Authors: Webb Robert B. , Brown Mickey S.
Published: January 2008

Abstract— Action spectra for lethality of E. coli WP2s under aerobic and anaerobic conditions. based on final slopes of the survival curves, reveal the absence of oxygen dependence at 313 nm and shorter wavelengths and a strong oxygen dependence (OER of 12 at 334 nm and 16 at 365 nm) at wavelengths longer than 313 nm. Shoulders or small peaks at340, 365, 410 and 500 nm suggest the participation of non‐DNA chromophores in aerobic lethality at these wavelength ranges.
PHYTOCHROME MEDIATED CAROTENOID SYNTHESIS IN THE FUNGUS VERTICILLIUM AGARZCZNUM
Authors: Valadon L. R. G. , Osman Mohamed , Mummery Rosemary S.
Published: January 2008

Abstract— Ten minutes of red irradiation (R) increased carotenogenesis in Verticillium agoricinum and this effect was reversed by 10min of far‐red (FR) irradiation indicating that phytochrome is involved. A far‐red minus red difference spectrum of a crude extract shows a peak at 670 nm and a dip at 750 nm wavelength, values slightly larger than higher plant phytochrome. indicating the presence of phytochrome.
LACK OF HEAVY ATOM EFFECT ON THE ACTIVATION PARAMETERS OF BROMINE SUBSTITUTED 1,2‐DIOXETANES*
Authors: Adam Waldemar , Sakanishi Katsumasa
Published: January 2008

Abstract— The continuous temperature variation kinetic method was applied to the direct chemilu‐minescence of tetramethyl‐1,2‐dioxetane (1a), 3‐bromomethyl‐3,4,4‐trimethyl‐1,2‐dioxetane (1b), 3,3–bis‐(bromomethyl‐4,4–dimethyl‐1,2–dioxetane (1c) and 3,4–bis(bromomethyl)‐3,4–dimethyl‐1,2‐dioxetane (1d). The activation energies (Ea) were found to be 27.6 ± 0.1, 28.4 ± 0.1, 28.0 ± 0.2, and 27.6 ± 0.2 kcal/mol, respectively. These results show that the heavy atom effect by the bromine substituents on the activation energies is negligible, confirming previous conclusions that a diradical mechanism operates in the thermal decomposition of these dioxetanes.
ENERGY TRANSFER FROM ENZYME‐GENERATED TRIPLET ACETONE TO RIBOFLAVIN PERTURBED BY MOLECULES RELATED TO THYROXINE
Authors: Rivas‐Suarez Edy , Duran Nelson , Cilento Giuseppe
Published: January 2008

Abstract— The rate of energy transfer from enzyme‐generated triplet acetone to riboflavin increases by three orders of magnitude when the flavin is charge‐transfer complexed with 3,5‐dihalogenotyrosines or with thyroxine. A very fast long‐range energy transfer to form the first excited singlet state of riboflavin in the complex, followed by a very efficient intersystem crossing to the triplet manifold, is postulated to account for the results.
DYE‐SENSITIZED PHOTOLYSTS OF DISODIUM PHENYL PHOSPHATE IN AQUEOUS SOLUTION UNDER OXYGEN: INVOLVEMENT OF SINGLET OXYGEN
Authors: Halma Mordehai , Levy Daniel
Published: January 2008

Abstract— The release of orthophosphate from oxygen‐saturated aqueous solutions of disodium phenyl phosphate by near‐UV and visible light was enhanced in the presence of the sensitizing dyes methylene blue, rose bengal and thionine. The reaction was accompanied by the bleaching of these dyes. In the absence of oxygen, under nitrogen, the photodecomposition was very much slower. In deuterium oxide as the solvent, the dye‐sensitized photodecomposition was 9 times faster than in normal water. This result suggests that singlet oxygen is probably the reactive species in the dye‐sensitized reaction.
USE OF REGRESSION ANALYSIS TO ESTIMATE UV SPECTRAL IRRADIANCE FROM BROAD BAND RADIOMETER READINGS UNDER FS‐40 FLUORESCENT SUNLAMPS FILTERED WITH CELLULOSE ACETATE
Authors: Krizek Donald T. , Koch E. James
Published: January 2008

Abstract— Weighted and unweighted UV spectral irradiances were measured under a 2‐lamp fluorescent fixture containing Westinghouse FS‐40 fluorescent sunlamps filtered with (6 h aged) 0.127 mm (0.005 in.) cellulose acetate by use of newly developed broadband UV radiometers and an automated UV spectro‐radiometer. Measurements were taken at 10‐cm intervals between 20 and 110 cm from the lamps. Correlations were determined between sets of data measured with the broadband radiometers and the UV spectroradiometer.

By use of linear regression analyses on the weighted and unweighted spectral data, regression equations were developed for predicting UV‐B irradiance (unweighted mWm‐2), biologically effective UV (BUV) (weighted mWm) in the 280–320 nm (UV‐B) region, UV‐B sun equivalents, and incident flux density in the UV‐B region in photons m‐2× 1021 integrated over a 6‐h exposure. Examination of the correlation coefficients (r values) indicated that agreement was excellent between measured and predicted values for all comparisons (r values from 0.9972 to 0.9998).

Use of regression equations should permit accurate. rapid estimation of both weighted and unweighted UV irradiances at any location in an experimental set‐up and provide a useful means for intra‐ and inter‐laboratory comparisons of spectral measurements, made in the interagency BACER program under FS‐40 fluorescent sunlamps filtered with 0.127 mm cellulose acetate (aged for 6h).
PHOTOTACTIC RESPONSE OF CHLAMYDOMONAS TO FLASHES OF LIGHT –II. RESPONSE OF INDIVIDUAL CELLS
Authors: Boscov James S. , Feinleib Mary Ella
Published: January 2008

Abstract— –Video‐microscope studies provide further evidence that Chlamydomonas can become oriented in response to a single short flash of light. Following a flash, 50% of the cells in a negatively phototactic population undergo a transient deflection in swimming path (‘turn response’), 10% show a ‘stop response’, and 40% continue to swim straight ahead. The direction of turning is related to the direction of the stimulus; a majority of cells turn away from the flash source. Repetitive flashing at 60 per s elicits oriented swimming, indistinguishable from that observed with continuous light. Responses at the onset of repetitive flashing resemble single‐flash responses, reinforcing the idea that response to a single flash corresponds to the initial stages of orientation to continuous light. A stop response sometimes occurs at the onset of orientation to repetitive flashing, but it is apparently not an essential component of orientation. The fact that only 60% of the cells turn or stop in response to a flash is consistent with the hypothesis that light direction is perceived by comparing light absorbed in one photoreceptive region at two instants in time (before and during the flash). The only cells to turn or to stop would be those in which the photoreceptor organelle is appropriately oriented at the instant of the flash.
CHLORPROMAZINE AND PROTRIPTYLINE PHOTOTOXICITY: PHOTOSENSITIZED, OXYGEN INDEPENDENT RED CELL HEMOLYSIS
Authors: Kochevar Irene E. , LAmola Angelo A.
Published: January 2008

Abstract—Red blood cell lysis photosensitized by chlorpromazine and protriptyline was investigated. Oxygen independent sensitized photohemolysis was observed with both compounds. When chlorpromazine and protriptyline were irradiated in the absence of red cells, both formed photoproducts which lysed red cells. These results indicate that chlorpromazine and protriptyline represent a new mechanistic class of phototoxic compounds which photosensitize membrane disruption by oxygen independent processes.
THE TRIPLET STATE OF 8‐METHOXYPSORALEN
Authors: Sloper R. W. , Truscott T. G. , Land E. J.
Published: January 2008

Abstract— Transient absorption spectra produced by laser flash photolysis of an aqueous solution of 8‐methoxypsoralen (8‐MOP) have been studied. The biphotonic production of hydrated electrons and of the radical ions, 8‐MOP+ and 8‐MOP‐ is reported. The hydrated electron was found to react with ground state 8‐MOP with k ˜ 3 × 1010M‐1 s‐1. In order to obtain a true triplet‐triplet absorption spectrum. contributions from the radical ions were subtracted from the overall transient absorption. In addition, contributions from e‐aq to the transient spectrum were removed by using N2O, low laser intensity to minimize photoionization or by measuring the transient O.D. after the electron has decayed. These three methods each produced the same triplet‐triplet spectrum which differs in the red region from previously reported spectra.
CHANGES IN THE RATES OF PHOTOCONVERSION OF PHYTOCHROME DURING ETIOLATION IN MUSTARD SEEDLINGS
Authors: Schäfer E. , Mohr H.
Published: January 2008

Abstract— The relative phytochrome photoconversion rates in cotyledons and hypocotylar hook of etiolating mustard (Sinapis alba L.) seedlings were measured between 16 and 96 h after sowing. It was found that at constant fluence rates photoconversion rate in red light increases in both organs with time whereas the photoconversion rate in far‐red (756 nm) light decreases with time of development. Since the isosbestic point remains constant, it was concluded that the observed changes cannot be attributed to changes of extinction coefficients. It was not possible, however, to decide whether the observed changes are due to changes of light attenuation or quantum yields.
ROSEOFLAVIN AS A BLUE LIGHT RECEPTOR ANALOG: SPECTROSCOPIC CHARACTERIZATION
Authors: Song Pill‐Soon , Walker Edward B. , Vierstra Richard D. , Poff Kenneth L.
Published: January 2008

Abstract— The blue light absorption band of roseoflavin is polarized along the axis roughly connecting N3‐C8 positions. A weak, second π→π* transition with a polarization angle of ca. 25° is hidden under the short wavelength side of the blue absorption band. The excited state of roseoflavin is somewhat more basic than the ground state, by a 1.5 pKa unit. The fluorescence quantum yield and lifetime of roseoflavin are substantially lower than those of other flavins, thus making it kinetically less efficient as a blue light photoreceptor.
FUNCTIONAL ROLE OF CALCIUM IN PHOTORECEPTOR CELLS
Authors: Miki Naomasa , Kuo Che‐Hui , Hayashi Yokichi , Akiyama Mariko
Published: January 2008

Abstract— Ca‐uptake by disc membranes prepared from frog rod photoreceptor outer segments was examined. Ca‐uptake study revealed two affinity sites which were saturated with 10–5M and 10–3M of ATP. When disc membranes in 20 mM Tris‐HCl buffer (pH 7.5) were stored at ‐20°C for 6 h, more than 95% of Ca‐uptake activity was lost. Ca‐uptake activity was, however, preserved if the disc membrane suspension was mixed with 1–10mM ATP and stored at ‐20°C. Furthermore the reactivation of Ca‐uptake was observed if disc membranes, which had lost Ca‐uptake ability by storing at 4°C for 3 h, were mixed with 10 mM ATP and then frozen at ‐20°C for 5 h or 28 h (ATP‐induced ATP‐dependent Ca‐uptake). When the contents of ATP bound to disc membranes were measured during a brief aging at 37°C, the decrement of bound ATP content was correlated well with the decreasing of Ca‐uptake activity. Carbonylcyanide m‐chlorophenylhydrazone (CCCP), a conductor of protons, inhibited Ca‐uptake activity and half maximal inhibition was achieved at 2 × 10–8M. When 10–6M of CCCP was added to the 45Ca‐accumulated disc membranes, rapid release of 45Ca from the disc membranes was observed. These results suggest that ATP may play a role in the Ca‐pump regulation in disc membranes and a [H+] gradient across disc membrane may be linked to Ca‐uptake mechanism.
EFFECT OF INTRACELLULAR INJECTION OF EGTA AND TETRAETHYLAMMONIUM CHLORIDE ON THE RECEPTOR POTENTIAL OF LOCUST PHOTORECEPTORS
Authors: Tsukahara Yasuo
Published: January 2008

Abstract— The depolarizing photoreceptor potential of locust, Valanga irregularis, as that of other arthropods, has an initial transient phase that declines to a stable sustained phase. In this work, the effect of intracellular injection of EGTA and TEA on these phases was studied.

(1) Reversal potential of the transient phase was higher than that of the sustained phase.

(2) EGTA and TEA enhanced both phases and the enhancement was more prominent in the sustained phase.

(3) Resting potential was shifted slightly upward by the injection. The amplitude of the maximum response was also increased.

(4) Current injected through an electrode filled with 2 M KCl had a significant effect on the shape of the response depending on the direction of the current.

(5) It is suggested that the activation of K+ conductance induced by an increase of intracellular free Ca2+ concentration causes a decrease in amplitude of the sustained phase.
RHODOPSIN REGENERATION, CALCIUM, AND THE CONTROL OF THE DARK CURRENT IN VERTEBRATE RODS
Authors: Albani C. , Nöll G. N. , Yoshikami S.
Published: January 2008

Abstract— The dark current of retinal rods is suppressed for an extended period when their rhodopsin is bleached. An 8% bleach completely suppresses the current for 8 min and after 35 min it is fully recovered. The dark current can recover fully from a bleaching flash without any rhodopsin being regenerated. Moreover the recovery can be hastened either by lowering the activity of calcium ions surrounding the rods or by regenerating the rhodopsin. The recovery of the dark current following these bleaches showed zero order kinetics, regardless of whether the recovery was hastened by low calcium, 11‐cis retinaldehyde or not. If all the rhodopsin is bleached in the retina, the dark current does not recover; the addition of 11‐cis retinaldehyde, but not all‐trans retinaldehyde, to the bleached retina causes the dark current to begin its recovery as early as 10 min after the addition with zero order kinetics (1.3% min‐1). In two of three similar experiments, the dark current recovered 100%. When the recovery rate of the dark current from the retina showing the earliest response is compared with the rate of the regeneration of rhodopsin in the plasma and disc membranes, the dark current begins its recovery after the plasma membrane rhodopsin is fully regenerated and the disc rhodopsin is half regenerated. When the disc rhodopsin is fully regenerated, the dark current is recovered 75%, and 20 min later it is completely recovered.
SPECIFIC PHOTOALKYLATION OF POLY U AND OF POLY A WITH 2‐PROPANOL AND THEIR MESSENGER PROPERTIES
Authors: Livneh Zvi , (Noy) Etta Livneh , Sperling Joseph
Published: January 2008

Abstract—

Ultraviolet light induced free radical alkylation of poly U or of poly A with 2‐propanol leads to the specific formation of 6‐(2‐hydroxy 2‐propyl) 5,6‐dihydro‐UMP or 8‐(2‐hydroxy 2‐propyl)‐AMP residues, respectively. The biochemical significance of the alterations in the modified polynucleotides was studied by testing their messenger activities in a cell free system of E. coli. Both photoalkylated poly U and poly A have reduced functional activity, with no change in functional specificity. This was demonstrated by inhibition of polymerization of phenylalanine and lysine directed by photoalkylated poly U and poly A, respectively, and by lack of misincorporation of other amino acids. The modification of poly U also caused the disappearance of misincorporation of serine that was found with the native polynucleotide.
PHOTOREACTIVATION OF ULTRAVIOLET LIGHT‐INDUCED DAMAGE IN CULTURED FISH CELLS AS REVEALED BY INCREASED COLONY FORMING ABILITY AND DECREASED CONTENT OF PYRIMIDINE DIMERS
Authors: Shima Akihiro , Kenaga Mituo , Nikaido Osamu , Takebe Hiraku , Egami Nobuo
Published: January 2008

Abstract— Cultured cells derived from a goldfish were irradiated with 254nm ultraviolet light. Cell survival and splitting of pyrimidine dimers after photoreactivation treatment with white fluorescent lamps were examined by colony forming ability and by a direct dimer assay, respectively. When UV‐irradiated (5 J/m2) cells were illuminated by photoreactivating light, cell survival was enhanced up to a factor of 9 (40min) followed by a decline after prolonged exposures. Exposure of UV‐irradiated (15 J/m2) cells to radiation from white fluorescent lamps reduced the amounts of thymine‐containing dimers in a photoreactivating fluence dependent manner, up to about 60% reduction at 120 min exposure. Keeping UV‐irradiated cells in the dark for up to 120min did not affect either cell survival or the amount of pyrimidine dimers in DNA, indicating that there were not detectable levels of a dark‐repair system in the cells under our conditions. Correlation between photoreactivation of colony forming ability and photoreactivation of the pyrimidine dimers was demonstrated, at least at relatively low fluences of photoreactivating light.
THE PHOTOREACTIONS AND PHOTOSENSITIVITY OF 3,4‐DEHYDRO‐BACTERIORHODOPSIN AT LOW TEMPERATURES
Authors: Iwasa Tatsuo , Tokunaga Fumio , Ebrey Thomas G. , Yoshizawa Tǒru
Published: January 2008

Abstract— The photoreaction of the artificial pigment synthesized from bacterioopsin and rrans‐3,4‐dehydro‐retinal, [3,4‐dehydro]bacteriorhodopsin ([3,4‐deH]bRt) was investigated with low temperature spectrophotometry.

The amount of batho‐product formed from the light‐adapted pigment of [3,4‐deH]bR (designated as batho‐[3,4‐deH]bRt) by irradiation at 77 K was much less than that from trans‐bacteriorhodopsin (bRt) and depends on temperature at irradiation of the sample. The kinetics of photoconversion of [3,4‐deH]bRt to batho‐[3,4‐deH]bRt and that of its reversion were measured at several temperatures with a so‐called “double Dewar system”. The results showed that the photosensitivity of [3,4‐deH]bRt was temperature dependent. When batho‐[3,4‐deH]bRt was warmed above 143 K, it was converted to lumi‐[3,4‐deH]bRt. Lumi‐[3,4‐deH]bRt was also produced by irradiation of [3,4‐deH]bRt at 143 or 163 K. The maximum in the difference spectrum between lumi‐[3,4‐deH]bRt and [3,4‐deH]bRt was located at about 540 nm. The irradiation of [3,4‐deH]bRt at 183 K produced an intermediate analogous to meta‐bRt, but under similar conditions bRt does not produce meta‐bRt. These results indicate that intermediates of [3,4‐deH]bRt are less stable than those of bRt.

The differences between bacteriorhodopsin and [3,4‐dehydro]bacteriorhodopsin were discussed and compared with the differences between rhodopsin and [3,4‐dehydro]rhodopsin.