bluuebunny/crossref_metadata_2025 huggingface dataset:
THE SPECTRUM OF BACTERIOCHLOROPHYLL IN VIVO: OBSERVATIONS ON MUTANTS OF RHODOPSEUDOMONAS SPHEROIDES UNABLE TO GROW PHOTOSYNTHETICALLY
Authors: Sistrom W. R.
Published: January 2008

Abstract— The major blue pigment from a mutant of Rhodopseudomonas spheroides that is unable to grow photosynthetically has been compared with authentic bacteriochlorophyll. By the following criteria the pigments are identical: chromatographic behavior; visible and i.r. epectra of the pigments and of their Mg‐free derivatives in a varity of solvents; reaction in the Molisch phase test; isolation of phytol.

The spectra in vivo in the region of bacteriochlorophyll absorption of the following strains grown under a variety of conditions have been compared:(a) wild‐type (strain Ga), (b) photosynthetically deficient mutant (strain PM‐8), (c) secondary mutants derived from PM‐8 lacking colored carotenoid pigments, and (d) carotenoid‐less, photosynthetically competent revertants from strains of type (c). It is concluded (1) that the spectrum of reaction center bacteriochlorophyll (P870) includes an absorption band at 805 mμ as well as at 870 mμ and (2) that the relative heights of the three absorption bands of bulk bacteriochlorophyll (at 805, 850 and 875 mp) are strongly influenced by the presence of P870.
LIGHT‐INDUCED ELECTRON TRANSFER BETWEEN CHLOROPHYLL AND HYDROQUINONE AND THE EFFECT OF OXYGEN AND β‐CAROTENE
Authors: Fujimori Eeji , Tavla Maria
Published: January 2008

Abstract— Light‐induced electron spin resonance (ESR) absorption is not observed in degassed benzene solutions of chlorophyll a with hydroquinone. In the presence of methanol, however, the characteristic hyperfine pattern of p‐benzosemiquinone ion radical is formed. This photo‐reduction of chlorophyll a by hydroquinone is enhanced apparently by a small amount of triethylamine and inhibited by β‐carotene.

Chlorophyll excited in the presence of oxygen produces a single broad ESR signal in benzene solutions which is enhanced by hydroquinone and quenched by β‐carotene, alcohol, and a mine. Their quenching effect is in parallel with their inhibition of the photoauto‐oxidation of chlorophyll. The high quenching capacity of triethylamine for this ESR signal is reduced by the addition of β‐carotene. In methanol solutions, the initial production of the single broad signal is followed by gradual development of the hypertine structure of p‐benzo‐semiquinone ion radical. This development can be accelerated by triethylamine. The mechanism of these changes is discussed on the primary interaction of excited chlorophyll with oxygen.
THE EFFECT OF ULTRAVIOLET RADIATION UPON OSMOREGULATION IN PARAMECIUM*
Authors: Saier F. L. , Giese A. C.
Published: January 2008

Abstract Paramecium multimicronucleatum was irradiated with U.V. in solutions of differing osmotic pressures and ionic content. The rates of contraction and the diameters of the anterior contractile vacuoles were measured and changes in the volumes of solution entering the contractile vacuoles upon U.V. irradiation for paramecia maintained in solutions of differing ionic content were calculated. The volume of fluid entering the contractile vacuoles of paramecia irradiated (1) in standard balanced salt solution (SBSS) was regulated by a compensatory mechanism at lower U.V. doses but increased after relatively large U.V. doses; (2) in distilled water, increased after much smaller U.V. doses; (3) in isotonic balanced salt solution, showed little change upon irradiation.

Increased osmotic pressure (with added sucrose) was found to reduce u.v.‐induced blistering of the pellicle, but in general U.V. damage was similar to that of paramecia in solutions of identical ionic content but lacking sucrose. Paramecia in SBSS with added sucrose to make it isomotic to the interior of the cell ruptured only after doses larger than for paramecia in SBSS lacking sucrose. Cell rupture of paramecia in solutions containing high CaCl2 concentrations generally occurred later than for those in SBSS. High KCI concentration (unbalanced salt solution) in the presence of high CaCl2 concentration provided some protection from U.V. irradiation to the paramecia. High NaCl concentration (unbalanced salt solution) in the presence of high CaCl2 concentration appeared to increase u.v. damage to paramecia. Paramecia were most resistant to u.v. irradiation, as judged by the above criteria, when present in balanced salt solution enriched with calcium, thus simulating pond water.
QUANTITATIVE SPECTROFLUORIMETRY‐THE FLUORESCENCE QUANTUM YIELD OF QUININE SULFATE
Authors: Eastman J. W.
Published: January 2008

Abstract— By idealizing the design of a typical spectrofluorimeter that measures fluorescence from dilute solutions, we are able to derive an equation that predicts the dependence of the observable amplitude on the concentration of the solute and on several instrumental parameters. The result of the derivation, the fluorescence function, is used together with measurements of rhodamine B fluorescence and colloidal silica scattering to calibrate a spectrofluorimeter.

The fluorescence function and the calibration data are used to determine the absolute fluorescence quantum yield of quinine sulfate in 0–1 N H2 So4. The results, Ø250=0.582 with excitation at 250 mμ, adn Ø350=0.577 with excitation at 350mμ. agree well with the previous evaluation of Melhuish, Ø345=0.546.
EXCITED STATES OF FLAVINE COENZYMES–II. ANAEROBIC OXIDATION OF AMINO ACIDS BY EXCITED RIBOFLAVINE DEVRIVATIVES
Authors: Byrom P. , Turnbull J. H.
Published: January 2008

Abstract— Flavines in the excited state can effect anaerobic oxidation of amino acids to keto acid and ammonia. The rate of the process depends on the structure of the amino acid. These systems show similarities to the amino acid oxidases.
SPECTROSCOPIE DE LA CHLOROPHYLLE DANS LES CHLOROPLASTES ENTIERS ET DES FRAGMENTS CHLOROPLASTIQUES
Authors: Briantais Jean‐Marie
Published: January 2008

Abstract— Chloroplast fragments obtained after treatment with a non‐ionic detergent (Triton X‐100) are studied spectroscopically. Their absorption and fluorescence spectra show the possibility of obtaining separately, without any visible alteration, the two groups of chlorophyll holochromes corresponding to the two photochemical systems. One of the chloroplastic fractions, enriched in chlorophyll‐b shows, like whole chloroplasts, an oxygen burst upon illumination.
THE MECHANISM OF THE FLAVIN SENSITIZED PHOTODESTRUCTION OF INDOLEACETIC ACID*
Authors: Nathanson B. , Brody M. , Brody S. , Broyde S. B.
Published: January 2008

Abstract— A detailed in vitro study was made of the flavin sensitized photoinactivation of indoleacetic acid, using primarily riboflavin as sensitizer. The dependence of the quantum yield on reactant concentrations, pH, presence of oxygen, viscosity, temperature, KI concentration, and solvent was determined. The involvement of a limiting dark reaction was demonstrated, using an intermittent light technique. The results are consistent with a mechanism involving a metastable state of riboflavin as the photochemically reactive species. The calculated rate constant for intersystem crossing to this state was found to be 2.5 times 108/sec. Riboflavin, in the metastable state, is believed to oxidize indoleacetic acid to indolealdehyde, with subsequent recovery of riboflavin by autoxidation. The maximum quantum yield of the photoinactivation of IAA is 0.71, indicating a highly efficient process, approaching 100% when energy loss due to riboflavin fluorescence is taken into account. Both carotenoids and pure chlorophyll‐a were found to be inactive as sensitizers.
PYRIMIDINE DIMER FORMATION IN ULTRAVIOLET IRRADIATED TMV‐RNA
Authors: Merriam Virginia , Gordon Milton P.
Published: January 2008

Abstract— The formation of pyrimidine dimers on ultraviolet irradiation of TMV‐RNA in water is demonstrated in the region from 254 nm to 302 nm. No dimer is present in either unirradiated E. coli ribosomal RNA or TMV‐RNA. Dimer formation was also examined in TMV‐RNA irradiated in the presence of 5times10‐6 M proflavin, in high salt, on dry ice, and in 90% methanol. No correlation of pyrimidine dimers with any biologically defined lesion is presently possible and it is suggested that dimer may not be involved in the inactivation of this material.
LA PHOTOOXYDATION DU GROUPE PEPTIDE—II. PEPTIDES ET POLYAMINOACIDES A L‘ÉTAT SOLIDE*
Authors: Meybeck A. , Meybeck J.
Published: January 2008

Abstract— The determination of glyoxylic and pyruvic acids in oligo‐and poly‐, glycine and alanine shows that the peptide group is photooxydized, probably with the radical ‐NH‐CR‐CO‐ as an intermediate.

The characterisation of pyruvic acid in glutathione and oxydized glutathione confirms the photolysis of the C‐S bond in combined cysteine and cystine.

Finally, a comparison of the photoreactivity of peptides of the types aliphatic amino acid‐aromatic amino acid and aromatic amino acid‐aliphatic amino acid allows us to propose a selective mechanism for the transfer of excitation energy from the phenyl group to the preceding amino acid residue in the polypeptide chain.
EXCITATION TRANSFER BY CHLOROPHYLL a IN MONOLAYERS AND THE INTERACTION WITH CHLOROPLAST GLYCOLIPIDS*
Authors: TROSPER T. , PARK R. B. , SAUER K.
Published: January 2008

In mixed monolayers with purified chloroplast glycolipids and other colorless lipids, chlorophyll a fluorescence exhibits a decrease in quantum efficiency with increasing chlorophyll concentration. The fluorescence, which is strongly polarized in dilute films, becomes progressively depolarized as the area fraction of chlorophyll increases, and it is completely depolarized in a pure chlorophyll a monolayer. The observed behavior is consistent with an inductive resonance mechanism of energy transfer among the chlorophyll molecules with a critical transfer distance of 20–90 Å, depending on the model chosen for the energy transfer mechanism.

The purified glycolipids–mono‐and digalactosyl diglycerides and sulfoquinovodiglyceride–separately form stable, compressible monolayers of the liquid‐expanded type on an aqueous subphase and in an atompshere of nitrogen. At maximum compression the three glycolipids occupy areas of 55, 80 and 47 A2‐molecule‐1, respectively, in the monolayer. Mixed monolayers of chlorophyll a with, separately, the monogalactolipid and the sulfolipid behave upon compression as two‐dimensional solutions. The fluorescence polarization at high chlorophyll concentrations in mixed monolayers indicates that several of the lipid diluents facilitate local ordering of the pigment molecules.
FLASH PHOTOLYSIS OF FLAVINS‐I. PHOTOREDUCTION IN NON‐AQUEOUS SOLVENTS*
Authors: GREEN MAURICE , TOLLIN GORDON
Published: January 2008

Abstract— The photoreduction of riboflavin, FMN, and lumiflavin in a series of hydroxylic solvents has been examined using flash photolysis. A comparison of the relative quantum yields for the photoxidation of several alcohols and esters by lumiflavin demonstrated that the hydroxyl hydrogen of the alcohol is abstracted approximately twice as readily as is the alpha hydrogen. The use of glycerol as both solvent and reductant provided direct evidence that the initial reaction proceeds by a one‐electron reduction to form the flavin semi‐quinone. In the case of riboflavin (and FMN) the kinetic results are consistent with an initial intramolecular hydrogen atom transfer, analogous to photobleaching in aqueous solution, followed by a reaction of the semi‐quinone with the reductant which prevents degradation of the ribityl side‐chain. Quenching by iodide indicates that all the reactions proceed via the flavin triplet state, as is the case in aqueous systems.
LIGHT‐INDUCED CHANGES IN CYTOCHROME b‐559 IN SPINACH CHLOROPLASTS
Authors: HIND G.
Published: January 2008

Abstract— In isolated spinach chloroplasts, the reduction of cytochrome b‐559 by System II and its oxidation by System I can be observed when electron acceptor concentration limits System I activity and when one of a particular class of uncoupling agents is present. This class includes CCCP, desaspidin, Triton X‐100 and antimycinA; but not simple amines or atebrin.

The effect of the uncoupler is to speed the cytochrome b‐559 oxidation rate. In addition, the rate of the off‐response of the light‐induced P518 absorbance change is increased. To explain these findings, an electron transfer scheme is proposed having two distinct pathways between System II and System I.
MECHANISM OF BIOLUMINESCENCE, CHEMI‐LUMINESCENCE AND ENZYME FUNCTION IN THE OXIDATION OF FIREFLY LUCIFERIN*,†
Authors: Mcelroy W. D. , Seliger H. H. , White E. H.
Published: January 2008

Abstract— The chemical steps and the products of the bioluminescent and chemiluminescent oxidations of firefly luciferin are elucidated. The colors of firefly bioluminescence can be explained in terms of different ionic excited states and spectral shifts due to changes in molecular environment. Firefly luciferase undergoes conformational changes during catalysis. There are two sites for light production per 100,000 mW. A regulatory mechanism involving dehydro‐luciferin is proposed for control of firefly flashing.
SENSITIZED PHOTOOXYGENATION REACTIONS AND THE ROLE OF SINGLET OXYGEN†,‡
Authors: Kearns David R. , Khan Ahsan U.
Published: January 2008

Abstract— In this paper we discuss various theoretical and experimental aspects of the role of singlet oxygen in sensitized photooxygenation reactions. New spectroscopic observations on the photosensitized production of singlet oxygen molecules are presented. The various factors which control the generation and reactions of singlet oxygen molecules are considered in detail. A relatively simple theoretical procedure is developed to predict the relative reactivities of 1σ, 1δ and 3σ oxygen toward various organic acceptors, and is used to discuss the chemical and photochemical properties of some of the oxygenation products. Finally, the properties of dioxetanes are examined in connection with the role which they may play in chemi‐ and bioluminescence. While we have said rather little about photodynamic reactions per se, the results presented in this paper strongly support the suggestion that many of the observed photodynamic effects could be due to reactions of singlet oxygen. Clearly a careful reexamination of various photodynamic effects at the molecular level to establish whether or not reactions of singlet oxygen are involved is now in order.
KINETICS OF ENZYMATIC PHOTOREACTIVATION STUDIED WITH PHAGE T1 AND ESCHERZCHZA COLI Bs‐1*
Authors: Muraoka Noriko , Kondo Sohei
Published: January 2008

Abstract— The kinetics of enzymatic photoreactivation (PR) of u.v.‐induced killing was compared among E. coli Bs‐1, phage T1 in Bs‐1 and phage T1 in irradiated Bs‐1. The PR action spectrum showed no substantial difference between PR of Bs‐1 and PR of T1 in Bs‐1. The PR D37 (i.e. the PR dose required to reactivate all but 37 per cent of the reactivable lethal lesions) was found to decrease linearly with decreasing U.V. dose whether U.V. was given to produce pyrimidine dimers in Bs‐1 DNA, which then compete with irradiated T1 DNA for PR enzyme, or to Bs‐1 or T1 DNA to produce dimers serving as substrate for the PR enzyme. A generalized Michaelis‐Menten formula was used to analyze the data and the following conclusions were drawn. (1) The number of PR enzyme molecules per cell available for PR of T1 DNA inside the Bs‐1 host is only a quarter of the number available for PR of the Bs‐1 host itself. (2) The Michaelis constant Km for reaction of host‐DNA‐damage and PR‐enzyme becomes larger when the host damage acts as competitive inhibitor to PR of T1 DNA than when it is the substrate for PR enzyme. (3) PR enzyme retains almost all its initial catalytic efficiency even after about two‐hundred rounds of catalytic functioning. Conclusions (1) and (2) suggest that PR enzyme is concentrated within the nuclear area surrounding the host DNA.
PHYCOCYANIN‐SENSITIZED PHOTOREDUCTION OF AZO DYES*
Authors: Bellin Judith S. , Gergel Carol A.
Published: January 2008

Abstract— Phycocyanin can sensitize the photobleaching of azo dyes in a reaction which is analogous to one sensitized by chlorophyll. The quantum yield of the phycocyanin‐sensitized photobleaching of congo red is low compared to the analogous reaction as sensitized by chlorophyll in aqueous pyridine. A kinetic mechanism for the former reaction is proposed and it was found that the manner in which phycocyanin sensitizes photoreduction of azo dyes is in several respects similar to that proposed for chlorophyll.
A REVERSIBLE PHOTOCHEMICAL REACTION OF CHLOROPHYLL a WITH I2
Authors: Livingston Robert , Conrad J. R.
Published: January 2008

Abstract— Chlorophyll a and I2 form a 1:1 addition compound, which exhibits a strong absorption maximum at about 360 nm. When dissolved in anaerobic methanol, this compound can be reversibly bleached by illumination with red light. Prolonged illumination at low temperatures (˜– 75°C) or intense illumination at room temperature reduces the height of the red absorp tion maximum to about half of its normal value. Since the thermal back reaction is negligibly slow at – 75°C, presumably the chlorophyll‐I2 complex is converted completely to its bleached form, when illuminated under those conditions. This assumption leads to a simple mechanism which is consistent with the experimental data.
AN IDENTIFICATION OF THE RADICAL GIVING RISE TO THE LIGHT‐INDUCED ELECTRON SPIN RESONANCE SIGNAL IN PHOTOSYNTHETIC BACTERIA
Authors: BOLTON JAMES R. , CLAYTON RODERlCK K. , REED DAN W.
Published: January 2008

Abstract— A reaction‐center fraction isolated from Rhodopseudomonas spheroides chromatophores exhibits light‐induced changes in its optical and electron spin‐resonance (ESR) spectra. In particular, a bleaching at 870nm (P870) has been found to be closely correlated with the appearance of an ESR signal with a g factor of 2.0025 and a peak‐to‐peak line width of 10 G. The ESR signal is indistinguishable from light‐induced signals found in chromatophores or whole cells.

A careful measurement of the spin concentration showed that the ratio of the light‐induced spins to bleached P870 molecules is 1.1 ± 0.1. In addition the formation and decay kinetics are identical within experimental error under a variety of experimental conditions.

Previous work has shown that P870 is a bacteriochlorophyll molecule in a specialized environment and that the bleaching signifies oxidation. The present work provides strong evidence that the photo‐bleaching of P870 produces the radical cation of bacteriochlorophyll, P870+, and that this radical is the source of the ESR signal in whole cells.

The quantum yield for the bleaching of P870 in reaction centers has been measured, using actinic light of wavelengths 880, 800, 760 and 680 nm. For light absorbed at 880 or 800 nm the efficiency is close to 100 per cent. In a coupled reaction, the oxidation of mammalian cytochrome c by P870+ proceeds with nearly the same efficiency.

The above results place definite limits on the possibilities for the identity of the primary acceptor. These possibilities are discussed.
A PHOTOREACTIVATIONLESS MUTANT OF SACCHAROMYCES CEREVISIAE*,†
Authors: RESNICK MICHAEL A.
Published: January 2008

Abstract— A mutant of S. cerevisiue has been isolated that is incapable of photoreactivating u.v.‐induced lethal damage. The mutant resulted from mutation of the chromosomal gene PHR 1, which was determined to be dominant. This gene is involved with the production of photoreactivating enzyme.
SENSITIZED PHOTO‐OXIDATION OF WOOL AND SILK BY A TRIAZINYLSTILBENE
Authors: LEAVER I. H. , RAMSAY G. CAIRD
Published: January 2008

Abstract— The photo‐oxidation of wool and silk treated with a fluorescent brightening agent (a triazinylstilbene) has been studied. Complete amino acid analyses of the irradiated keratins showed that in the presence of this sensitizer, only tryptophyl and histidyl residues were susceptible to photodecomposition; the former were oxidized at a faster rate than the latter. Sixty per cent of the tryptophyl residues in silk were photo‐oxidized during a 4 hr exposure to an artificial light source designed to simulate summer sunlight conditions. The rate of discoloration of the irradiated silk fabric, measured spectrophotometrically, was found to parallel closely the rate of photo‐oxidation of the tryptophyl residues in the fabric.
EFFECT OF SPLIT‐DOSE U.V. IRRADIATION ON DIPLOID YEAST
Authors: Kiefer J.
Published: January 2008

Abstract— Recovery from sublethal damage by u.v. irradiation as measured by the split‐dose technique was investigated in stationary phase populations of diploid yeast Saccharomyces cerevisiae. Ft has been found that only about 35 per cent of the irradiated population is able to undergo recovery before the first subsequent cell division. The qualitative pattern is not changed if maximum photoreactivation is allowed after the first dose. Measurements of the decay of photoreactibility show that primary photo‐products are still present up to six hours after irradiation.
DEGRADATION OF THE DNA OF recA MUTANTS OF ESCHERICHIA COLI K‐12 AFTER IRRADIATION WITH ULTRAVIOLET LIGHT‐II. FURTHER STUDIES INCLUDING A recA uvrA DOUBLE MUTANT*
Authors: HORII ZEN‐ICHIRO , SUZUKI KENSHI
Published: January 2008

Abstract— The u.v.‐induced degradation of the DNA of the recA1 mutant of Escherichia coli K‐12 has been further investigated. The extensive degradation was mostly prevented by an additional mutation in the uvrA gene. Furthermore, when amino acid‐starved recA bacteria were irradiated and held under a condition preventing DNA replication, the DNA was degraded very little. The mode of u.v.‐induced DNA degradation was investigated by comparing the time course of release of label from the acid‐insoluble fraction of two growing cultures of a recA uvrA double mutant; the one was pulse‐labeled with 3H‐thymidine and the other was pulse‐labeled and chased thereafter for 12 min. It was found that, in spite of very little degradation of the bulk of DNA. the label incorporated into the former culture was lost rapidly from the acid‐insoluble fraction. while the label incorporated into the latter culture was not. It was concluded. therefore. that breakdown of the replicating point is characteristic of recA mutants and that degradation of the bulk of DNA is induced in some way by the function of the uvrA gene. Therefore, the degradation of the major part of DNA which follows the degradation of the replicating point appears to be a secondary phenomenon.
Advances in Photochemistry: Volume 6
Authors: GORDON MILTON P.
Published: January 2008

Advances in Photochemistry: Volume 6, W. A. NOYES, Jr., G. S. HAMMOND and J. N. Pins, Jr. (Editors).
SENSITIZED PHOTOINACTIVATION OF BACTERIOPHAGE T4
Authors: MEISTRICH M. L. , LAMOLA A. A. , GABBAY E.
Published: January 2008

Abstract— The photoinactivation of an osmotic shock resistant mutant of the bacteriophage T4 can be sensitized by two cationic derivatives of acetophenone. At least part of the sensitized inactivation appears to be due to the formation of thymine dimers in phage DNA by a mechanism which involves triplet excitation transfer from the sensitizer to thymine in the DNA. The photoreactivable sector of the phage inactivated by sensitized irradiation is about 0.6, almost twice as large as the sector for u.v. irradiated phage.
FAR‐RED INDUCED, LONG‐LIVED AFTERGLOW FROM PHOTOSYNTHETIC CELLS. SIZE OF AFTERGLOW UNIT AND PATHS OF ENERGY ACCUMULATION AND DISSIPATION
Authors: BJÖRN L. O.
Published: January 2008

Abstract— –Small amounts of N‐methyl phenazonium methosulphate (PMS) added to a suspension of Chlorella pyrenoidosa accelerate the emission of the long‐lived far‐red induced afterglow without greatly changing the amount of light emitted. The effect is noticeable in dilute suspensions at a PMS concentration of 10‐9M. The concept of afterglow unit is introduced and defined as that part of the sample in which the rate of energy reemission can be controlled by a single molecule of PMS. The number of chlorophyll molecules per afterglow unit is about 105. It is possible that the afterglow unit is identical to the thylakoid.

The rate constant for the final first order decay phase of afterglow at room temperature is about 0.7 min‐1 without PMS and about 3 times larger for a unit with one PMS molecule.

Diuron (DCMU) lowers the rate of afterglow decay. Desaspidin on the other hand decreases the amount of light emitted without affecting the decay rate. Carbonylcyanide‐m‐chlorophenyl hydrazone (CCCP) decreases the afterglow over the whole time‐range and increases the decay rate. A kinetic model is developed to account for the results.
PROTON MOVEMENT ACCOMPANYING THE LIGHT‐INDUCED ELECTRON TRANSFER IN THE CHLOROPHYLL‐QUINONE SYSTEMS
Authors: QUINLAN K. P.
Published: January 2008

Abstract— –Previous studies have shown that chlorophyll can either mediate proton ejection or uptake in the light sensitive chlorophyll‐p‐benzoquinone system. The present investigation is a detailed study of the effect of the following variables on these processes: pH, benzoquinone and chlorophyll concentration, and the presence of oxygen.
CHEMILUMINESCENCE FROM THE REDUCTION OF AROMATIC AMINE CATIONS AND RUTHENIUM(III) CHELATES*,‡
Authors: LYTLE FRED E. , HERCULES DAVID M.
Published: January 2008

Abstract— –Chemiluminescence is reported from two types of reactions; those involving the reduction of amine cations yield fluorescence amines: RN H2+m+ reductant → RN H2+hv and those involving reduction of transition metal chelates where the reduced form of the chelate is fluorescent: MLx+(n+1)+ reductant →MLx+n+hv The results reported here are for reduction of the cation radical of 1,6‐diaminopyrene and ruthenium (III) chelates where chelate ligands are substituted 1,10‐phenanthrolines or 2,2'‐bipyridine. Reducing agents for 1,6‐diaminopyrene were hydrazine or the naphthalene radical anion; for the ruthenium chelates either hydroxyl ion or hydrazine in acid solution. A detailed study is reported for the kinetics of the ruthenium (III)‐hydrazine reaction, using a computer kinetic modeling program. A quantitative fit of the experimental data to computer‐generated curves can be accomplished at low hydrazine concentrations. At higher hydrazine concentrations the correct qualitative shapes of curves can be generated but the quantitative fit is not exact.
THE U.V. PHOTOLYSIS (Λ= 185nm) OF ETHYLENE GLYCOL IN AQUEOUS SOLUTION*
Authors: LINDE H. J. VAN DER , SONNTAG C. v.
Published: January 2008

Abstract— –The u.v. photolysis (Λ= 185 nm) of 2 M aqueous solutions of ethylene glycol was studied at 22°C. Products (quantum yields) are hydrogen (0.204) formaldehyde (0.194), glycolaldehyde (0.08), methanol (0.074), glycerol (0.06), erythritol (0.03), acetaldehyde (0.02), 3,4‐dihydroxybutanal (0.01) and succinaldehyde (0.001). With increasing temperature the yields of all products remain essentially unchanged except that of acetaldehyde (φ= 0.32 at 90°C) which is formed in a chain reaction. The photolysis of (CD2OH)2 yields 91% HD, indicating that the most important primary process is the homolytic splitting of the O‐H bond. The resulting oxy radicals fragmentate largely into formaldehyde and CH2OH radicals. Molecular fragmentation processes yielding hydrogen and glycolaldehyde, as well as formaldehyde and methanol, are discussed in the proposed decomposition scheme.
A SELF‐CONSISTENT‐FIELD STUDY OF THE EXCITED STATE π‐ELECTRON CHARGES IN PHENOL
Authors: YEARGERS EDWARD
Published: January 2008

Abstract— –The semiempirical self‐consistent‐field (SCF) method was used to calculate the net π‐electron charges for phenol in the first excited singlet and first excited triplet states. These calculations differ from the usual ground state calculations in that (i) recently available static excited state data were used wherever possible as the empirical basis for evaluating SCF parameters and (ii) the theory of density matrices was used to include the effects of all singly‐excited configurations in the configuration interaction contributions to the excited state π‐electron charge densities.
PHOTOELECTRIC EFFECTS IN A BIMOLECULAR LIPID MEMBRANE IN THE PRESENCE OF LIGHT SENSITIVE INORGANIC IONS
Authors: PANT HARISH C. , ROSENBERG BARNETT
Published: January 2008

Abstract— A new membrane photoeffect of high quantum efficiency is reported. The presence of a number of inorganic ions in the bathing solution of a bimolecular lipid film of oxidized cholesterol causes a change in the measured e.m.f. from ‐100 to ‐40 mV (photo e.m.f. effect) and increase in the conductivity by a factor of 100–200 (photoconductive effect) when the ions are excited by light. A model system, based upon the classical Becquerel Effect phenomenon of electronic charge injection into the membrane from electronically excited ions, is suggested and experiments verifying this model are reported. An extension of this model is used to suggest a new mechanism of the visual receptor process in biological photoreceptor structures.
ELECTRON TRANSPORT IN RHODOPSEUDOMONAS VIRIDIS* AT LOW TEMPERATURES
Authors: FLEISCHMAN DARRELL E. , COOKE JACQUELINE A.
Published: January 2008

Abstract— When chromatophores of Rhodopseudomonas viridis are briefly illuminated with very bright light at temperatures between —20°C and —196°C, reaction center chlorophyll (P985) is oxidized rapidly and becomes reduced in less than 0.1 sec upon cessation of illumination. In moderate exciting light one molecule of cytochrome 558 per molecule of P985 is oxidized rapidly and irreversibly while P985 oxidation is much slower and its oxidation rate is highly temperature‐dependent. After a long illumination ends, P985 reduction occurs in two temperature‐dependent phases, in 1 to 1 ratio. The data are interpreted as follows.

P985 and one mole of cytochrome 588 per mole of P985 can be photooxidized at low temperatures.

Electron transfer from the primary electron acceptor to the secondary acceptor or back to P985+ occurs in less than 0.1 sec at low temperatures.

There is one mole of secondary acceptor (a one‐electron acceptor) per mole of P985. and electron transfer from the secondary acceptor to tertiary acceptors is highly temperature‐dependent.
AN ANALYSIS OF A TRIPLET EXCITON MODEL FOR THE DELAYED LIGHT IN CHLORELLA*
Authors: STACY W. T. , MAR T. , SWENBERG C. E. , GOVINDJEE
Published: January 2008

Abstract— The time dependence of the delayed light in the green alga Chlorella pyrenoidosa has been examined quantitatively in the 1 to 12 msec range after excitation with light pulses (A = 6328 Å) of 100 μsec and 4.5 msec duration. We have confirmed the data of Tollin, Ruby, and Bertsch et al., on the time course of the delayed light in the msec range. New experiments, with 100 μsec flash excitation, on the time dependence of the delayed light emitted by Chlorella treated with 3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea (DMU), hydroxylamine, methyl violgen, and various combinations of these chemicals are presented. Also, data on the dependence of the delayed light intensity on the intensity of the excitation light in the 1.5 and 5.0 msec range are reported. The square law dependence, reported by Jones, in the 140 and 250 msec range is confirmed in the 1.5 and 5.0 msec range at very low light levels.

The experimental data on delayed light has been analyzed in terms of a model which incorporates triplet exciton fusion. The following major points result from this analysis: (1) A triplet exciton kinetic model can explain both the time dependence and the excitation intensity dependence of the delayed light emitted by Chlorella. (2) The density of triplet excitons predicted by the model from the observed delayed light intensity is much less than that which can be detected by flash photolysis measurements. Therefore, the failure of such measurements to detect triplet states in vivo does not disprove the model. (3) The possibility of changes in the rate of electron transfer reactions of photosynthesis is included in the kinetic model. The predictions from the model are compared with the effects of chemical additives on the time dependence of the delayed light decay. (4) The proposed triplet exciton model predicts that the delayed light intensity may, under certain specific conditions, be affected by a magnetic field. The negative result of an attempt to observe this effect is reported and discussed. (5) It is concluded that the proposed triplet ‘fusion’ model is a valid alternative to the electron‐hole recombination model.
FLUORESCENCE AND LUMINESCENCE STUDIES OF IN VIVO CHLOROPHYLL WITH A LASER PHOSPHOROSCOPE*
Authors: LAVOREL J.
Published: January 2008

Abstract— A simple apparatus using a He‐Ne laser and a rotating sector gives repetitive light pulses with rise and fall times of a few μsec and intensities of up to 0.65 W/cm2. Fluorescence during the actinic pulse and luminescence following it (after 20 μsec) may be recorded and compared. Sampling of the suspension of photosynthetic cells or chloroplasts by intermittent flow permits the averaging of 25 such measurements. With Chlorella, the fast (30 μsec) and the medium (30 msec) components of luminescence do not saturate at the same light intensity. The former saturates in the same range as the photochemical fluorescence rise, whereas the latter saturates at higher intensities. Under a variety of conditions, the decay of luminescence intensity is always strongly polyphasic. Analysis of the kinetics discloses a dependency with the log concentration of the hypothetical precursor, suggesting a connection of luminescence with electrochemical phenomena. The shape of the luminescence integral, as well as the light saturation pattern, suggests another kind of interpretation, in terms of several pools, possibly two of equal size. In the presence of hydroxylamine, only one pool is seen. The stimulating effect of preillumination is only observed for the medium component. However, a stimulation of short duration also exists for the fast component. The problems of number of pools, mechanism, and stimulation are briefly discussed.
STRUCTURE OF PHOTOSYSTEM I AND PHOTOSYSTEM II OF PLANT CHLOROPLASTS*,†,§
Authors: VERNON L. P. , SHAW E. R. , OGAWA T. , RAVEED D.
Published: January 2008

Abstract— The action of Triton X‐100 upon photosynthetic membranes which are devoid of carotenoids produces a small Photosystem I particle (HP700 particle) which is active in N ADP photoreduction and has a [Chl]/[P700] ratio of 30. The properties of the HP700 particle indicate that it is a reaction center complex which is served by an accessory complex containing the additional light‐harvesting chlorophyll of Photosystem I as well as the cytochromes and plastoquinone. When Photosystem II particles obtained by the action of Triton X‐100 are further washed with a solution 0.5 M in sucrose and 0.05 M in Tris buffer (pH 8.0), chlorophyll‐containing material is released. After centrifugation, the supernatant contains about 1 per cent of the chlorophyll and contains three types of particles which can be separated by sucrose density gradient centrifugation. One of these particles, designated TSF‐2b, has the same pigment composition as the original Photosystem II fragment, contains cytochrome 559, and shows Photosystem II activity (DCMU‐sensitive diphenylcarbazide‐supported photoreduction of 2,6‐dichlorophenolindophenol). The other two particles (TSF‐2a and TSF‐2a′) have a [Chl a]/[Chl b] ratio of 8, have a low concentration of xanthophylls, and show a [Chl]/[Cyt 5591 ratio of about 20. Only the TSF‐2a particle is active in the Photosystem II reaction described above. On the basis of these data, it is proposed that the Photosystem II unit consists of a reaction center complex which contains Chl a, Cyt 559, and an acceptor for the photochemical reaction. The reaction center complex would be served by an accessory complex which contains the light‐harvesting pigments, Chl a. Chi b, and xanthophyils.
THREE LIGHT REACTIONS AND THE TWO PHOTOSYSTEMS OF PLANT PHOTOSYNTHESIS*
Authors: ARNON D. I. , KNAFF D. B. , McSWAIN B. D. , CHAIN R. K. , TSUJIMOTO H. Y.
Published: January 2008

Abstract—Recent work in our laboratory yielded new evidence that noncyclic electron transport in chloroplasts from water to ferredoxin (Fd) and N ADP is carried out solely by System II which, unexpectedly, was found to include not one but two photoreactions (IIa and IIb). The evidence suggests that these operate in series, being joined together by a ‘dark’ chain of electron carriers that includes (but is not limited to) cytochromeb559and plastocyanin (PC):

H2O → IIbhv→ C550 → Cytb559rarr;PC→IIahv→ Fd → NADP.

Photoreaction IIb involves an electron transfer from water to C550, a new chloroplast component distinct from cytochromes, whose photoreduction is observed as a decrease in absorb‐ance with a maximum at 550 nm. The photoreduction of CSSO proceeds effectively only in short‐wavelength System II light, is insensitive to low temperature (at least down to — 189°C). does not require plastocyanin, and is the first known System II photoreaction which is resistant to inhibition by DCMU oro‐phenanthroline. Photoreaction IIa involves an electron transfer from cytochromeb559to ferredoxin‐NADP and also proceeds effectively only in System II light. The photooxidation of cytochromeb559requires plastocyanin. Cytochromeb559is reduced by C550 in a reaction that is readily inhibited by DCMU oro‐phenanthroline. Thus, the site of DCMU (ando‐phenanthroline) inhibition of System II appears to lie between C550 and cytochromeb559. System I, comprising a single long‐wavelength light reaction and a cyclic electron transport chain that includes cytochromesb6andf, is viewed as operating in parallel to System II. The photoreduction of NADP by artificial electron donors via System I involves a portion of the cyclic electron transport chain and appears to be independent of plastocyanin. Chloroplast fragments have been prepared which either (a) exhibit System II activity (water → NADP) and lack functional cytochromefand P700 or (b) exhibit System I activity and lack plastocyanin. The present concept is consistent with the following: (i) No enhancement effect was found for NADP reduction by water where only System II is thought to be involved, but a large enhancement effect was observed in chloroplasts engaged in complete photosynthesis where both cyclic (System I) and noncyclic photophosphorylation (System II) are needed for CO2assimilation. (ii) The transfer of one electron from water to ferredoxin via System II requires optimally two quanta, but the transfer of one electron from reduced dye to ferredoxin via System I requires optimally only one quantum of light.
ACTION SPECTRA FOR THE ABSORBANCE CHANGE AT 880 nm AND FOR P870 FLUORESCENCE FROM A PHOTOSYNTHETIC REACTION CENTER*
Authors: YAU HON F.
Published: January 2008

Abstract— Photosynthetic reaction centers isolated from blue‐green mutant strain R‐26 of Rhodopseudomonas spheroides were used to study the action spectra for the light‐induced absorption changes at 880 nm, and for the P870 fluorescence. These spectra indicated that a pigment, possibly bacteriopheophytin, with an absorption maximum at 757 nm is an intrinsic component of the reaction center and transfers energy to P870 with relatively high efficiency.
THE INFLUENCE OF NUTRITION ON THE DNA CONTENT OF ESCHERICHZA COLI AND ITS RESPONSE TO ULTRAVIOLET LIGHT
Authors: WEBB S. J. , ROKOSH D. A.
Published: January 2008

Abstract— The influence of nutrition on the sensitivity of Escherichia coli 15T‐ to ultraviolet light (u.v.) and the synthesis of DNA has been studied. Growth in media containing glucose or NH,+ has been found to endow cells with a greater resistance to lethal u.v. damage than those grown in media containing succinate or amino acids, respectively. In addition, the sensitivity of the lactose (lac) locus of the DNA to mutagenic damage has been found to be altered by changes in the carbon supply but not by changes in the nitrogen source, while the sensitivity of loci controlling amino acid synthesis was altered by changes in the nitrogen source but not in the carbon source. Cells fed with glucose or NH4+ have been found to possess more DNA than cells fed with succinate or amino acids, respectively. The data indicate that the type of carbon and nitrogen supplied to the cells will determine whether or not set regions of the DNA will undergo more than one round of replication. The presence in the cell of identical genetic loci either in duplicate or in multiples, directed by the particular types of carbon and nitrogen supplied, is suggested to be, in part, the reason why an alteration in nutrition is able to influence the sensitivity of bacterial cells to radiation.
LUMINESCENCE SPECTRA AND PHOTOCYCLOADDITION OF THE EXCITED COUMARINS TO DNA BASES
Authors: SONG PILL‐SOON , HARTER MARIAN L. , MOORE THOMAS A. , HERNDON WILLIAM C.
Published: January 2008

Abstract— The lowest excited singlet and triplet states of coumarin, psoralen, and 4‐hydroxy‐coumarin have been assigned to the (π,π*) type on the basis of the luminescence spectroscopy and MO calculations. The mechanism of photocycloaddition of courmarin and psoralen to thymine has been described in terms of the perturbational MO model and MO reactivity indices. All possible cycloaddition patterns have been examined. Results suggest that the 3,4‐bond of coumarin in the excited state is somewhat more reactive than the same bond of psoralen in the excited state. It is also predicted that the 3,4‐bond of psoralen in the triplet state is more reactive than the 4′, 5′‐bond. The results have been favorably correlated with the electronic characteristics of excited coumarin molecules and with available experimental data on the relative yields of photoadducts.
RELATIONSHIP BETWEEN SURVIVAL AND THYMINE‐DIMER EXCISION IN ULTRAVIOLET‐IRRADIATED ESCHERICHIA COLI
Authors: SEDLIAKOVÁ M. , MAŠEK F. , BERNÁTOVÁ Ľ.
Published: January 2008

Abstract— The influence of amino acid prestarvation on both the resistance to u.v. light and excision of thymine dimers of bacterial strains E. coli B/r hcr+ thy‐ trp‐, E. coli B/r hcr‐thy‐trp‐, and E, coli 15 T‐ 555–7 thy‐meth‐trp‐arg‐ has been studied.

The prestarvation increased the resistance of all the strains but reasonably inhibited excision of thymine dimers. Thus the enhancement of u.v. resistance after amino acid prestarvation was not due to more complete excision of thymine dimers.
ULTRAVIOLET IRRADIATION OF TOBACCO LEAVES: INHIBITION OF TOBACCO MOSAIC VIRUS‐RIBONUCLEIC ACID PHOTOREACTIVATION*
Authors: MURPHY T. M. , GORDON M. P.
Published: January 2008

Abstract— Short‐wave (254‐nm) ultraviolet irradiation of the leaves of Nicotiana tabacum var. Xanthi, n.c. inhibits their ability to photoreactivate ultraviolet‐inactivated tobacco mosaic virus ribonucleic acid (TMV‐RNA). The inhibition is stable in the dark; however, subsequent illumination of the leaves relaxes the inhibition. The spectral region most effective in relaxing the inhibition is the same one effective in photoreactivation. These results are consistent with the hypothesis that ultraviolet‐induced lesions in cellular nucleic acids in the dark form stable complexes with agents responsible for the photoreactivation of TMV‐RNA (effectively isolating the agents from the TMV‐RNA) and that upon illumination these complexes dissociate (presumably with repair of the lesions). We therefore suggest that the system which photoreactivates ultraviolet‐damaged TMV‐RNA also photorepairs ultraviolet damage in cellular nucleic acids.
PRIMARY PRODUCTS IN THE FLASH PHOTOLYSIS OF TRYPTOPHAN*
Authors: SANTUS R. , GROSSWEINER L. I.
Published: January 2008

There has been considerable interest in the photochemistry of tryptophan in connection with ultraviolet inactivation of enzymes. Earlier flash photolysis work has demonstrated that the hydrated electron (e‐aq) is an initial product in the irradiation of indole derivatives, accompanied by a longer‐lived transient absorption near 500 nm attributed to an aromatic radical species[1–5]. Similar transients were observed in a recent flash photolysis study of lysozyme[6] in which it was proposed that inactivation is a consequence of electron ejection from 1 to 2 essential tryptophan residues in the active center. However, there has been uncertainty concerning the tryptophan radical structure and its relationship to the triplet state and radical spectra reported for tryptophan photolysis in low‐temperature rigid media. This note reports a flash photolysis investigation of L‐tryptophan (Trp) and 1‐Methyl‐L‐tryptophan (1‐MeTrp) undertaken to clarify these points. The flash photolysis apparatus and methods employed are described in Ref. [6].
CONTROL OF SYNTHESIS OF REACTION CENTER BACTERIOCHLOROPHYLL IN PHOTOSYNTHETIC BACTERIA
Authors: AAGAARD JEANETTE , SISTROM W. R.
Published: January 2008

Abstract— The ratio of total bacteriochlorophyll (BChl) to reaction center BChl has been determined in the wild‐type and carotenoid‐less mutants of Rhodopseudomonas spheroides and Rhodospirillum rubrum with various specific BChl contents. In wild‐type R. spheroides the ratio increases as the specific BChl content increases; in the other strains the ratio is almost invariant.

The ability of the wild‐type of R. spheroides to alter the size of the photosynthetic unit is apparently correlated with its multi‐component BChl spectrum. The amount of reaction center BChl relative to the amount of the longest wavelength component of the spectrum is constant. The variation in the size of the photosynthetic unit is due to variation in the amount of this component relative to total BChl.

The size of the photosynthetic unit does not change as the specific BChl content decreases during growth under aerobic conditions of a culture grown previously under photosynthetic conditions.
CONCERNING THE PRODUCTION OF FREE RADICALS IN PROTEINS BY ULTRAVIOLET LIGHT
Authors: ANDROES G. M. , GLORIA H. R. , REINISCH R. F.
Published: January 2008

Abstract— Using electron paramagnetic resonance techniques, the response to u.v. light of several solid proteins and model compounds has been studied in vacuum and at low temperature. Emphasis has been placed on determining the response as a function of the wavelength (Λ 250 nm) and intensity of the incident radiation. Correlation of the parameters of radical production with sample luminescence, molecular amino‐acid sequence and tertiary structure, light intensity and total irradiation time has allowed some insight into the mechanisms of free radical formation.

It is shown that the details of amino acid composition, sequence and the tertiary structure of a protein are important in determining both the rate of, and the mechanism for, radical production (two basic mechanisms are described), and in determining the conditions under which sulfur‐type radicals can be produced. The results are related to enzyme inactivation and to the u.v. stability of proteins generally.
DECAY KINETICS OF FREE RADICALS IN IRRADIATED PROTEINS
Authors: SHATKAY A. , MICHAELI I.
Published: January 2008

Abstract— A detailed analysis is presented of the decay kinetics of free radicals in irradiated biopolymers. Available data in the literature are critically evaluated and new data for irradiated keratin are presented. It is shown that a rigorous analysis of the data available in the literature leads to more detailed information on the decay mechanisms than the conclusions which have been previously given; in some cases the analysis leads to mechanisms contradicting those claimed in the literature.

Our results suggest that the free radicals in illuminated keratin consist of three distinct species: one of the species decays with a half life of approximately 20 hr, the second has a half life of about 4600 hr, while the half life of the third is so long that the free radical concentration is practically constant. A similar behaviour is obtained on assumption of second order decay.

The consistency of the kinetic constants obtained has been verified in kinetic experiments using samples prepared under very different experimental conditions.