bluuebunny/crossref_metadata_2025 huggingface dataset:
PHOTOSYNTHETIC ACTIVITY AND CHLOROPHYLL ABSORPTION SPECTRA OF FRACTIONS FROM THE ALGA, DUNALIELLA*
Authors: Brown J. S. , Gasanov R.
Published: January 2008

Abstract— Dunaliella chloroplasts were fractionated according to C. Arntzen et al, Biochim. Biophys. Acta256, 85–107, 1972. The initial French‐press treatment and differential centrifugation produced Fraction 1 (Fr 1) enriched in photosystem I activity and a heavier Fraction 2 (Fr 2). When Fr 2 was treated with digitonin followed by either gradient or differential centrifugation, two more fractions were recovered: Fr 1 g with a photosystem 1 activity similar to that of Fr 1, and Fr 2 g with very low photosystem II activity.

Photosystem II activity was considerably lower in these Dunaliella chloroplasts and fractions than in spinach particles measured under the same conditions, but the relative activities between the fractions were similar to those for spinach. Fr 2 always had greater photosystem II activity than Fr 1, but the digitonin fractions were low and similar in photosystem II activity.

Photosystem II activity was measured as the reduction of 2, 6–dichlorophenol indophenol (DCIP) with H2O, diphenylcarbazide (DPC) or Mn2+ as electron donor. The results indicated that exogenous manganous ion competed with H2O as an electron donor to photosystem II in broken chloroplasts initially, but after 10–15 s of illumination, the Mn3+ formed began to reoxidize DCIP and a cyclic reaction ensued. DPC and Mn2+ appeared to react at different sites.

Computer‐assisted curve analysis of the absorption spectrum of each fraction revealed four major component curves representing the absorbing forms of chlorophyll a at 663, 670, 679 and 684 nm seen in numerous other in vivo chlorophyll spectra (C. S. French et al., Plant Physiol.49, 421–429, 1972). However, Fr 2g had approx. 20 percent more of Ca663 and Ca670 and 10% more absorption by chl b than Fr 1 which correlated with the difference in photosystem II activity. On the long wavelength side, Fr 2 g had no Ca694 and almost no photosystem I activity.

The results are not sufficient to answer the question of whether the photosystem I particle obtained from the original homogenate is significantly similar to or different from the corresponding fraction obtained from Fr 2 with digitonin.
TRANSFER OF PYRIMIDINE DIMERS DURING BACTERIAL CONJUGATION
Authors: Riazuddin S. , Muhammed Amir
Published: January 2008

When male strains of Escherichia coli are irradiated with 254 nm ultraviolet (UV) light and mated with suitable females, DNA is transferred at almost the normal frequency (Howard‐Flanders et al., 1968). Cole (1971) observed that an episome damaged by UV irradiation of the male parent could be transferred to a recipient and restored to activity by administering photoreactivating light. He therefore deduced that UV lesions are transferred to the recipients during bacterial conjugation. The object of this Research Note is to report experiments providing direct evidence of the transfer of pyrimidine dimers ‐the main lesions of UV irradiation.
IN VITRO PHOTOREACTIVATION OF ULTRAVIOLET‐INACTIVATED RIBONUCLEIC ACID FROM TOBACCO MOSAIC VIRUS
Authors: Hurter Jakob , Gordon Milton P. , Kirwan James P. , McLaren A. Douglas
Published: January 2008

Abstract— Treatment of ultraviolet‐inactivated tobacco mosaic virus ribonucleic acid (TMV–RNA) with extracts obtained from the local lesion host, Nicotiana tabacum var. Xanthi, n.c., and simultaneous illumination at 365 nm results in up to a four‐fold increase in infectivity over non‐illuminated controls. The active material in the extract appears to be associated with protein, based on its inactivation by boiling, precipitation with ammonium sulfate, and exclusion from Bio‐Rad P100 polyacrylamide. Partially purified DNA photoreactivating enzyme from yeast or pinto bean has no activity on ultraviolet‐irradiated TMV–RNA.
PHOTOREGULATION OF POLYMER CONFORMATION BY PHOTOCHROMIC MOIETIES–II. CATIONIC AND NEUTRAL MOIETIES ON AN ANIONIC POLYMER*
Authors: Veen G. van der , Hoguet R. , Prins W.
Published: January 2008

Abstract— Photoregulation of the conformation of poly (methacrylic acid) (PMA) in the range 4·5 < pH > 6·5 has been achieved by means of the cationic photochromic ligand, p‐phenyl‐azophenyl trimethyl ammonium iodide (PTA), as well as by means of copolymerization of methacrylic acid (MA) with the neutral photochromic co‐monomer, p‐phenyl azomethacrylanilid (PM). At degrees of ionization α, corresponding to the conformational unfolding of PMA, the pKapp is 0·2 units higher when the ligand PTA is trans than when PTA is in the photostationary 80%“cis” state. Equilibrium dialysis shows that the binding of PTA is independent of the cis/trans ratio at high α (after the conformational unfolding), but at lower αtrans‐PTA binds positively and cis‐PTA negatively. In the transition region, the presence of non‐polar trans‐azo ligand is therefore held responsible for a shift of the conformational equilibrium toward the more compact, folded form, which is harder to ionize than the unfolded form. Because of the relation pKapp# pH + log [(1 –α)/α], the degree of ionization of PMA, and thus the polymer conformation, as reflected in the reduced viscosity, can be photochemically regulated in pH buffers. At pH # 5·5 (α# 0·20) a maximal relative shift of Δα/α= 20 per cent was found, with a corresponding relative shift in reduced viscosity of 20·5 per cent. In the photochromic copolymer a pKapp switch of similar magnitude was found. In this case the azo‐moiety is permanently affixed to the PMA so that the photosensitivity of the pKapp in the range of the conformational unfolding is due to a shift in the conformational equilibrium induced by the presence of non‐polar trans‐azo and polar “cis” azo, respectively. In both cases only about 1 photochromic moiety per 100 monomer units is capable of appreciably shifting the conformational manifold of PMA and/or the degree of ionization in constant pH buffers, provided one stays close to the unfolding transition. Mention is made of the implications for photoregulation of the permeability of, and the potential across. model membranes made of photochromic PMA molecules.
CAROTENOID CHROMOPHORE LENGTH AND PROTECTION AGAINST PHOTOSENSITIZATION
Authors: Mathews‐Roth Micheline M. , Wilson Thérèse , Fujimori Eiji , Krinsky Norman I.
Published: January 2008

Abstract— Carotenoid pigments were extracted and purified from wild‐type and mutants 7 and 93a of Sarcina lutea, and tested for their ability to quench 1O2. The wild‐type pigment (P‐438, 9 conjugated double bonds) is as active in quenching 1O2 as is β‐carotene. On the other hand, the pigment P‐422 (8 conjugated double bonds) from mutant 7 is 2 or 3 times less efficient, whereas phytofluene and phytoene from S. lutea are 100 and 1000 times less efficient, respectively, than is β‐carotene at quenching 1O2. It was also found that the broad EPR signal, induced by light in benzene solutions of chlorophyll a and hydroquinone, and related to chlorophyll oxidation, is efficiently quenched by P‐438 and to a much smaller extent also by Sarcina phytoene.
THE FORMATION OF PHOTOREVERSIBLE CYCLOBUTANE‐TYPE PYRIMIDINE DIMERS IN ULTRAVIOLET‐IRRADIATED POTATO VIRUS X*
Authors: Huang C. W. , Gordon Milton P.
Published: January 2008

Abstract— Photoreversible cyclobutane‐type pyrimidine dimers were found in 32P‐labeled RN A isolated from intact potato virus X irradiated with 254 nm light. The number of dimers was correlated with the biological infectivity of the ultraviolet‐treated virus. Assuming that incorporated 32P is homogeneously distributed in the viral RNA chain, it can be calculated that about 5·7±1·7 dimers are present in each strand of virus per lethal biological hit.
EFFECTS OF SIMULATED SPACE ULTRAVIOLET AND VISIBLE RADIATION UPON DRY CYSTS OF COLPODA INFLATA
Authors: Giese Arthur C. , Rushbrook Peter
Published: January 2008

Abstract— Dry cysts of Colpoda inflata were irradiated with an argon plasma arc lamp, the output of which simulates space radiation in its wavelength distribution although it is of higher intensity. Rapid evacuation reduced the rate of excystment as well as the percentage excysting; low temperature (near that of liquid nitrogen) had little effect on either measurement. All cysts were therefore irradiated at room temperature in a cell flushed with dry nitrogen. Radiation passed for 1 min through a sapphire filter, with a cutoff at 145 nm, prevented excystment. At smaller doses progressively less damaging effects were observed as judged by both the increase in time required for excystment and the percentage excysted. No dark recovery was observed in dry cysts. Exposure of cysts to radiation passed through a series of filters which progressively remove short ultraviolet wavelengths indicate that it is mainly the quartz‐transmitted wavelengths (cutoff 185 nm) which damage the cysts. The presumption is that most of the vacuum‐ultraviolet wavelengths are superficially absorbed; their lesser effect is also partially attributable to their lower intensity. Inasmuch as 1 min of argon lamp radiation is equivalent to 24 min in space, it is evident that Colpoda cysts would not long survive a journey in space, had they reached there in viable condition.
ELECTRON PARAMAGNETIC RESONANCE OF SOME TRIPHENYLMETHANE DYES IN THE TRIPLET STATE
Authors: Leaver I. H.
Published: January 2008

Abstract— Electron paramagnetic resonance spectra of the triplet states of several triphenylmethane dyes in glassy solutions at 90 K have been measured and their zero‐field splitting parameters estimated. Crystal violet and para rosaniline do not possess trigonal symmetry in their triplet states, and the unusually broad absorptions in the ΔM8= 1 region of the spectra have been attributed to the presence of different rotational isomers of the dye cations. A number of malachite green derivatives were investigated, but absorption of the triplet states of these dyes was only observed in the low field ΔM8= 2 region of the spectrum.
NEAR‐ULTRAVIOLET MODIFICATION OF ESCHERICHIA COLI B UBIQUINONE IN VIVO AND IN VITRO*
Authors: Werbin Harold , Lakchaura Bala D. , Jagger John
Published: January 2008

Abstract— Ubiquinone Q‐8 in Escherichia coli B was labeled by growing the bacteria in a synthetic growth medium containing p‐hydroxybenzoic acid‐ 14C(U). The cells were then irradiated with light of wavelengths 313, 334, 366, and 405 nm, and Q‐8‐ 14C was extracted and assayed. Q‐8‐ 14C was also isolated from unirradiated bacteria, partially purified, and then irradiated similarly in hexane and assayed. Ubiquinone in the cells was four to eight times as resistant to radiation as ubiquinone in hexane. From 313 to 366 nm, the in vivo and in vitro action spectra were similar to each other and to the absorption spectra of synthetic Q‐8 dissolved in hexane or ethanol, but at 405 nm the action spectra deviated from the absorption spectra. Quantum yields for the modification (loss) of ubiquinone in hexane decreased from 0·021. at 313 nm to 0·005 at 405 nm.

The chromenol of Q‐8 was not detected in labeled cells irradiated at 334 nm, but several more‐polar photoproducts were separated by thin‐layer chromatography.
SOME PROBLEMS IN THE ABSOLUTE MEASUREMENT OF GERMICIDAL ULTRAVIOLET RADIATION: THE USE OF ‘PEN RAY’ LAMPS AS A CALIBRATION STANDARD
Authors: Věchet B.
Published: January 2008

Abstract— Problems of absolute measurement of the dose rate of ultraviolet radiation of germicidal lamps in energetic units were studied. Irradiance at 254 nm generated by three different Pen Ray SC‐1 low‐pressure mercury lamps was measured independently in different laboratories using different instruments: (a) Westinghouse SM‐600 Meter, (b) General Electric Germicidal Meter, and (c) large‐surface thermopile with a Bäckström filter. These lamps were then used as secondary standards of absolute irradiance at wavelength 254 nm and compared with the Latarjet dosimeter and the International Light IL‐254 Germicidal Photometer. Mutual agreement of calibration coefficients of three calibrated Pen Ray SC‐1 lamps was roughly within ±5 per cent error. This calibration uncertainty indicates limits of the usefulness of Pen Ray lamps as standards. A direct radiometric calibration using an FT‐16 Schwarz‐Hilger vacuum thermopile, with interference filter NB‐254 or UVR‐250, was in agreement with the above comparison. On the basis of above radiometric calibration absolute D37 lethal doses were determined equaling 2·7. J/m2 for the bacteriophage T2 and 11·0 J/m2 for the bacteriophage φX‐174, the values being read from exponential survival curves.
FLUORESCENCE CHARACTERISTICS OF INDOLES IN NON‐POLAR SOLVENTS: LIFETIMES, QUANTUM YIELDS AND POLARIZATION SPECTRA
Authors: Andrews Leonard J. , Forster Leslie S.
Published: January 2008

Abstract— Fluorescence lifetimes, quantum yields and polarization spectra were measured for indole, 3‐methylindole and 2,3‐dimethylindole in non‐polar solvents. The results indicate simultaneous emission from thermally equilibrated 1La and 1Lb levels, with 1La→1A dominating the 2,3‐dimethylindole emission, and 1Lb→1A dominating the indole emission. These results are consistent with previous assignments of the 0‐0 transitions in absorption for these compounds. Radiative rates are: 1La→1A, 2·0 × 108 S‐1 and 1Lb→1A. 0·62 → 108 S‐1. In addition, the temperature dependence of the excitation and emission spectra are presented, which show that aggregation occurs with these indoles in hydrocarbons below approximately ‐ 110°C. Possible applications to tryptophyl emission in the hydrophobic interiors of proteins are briefly discussed.
QUENCHING OF TRYPTOPHYL FLUORESCENCE IN PROTEINS BY N‘‐METHYLNICOTINAMIDE CHLORIDE*
Authors: Holmes L. G. , Robbins F. M.
Published: January 2008

Abstract— N‘‐methylnicotinamide chloride has been investigated as a quencher of the intrinsic fluorescence of tryptophyl residues in proteins. Quenching of the tryptophyl fluorescence (excitation at 305 nm) of model compounds and a select group of proteins provide evidence for a mechanism that follows the classical Stern‐Volmer relation. The apparent number of exposed tryptophyl residues was obtained in 6M guanidine hydrochloride and aqueous solution at constant pH. Evidence that quenching occurs predominantly by a collisional mechanism was obtained by comparing the equilibrium constant of the non‐fluorescent static state with the much larger quenching constant of the excited state.
SOME PROPERTIES OF PHOTOTRANSFORMATION OF RYE PHYTOCHROME IN VITRO
Authors: Gardner G. , Briggs W. R.
Published: January 2008

Abstract— Much of the experimental data in the phytochrome literature has been obtained using a small‐molecular‐weight protein fragment. Hence, several properties of phototransformation were re‐examined using large‐molecular‐weight rye phytochrome. The kinetics of phototransformation are first‐order, both for the conversion of Pr to Pfr and for the reverse reaction. The quantum yield of phototransformation was found to be 0·28 mol Einstein‐1 for the conversion of Pr to Pfr and 0·20 mol Einstein‐1 for the conversion of Pfr to Pr. Intermediates in phototransformation were measured by cycling the pigment with high‐intensity mixed red and far–red light. The difference spectrum of these intermediates between 367 and 575 nm was found to be similar to that previously reported for oat and pea phytochrome. Analysis of intermediate decay indicated complex kinetics and not a single first‐order species. Transient absorbancy changes in the blue region of the spectrum upon actinic illumination could be attributed to differential rates of initial bleaching of the two forms of the pigment and a consequent alteration in the proportion of the two forms in the mixture until photostationary equilibrium is re‐established.
N‐FORMYL‐KYNURENINE, A TRYPTOPHAN PHOTOOXIDATION PRODUCT, AS A PHOTODYNAMIC SENSITIZER
Authors: Walrant P. , Santus R.
Published: January 2008

Abstract— Photodynamic properties of a tryptophan ultraviolet‐photooxidation product, N‐formylkynurenine, were investigated with amino acids and nucleotides as substrates. Steady‐state kinetic studies are presented as a function of sensitizer, substrate, oxygen concentration and pH. Involvement of singlet oxygen has been suggested for the sensitized oxidation of histidine and tryptophan. For the latter, 02‐ is suggested as a supplementary oxidizing species. Lifetime computations from kinetic and quenching experiments suggest that sensitization occurs via the N‐formyl‐kynurenine triplet state. The importance of the photodynamic properties of N‐formyl‐kynurenine in protein and DNA photochemistry is discussed.

Les propriétés photodynamiques d'un produit de photooxydation ultraviolette du tryptophane, la N‐formyl‐cynurénine, ont étéétudiées vis‐à‐vis d'acides aminés et de nucléotides tenant lieu de substrats. La cinétique de l'action photodynamique a étéétudiée en fonction des concentrations en sensibilisateur, en substrat et en oxygène, et en fonction du pH. La participation de l'oxygène singulet a été mise en évidence dans l'oxydation sensibilisée de l'histidine et du tryptophane. Pour ce dernier, nous suggérons l'intervention de O2‐ comme agent oxydant supplémentaire. A partir d'expériences cinétiques et d'extinction, le calcul du temps de vie de l'état excite du sensibilisateur initiant la réaction suggère que ce dernier est l'état triplet. L'importance des proprifétés photodynamiques de la N‐formyl‐cynurénine dans la photochimie des protéines et de l'ADN est discutée.
PHOTOOXIDATION OF LANTHANIDE ION‐LYSOZYME COMPLEXES. A NEW APPROACH TO THE EVALUATION OF INTRAMOLECULAR DISTANCES IN PROTEINS
Authors: Jori Giulio , Folin Marcella , Gennari Giorgio , Galiazzo Guido , Buso Orfeo
Published: January 2008

Abstract— Rare‐earth metal ions give 1:1 complexes with hen's egg‐white lysozyme. Spectroscopic and enzymic activity measurements suggest that the binding site consists of the side chains of glutamic‐35 and aspartic‐52. The spatial conformation of these complexes is practically identical to that of native lysozyme, especially as concerns the environment of the tryptophyl side chains. Irradiation of La3+‐lysozyme by visible light, in the presence of proflavine as photosensitizer, causes the oxidative modification of all the tryptophyl and methionyl residues at almost the same rate as in uncomplexed protein. On the other hand, when lanthanide ions with nonvanishing magnetic moments were coordinated with lysozyme, at least some tryptophans and methionines were protected from photooxidative attack. The distance of the protected residues from the coordination site increased with increasing magnetic moment of the bound metal ion, which suggests that inhibition of the photoprocess was mainly due to perturbation of the lifetime of the electronically excited intermediate species. On the basis of the atomic coordinates of lysozyme in the crystal state, it is thus possible to define a “quenching radius” for the various lanthanide ions; these radii could in turn be used to evaluate intramolecular distances in proteins of unknown tertiary structure, by identifying the amino acid residues that are protected or photooxidized upon irradiation of complexes between the given protein and several different lanthanide ions. Our studieson lysozyme allow us to define five radii of protection, ranging from 6·7 Å for Sm3+ to over 17 Å for Dy3+, Ho3+, Er3+ and Tb3+. Therefore, this technique opens the possibility of mapping appreciably large regions of a protein molecule.
ON THE PHOTORECEPTOR PIGMENT FOR PHOTOTROPISM AND PHOTOTAXIS: IS A CAROTENOID THE MOST LIKELY CANDIDATE?*
Authors: Song Pill‐Soon , Moore Thomas A.
Published: January 2008

Abstract— The absorption spectrum of lycopene can be altered to show significant absorption in the 350–360 nm region in an ethanol‐water mixture, thus resembling the phototropic action spectrum of Avena coleoptiles. The hypochromicity (bleaching) of the main absorption band and appearance of the new band at 350–360 nm can be attributed to exciton interactions between two stacked lycopene molecules. β‐Carotene does not show anomalous bleaching under identical conditions. Thus, the apparent modification of the absorption spectra of carotenoids in ethanol‐water mixtures cannot be used as an argument to resolve the action spectrum in terms of carotenoids. In addition, we have critically reviewed the spectroscopic characteristics of carotenoids. Short lifetimes of the excited singlet states and inefficient intersystem crossing of carotenoids are not compatible with the suggestion that carotenoids are the most likely candidate for the photoreceptor pigment in phototropism.
A SPECTROPHOTOFLUOROMETER FOR MEASURING VERY WEAK FLUORESCENCES FROM BIOLOGICAL MOLECULES
Authors: Vigny P. , Duquesne M.
Published: January 2008

Abstract—A spectrophotometer using the photon‐counting method is described. The sample cuvette is mounted on a table which can be displaced in the X and Y directions, permitting investigation of absorption and self‐absorption processes within the cuvette. Fluorescence detection is performed at right angles to the direction of the exciting beam, the analysis grating being driven by a stepping motor. The apparent spectrum is fed into a multichannel analyser and printed. Corrections are made to the data provided by the printer. Signal‐to‐noise ratio, fluorescence spectra and fluorescence excitation spectra are discussed in more detail for the case of more concentrated solutions. This very high sensitivity device allows room‐temperature investigation of the fluorescent emission from neutral aqueous solutions of nucleic acid bases, nucleosides, nucleotides, dinucleotides etc., quantum yields for these molecules being of the order of 10‐4. A table of minimum concentration values of some commonly used fluorescent probes is given.
MECHANISM OF FORMATION OF FORMALDEHYDE IN THE FLASH PHOTOLYSIS OF METHYL FORMATE
Authors: Krishnamachari S. L. N. G.
Published: January 2008

Abstract—From flash photolyses of methyl formate (HCOOCH3), d‐methyl formate (DCOOCH3), methyl formate‐d3 (HCOOCD3) and fully ***deuterated methyl formate (DCOOCD3) in the vapour phase at room temperature, the relative efficiencies of the formyl and methoxyl radicals in producing formaldehyde have been determined.
ULTRAVIOLET‐INDUCED REACTIONS OF THYMINE AND URACIL IN THE PRESENCE OF CYSTEINE
Authors: Fisher G. J. , Varghese A. J. , Johns H. E.
Published: January 2008

Abstract—Ultraviolet‐radiation photolysis of thymine in the presence of cysteine gives rise to four isomeric dimers, dihydrothymine, and at least five cysteine addition products. Similar reactions occur for uracil but the products have not all been characterized in detail. The addition reactions arise from the triplet state of the pyrimidine. The initial step is production of a hydropyrimidine radical, which then reacts with cysteine to give the addition products. The triplet is quenched by cysteine with a rate constant of about 2 times 108 M‐1 s‐1 for thymine and 2–9 times 108 for uracil. The total yield of products gives a lower‐limit estimate of the triplet yield and hence of the intersystem‐crossing efficiency. These studies, combined with earlier determinations of dimer yields, show that 93% of the thymine triplets which interact with another thymine molecule are quenched without forming stable dimers. For uracil, the corresponding figure is 75%.
EFFECT OF BASE SEQUENCE ON THE ULTRAVIOLET IRRADIATION PRODUCTS OF DOUBLE‐STRANDED POLYNUCLEOTIDES CONTAINING BROMOURACIL AND ADENINE
Authors: Ehrlich Melanie , Riley Monica
Published: January 2008

Abstract—The effects of ultraviolet irradiation of double‐stranded synthetic polynucleotides containing BrU and A have been investigated. Homopolymer pairs and alternating copolymers composed of either ribo‐ or deoxyribo‐nucleotides were prepared and were irradiated with either 313 nm or ˜ 285 nm light. Strand separation and a modest amount of strand breakage followed irradiation of the homopolymer pairs. Changes in the ultraviolet absorption spectra of the polymers during irradiation reflected the sum of hyperchromic increases caused by progressive strand separation and loss of absorbance caused by photoproduct formation. Extensive debromination occurred. An RNase digest of irradiated poly(rA)–poly14C(rBrU), analysed by column chromatography, showed components similar to those found previously upon irradiation of single‐stranded poly(rBrU). Little photoproduct was released by RNase digestion as mononucleotides. The major photoproduct was in the dinucleotide fraction, and may be 5,5′‐diuracil. Base sequence had a profound effect on the sensitivity of the polynucleotides. Irradiation of alternating copolymers with doses of light comparable to those that produced major photochemical changes in the homopolymer pairs brought about little if any change in the copolymers of alternating base sequence.
INTERACTION OF VIOLOGEN DYES WITH CHROMATOPHORES AND REACTION‐CENTER PREPARATIONS FROM RHODOSPIRILLUM RUBRUM
Authors: Govindjee Rajni , Smith William R. , Govindjee
Published: January 2008

Abstract—Various low‐potential viologen dyes enhance light‐induced absorption changes in the near‐infrared region (ΔA870) in chromatophore preparations from Rhodospirillum rubrum in the presence of dichlorophenol indophenol and a high concentration of ascorbate (DCPIP + asc). An increase in ΔA870 was also observed in large reaction‐center preparations from R. rubrum with viologens in the presence of ascorbate. Our results indicate that E'0, of the primary electron acceptor X may be as low as ‐0.37 V, as suggested recently by P. A. Loach (1973, personal communication).
THE RELATION OF THE ESR SIGNAL II TO ELECTRON TRANSPORT IN PHOTOSYSTEM II OF SPINACH CHLOROPLASTS*
Authors: Warden Joseph T. , Bolton James R.
Published: January 2008

Abstract—The kinetic behavior of the ESR Signal II in spinach chloroplasts has been studied under steady‐state illumination and under flash conditions. In controls Signal II exhibits biphasic decay following cessation of illumination—a moderately fast phase (t1/2 10‐60s) and a slow phase (t1/2˜ 2–3 h). Addition of 3‐(3, 4‐dichlorophenyl)‐1, 1‐dimethylurea (DCMU), o‐phenanthroline, NH4Cl or gramicidin had no effect on the decay of Signal II; however, agents such as antimycin A, carbonyl cyanide‐m‐chlorophenylhydrazone (CCCP), NH2OH or tris washing greatly accelerated the decay of Signal II. Flash photolysis‐electron spin resonance experiments on Jensen‐Bassham type chloroplasts reveal the presence of a previously unnoticed decay component in the g ˜ 2 region. This species is formed in less than 1 ms and exhibits a decay half life of ˜6‐10s. The spectral profile corresponds to the steady‐state Signal II spectrum. This new transient is formed in approximately equimolar amounts to Signal I. The results are discussed in terms of two prevalent hypotheses—one which would place the Signal II component on the reducing side of PSII and another which would place the Signal II component on the oxidizing side.
FLASH PHOTOLYSIS‐ELECTRON SPIN RESONANCE STUDIES OF THE DYNAMICS OF PHOTOSYSTEM I IN GREEN‐PLANT PHOTOSYNTHESIS‐I. EFFECTS OF ACCEPTORS AND DONORS IN SUBCHLOROPLAST PARTICLES*
Authors: Warden Joseph T. , Bolton James R.
Published: January 2008

Abstract—Transient decay kinetics of Signal I in spinach subchloroplast particles have been studied in the presence of artificial donors [5‐methyl phenazonium methyl sulfate (PMS), 2, 6‐dichlorophenolindophenol (DPIP), N, N, N', N'‐tetramethyl‐p‐phenylenediamine (TMPD) and ascorbate], artificial acceptors [benzyl viologen (BV) and methyl viologen (MV)] and various natural donor and acceptor moieties, using the technique of flash photolysis‐electron spin resonance spectroscopy. The results are discussed in the framework of three mechanisms for reduction of P700+: (1) direct electron return from the primary acceptor to P700+, (2) cyclic electron flow via an electron carrier, and (3) noncvclic electron flow.
FLASH PHOTOLYSIS‐ELECTRON SPIN RESONANCE STUDIES OF THE DYNAMICS OF PHOTOSYSTEM I IN GREEN‐PLANT PHOTOSYNTHESIS—II. INTACT AND BROKEN SPINACH CHLOROPLASTS*
Authors: Warden Joseph T. , Bolton James R.
Published: January 2008

Abstract—The transient oxidation and subsequent reduction of P700+ in spinach chloroplasts has been monitored by flash photolysis‐electron spin resonance spectroscopy in the presence of various donors and acceptors. In general, the results obtained correlate well with results on Photosystem I subchloroplast particles, with two major differences. For Type A and B intact chloroplasts in the presence of 3‐(3, 4‐dichlorophenyl)‐1, 1‐dimethylurea (DCMU), the electron acceptor methyl viologen has no effect on the decay kinetics. This phenomenon is interpreted in terms of a functioning cyclic electron flow path around Photosystem I. Also, the photoresponse of Signal I depends on the length of the photolyzing flash. This is interpreted in terms of the existence of a primary electron donor to P700+ with a transfer time of ˜ 10 μs.
ESR EVIDENCE FOR CHLOROPHYLL‐PHOTOSENSITIZED ONE‐ELECTRON OXIDATION OF WATER BY BENZOQUINONE*
Authors: Harbour John R. , Tollin Gordon
Published: January 2008

Abstract—Illumination with red light of degassed solutions of chlorophyll and benzoquinone in dry acetone does not result in quinone radical formation, even though the presence of quinone greatly enhances the photoproduction of chlorophyll cation radical at low temperatures. However, when small amounts of water (or alcohols) are added to this system, large benzoquinone anion radical electron spin resonance (ESR) signals are generated. The effects on the low‐temperature ESR signals of microwave power saturation, replacement of chlorophyll and quinone by their deuterated analogs, and replacement of H2O by D2O, lead to the suggestion that a one‐electron oxidation of water is occurring. Pheophytin and bacteriochlorophyll are shown to sensitize a similar photoreaction. These results could lead to new insights into the mechanism of oxygen formation in photosynthesis.
LASER PHOTOLYSIS STUDY OF TRIPLET EOSIN AND THIONINE REACTIONS IN PHOTOSENSITIZED OXIDATIONS
Authors: Kraljić I. , Lindqvist L.
Published: January 2008

Abstract—Nanosecond laser photolysis was used to determine the rate constants of quenching (including chemical reactions) of the triplet states of eosin and thionine, at pH 7, by imidazole, l‐histidine, l‐methionine, l‐phenylalanine, l‐tryptophan, 3‐indole‐acetic acid, cytidine, guanosine, α‐chymotrypsin, lysozyme, allylthiourea, thiourea, p‐nitrosodimethylaniline, I‐ N3‐ and Fe(CN)64‐. The quenching rate constants for thionine were found to be up to three orders of magnitude higher than those for eosin. The mechanism of photosensitized oxygenations (free radical vs singlet oxygen) is discussed on the basis of the present results.
PHOTOOXIDATION OF HORSE AND SPERM‐WHALE MYOGLOBIN SENSITIZED BY THE HEME GROUP
Authors: Folin Marcella , Gennari Giorgio , Jori Giulio
Published: January 2008

Abstract—The irradiation of horse and sperm‐whale Fe 3 * or Fe 2* myoglobins with visible light showed that axial ligands that render the heme diamagnetic (e.g. O2, CO or CN‐) endow the hemoproteins with a marked photosensitivity. In contrast, high‐spin myoglobins are unaffected by visible light. These findings appear to be of general validity for all hemo‐proteins and are in agreement with the involvment of the triplet state of the heme as the reactive intermediate. In all cases, the overall photoprocess occurs within a very narrow spatial range, leading to specific modification of these photooxidizable side chains adjacent to the chromophore. Therefore, this technique can be used to probe the environment of the prosthetic group in hemoproteins. In particular, our data suggest that, in horse myoglobin, histidines‐93 and ‐64 represent the heme‐linked and the distal imidazole groups, respectively; moreover, the thioether function of methionine‐131 must be nearer the heme in horse than in sperm‐whale myoglobin. The selectivity of the photoreaction can be further enhanced by a suitable choice of the sixth ligand, and/or by controlling the pH of the irradiated solution. For example, for both proteins, irradiation of the cyanide derivative results in specific photooxidation of the proximal histidine, whereas irradiation of horse CO‐ferromyoglobin at pH values below 6 causes specific photooxidation of methionine‐131. Consequently, this photooxidative procedure can also be utilized to monitor conformational changes upon binding of the heme with different ligands, as well as to achieve the selective modification of amino acid residues, which are usually buried inside the protein molecule.
THE EFFECT OF AROMATIC AMINO ACIDS ON THE PHOTOCHEMISTRY OF A DISULFIDE: ENERGY TRANSFER AND REACTION WITH HYDRATED ELECTRONS
Authors: Shafferman Avigdor , Stein Gabriel
Published: January 2008

Abstract—The decomposition of dithioglycolic acid in oxygen‐free solutions illuminated by low‐intensity 254 nm light at pH 1.5‐4.7 is enhanced by light absorbed in tyrosine. This occurs through an interaction with excited tyrosine, leading to the formation of excited dithioglycolic acid. At pH 6‐1 an additional pathway appears, through the formation of a hydrated electron from excited tyrosine.

In the presence of tryptophan at pH 1 ‐2–6‐1 the pathway involving sensitized formation of excited dithioglycolic acid is much less important, and that due to hydrated‐electron (or H) formation from excited tryptophan of greater importance.
ULTRAVIOLET AND N‐FORMYL‐KYNURENINE‐SENSITIZED PHOTOINACTIVATION OF BOVINE CARBONIC ANHYDRASE: AN INTERNAL PHOTODYNAMIC EFFECT
Authors: Walrant P. , Santus R.
Published: January 2008

Abstract—Direct photoinactivation by UV light of bovine carbonic anhydrase, as well as its photosensitization by N‐formyl‐kynurenine, a tryptophan photooxidation product, have been investigated. In the presence of oxygen both methods lead to similar results: the enzyme loses its activity, the tryptophanyl, histidyl and, to a lesser extent, tyrosyl residues being destroyed. In nitrogen‐saturated solutions, a dramatic drop is observed in the photoinacitivation yield under the direct action of ultraviolet light, whereas histidyl residues remain intact. Evidence indicates an internal photodynamic action of N‐formyl‐kynurenine in the protein core produced by the UV photooxidation of tryptophanyl residues. Photoinactivation of oxygenated enzyme solutions by external and internal photodynamic action correlates with histidyl residue destruction via singlet oxygen. The possible importance of the photodynamic ability of N‐formyl‐kynurenine in the photochemistry of proteins, DNA, and cells is discussed.
EFFECT OF CHLORIDE AND BENZOATE ANIONS ON THE DELAYED LIGHT EMISSION IN DCMU‐TREATED SPINACH CHLOROPLASTS
Authors: Mar Ted , Roy Guy , Govindjee
Published: January 2008

Abstract—Chloride anions, when added to DCMU [3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea]‐treated spinach chloroplasts, change the rate of decay of the delayed light emission in the seconds region but do not change the shape or the temperature dependence of the decay. Benzoate anions, on the other hand, change both the rate and the shape of the decay of the delayed light emission. These results are consistent with a model in which the membrane potential and the structure of the reaction center affect the decay kinetics of the delayed light emission in the seconds region.
ON THE QUENCHING OF SINGLET OXYGEN BY α‐TOCOPHEROL
Authors: Fahrenholtz S. R. , Doleiden F. H. , Trozzolo A. M. , Lamola A. A.
Published: January 2008

Abstract—D‐α‐tocopherol was found to be an effective quencher of 1O2 molecules (k= 2.5 times 108→mol‐1 s‐1 in pyridine) by measuring its effect on the autosensitized photooxidation of rubrene. The quenching process was shown to be almost entirely ‘physical’, that is, α‐tocopherol deactivated about 120 1O2 molecules before being destroyed. The results suggest that this process may be a mechanism for the protective effect of α ‐ tocopherol in photodynamic action.
PHOTOCHEMISTRY OF SOME FURO (3,2‐g)‐COUMARIN AND 2,3‐DIHYDROFURO (3,2‐g)‐COUMARIN DERIVATIVES
Authors: Gervais J. , Schryver F. C. De
Published: January 2008

Abstract— In order to gain further insight into the photocrosslinking of DNA by furocoumarin derivatives, the photoreactivity of furocoumarins and bisfurocoumarins was studied. While the triplet dimerization of furocoumarins occurs at the pyrone side, incorporation of furocoumarins in nonconjugated bichromophoric systems leads to reactions at the furan side as well. Furthermore, 2,3‐dihydrofurocoumarins show both triplet and singlet reactivity.
ELLIPSOMETRY OF BLACK LIPID MEMBRANES OF EGG LECITHIN AND CHLOROPLAST EXTRACTS
Authors: Engelsen Daan DEN , Koning Bob DE
Published: January 2008

Abstract— Ellipsometric angles and reflectivity of black lipid membranes containing either egg lecithin or chloroplast extracts were measured at a wavelength of 6328 Å. Evidence was found for positive uniaxial anisotropy in membranes of lecithin. If the thickness of those films is assumed to be 62 Å, the refractive index normal to the film surface is 1.471 ± 0.004, and the refractive index parallel to the film surface is 1.454 ± 0.003. The results for membranes of chloroplast extracts also indicate a positive anisotropy in the indices of absorption.
SPECTRAL PROPERTIES OF PHYCOBILISOMES AND PHYCOBILIPROTEINS FROM THE BLUE‐GREEN ALGA‐NOSTOC SP.*
Authors: Gray B. H. , Gantt E.
Published: January 2008

Abstract— An improved method for phycobilisome isolation from a blue‐green alga Nostoc sp. was developed using 1% Triton X‐100. The phycobilisome preparations showed little fragmentation and had structures similar in size to those observed in thin sections of the organism. Phycobiliproteins isolated from phycobilisomes and examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis, had subunits with the following molecular weights: phycoerythrin (PE), 20,000 and 16,900; phycocyanin (PC), 14,700 and 16,300; and allophycocyanin (APC), 14,000. Isoelectric focusing of each phycobiliprotein resulted in major bands isoelectric at the following pH values: PE, 4.43, 4.45; PC 4.32; APC, 4.38. Absorption spectra at ‐196°c showed maxima at 551 and 566 nm for PE; 598 and 631 nm for PC; and 590, 600, 629 and 650 nm for APC. Concentrated vs dilute difference spectra of phycobiliproteins showed increased absorption at 574 nm (PE), 630 nm (PC) and 651 nm (APC) suggesting that spectral changes resulted from aggregation. Fluorescence analysis of each phycobiliprotein and of intact phycobilisome preparations showed that energy absorbed by phycoerythrin is transferred to allophycocyanin, possibly by a resonance transfer mechanism. These observations support a model where allophycocyanin forms the base of the phycobilisome which is attached to the photosynthetic membrane. The next layer is assumed to be phycocyanin, which in turn is followed by a phycoerythrin layer that is the outermost layer (on the stroma side) of the phycobilisome.
INDUCTION OF SKIN TUMORS IN HAIRLESS MICE BY A SINGLE EXPOSURE TO UV RADIATION*
Authors: Hsu J. , Forbes P. D. , Harber L. C. , Lakow E.
Published: January 2008

Abstract— Skin tumors were induced in hairless mutant mice following a single exposure to ultraviolet radiation (UV). Tumors were first noted as early as 7 weeks following irradiation. The UV, emitted by FS20/40T12 fluorescent lamps, was principally in the 280–320 nm spectral region with a peak at 313 nm. Single (skin surface) doses of 3 times 104 J/m2 to 24 times 104 J/m2 were delivered in 3 h or less. The higher doses resulted in more severe acute damage as well as greater tumor yield.

Most of the tumors were benign hyperplastic epithelial papillomas; 4 out of 96 tumors examined histologically proved to be squamous cell carcinomas. This appears to be the first report of experimental carcinogenesis due to a single UV exposure, not requiring exogenous chemical promotion.
ACTION SPECTRUM FOR THE OXYGEN‐INDEPENDENT INACTIVATION OF HAEMOPHILUS INFLUENZAE TRANSFORMING DNA WITH NEAR ULTRA‐VIOLET LIGHT*
Authors: Cabrera‐Juarez E. , Swenson P. A.
Published: January 2008

Abstract— The oxygen‐independent inactivation of Haemophilis influenzae transforming DNA by near UV light (300–380 nm) has an action spectrum in which the efficiency of inactivation drops rapidly between 313 and 334 nm and more slowly between 334 and 405 nm, with a shoulder between 334 and 365 nm.
INHIBITION OF PROTEIN SYNTHESIS IN CULTURED TOBACCO CELLS BY ULTRAVIOLET RADIATION
Authors: Murphy Terence M. , Wright Lawrence A. , Murphy Judith B.
Published: January 2008

Abstract— Ultraviolet (254 nm) irradiation of liquid‐cultured tobacco cells strongly and quickly inhibited their ability to incorporate labeled amino acids into protein. An incident dose of only 388 J/m2 reduced incorporation to 37 per cent of the original rate. The effect on amino acid incorporation did not seem to depend on inhibition of amino acid uptake, inhibition of the supply of nucleoside triphosphates, or inhibition of the supply of messenger RNA to cytoplasmic ribosomes.
EPIDERMAL HYPERPLASIA INDUCED BY ULTRAVIOLET RADIATION; ERROR AND UNCERTAINTY OF MEASUREMENT*
Authors: Blum Harold F. , McVaugh Julia , Ward Margery , Bush Harry L.
Published: January 2008

Abstract— Measurements of epidermal hyperplasia induced by UV in albino mice, using an improved method of sampling and counting of cells, show wide variability attributable largely to basic uncertainty rather than experimental error. Factors are analyzed that may contribute to the infeasibility of determining simultaneously the size of cell population and rate of cell duplication, including recovery of cell activity enhanced by photoreactivation. A hyperplasia‐inducing factor is isolated from epidermis exposed to UV.
2‐ANTHRAQUINONESULFONIC ACID PHOTOSENSITIZED AUTOXIDATION OF HEPES BUFFER
Authors: Swader J. A. , Kumamoto Junji
Published: January 2008

Abstract— Autoxidation of N‐2‐hydroxyethylpiperazine‐N'‐2‐ethanesulfonic acid buffer occurred in the presence of 2‐anthraquinonesulfonic acid and light. The disappearance of oxygen, measured with an oxygen electrode, followed zero‐order kinetics until 75 per cent of the oxygen in solution was consumed. The actual rate observed depended upon pH, light intensity, temperature, and concentrations of 2‐anthraquinonesulfonic acid and buffer. The oxygen consumption was inhibited by hydroquinone and superoxide dismutase. Autoxidation of N‐tris(hydroxymethyl)methylglycine was analogous, but no oxygen was consumed by phosphate buffer in the presence of 2‐anthraquinonesulfonic acid and light.
FAST AND SLOW PHASES OF LUMINESCENCE IN CHLORELLA
Authors: Lavorel J.
Published: January 2008

Abstract— The decay of luminescence of Chlorella in repetitive steady‐state flashing light displays two categories of phase, broadly characterized as ‘fast’ and ‘slow’. They are strongly contrasted in amplitude and lifetime; the transition from fast to slow occurs a few milliseconds after the flash.

The slow phases observed in the presence of 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DCMU) are clearly of the deactivation type. i.e. the luminescence intensity is quantitatively correlated with the rate of relaxation of the System II reaction center to its photoactive state. The significance of the deactivation type is a reverse flow of the light‐produced ⊕ and ⊖ charges through the luminescence‐producing recombination path. This mechanism is probably not limited to the DCMU‐poisoned systems. The light regime (flash duration, flashing period, induction effects) modifies specifically the amplitude of the slow phases; this effect is strikingly not dependent on the presence of DCMU. Although the light‐driven pH gradient is the likely explanation, it is argued that its action bears more directly on the exciton and/or emission yield of luminescence rather than on the rate of recombination itself.

Most of the fast‐phase components are ascribed under normal conditions to stabilization steps involving the donor side of the System II reaction centers. However, when the reaction center turnover is much reduced (DCMU) or completely abolished (DCMU + NH2OH, after preillumination), a fast luminescence phase is still visible. This phase is barely affected by the light regime (notably the flash duration). It must be attributed to an anomalous residual photochemical turnover of the reaction centers. Another type of fast photochemical turnover has been characterized with NH2OH‐pretreated cells.

A two‐quantum functioning of some sort seems required to account for the anomalous photochemical turnover. The importance of the luminescence loss during the fast phases and its possible connection with the ‘misses’ of the O2‐evolving system are discussed.
RADIATIVE LIFETIME AND THERMODYNAMIC POTENTIAL OF EXCITED STATES
Authors: Ross Robert T.
Published: January 2008

Abstract— To clarify their similarities and common assumptions, a unified derivation is presented of the methods of evaluating the radiative lifetime of an electronically‐excited state by integration of the absorption spectrum or of the fluorescence spectrum. Previous examinations of the accuracy of these methods are briefly reviewed. The radiative lifetime of eleven aromatic molecules is computed by the fluorescence spectrum method, and compared with published lifetimes determined experimentally and by integration of the absorption spectrum; from this it is concluded that the fluorescence spectrum method is accurate to about 25 per cent, and that the common assumption of equal partition functions for the ground and excited states is often not true. Extension of the derivation of formulas for the radiative lifetime shows that the standard chemical potential of the excited state may be determined from the experimental radiative lifetime and appropriately scaled integration of the fluorescence spectrum.
COMPARISON OF THE LETHAL EFFECT OF 5‐IODOURACIL INCORPORATED INTO BACTERIOPHAGE T4 IN THE PRESENCE AND ABSENCE OF NEAR‐VISIBLE LIGHT
Authors: Byrd Daniel M. , Goz Barry , Prusoff William H.
Published: January 2008

Abstract— Bacteriophages T2 or T4 containing 5‐iodouracil (IUra) substituted for thymine in their DNA are inactivated by near‐visible light, with fluorescent lamps as the source of near‐visible light. Inactivation increases with the dose of near‐visible light and follows first order kinetics. Relative inactivation rates are linearly proportional to percent substitution. Equivalent per cent substitution by IUra or 5‐iodo‐2'‐deoxyuridine (IdUrd) results in equivalent sensitization to inactivation with both T2 and T4. However, incorporation of IUra into T4 and T2 also is lethal in the absence of light. The lethal effect of IUra substitution differs from the lethal effect of IUra substitution plus near‐visible light irradiation in at least three respects: (1) IUra substitution is lethal for T4 under conditions where the residual viability is stable and where environmental light cannot account for the inactivation. (2) The hit curve for IUra lethality, as a function of per cent IUra substitution, has a large shoulder while the hit curve for sensitization to inactivation by near‐visible light, as a function of per cent IUra substitution, has no shoulder. (3) At equivalent extents of inactivation. IdUrd substitution in the absence of light has a greater effect on phenotypic expression of T4 than either near‐visible light irradiation alone or IUra substitution plus near‐visible light irradiation, as measured by either delay in appearance or decrease in total amount of two induced enzyme activities (dihydrofolate reductase and deoxycytidylate hydroxymethylase).