Showing papers on "Photosynthetic reaction centre published in 1977"
TL;DR: It was concluded that Subunit III mediates reduction of P,,,+ by plastocyanin in Photosystem I and suggested that a unit of about 20 chlorophyll a molecules is specifically associated with the reaction center protein 02, = 70,000) in the vicinity of PToO.
272 citations
TL;DR: The results support a model in which electrons are transferred one by one from UQ1 to UZ2 with a half-time 200 micro seconds, and two by two from fully reduced UQ2 to the secondary acceptor pool.
147 citations
TL;DR: The spectroscopic properties of the intermediary electron carrier (I), which functions between the bacteriochlorophyll dimer and the primary acceptor quinone · iron, QFe, have been characterized in Rhodopseudomonas viridis are characterized and it is concluded that there is no direct correlation between the two optical and the two EPR signals of I⨪.
100 citations
TL;DR: Analysis of the reduction kinetics of c+-551 in the absence and presence of external donors suggests that c-551 is partly reduced via a cyclic pathway, which is blocked by addition of o-phenanthroline, and partly via a non-cyclic pathway.
81 citations
TL;DR: Equations for fluorescence and the rates of photochemistry of photosystem I and photosystem II are derived from a photochemical model for the photosynthetic apparatus and provide new and credible insights into the photochemical apparatus of photosynthesis.
Abstract: Equations for fluorescence and the rates of photochemistry of photosystem I and photosystem II are derived from a photochemical model for the photosynthetic apparatus that includes the various interactions of the light-harvesting chlorophyll a/b complex with photosystem I and photosystem II as specific photochemical rate constants. The degree of coupling between photosystem II and the chlorophyll a/b complex which is expressed as a product of two probability terms plays a central role in this three-pigment system. The cycling of excitation energy back and forth between photosystem II and the chlorophyll a/b complex increases the exciton density in both arrays of chlorophyll according to a simple analytical expression in the equations. These equations of the tripartite model provide new and credible insights into the photochemical apparatus of photosynthesis.
76 citations
TL;DR: In this paper, the authors suggest that this delayed light emission could originate from a one quantum process in agreement with the hypothesis that recombination of primary charges leads to this light emission.
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.
76 citations
TL;DR: This deceleration is the major effect of bicarbonate depletion and must be associated with the 4 to 8-fold loss in Hill activity observed by earlier workers.
60 citations
TL;DR: The results indicate that initially small PS II units are formed, which contain mainly the reaction center with a few chlorophyll a molecules closely packed around it, and these small units are very efficient for photochemistry.
59 citations
TL;DR: Electron paramagnetic resonance (EPR) and optical absorbance difference spectra and kinetics upon illumination by saturating flashes and continuous light of spinach chloroplasts frozen under various conditions were measured and a model is given to explain the observed reactions of Photosystem II at 10-180 K.
58 citations
TL;DR: Changes in the 790 and 544 nm bands upon illumination of the reaction center preparation at low redox potential may be indicative of a role for bacteriophaeophytin b in primary photochemical events.
55 citations
TL;DR: In both cases, the results demonstrated that the intermediary carrier, which the authors designate I, alone governs the capability for reaction center bacteriochlorophyll photooxidation, and as such I appears to be the immediate and sole electron acceptor from the light excited reaction centre bacterio chlorophyll dimer.
TL;DR: S-S type of energy migration to the RCs predicts the following relation between the quantum yield of primary energy trapping by active RC (+,h) and maximal increase in fluorescence yield (qfl) under transition from active to saturated photosynthesis.
TL;DR: Analysis of the changes of pigment absorption upon illumination of chromatophores of Rhodopseudomonas sphaeroides at −35 °C showed that there are at least two pools of carotenoid and the differences in band location may be explained by the assumption that only the first pool is subjected to a local electric field which induces an electric dipole even at zero membrane potential.
TL;DR: The close interrelationship between ΔA 0 (chlorophyll- a II ) and delayed fluorescence intensity in the μs range is shown to be interpretable mainly by kinetical rather than by energetical effects.
TL;DR: Evidence was obtained that a naphthoquinone was photoreduced to the semiquinone anion, giving support to the hypothesis that vitamin K 2 (menaquinone) may act as the primary electron acceptor in C. vinosum.
TL;DR: It is concluded that the H protein is largely exposed at the cytoplasmic side of the membranes but might also be accessible for iodination on the inside of the membrane while the L and M proteins are almost completely embedded in the membrane.
TL;DR: It is observed that the dichroic ratio of the absorption changes of chlorophyll a1 does not exceed a figure of 4 3 , which characterizes a circularly degenerate system, even at far red excitation (724 nm), which will hit selectively those few chlorophyLL a molecules with their peak absorption at about 700 nm (including the photooxidizable dimer).
TL;DR: The information available on anaerobic electron transfer systems and evidences that these systems are coupled to active transport of metabolites are summarized in the chapter.
Abstract: Publisher Summary This chapter discusses anaerobic electron transfer and active transport in bacteria. The energy present in an oxidizable substrate can be released through a graded series of reversible oxidation-reduction reactions, with reducing equivalents transferred to a terminal electron acceptor via the electron carriers of an electron transfer system. In bacteria, several inorganic and organic compounds function as terminal electron acceptor. Bacterial electron transfer systems vary from simple to very complex, and a wide diversity exists in the electron carriers that participate in these systems. In obligately aerobic bacteria, oxygen is the only terminal electron acceptor and cytochromes of a, d, and o types can function as terminal oxidases. The electron transfer system of these bacteria, the respiratory chain, resembles most closely the electron transport chain in mitochondria. In facultative anaerobes, the terminal electron acceptors are more complex. Anaerobic bacteria are defined as organisms that can never use oxygen as terminal electron acceptor. Bacterial electron transfer systems are presented as a linear series of electron carriers. Electrons transferred through these pathways are derived from reduced bacteriochlorophyll in a light-dependent process. In bacterial cytoplasmic membranes, the same energy-dependent processes occur: (1) synthesis of ATP, (2) accumulation of substrates and ions against concentration gradients, (3) reversal of the direction of oxidation, and (4) trans-hydrogenation, the reduction of NADP by NADH. The information available on anaerobic electron transfer systems and evidences that these systems are coupled to active transport of metabolites are summarized in the chapter.
TL;DR: The results indicate the generation of large membrane potentials at low temperature, caused by sustained electron transport across the chromatophore membrane, which agrees with the hypothesis that P-870 is located inside the membrane.
TL;DR: In this article, parallel measurements of the rise in chlorophyll a fluorescence yield and delayed light emission decay, after a 10 ns saturating excitation flash, have been made in tris(hydroxymethyl)aminomethane-washed chloroplasts.
TL;DR: Using the pulse picosecond fluorometric technique the fluorescence properties of intact cells, isolated chromatophores and photosynthetic reaction centres were studied in bacteria Rhodopseudomonas sphaeroides and the rate for energy migration was estimated to be 10 9 s −1.
TL;DR: Reaction centers, isolated from chromatophores of Rhodopseudomonas sphaeroides, contain three protein subunits, four molecules of bacteriochlorophyll (BChl), two molecule of bacteriopheophytin (Bph), one or two molecules of ubiquinone and one atom of iron
TL;DR: In this paper, the absorption and fluorescence characteristics of subchloroplast particles highly enriched in P700 (1 P700 to 10-15 chlorophyll a molecules) and of two artificial systems are presented.
Abstract: . –The absorption and fluorescence characteristics of subchloroplast particles highly enriched in P700 (1 P700 to 10–15 chlorophyll a molecules) and of two artificial systems are presented here. The fluorescence characteristics measured were excitation and emission spectra, and the degree of polarization of fluorescence. The model systems studied were chlorophyll a and pheophytin a in a polystyrene matrix, and a colloidal mixture of these two pigments with bovine serum albumin. Effects of 0.5% sodium dodecyl sulfate on the optical properties of the P700-enriched particles are also described. The importance of pigment-pigment and pigment-protein interactions in determining the fluorescence properties of these particles are discussed. The possible role of pheophytin in these preparations needs further investigation.
01 Jan 1977
TL;DR: The use of artificial electron donors and acceptors has been one of the biochemical approaches to the elucidation of complex electron transport chains in biological membranes and taught us about the sequence, about the energy-conserving steps, and more recently about the topography of the photosynthetic electron transport chain in the chloroplast membrane.
Abstract: The use of artificial electron donors and acceptors has been one of the biochemical approaches to the elucidation of complex electron transport chains in biological membranes. In photosynthesis it started with Hill’s discovery that ferric salts could induce light-dependent oxygen evolution in cell-free leaf extracts (Hill, 1937). Since then the results of this approach have taught us about the sequence, about the energy-conserving steps, and more recently about the topography of the photosynthetic electron transport chain in the chloroplast membrane. It has also made possible the design of assays for parts of the chain in a physiologically nonfunctional state, i.e. for the reaction center complexes, either during biochemical isolation (see this vol., Chap. IV.5) or during biogenesis of the photosynthetic apparatus (see this vol. Chap. IV.6).
TL;DR: In this article, a review of recent spectroscopic studies aimed at discovering the structure, orientation, and function of chlorophyll in vivo is presented, and the most promising, newly synthesized model for the reaction center, P700, is a covalently bound dimeric derivative of pyrochlorophyllide.
Abstract: . –This review discusses recent spectroscopic studies aimed at discovering the structure, orientation, and function of chlorophyll in vivo. In plant membranes there appear to be at least two distinct types of chlorophyll a. The greater part, over 99%, is antenna chlorophyll which absorbs and transfers radiant energy to a few specialized chlorophyll molecules in a reaction center where the actual charge separation occurs.
A dimer-oligomer model for antenna chlorophyll has been proposed on the basis of comparative studies of the absorption spectra of chlorophyll in various dry solvents and in vivo. Unfortunately a similarity between essentially structureless broad spectra is very weak evidence for their original identity. Also the requirement of an anhydrous environment for most of the chlorophyll in biological material is an unlikely postulate. A cross-linked, linear polymer model of chlorophyll in vivo has also been proposed. Recent Resonance Raman spectroscopic results appear to rule out, in large part, either polymer model and once again suggest that it is the various attachments of chlorophyll to proteins which determine its function as antenna pigment in vivo. Circular dichroism measurements of chlorophyll in various plant materials have also led to the conclusion that antenna chlorophyll has strong interaction with protein. However, some doubt still exists as to the interpretation of these CD results. New studies of fluorescence, polarized fluorescence and Resonance Raman spectroscopy of various plant species corroborate the original proposition, based upon deconvolution of absorption spectra, that antenna chlorophyll occurs in vivo in at least five discrete pools, and that each pool is likely to be located in the same environment in different plants.
A new model-systems approach to simulating chlorophyll in vivo has come through the use of lipid bilayers and liposomes. Charge transfer has been observed between chlorophyll in a lipid phase and phycobiliproteins or cytochrome c.
The most promising, newly synthesized model for the reaction center, P700, is a covalently bound dimeric derivative of pyrochlorophyllide a. Its properties are similar to P700 in several respects except for reversible photooxidation which has not yet been observed. By detergent treatments chlorophyll-protein complexes having about 20–40 chlorophyll a molecules for every P700 have been isolated from different plants, and their spectroscopic properties are under investigation in several laboratories. The several hypotheses to explain the shape of the oxidized minus reduced absorption difference spectrum of P700 have not yet been reconciled. The nature of the photosystem II reaction center chlorophyll, P680, is also a subject of active investigation. Its absorption difference spectrum appears to have two kinetic components.
TL;DR: Apparently, rupture of the photosynthetic complex of chloroplasts prevents the formation of this triplet, which is formed by an excitation energy transfer from the PS2 units with closed traps to PSI units, and is trapped on a fraction of antenna chlorophyll that after digitonin treatment.
TL;DR: Action spectra of light reaction I and light reaction II from red algae were measured with 550 nm or 699 nm background light, using a Teflon-covered platinum electrode for O2 measurement and some evidence is shown that strongly supports model 2.
TL;DR: The present general consensus is that the initial photoactivated electron transport steps occurring in the photochemical reaction center of purple bacteria involve the oxidation of a bacteriochlorophyll dimer with the concomitant reduction of an intermediary electron carrier.
TL;DR: In this article, a photooxidized P700 dimer (Chl+-Chl) absorbing near 690 nm was found to be an absorbing form of antenna chlorophyll that may be somewhat enriched along with P700 in Photosystem I fractions.
Abstract: . Chlorophyll-protein complexes enriched in the Photosystem I reaction center chlorophyll (P700) exhibit a fluorescence emission maximum at 696 nm at - 196°C The height of this 696 nm emission relative to the emission at 683 nm from antenna chlorophyll a increases proportionally with the P700 concentration while the total fluorescence yield of the complex decreases. The 696 nm emission could possibly be from an absorbing form of antenna chlorophyll a that may be somewhat enriched along with P700 in Photosystem I fractions. However, evidence resulting from glycerol treatment which appears to decrease the rate of resonance energy transfer between antenna chlorophyll and P700 favors the hypothesis that the emission comes from a photooxidized P700 dimer (Chl+-Chl) absorbing near 690 nm. In turn, this fluorescence evidence provides additional support for the model of a P700 dimer involving exciton interaction. Absorption in the wavelength region of 450 nm specifically excites emission at 696 nm from the P700-chlorophyll complex.
Journal Article•
TL;DR: The temperature dependencies of the photoconversion of pigments P870--P890 were studied using isolated chromatophores and photosynthetic reaction centres of purple bacteria to indicate on the essential role of macromolecular components in the RC's functioning and suggest that the photochemical charge separation is conformation-controlled.
Abstract: The temperature dependencies of the photoconversion of pigments P870--P890 were studied using isolated chromatophores and photosynthetic reaction centres (RC's) of purple bacteria. The samples were prepared by extraction with organic solvents (light petroleum and a combination of light petroleum and methanol) and modified through cross-linking the functional groups of proteins by treatment with glutaraldehyde or denatured by various physical and chemical treatments. The data provide further evidence that the pool of RC secondary acceptors is formed by the compounds of quinone nature located in the hydrophobic surrounding. Similar molecules localized in a more polar medium act as primary acceptors. The findings indicate on the essential role of macromolecular components in the RC's functioning and also suggest that the photochemical charge separation is conformation-controlled.