bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
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.
EFFECT OF DIPICOLINIC ACID ON THE ULTRAVIOLET RADIATION RESISTANCE OF BACILLUS CEREUS SPORES
Authors: GERMAINE G. R. , MURRELL W. G. 
Published: January 2008

Abstract— The ultraviolet radiation (UV) resistance of B. cereus spores was shown to depend on their content of dipicolinic acid (DPA). Wild‐type spores with decreasing amounts of DPA exhibited increased UV resistance. Similarly, spores devoid of DPA (DPA‐minus), produced by a mutant strain of B. cereus unable to synthesize DPA, were more resistant to UV than mutant spores (DPA‐plus) produced in the presence of exogenously supplied DPA. Resistance of both the wild type and mutant strains to ionizing radiation, however, was unaffected by DPA content. Comparison of the resistance of DPA‐minus and DPA‐plus mutant spores to UV of various wavelengths showed that the greater sensitivity of the latter DPA‐plus spores appeared at wavelengths corresponding to the region of the first molecular absorption band of the calcium chelate of DPA. In the wild type and mutant, thymine photoproducts were produced at a greater rate and to a greater extent in spores with high levels of DPA than in spores with low DPA.The data indicate that DPA transfers energy to DN A in vivo, which leads to the conclusion that DPA occurs in the spore protoplast.
PHOTOLYSIS OF AQUEOUS SOLUTIONS OF POTASSIUM CIS‐DIAQUOBIS (OXALATO) CHROMATE (III)
Authors: ROPHAEL M. W. , MALATI M. A. 
Published: January 2008

Abstract— The photolysis of aqueous solutions of cis‐[Cr(C2O4)2(H2O)2]‐ at 254 nm and pH 4 produced CO2 and H2 in nearly equal yields. The quantum yield of hydrogen, φ2, increased by 9% and the yield of carbon dioxide, φ, by 65% as the pH was lowered from 4 to I. The total gas yield, φgas, decreased in the presence of added oxalate or chromium (II) ions and when the light intensity was lowered. The gas yield in D2O was appreciably higher than in H2O. The variation of φgas with pH (D) and with added oxalate ion was roughly parallel in the two liquid media. The gas yield increased in the series:A tentative mechanism is suggested to explain the results.
OPTICALLY DETECTED MAGNETIC RESONANCE OF THE TRYPTOPHAN PHOSPHORESCENT STATE IN NATIVE PROTEINS*
Authors: Zuclich J. , Schweitzer D. , Maki A. H. 
Published: January 2008

Abstract— The phosphorescent triplet state of tryptophan has been studied by the method of optically detected magnetic resonance (ODMR) at pumped helium temperatures in zero magnetic field. Only one of the triplet sublevels is found to be significantly radiative; the other two decay radiationlessly. Although the phosphorescence and ODMR decay lifetimes are influenced by spin–lattice relaxation processes at T= 1.3°K, the lifetime of the radiative level can be estimated as approximately 2 s, whereas the lifetimes of the non–radiative levels are in excess of 10 s. Comparison of the ODMR signals and the phosphorescence spectra has been made for tryptophans in native proteins with the following results: the ODMR signals of the two types of tryptophan sites in horse liver alcohol dehydrogenase can be resolved due to a shift in the D and E values of the respective triplet states; binding of the substrate tri‐N‐acetylglucosamine to hen lysozyme leads to a considerable narrowing of the phosphorescence peaks and ODMR signals as well as to a shift in the E value of the triplet state.The following tentative conclusions can be reached: the tryptophan triplet D and E values are measurably affected by the environment of the chromophore in the protein, as are the linewidths of the magnetic resonance transitions. The |E| value is reduced and the magnetic resonance linewidth is increased with increasing exposure of the tryptophan to hydroxylic solvent. Although a considerable part of the width of the magnetic resonance transition can be ascribed to a heterogeneity of environments in the sample, there appears to exist an intrinsic line–broadening process which at present is not understood.
SIMPLE EXPLANATION OF THE MISSES IN THE COOPERATION OF CHARGES IN PHOTOSYNTHETIC O2 EVOLUTION
Authors: Delrieu Marie‐Jose 
Published: January 2008

Abstract—In the model of Forbush et at. (1971) the observed damping of the flash yield sequence of photosynthetic O2 evolution was related to a certain percentage of ‘misses’ (α; i.e. centers not converted). The possibility of a miss was supposed to be equal for all states S0.1,2,3. We propose a new model and a new recurrence law that gives better quantitative agreement with the O2 yield oscillations observed in Chlorella during a sequence of flashes. We find a better fit with all experimental results by assuming very unequal misses; the misses occur nearly exclusively on S2 (and also sometimes on S3). In the simpler case of only one miss on one state, half of S2 exists as an inactive form S2+‐ because it is in apparent equilibrium with pool A. The active form of S2 is converted to S3 in a flash and the unchanged inactive form S2+‐ explains the miss: S
1
hv→S2+‐=S2hv→S3(S2+‐ is a transition state between S1 to S2 associated with Q‐).In the dark, the apparent equilibrium constant KA between pool A and Q (i.e. S0, S1 in the dark) is very large; this explains why there is no miss on these states. In light, the experimental value of KA between pool A and Q (i.e. S2, S3 in the light) is 1, and this explains why the misses are large for states S2, S3; i.e., S2+‐/S2‐ 1 and sometimes S3+‐/S3˜0–1.This new model predicts that the total number of active states ΣSi=S0+S1+S2+S3 is an oscillating function of the flash number. This sum 2S, is also the number of trapping centers for excitons. As fluorescence is proportional to excitons that are not trapped, our model explains why the fluorescence oscillates as a function of the flash number. We find also that the initial rates of O2 evolution after (n ‐ 1) flashes vs the 02 yield of the nth flash are not exactly on a straight line, which also favors our model.
ON THE PHYSIOLOGICAL SIGNIFICANCE OF DARK REVERSION OF PHYTOCHROME IN THE MUSTARD SEEDLING
Authors: Oelze‐Karow H. , Scháfer E. , Mohr H. 
Published: January 2008

Abstract—We present physiological evidence using the threshold control of lipoxygenase synthesis† by Pfr in the mustard seedling (LOG response) that there is no dark reversion of phytochromewhich would be relevant for this response. Such Ptr which can be detected with the lipoxygenase response disappears exclusively through degradation with a half‐life of 45 min at 25°C. De novo synthesis of P*r in the hypocotylar hook takes place at a constant rate (zero order rate constant) irrespective of the level of Pr or P*tot, i.e. there is no detectable feedback control of Pr synthesis during the period of experimentation. The data of the present paper are consistent with a quantitative phytochrome model (Scheme 1) which has been advanced and treated quantitatively in the companion paper (Oelze‐Karow and Mohr, 1976).
THE ROLE OF SOLAR ULTRAVIOLET RADIATION IN ‘NATURAL’ WATER PURIFICATION
Authors: Calkins John , Buckles James D. , Moeller John R. 
Published: January 2008

Abstract— The concentration of Escherichia coli in the input and output of a tertiary wastewater system (4 lagoons) has been monitored over an 11 month period. The integrated flux of biologically active solar ultraviolet (UV) radiation was measured during this period. By also determining (1) the effective temperature in the system, (2) the growth rate of E. coli at the effective temperature, (3) the penetration of the solar UV into the lagoons, (4) the dose‐response relation for killing of E. coli by UV and (5) the retention time of water in the system, it is possible to compare the ‘die off’ expected from solar UV exposure to the actual ‘die off’ observed for different batches of water.The observed killing of E. coli was quite close to the values calculated, considering the numerous factors involved. Solar UV light would thus seem to be a very important factor in the natural purification of water. Because each successful species must possess characteristics (physiological or behavioral) which provide adequate resistance to solar UV, the ecological role of solar UV radiation has not been widely appreciated.
ELECTRONIC PROCESSES AND PHOTOELECTRIC ASPECTS OF BILAYER LIPID MEMBRANES
Authors: Tien H. Ti 
Published: January 2008

Abstract— Owing to the complexity of biological membranes, many model systems have been studied in order to gain insight into the molecular mechanism of specific functions. One such model membrane extensively investigated in the past decade is the so‐called bilayer lipid membrane (BLM). With suitable modifications, a BLM less than 100 A thick separating two aqueous solutions has been used as a model for a variety of biological membranes. This paper is devoted to a review of the properties and electronic processes of modified BLM.Recent experiments using these membranes which contain photosynthetic pigments or dyes have demonstrated that, upon illumination, an EMF and a current can be generated. The connection between the photoelectric BLM and light‐sensitive biological membranes and the rationale for this work are described.Additionally, the effects of physical chemical parameters such as electric field, temperature, light intensity, duration of illumination and chemical agents (electron acceptors, donors, uncouplers, etc.) on the photoresponses of BLM are discussed. Other results indicate that BLM containing photoactive compounds behave similar to that of a silicon solar cell with one side of the membrane reducing and the other side oxidizing. The transverse pathway for the electron across the BLM could be provided by carotenoids such as β‐carotene. Photoelectric BLM of this type represents a unique kind of energy transducing system and may well be useful in the conversion of solar energy into electricity and/or other forms of energy.
EXCITED STATE INTERACTIONS OF 7‐AZAINDOLE WITH ALCOHOL AND WATER
Authors: Avouris Phaedon , Yang Li L. , El‐Bayoumi M. Ashraf 
Published: January 2008

Abstract— The fluorescence spectrum of 7‐azaindole in alcohol is composed of two fluorescence bands. Effects of pH, temperature and solvent deuteration on the fluorescence spectra and quantum yields of 7‐azaindole and other model compounds in ethanol and in water are reported. The long wavelength band arises from a tautomeric species formed in an adiabatic photoreaction involving double proton transfer between one molecule of 7‐azaindole and one molecule of alcohol.The fluorescence spectrum of 7‐azaindole in water is composed of only one band, but the emission is weak and shows a large solvent isotope effect. The possibility of a double proton transfer reaction between 7‐azaindole and water is discussed.
TEMPERATURE DEPENDENCE OF DELAYED LIGHT EMISSION IN THE 6 to 340 MICROSECOND RANGE AFTER A SINGLE FLASH IN CHLOROPLASTS
Authors: Jursinic P. , Govindjee  
Published: January 2008

Abstract. The delayed light emission decay rate (up to 120 μs) and the rise in chlorophyll a fluorescence yield (from 3 to 35 μs) in isolated chloroplasts from several species, following a saturating 10 ns flash, are temperature independent in the 0–35°C range. However, delayed light in the 120–340 μs range is temperature dependent. Arrhenius plots of the exponential decay constants are: (a) linear for lettuce and pea chloroplasts but discontinuous for bush bean (12–17°C) and spinach (12–20°C) chloroplasts; (b) unaffected by 3‐(3,4 dichlorophenyl)‐1,1‐dimethylurea (inhibitor of electron flow), gramicidin D (which eliminates light‐induced membrane potential) and glutaraldehyde fixation (which stops gross structural changes).The discontinuities, noted above for bush bean and spinach chloroplasts, are correlated with abrupt changes in (a) the thylakoid membrane lipid fluidity (monitored by EPR spectra of 12 nixtroxide stearate, 12NS) and (b) the fluidity of extracted lipids (monitored by differential calorimetry and EPR spectra of 12 NS). However, no such discontinuity was observed in (a) chlorophyll a fluorescence intensity of thylakoids and (b) fluorescence of tryptophan residues of delipidated chloroplasts.Microsecond delayed light is linearly dependent on light intensity at flash intensities as low as one quantum per 2 times 104 chlorophyll molecules. We suggest that this delayed light could originate from a one quantum process in agreement with the hypothesis that recombination of primary charges leads to this light emission. A working hypothesis for the energy levels of Photosystem II components is proposed involving a charge stabilization step on the primary acceptor side, which is in a lipid environment.Finally, the redox potential of P680 (the reaction center for chlorophyll of system II) is calculated to be close to 1.0–1.3 V.
ENERGY TRANSFER IN THE ACCESSORY PIGMENTS R‐PHYCOERYTHRIN AND C‐PHYCOCYANIN
Authors: Barber D. J. W. , Richards J. T. 
Published: January 2008

Abstract— The photosynthetic accessory pigments R‐phycoerythrin and C‐phycocyanin were extracted from a red sea‐weed and a filamentous blue‐green alga. Investigation of quenching of phycoerythrin fluorescence by phycocyanin at room and liquid nitrogen temperatures yielded rates for the SternVolmer quenching constants (Kq From these values, rate constants k(D–A) were calculated for the transfer of energy from phycoerythrin to phycocyanin.The transfer rate constants obtained were such that a collisional transfer mechanism was ruled out, and were of similar order of magnitude as the rate constants for transfer of electronic energy in mixed organic crystals.