bluuebunny/crossref_metadata_2025 huggingface dataset:
PHOTOREGULATION OF LOGARITHMIC FLUENCE‐RESPONSE CURVES FOR PHYTOCHROME CONTROL OF CHLOROPHYLL FORMATION IN PISUM SATIVUM L*
Authors: Raven C. W. , Shropshire W.
Published: January 2008

Abstract— Logarithmic fluence‐response curves for red (660 nm) and far red (730 nm) light induction of rapid chlorophyll a (Chi a) accumulation in pea seedlings (Pisum sativum L. cv. Early Alaska) indicate extreme light sensitivity in dark‐grown seedlings. The energy requirement for onset of 660 nm light induction is less than 20 μJ m‐2 and for 730 nm is about 1 mJ m‐2. De‐etiolation produced by a saturating exposure of red light (3–8 kJ m‐2) 24 h prior to the construction of the logarithmic fluence‐response curves resulted in approximately a 3 fold increase in slope for 660 nm light, whereas the energy requirement for onset of induction shifted to about 100 mJ m‐2. In such de‐etiolated plant material, far red applied at low incident energies almost completely lost its inductive capacity. The inductive capacity of far red applied as high irradiance over a long period of time (16h) appeared not to be affected by the de‐etiolation treatment. Reciprocity failed for both dark‐grown and de‐etiolated seedlings upon exposures exceeding 1,000s. Nearly identical results were obtained for seedlings de‐etiolated by red exposures immediately followed by far red (4.8 kJ m‐2), although this treatment did not lead to any significant decrease in spectrophotometrically measurable phytochrome. Therefore, no simple correlation was observed between the level of phytochrome present and the sensitivity of seedlings for induction of rapid Chl a accumulation. In order to explain this apparent phytochrome paradox the possibility was tested and ruled out for changes in the degree of synchronization of seedlings, or for induction of some sort of circadian rhythmicity in light sensitivity being involved. In addition, no correlation was observed between induction of morphogenic development and changing light sensitivity. These results formed, therefore, additional support for a model for phytochrome action involving its intracellular transport and local concentration during the process of seedling de‐etiolation.
AN ANALYSIS OF PORPHYRIDIUM ABSORPTION BANDS WITH A DIGITAL SPECTROPHOTOMETER
Authors: Leclerc J. C. , Hoarau J. , Guérin‐Dumartrait E.
Published: January 2008

Abstract— –Numerical absorbance values treated by a computer allow one to easily obtain precise absorption spectra from intact cells or extracts. An attempt has been made to determine the number and position of the individual bands by the difference spectra and the fourth derivative method. These two methods resulted in an accurate curve resolution with single Gaussian components and yielded relative proportions of chl a forms in Porphyridium.
STUDIES ON THYMINE AND URACIL TRIPLET EXCITED STATE IN ACETONITRILE AND WATER
Authors: Salet C. , Bensasson R.
Published: January 2008

Abstract— Thymine and uracil triplet‐triplet absorption spectra and triplet excited state lifetimes have been observed in acetonitrile and water by nanosecond laser flash spectroscopy. A study of triplet energy transfer from these pyrimidines to retino! has also allowed an estimation of the triplet extinction coefficient εTT of thymine and uracil. These εTT were then used to determine the triplet quantum yields ØT of both pyrimidines in acetonitrile and water.
ANION INDUCED REGULATION OF THE ABSORPTION MAXIMUM OF THE TWENTY TWO CARBON ANALOG OF THE JV‐RETINYLIDENE‐n‐BUTYLAMMONIUM CATION*
Authors: Blatz Paul E. , Lane Larry , Aumiller James C.
Published: January 2008

Abstract— This study was undertaken to further investigate the way in which the counter anion controls the Λmax of the absorption spectrum of compounds similar to N‐retinylidene‐n‐butylammonium salts (NRBA). The following relationship had been found: ΔE =ΔEo ‐F d0e2/εd2; here ΔE is the observed excitation energy, e the charge on the electron, ε the dielectric constant, d0 a constant and d the distance between centers of opposite charge as estimated from crystallographic radii. Resonance theory implies that ΔEo should be of the same numerical value as the corresponding carbonium ion which can be generated readily from the corresponding alcohol. The C22SB analog of NRBA was prepared and then converted to the halide salts. The Δmax of these salts was determined in several halohydrocar‐bon solvents, and ΔEo was determined by least squares for each solvent. The average value of ΔEo was found to be 653 nm, while the Λmax, for the carbonium ion was previously found to be 644 nm. The results are supportive of previous work.
THE PHOTOSENSITIZED OXIDATION OF TYROSINE REACTION UNDER HOMOGENEOUS CONDITIONS DERIVATIVES IN THE PRESENCE OF ALGINATE‐I
Authors: Seely G. R. , Hart R. L.
Published: January 2008

Abstract—The rates of dye‐sensitized photooxidation of tyrosine and tyramine to brown products were compared in the presence and the absence of the anionic polysaccharide, alginate. The polyelectrolyte did not affect the reaction when it was sensitized by monochromatic light absorbed mainly by the monomeric form of the dye. In white light, the rate of oxidation sensitized by thionine or phenosafranine was increased in the presence of alginate for tyramine, but not for tyrosine. In the thionine sensitized reaction, the ratio of brown product formation to tyramine consumption increased with decreasing wavelength of monochromatic excitation. These and other phenomena are believed related to the formation of complexes between the dyes and some of the oxidation products, and to association between some of the oxidation products and alginate. A mechanism for oxidation of phenols is proposed, based on the addition of O2 (1Δ9) across a double bond ortho to the phenolate oxygen. Dyes bind to alginate in monomeric and in aggregated forms; only the monomeric forms of thiazine dyes are photochemically active, but both the monomeric and the aggregated forms of crystal violet are active.
AZOALDOLASE PHOTOSENSITIVITY
Authors: Montagnoli Giorgio , Monti Sandra , Nannicini Luciano , Felicioli Romano
Published: January 2008

Abstract—The chemical modification of rabbit muscle aldolase by coupling with diazotized p‐amino benzoate results in the preparation of a photosensitive enzyme. The photosensitivity is realized with the presence of arene diazothioether chromophores, due to the substitution on cysteine residues (eight groups per enzyme molecule). By absorption and emission spectroscopy it has been shown that at neutral pH visible light causes E→Z isomerization of the extrinsic chromophore. The reaction is thermally reversed with τ= 2.3 min at 24.3°C. Fading of the chromophore is observed after long irradiation time, especially in alkali solution; at pH 13 some of the diazo groups are exchanged with histidine residues to form azo derivatives of the imidazole anion. Optimum condition for photochromic behaviour of azoaldolase is irradiation with visible light centered at 450 nm, by using neutral solutions of the protein. Within the photochromic cycle slight differences have been observed in the gel electrophoretic behaviour of the azoprotein.
AN ATTEMPT TO LOCALIZE THE THRESHOLD REACTION IN PHYTOCHROME‐MEDIATED CONTROL OF LIPOXYGENASE SYNTHESIS IN THE MUSTARD SEEDLING
Authors: Oelze‐Karow H. , Mohr H.
Published: January 2008

Abstract—Synthesis* of the enzyme lipoxygenase (LOG)† in the cotyledons of the mustard seedling (Sinapis alba L.) is controlled by phytochrome (Pfr) through a threshold (all‐or‐none) mechanism. The data of the present paper confirm the previous assumption (Oelze‐Karow and Mohr, 1973) that the primary reaction of Pfr (Pfr+ X → PfrX ⇄ PfrX‘) is the site of the highly cooperative threshold reaction. Suppression of LOG synthesis depends on the presence of PfrX’. However, PfrX‘ is only stable above the threshold level of Pfr. If the level of Pfr is below the threshold, PfrX is stable, and no suppression of LOG synthesis occurs. As long as the level of Pfr remains below the threshold, no destruction of Pfr takes place. Destruction of Pfr occurs only as long as [Pfr]†is above the threshold level. Thus the simplest formulation of the actual threshold reaction in the LOG response is PfrX⇄frX’ state at [Pfr] below threshold no Pfr destruction LOG synthesis suppressed state at [Pfr] above threshold Pfr destruction(1kd LOG synthesis unimpaired The reversible threshold reaction is thus an integral part of the “primary reaction” of Pfr occurring at the “matrix” specific for the LOG response. The data and conclusions on the LOG response are consistent with an “open phytochrome‐receptor model” recently advanced by E. Schäfer (1975). The data are not consistent with the concept that a rapid dark reversion (Pfr→Pr) exists in dicotyledonous seedlings and that the degree of Pfr dark reversion strongly depends on the initial photostationary state, φ†, established by a saturating light pulse.
THE ELECTROPHOTOLUMINESCENCE OF CHLOROPLASTS
Authors: Ellenson James L. , Sauer Kenneth
Published: January 2008

Abstract— Delayed light emission emanating from preilluminated chloroplasts can be perturbed with pulsed DC electric fields (200–4000 V cm‐1), The perturbation produces a strong stimulation of chlorophyll luminescence. During the field perturbation the stimulated emission rises to a maximum, typically within 100μs. and then decays. Two kinetic components, R (rapid) and S (slow)†, are distinguished on the basis of their rise and decay times and their field‐dependence. The R component increases exponentially at high fields, decays within 100–300μs during the field pulse and collapses with t1/2= 15 μs at the end of the field pulse. The S component occurs at low fields, exhibits near saturation at 500 V cm‐1, decays with t1/2 about 3 ms during the field pulse, and collapses with t1/2= 38μs at the end of the field pulse. Studies using inhibitors, ionophores, electron donors and electron acceptors associate the R component with ion transport processes. The relation to electron transport associated with Photosystem II is discussed.
PHOTOCHEMICAL PROBES OF BIOMEMBRANE STRUCTURE AND FUNCTION. CYCLOHEXANONE PHOTOCHEMISTRY IN A MODEL SYSTEM
Authors: McDaniel D. M. , Cully D. , Ianno F.
Published: January 2008

Abstract— The photochemical reactions of cyclohexanone have been studied in the system sodium octanoate/1‐decanol/water which is known to form bilayers under the conditions used. Cyclohexanone photochemistry was also studied in aqueous media, 1‐decanol, and decane. The photoproducts from the bilayer system result predominantly from reaction of the carbonyl group of cyclohexanone at the hydroxy methylene group of 1‐decanol. These products include cyclohexanol, decanal, and n‐decyl hexanoate. It is concluded that cyclohexanone in the bilayer system is largely concentrated near the hydroxy methylene group of 1‐decanol.
ROLE OF COMPLEX FORMATION IN THE PHOTOSENSITIZED DEGRADATION OF DNA INDUCED BY N‘‐FORMYLKYNURENINE
Authors: Walrant P. , Santos R. , Charlier M.
Published: January 2008

Abstract— N'‐Formylkynurenine derivatives efficiently bind to DNA or polynucleotides. Homopolynucleotides and DNA display marked differences in the binding process. Association constants are derived which indicate that the oxidized indole ring is more strongly bound to DNA than the unoxidized one. Irradiation of such complexes with wavelengths greater than 320 nm induces pyrimidine dimer formation as well as DNA chain breaks. Complex formation is shown to play an important role in these photosensitized reactions.

The photodynamic action of N'‐formylkynurenine on DNA constituents is negligible at neutral pH but guanine and xanthine derivatives are sensitizable at higher pH. Thymine dimer splitting can occur in aggregated frozen aqueous solutions of N'‐formylkynurenine and thymine dimer but this photosensitized splitting is negligible in liquid solutions at room temperature.
PHOTOOXIDATION OF XANTHOBILIRUBIC ACID IN AQUEOUS SOLUTION: PRODUCT AND MECHANISM STUDIES
Authors: Grunewald J. O. , Walker J. C. , Strope E. R.
Published: January 2008

Abstract— Xanthobilirubic acid, an oxodipyrrylmethene with a chromophore very similar to that of bilirubin, was aerobically irradiated as its sodium salt in borate buffer at pH 8. Two photooxidation products, methylethylmaleimide and 5‐formyl‐2,4‐dimethyl‐1H‐pyrrole‐3‐propanoic acid, were isolated. These products can be rationalized on the basis of either a Type I or a Type II (singlet oxygen) photooxygenation mechanism. The reaction is inhibited by azide, a singlet oxygen quencher, and sensitized by methylene blue. However, both the self‐sensitized and the methylene blue‐sensitized reactions are enhanced, rather than inhibited, by high concentrations of 1,4‐diazabicyclo[2.2.2]octane, another known singlet oxygen quencher. It is therefore proposed that the diazabicyclooctane can also act as an electron donor.

The self‐sensitized photooxidation of xanthobilirubic acid is an autocatalytic reaction. This is supported by the fact that addition of a previously irradiated solution to a freshly‐prepared solution significantly increases the rate of photodegradation. A similar catalyst is formed, but much more slowly, from xanthobilirubic acid in the dark in the presence of oxygen.
CHARGE TRANSFER ACROSS PIGMENTED BILAYER LIPID MEMBRANE AND ITS INTERFACES
Authors: Hong Felix T.
Published: January 2008

Abstract— The technique of forming bilayer lipid membranes (BLM) has made it possible to study photoreactions of pigments in an environment that is much closer to those in photosynthetic and visual membranes. A pigmented BLM system with Mg2+‐porphyrins as membrane‐bound pigments and with ferricyanide and ferrocyanide as the aqueous electron acceptor and donor, respectively, was used to illustrate the photoelectric effects due to coupled interfacial charge transfer reactions.

The steady‐state continuous photoresponse was studied by means of the voltage clamp method and a null current method. The independence of the pigment conductance channel and the ionic conductance channel was demonstrated. A tunable voltage clamp method was used to study the transient pulsed photoresponses. Such a measurement permits us to characterize the photosystem in terms of an equivalent circuit model which contains a novel chemical capacitance. Molecular interpretation of this equivalent circuit model was given.

A microscopic model based on the Gouy–Chapman theory and chemical kinetics calculation leads to an equivalent circuit which is also equivalent to the previous one. Generalization of this microscopic model further leads to a physical mechanism of the generation of the early receptor potential (ERP) in visual membranes. Relevance of pigmented BLM research to photosynthesis and other disciplines was also discussed.
THE SPECTROSCOPY AND PHOTOCHEMISTRY OF ENAMINONITRILES INCLUDING THE SYNTHESIS AND IDENTIFICATION OF CIS‐β‐AMINOACRYLONITRILE
Authors: Hong Jane Huey , Pownall Henry J. , Becker Ralph S.
Published: January 2008

Abstract— The absorption spectral and photochemical properties of β‐aminoacrylonitrile (AAN), β‐aminocrotonitrile (ACN) and three other enaminonitriles have been studied. The synthesis and identification of cis‐β‐aminoacrylonitrile are also included. Each enaminonitrile has one intense absorption band (1–2 × 104M‐1cm‐1) in the 254–273 nm region. Photoisomerization and photocyclization to imidazoles are observed. Imidazole formation is quite strongly inhibited by oxygen and the presence of oxygen can cause wavelength dependent photochemistry, other reactions and destruction of the reactant. The quantum yield of formation of imidazoles is low (<10‐4) for β‐aminoacrylonitrile and β‐aminocrotonitrile and photoisomerization dominates in those four cases where it can occur. Imidazole formation from a dimethylamino compound proves that the presence of H atoms on the amino group is not a prerequisite for photocyclization.
SUBSTRATE DEPENDENCE OF THE ACTION SPECTRUM FOR PHOTOENZYMATIC REPAIR OF DNA
Authors: Rupert Claud S. , To Kathleen
Published: January 2008

Abstract— The absolute action spectrum has been determined for photoenzymatic splitting of cyclobutadipyrimidines (“pyrimidine dimers”) from natural DNA, and from the synthetic polydeoxyribonucleotides poly(dA)·poly(dT) (forming only cyclobutadithymine) and poly(dG)·poly(dC) (forming only cyclobutadicytosine). These action spectra differ strikingly from each other, even when using the same enzyme preparations. On the other hand, the action spectrum for splitting cyclobutadithymine in natural DNA containing “dimers” of only this one type closely resembles the action spectrum for splitting the total mixture of “dimer” types in natural DNA, and is entirely different from the spectrum for splitting of the same photoproduct from poly(dA)·poly(dT). These results mean that the action spectrum is not simply the absorption spectrum of a chromophore carried by the photoreactivating enzyme, nor is it solely determined by the nature of the substrate photoproduct. It is at least partly determined by the over‐all polynueleotide structure (viz. exact helical dimensions, pattern of neighboring bases to the “dimers,” or both), affecting a ground state interaction between the enzyme and substrate in the enzyme‐substrate complex.
THE ULTRAVIOLET DOSE DEPENDENCE OF NON‐MELANOMA SKIN CANCER INCIDENCE
Authors: Green A. E. S. , Findley G. B. , Klenk K. F. , Wilson W. M. , Mo T.
Published: January 2008

Abstract— We correlate annual ultraviolet dose estimates with age specific and age adjusted incidence data for non‐melanoma skin cancer in the United States, United Kingdom, Canada and Australia. We first examine (1) a reciprocity or photographic model in which incidence rates (R) are related to exposure (E) which is the product of age (T) and annual dose (D). We also test several models which violate reciprocity including models identified by the labels: (2) Dose potency; (3) Double cause; (4) Age‐exposure and (5) separable. Our analyses together with the recent National Cancer Institute study favors the age‐exposure model and/or the double cause models. All models lead to biological amplification factors (defined as the ratio of the percent increase in skin cancer incidence due to a 1% increase in dose) greater than unity. For the U.S. we find the biological amplification to be approximately 1.8 for the population center but greater in regions of higher UV annual dose, and less in regions of lower annual UV dose.
INHERITANCE OF PHOTOREACTIVATING ENZYME DEFICIENCIES IN HUMAN CELLS
Authors: Sutherland Betsy M. , Oliver Rowena
Published: January 2008

Abstract— Cells from patients with xeroderma pigmentosum contain lowered levels of photoreactivating enzyme. We have examined the photoreactivating enzyme levels in cells from members of a family with three xeroderma children, one normal child and normal parents; the enzyme levels are consistent with a simple pattern of inheritance in which individuals with the normal enzyme level are PP, those with intermediate levels are PP, and those with very low enzyme levels are pp. We tested this hypothesis by examining enzyme levels in parent‐xeroderma child pairs in which the child possessed very low enzyme levels (pp). In all cases, the parents contained intermediate levels of enzyme (Pp). These results support the hypothesis of a simple pattern of inheritance of photoreactivating enzyme in humans.
BILIRUBIN‐SENSITIZED PHOTOINACTIVATION OF ENZYMES IN THE ISOLATED MEMBRANE OF THE HUMAN ERYTHROCYTE*
Authors: Girotti Albert W.
Published: January 2008

Abstract— Bilirubin has been found to sensitize the photodynamic inactivation of several enzymes in the isolated membrane (ghost) of the human red cell. When ghosts (pH 8.0, 10°C) + bilirubin (0.1 mM) were irradiated with blue light (350 Wm‐2), the activity of glyceraldehyde 3‐phosphate dehydrogenase decayed with t1/2≃ 15 min. No effect was observed in the absence of pigment or with incident yellow light. Diazabicyclo‐octane (DABCO) sharply reduced the inactivation rate, suggesting that 1O2 is involved. Sodium dodecyl sulfate‐gel electrophoresis of ghosts containing fully inactivated glyceraldehyde 3‐phosphate dehydrogenase revealed no change in the polypeptide band corresponding to the subunit of the enzyme. Solubilized enzyme, which was similarly photosensitive, could be partially protected by nicotinamide adenine dinucleotide or glyceraldehyde 3‐phosphate. The integral enzymes Mg2+‐ATPase, Na+, K+‐ATPase, and acetylcholinesterase were also affected. Under the above conditions and bilirubin = 0.37 mM, these enzymes were photoinactivated in first‐order fashion, k≃ 2, 1.2 and 0.2 h‐1, respectively. The rate of decay of total ATPase was found to vary as the square root of the bilirubin concentration over the range 7–370 μM. At a fixed bilirubin concentration (0.37 mM), this rate was also shown to be directly proportional to light intensity. Inasmuch as the —SH content of bilirubin‐containing ghosts diminished during irradiation, oxidation of essential cysteine residues could be responsible for the inactivation of some of the enzymes studied.
PHOTOCONTROL OF PHYTOCHROME DESTRUCTION AND BINDING IN DICOTYLEDONOUS vs MONOCOTYLE‐DONOUS SEEDLINGS. THE INFLUENCE OF WAVELENGTH AND IRRADIANCE
Authors: Schäfer E. , Lassig T.‐U. , Schopfer P.
Published: January 2008

Abstract— The irradiance and wavelength dependence of phytochrome destruction in vivo was analysed in etiolated cotyledons of Cucurbita pepo L. and etiolated seedlings of Amaranthus caudatus L. In contrast to grass seedlings, the rate of Ptot destruction could only be saturated by light sources that establish relatively high Pfr levels (about 50% of total phytochrome, corresponding to the photostationary state established by 693 nm light). To explain the irradiance dependence of Ptot destruction in dicots at irradiances above 0.1 Wm‐2, where the light reaction is at least one order of magnitude faster than Pfr destruction, we suggest there is a fast intercalary dark reaction between photoreaction and destruction. This dark reaction is probably—as in grass seedlings—the binding of Pfr to a receptor site. We conclude that the differences between dicots and grass seedlings with respect to the phytochrome system are of a quantitative rather than a qualitative nature.
MEASURING SUBNANOSECOND FLUORESCENT LIFETIMES USING PHOTON COUNTING
Authors: Wong David K. , Halpern Arthur M.
Published: January 2008

An evaluation is made of a typical time‐correlated single photon counting apparatus using a D2‐filled gated flash lamp. The aim is to determine: (1) the valid flash lamp profile, and (2) the reliability and sensitivity of subnanosecond lifetime measurements. As model systems for very short‐lived fluorescence possessing single exponential decay, concentrated JV‐methylpiperidine (NMP) solutions in n‐hexane were used. Stern‐Volmer self‐quenching kinetics were observed over a concentration range of 0.508 M to 1.00 × 10‐4M. Solutions having known subnanosecond lifetimes were accordingly prepared. The flash lamp profile was altered so that the tail‐portion (time > 3.6 ns after maximum) was reduced by a factor of 0.80. This altered profile provided the best convoluted functions as compared with the observed fluorescence decay curves. For lifetimes less than about 1 ns, the full‐width‐tenth‐maximum values of the convoluted and observed decay functions were used as the criterion for best fit. Using highly concentrated NMP solutions, lifetimes of 0.30, 0.50, and 0.70 ns could be clearly distinguished; a lower limit for reliable measurement is placed at ca 0.2 ns for a flash lamp having a FWHM of 2.6 ns and a 1/e value of 0.8 ns.
OXYGEN‐INDEPENDENT INACTIVATION OF HAEMOPHILUS INFLUENZAE TRANSFORMING DNA BY MONOCHROMATIC RADIATION: ACTION SPECTRUM, EFFECT OF HISTIDINE AND REPAIR*
Authors: Cabrera‐Juárez E. , Setlow J‐ K. , Swenson P. A. , Peak M. J.
Published: January 2008

Abstract— The action spectrum for the oxygen‐independent inactivation of native transforming DNA from Haemophilus influenzae with near‐UV radiation revealed a shoulder beginning at 334 and extending to 460 nm. The presence of 0.2 M histidine during irradiation produced a small increase in inactivation at 254, 290 and 313 nm, a large increase at 334 nm and a decrease in inactivation at 365, 405 and 460 nm. Photoreactivation did not reverse the DNA damage produced at pH 7.0 at 334, 365, 405 and 460 nm, but did reactivate the DNA after irradiation at 254, 290 and 313 nm. The inactivation of DNA irradiated at 254, 290 and 313 nm was considerably greater when the transforming ability was assayed in an excision‐defective mutant compared with the wild type, although DNA irradiated at 334, 365, 405 and 460 nm showed smaller differences. These results suggest that the oxygen‐independent inactivation of H. influenzae DNA at pH 7 by irradiation at 334, 365, 405 and 460 nm is caused by lesions other than pyrimidine dimers.
ON THE DISTRIBUTION OF EXCITATION ENERGY TO TWO PHOTOREACTIONS OF PHOTOSYNTHESIS
Authors: Wang Richard T. , Myers Jack
Published: January 2008

Abstract— From kinetic analysis of the Z‐scheme we have derived expressions for fractions of open reaction centers and throughput quantum yield. The fraction of absorbed quanta available to photoreaction II has been treated by the wavelength dependent function, α. However, for purposes of analysis in terms of throughput electron flow it is necessary to introduce a related function, α', for actual processing of excitations by photoreaction II; α' differs from α if the individual quantum yields of the two photoreactions are not equal. ‘Included in our findings are the following. As a close approximation quantum yield is maximum at α’= 0.5 and a symmetrical function of α' around the line α' =0.5. As previously noted, lowering of the apparent equilibrium constant between the photoreactions flattens dependence of quantum yield on α' near α' = 0.5 but also lowers the attainable quantum yield. For any given equilibrium constant the effective fractions of open reaction centers are equal at α' = 0.5 and mirror images of each other around the line α' = 0.5. Slow changes in quantum yield following changes in wavelength (the State 1‐State 2 phenomenon) are explainable in terms of changes in α' which also have the effect of flattening dependence of quantum yield on wavelength. We have used these changes to estimate the neutral wavelength for α' = 0.5 as 681–682 nm in Chlorella.
ELECTRON TRANSFER FROM PHOTOEXCITED SINGLET AND TRIPLET BACTERIOPHEOPHYTIN
Authors: Holten Dewey , Gouterman Martin , Parson William W. , Windsor Maurice W. , Rockley Mark G.
Published: January 2008

Abstract— Nanosecond and picosecond. kinetic techniques have been used to study electron transfer from the first excited singlet state (Bph*) and the first excited triplet state (BphT) of bacteriopheophytin to p‐benzoquinone. Quenching of the first excited singlet state by 40 mMp‐benzoquinone results in a decrease in the lifetime of Bph* but does not lead directly to the formation of the π‐cation radical (Bph†). In the presence of 8 M methyl iodide and 40 mMp‐benzoquinone together, the singlet lifetime is reduced further; however, the quantum yield of BphT is enhanced due to the increased rate of intersystem crossing between Bph* and BphT. Electron transfer from BphT to p‐benzoquinone leads to the formation and detection of Bph†. The results are discussed in terms of the spin‐selectivity of the reverse electron transfer process within the intermediate charge transfer complexes.
PHOTOELECTROCHEMICAL STUDIES OF SOLVATED ELECTRON INTERACTIONS WITH BIOLOGICAL SYSTEMS
Authors: Baldwin R. P. , Perone S. P.
Published: January 2008

Abstract— An approach employing hydrated electron photoemission from a mercury electrode and potentiostatic chronoamperometric monitoring of the associated electrochemical processes has been applied to the study of the hydrated electron scavenging reactions of simple biological molecules. The current‐voltage profiles of aqueous glutathione and triglycine solutions were measured following flash‐induced photoemission. The redox properties of the products of electron scavenging were characterized by comparison to similar current‐voltage measurements resulting from hydrated electron capture by nitrous oxide. The electrochemical behavior so determined was directly related to the particular scavenging process occurring with each scavenger and agreed generally with previous pulse radiolytic studies made on the same scavenging systems.
REPAIR OF PYRIMIDINE DIMERS IN ULTRAVIOLET‐IRRADIATED CHLAM YDOMONAS
Authors: Small Gary D. , Greimann Carolyn S.
Published: January 2008

Abstract— A UV‐specific endonuclease was used to monitor the presence of UV‐induced pyrimidine dimers in the DNA of Chlamydomonas reinhardi. All of the dimers induced by 50 J/m2 of 254 nm light are removed by a 2 h exposure to photoreactivating light. Nearly all of the dimers are removed by the wild‐type strain of Chlamydomonas upon incubation for 24h in the dark. Two UV‐sensitive mutants, UVS 1 and UVS 6, are deficient in removal of dimers in the dark. These results are interpreted to mean that Chlamydomonas has an excision‐repair pathway for coping with UV‐induced damage.
REPAIR SYNTHESIS IN HUMAN LYMPHOCYTES PROVOKED BY PHOTOLYSIS OF ETHIDIUM AZIDE
Authors: Cantrell Charles E. , Yielding K. Lemone
Published: January 2008

Abstract— The azide analog of ethidium was mixed with human lymphocytes and when photolyzed with visible light provoked repair synthesis as shown by incorporation of tritiated thymidine in the presence of hydroxyurea. The use of photolyzed drug, or incubation of drug‐cell mixtures in the dark was without effect. These experiments should prove useful in targeting drug action sites and in studying the details of DNA repair.
THE PHOTOCONVERSION OF CHENOPODIUM CHLOROPHYLL PROTEIN
Authors: Oku Tatsuo , Tomita Giiti
Published: January 2008

Abstract— Changes in the UV absorption spectrum with the photoconversion of Chenopodium chlorophyll protein, CP668 ⇆ CP743, and with the pH change of the CP668 and CP743 solutions, were measured. The change in the absorption spectrum of the apoprotein caused by the pH change was reversible, whereas that caused by the photoconversion was irreversible. The apoprotein may undergo a proton dissociation or association of the phenolic group in tyrosine residues upon pH change. A photooxidation in CP668 (loss of electron) caused by irradiation of CP668 solution may induce a change in the ionization state of some amino acid residues. The isoelectric points of CP668 and CP743 were determined to be 9.3 and 7.2, respectively.
PHOTOREACTIVATION OF DNA‐CONTAINING CAULIFLOWER MOSAIC VIRUS AND TOBACCO MOSAIC VIRUS RNA ON DATURA
Authors: Towill Leslie , Huang C. W. , Gordon M. P.
Published: January 2008

Abstract— Datura stramonium L. is a local lesion host for TMV‐RNA and DNA‐containing cauliflower mosaic virus (CAMV). Datura can photorepair UV‐damaged TMV‐RNA and CAMV, giving photoreac‐tivation sectors of 0.40 and 0.33, respectively. Dose response curves for photoreactivation of TMV‐RNA and CAMV show that 4540 min of cool white light (15 W.m‐2) is required for maximum photoreactivation. Blue light and near UV are equally effective in photoreactivating UV‐irradiated TMV‐RNA, whereas near UV is initially more effective than blue light for the photorepair of UV‐inactivated CAMV. Higher doses of near UV apparently inactivate the CAMV photorepair system. In the case of CAMV, photoreactivating light must be applied immediately after inoculation with the virus. Two to three hours of incubation in the dark after inoculation results in complete loss of response to photoreactivating irradiation. In contrast, limited photoreactivation of TMV‐RNA occurs even after 4 h of dark incubation after inoculation, although photoreactivating irradiation is most effective when applied immediately after inoculation. Light is required for the maintenance of photoreactivation for both TMV‐RNA and CAMV. Daturas placed in the dark for six days lose their ability to photoreacti‐vate. Recovery of the TMV‐RNA photorepair system is rapid; complete recovery attained with 90 or more min of white light (15 W m‐'). Recovery of CAMV photorepair system is slow; 90% recovery attained after only 20 h of light. However, full recovery can be induced by as little as 6h of light when CAMV is inoculated 24 h after the onset of illumination. These results suggest two photorepair systems are present in Datura.
WAVELENGTH DEPENDENCE OF SINGLET OXYGEN MECHANISM IN ACRIDINE ORANGE‐SENSITIZED PHOTODYNAMIC ACTION IN YEAST CELLS: EXPERIMENTS WITH 470 NM
Authors: Kobayashi Katsumi , Ito Takshi
Published: January 2008

Abstract— The singlet oxygen mechanism was evaluated in terms of acridine orange‐sensitized induction of gene conversion in Saccharomyces at 470 nm and by using a concentration dependent protective action of added N;. The singlet oxygen mechanism accounted for 96% of the total photodynamic efTect. This value is to be contrasted with 76% previously observed for 510 nm illumination.
FLUORESCENCE ANALYSIS ON SOLID SURFACES*
Authors: Guilbault George G.
Published: January 2008

Abstract— One of the recent uses of fluorescence has been in the assay of substances directly on solid surfaces such as paper chromatograms, thin‐layer chromatography (TLC) plates, potassium bromide disks, electrophoresis strips, and silicone‐rubber pads. Chromatography and electrophoresis are widely used analytical techniques and it is not surprising that fluorometric methods are used in conjunction with them. Advantages are increased sensitivity and rapidity of analysis.

In this paper the use of fluorescence in the assay of substances after separation on paper and TLC chromatograms, as well as the direct assay of substances on a solid surface placed directly in a commercial fluorometer, are discussed. Particular emphasis is placed on the direct analysis of enzymatic reactions.
SOLVENT EFFECTS ON THE FLUORESCENT STATES OF INDOLE DERIVATIVES‐DIPOLE MOMENTS
Authors: Sun Ming , Song Pill‐Soon
Published: January 2008

Abstract— Electronic spectra of indoles are very sensitive to solvents. These solvent effects are particularly pronounced in the case of the fluorescence spectra of indoles. In order to elucidate the solvent band shifts during the relaxation of the excited states, particularly in polar solvents, the dipole moments of the excited singlet states have been estimated from the data of solvent‐dependent Stokes shifts. In addition to indole, indole‐5‐carboxylic acid, indole‐3‐carboxylic acid, indole‐2‐carboxylic acid, 5‐cyano‐ and 5‐bromo‐indoles have been investigated. All indoles showed a substantial increase in dipole moment upon excitation to the emitting state. These results are generally consistent with the Pariser‐Parr‐Pople SCF MO calculations.
THE PHOTODYNAMIC IMMOBILIZATION OF ARTEMIA SALINA NAUPLII BY POLYCYCLIC AROMATIC HYDROCARBONS AND ITS RELATIONSHIP TO CARCINOGENIC ACTIVITY
Authors: Morgan David D. , Warshawsky David
Published: January 2008

Abstract— The rates of the photosensitized immobilization of the nauplii of the crustacean Artemia salina were measured as a function of irradiation time and the amount of light absorbed by the sensitizers. The nauplii were incubated in the dark in dilute solutions of the sensitizers for periods of 2 and 22 h prior to irradiation. Nineteen carcinogenic and 22 noncarcinogenic polycyclic aromatic hydrocarbons were used as sensitizers. Relative photodynamic activities (RPA) were determined from the rates of immobilization using benz[c]acridine as a standard (RPA = 1). High RPA was restricted to carcinogenic compounds with 4 and 5 fused rings, compounds with 6 or more fused rings had low RPA regardless of their carcinogenic activities. The correlation of RPA with carcinogenic activity was excellent (P= 0.006 and 0.009 for the 2 and 22 h dark incubations, respectively). It is suggested that carcinogenesis by polycyclic aromatics may result from sublethal photodynamic effects.
THE PHOTOEXCITED TRIPLET STATE OF TETRAPHENYL CHLORIN, MAGNESIUM TETRAPHENYL PORPHYRIN AND WHOLE CELLS OF CHLAMYDOMONAS REINHARDI. A LIGHT MODULATION‐EPR STUDY
Authors: Nissani Edna , Scherz Avigdor , Levanon Haim
Published: January 2008

Abstract— The photoexcited triplet states of frozen solutions of tetraphenyl chlorin (TPC), magnesium tetraphenyl porphyrin (MgTPP) and whole cells of Chlamydomonas reinhardi have been studied by light modulation‐EPR spectroscopy. The porphyrins were chosen to be studied as model compounds for chlorophyll molecules, From EPR spectra the zero field splitting parameters (ZFS) were calculated. For TPC, |D| = 0.0364 ± 0.0002 cm‐1, |E| = 0.0063 ± 0.0002 cm‐1. For MgTPP, |D| = 0.0310 ± 0.0002 cm‐1. For chloroplasts, |D| = 0.0280 ± 0.0004 cm‐1, |E| = 0.0032 ± 0.0004 cm‐1. In all compounds studied, except MgTPP, electron spin polarization (ESP) was observed. From the analysis of the kinetic curves at each canonical orientation we evaluated the spin lattice relaxation rate W, the depopulation rate constants kp, and the ratio between the population rate constants, Ap, at zero magnetic field. For TPC in ethanol‐toluene (5:1) kx= (0.70 ± 0.10) × 103 s‐1, ky= (0.40 ± 0.07) × 103 s‐1, kx= (0.24 ± 0.05) × 103 s‐1; Ax:Ay:Az⋍ 1.0:0.6:0.4; W= (2.60 ± 0.40) × 103 s‐1. For MgTPP, only the total decay rate constant, kT, was calculated: (1.5 ± 0.2) × 10 s‐1 in n‐octane and (4.8 ± 0.8) × 10 s‐1 in ethanol. The results for TPC and MgTPP are compared to those reported previously for chlorophyll. It is concluded that the dynamics of the photoexcited triplet state in chlorophylls are mainly governed by the chlorin macrocycle. From the EPR spectrum and ZFS parameters of chloroplasts, we propose that both chlorophyll a and chlorophyll b are the main constituents of the EPR spectrum. From the analysis of the kinetic curves we obtain separately the kinetic parameters for chlorophylls a and b, kax= (1.30 ± 0.20) × 103 s‐1, kay;= (0.85 ± 0.15) × 103 s‐1kax= (0.32 ± 0.05) × 103 s‐1; Aax:Aay:Aaz⋍ 1.0:0.7:0.2; Wa= (1.20 ± 0.20) × 103 s‐1; kbx= (0.56 ± 0.09) × 103 s‐1, kby= (0.30 ± 0.04) × 103 s‐1, kbz= (0.06 ± 0.01) × 103 s‐1; Abx:Aby:Abx⋍ 1.0:0.6:0.1; Wb= (5.00 ± 0.80) × 103 s‐1. These results are very close to those found separately for chlorophyll a and chlorophyll b oligomers in vitro.
ACTION SPECTRA FOR PHOTOREACTIONS I AND II OF PHOTOSYNTHESIS IN THE BLUE‐GREEN ALGA ANACYSTIS NIDULANS
Authors: Wang Richard T. , Stevens C. L. R. , Myers Jack
Published: January 2008

Abstract— Action spectra for photoreactions I and II of photosynthesis were obtained for Anacystis nidulans and three of its variants which had altered chlorophyll/phycocyanin ratios. The spectra are properly scaled to each other. They provide information on contributions of phycocyanin and chlorophyll to initial absorption and final distribution of excitation energy to reaction centers I and II. In normally pigmented cells the light harvesting pigments for photoreaction I include about 40% of the phycocyanin and 84% of the chlorophyll. Both in normal cells and in cells with altered pigmentation excitation energy from phycocyanin is delivered to photoreaction II via a small number of chlorophylls. In response to alterations in chlorophyll/phycocyanin ratio Action I spectra showed large variations whereas Action II spectra were essentially invariant. The result is taken to mean that alteration in chlorophyll components in Anacystis is attended by a special restriction: there are only small changes in amount of chlorophyll accessible to photoreaction II in the face of large changes in amount committed to photoreaction I.
QUENCHING OF OXONINE EXCITED STATES BY EDTA VIA ELECTRON TRANSFER AND DEACTIVATION PROCESSES. A COMPARATIVE STUDY OF EXCITED SINGLET AND TRIPLET STATE REACTIVITY
Authors: Bonneau Roland
Published: January 2008

The quenching of excited singlet oxonine by EDTA in aqueous solution leads mainly to deactivation of the dye to the ground state and, to a lesser extent, to electron abstraction. The rate constants for these processes have been measured and compared to those for the same reactions involving the oxonine triplet state. The rate constant of electron abstraction is about ten times greater via the singlet state than via the triplet state. However, the rate constant of deactivation to the ground state is 103‐104 times greater for the excited singlet state than for the triplet state, so that the efficiency of electron transfer is much smaller for the singlet state.
ULTRAVIOLET MICRO‐IRRADIATION ON LOCALIZED AREAS OF THE CELL NUCLEUS: EFFECTS ON RNA SYNTHESIS
Authors: Moreno G. , Nocentini S. , Salet C.
Published: January 2008

Abstract— …Ultraviolet (UV) micro‐irradiation of the cell nucleus was used to study RNA synthesis. CV‐1 cells in culture were irradiated in the nucleoplasm in an area of 5 µm in diameter, with UV doses of the order of 10 and 102 Jm‐2 at 254 nm and pulsed with 3H‐uridine (3HU) 1 h and 24h after irradiation. Parallel cultures were irradiated under the same conditions and labeled with 3H‐thymidine (3HTdR) to measure unscheduled DNA synthesis (UDS).

For the two incident doses used, 1h after irradiation, RNA synthesis was decreased over the whole nucleus by 50% compared to unirradiated control cells. Moreover, for irradiation with 102 Jm‐2, 3HU uptake was completely inhibited in the irradiated spot; UDS occurred only in the irradiated area. At 24h after irradiation, 3HU uptake occurred over the whole nucleus in the same amount as in non‐irradiated cells. At this time, UDS was undetectable. These studies indicate the occurrence of a repair process leading to a recovery of the function of transcription, and suggest the role of pyrimidine dimers in the inhibition of RNA synthesis.
FLUORESCENCE SPECTRA AND ZERO‐FIELD MAGNETIC RESONANCE OF CHLOROPHYLL a‐WATER COMPLEXES
Authors: Kooyman R. P. H. , Schaafsma Tjeerd J. , Kleibeuker Joop F.
Published: January 2008

Abstract. –Fluorescence detected magnetic resonance (FDMR) and fluorimetry have been used to study chlorophyll‐water complexes at T= 4.2 K. By combining these methods, zero‐field splitting (ZFS)‐parameters can be assigned to the triplet state of the various species. It is found that these parameters decrease upon aggregation and/or complexation. These results can be rationalized by using a simple free‐electron model for chlorophyll including excitonic interaction. Evidence is presented favouring a structure recently proposed by Shipman and Katz for a chlorophyll‐dimer involving hydrogen‐bonded water, present in non‐polar solutions at low temperature with spectral properties similar to those of chlorophyll in vivo.
MAGNESIUM ION EFFECTS ON CHLOROPLAST PHOTOSYSTEM II FLUORESCENCE AND PHOTOCHEMISTRY
Authors: Henkin Bruce M. , Sauer Kenneth
Published: January 2008

Abstract. –Although there have been several reports that divalent cations, especially Mg2+, can significantly affect chloroplast photoprocesses, the molecular mechanism of cation interaction is not well understood. We have investigated the interaction of Mg2+with Photosystem II photoprocesses by studying cation effects on chloroplast fluorescence and the Hill reaction. Our results are summarized as follows.

1. Mg2+stimulation of background fluorescence (20–30%) saturates at about 0.5 mM Mg2+, while Mg2+stimulation of variable fluorescence (250%) saturates at about 2.5 mM Mg2+.

2. Addition of Mg2+to chloroplasts treated with 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea or dithionite causes a doubling in the amount of total (background + variable) fluorescence.

3. Studies on chloroplasts in the presence of 2,6‐dichlorophenolindophenol indicate that Mg2doubles the relative yield of variable fluorescence under light‐limiting conditions.

4. Mg2causes large (70–120%) increases in the light‐limited rate of the DCIP Hill reaction.

We interpret these results in terms of a model involving two components of chloroplast emission. Our analysis indicates that Mg2+increases the effective absorption cross section (size) of the pigment array associated with Photosystem II photochemistry.
ACID DEPENDENT FLUORESCENCE QUANTUM YIELD AND TETRAMETHYL‐ 1,2‐DIOXETANE CHEMI‐ENERGIZED FLUORESCENCE OF ERGOSTATETRAENONE*
Authors: Adam Waldemar , Cilento Guiseppe , Rodriguez Luis O. , Rodriguez Osvaldo , Sarma Aluru S. , Zinner Klaus
Published: January 2008

Abstract. –In acidified acetonitrile, ergostatetraenone (E) efficiently quenches the tetramethyl‐1,2‐dioxetane (TMD) chemiluminescence at 410 nm, with the appearance of a new chemiluminescence at ca. 530 nm due to ergostatetraenone fluorescence. Control experiments exclude energization by triplet acetone and the trivial process (emission and reabsorption), establishing singlet‐singlet energy transfer between excited singlet acetone (A) and ground state ergostatetraenone as major pathway. From the kinetics the rate constant for singlet‐singlet energy transfer (KssA,1,) was estimated to be ca. 101 2S‐1. The chemiluminescence yield (φCL) for the TMD/ergostatetraenone system was determined to be ca. 12 × 10‐8. The fluorescence efficiency of ergostatetraenone (φ) in acidified acetonitrile is a function of acid concentration, ranging between 0.06‐0.82. The efficiency of singlet acetone production (α) was found to be 500‐fold lower than in neutral medium due to a competing acid‐catalysed, dark decomposition of TMD. A 60‐fold light enhancement has been established for this binary chemiluminescent system.
SYNERGISTIC INTERACTION BETWEEN THE TRYPTOPHAN PHOTOPRODUCTS AND NEAR‐ULTRAVIOLET LIGHT IN AMOEBA
Authors: Bhattacharjee S. K. , Chatterjee S.
Published: January 2008

Abstract. Both S‐ and G2‐phase cells of amoeba are found to be sensitized by coirradiation of cells with Tryptophan (Trp). At a fluence of 1.5 times 105 Jm‐2 to which G2 phase cells are resistant, they show a drastic (8‐fold) increase in sensitivity when irradiated in 0.5% Trp solution. Freshly irradiated Trp solution is found to be lethal to G2 cells that have received a sublethal fluence of near‐UV light. Irradiated Trp, however, does not kill unirradiated amoeba.

Nuclear transplantation experiments have shown that the lethality of cells when coirradiated with Trp is due to damage located predominantly in the cytoplasm. It is suggested that sublethal fluence of near‐UV light makes the cells “leaky” to the toxic photooxidation products of Trp solution.
THE WAVELENGTH DEPENDENCE OF ULTRAVIOLET INACTIVATION OF HOST CAPACITY IN A MAMMALIAN CELL‐VIRUS SYSTEM
Authors: Coohill Thomas P. , Moore Sharon P. , Drake Stephanie
Published: January 2008

Abstract. The ability of UV‐irradiated African green monkey kidney cells (CV‐1) to support the growth of unirradiated herpes simplex virus type 1 as measured by plaque forming ability has been investigated. The lowering of plaque formation by the virus when the host cell was irradiated was examined at thirteen different wavelengths. An action spectrum for this cellular parameter (capacity) was obtained in the wavelength region of 235–302 nm. This action spectrum points to nucleic acid as the critical target molecule for this effect.
ULTRAVIOLET SENSITIVITY OF VIBRIO PARAH AEMOLYTICUS, A CAUSATIVE BACTERIUM OF FOOD POISONING
Authors: Nozu Keiichi , Ohnishi Takeo
Published: January 2008

Abstract. A pathogenic strain of Vibrio parahaemolyticus, strain WP1, is about 5 times more sensitive to killing by ultraviolet light than is the non‐pathogenic strain WP28, but WP1 cells have an efficient liquid‐holding recovery. The cellular DNA of both strains is fragmented shortly after ultraviolet irradiation, but the fragmented DNA is converted in a short time to the initial large molecular size in WP28 cells. In WP1 cells, however, the DNA molecules were degraded rapidly without any apparent rejoining in a growth condition. Post‐irradiation liquid‐holding made the DNA of WP1 cells stable, as supported by the recovery of DNA synthetic activity in these cells.