Tentative identification of the apoproteins of iron-sulfur centers of Photosystem I

AbstractA newly purified Photosystem (PS) I particle is described, with still active iron-sulfur acceptors: A, B and X. Apart from the apoprotein of P700, 3 other main polypeptides of this particle are located at 20, 17 and 10 kDa, and two minor ones are detectable at 16.5 and 8 kDa. Both in vivo 35S labeling and carboxymethylation with iodo[14C]acetate show that most of the cysteine residues are located in the 8-kDa band. The amino acid composition of this band reveals important common features with small iron-sulfur proteins of the ferredoxin type

Electron transport pathways in isolated chromoplasts from Narcissus pseudonarcissus L.

During daffodil flower development, chloroplasts differentiate into photosynthetically inactive chromoplasts having lost functional photosynthetic reaction centers. Chromoplasts exhibit a respiratory activity reducing oxygen to water and generating ATP. Immunoblots revealed the presence of the plastid terminal oxidase (PTOX), the NAD(P)H dehydrogenase (NDH) complex, the cytochrome b(6)f complex, ATP synthase and several isoforms of ferredoxin-NADP(+) oxidoreductase (FNR), and ferredoxin (Fd). Fluorescence spectroscopy allowed the detection of chlorophyll a in the cytochrome b(6)f complex. Here we characterize the electron transport pathway of chromorespiration by using specific inhibitors for the NDH complex, the cytochrome b(6)f complex, FNR and redox-inactive Fd in which the iron was replaced by gallium. Our data suggest an electron flow via two separate pathways, both reducing plastoquinone (PQ) and using PTOX as oxidase. The first oxidizes NADPH via FNR, Fd and cytochrome b(h) of the cytochrome b(6)f complex, and does not result in the pumping of protons across the membrane. In the second, electron transport takes place via the NDH complex using both NADH and NADPH as electron donor. FNR and Fd are not involved in this pathway. The NDH complex is responsible for the generation of the proton gradient. We propose a model for chromorespiration that may also be relevant for the understanding of chlororespiration and for the characterization of the electron input from Fd to the cytochrome b(6)f complex during cyclic electron transport in chloroplasts.Significance Statement Chromorespiration takes place via two pathways, one depends on FNR, ferredoxin, the cytochrome b6f complex, and the other depends on the NDH complex and is ferredoxin independent. We propose an electron transport via the cytochrome b6f complex that involves neither a Q-cycle nor a high potential electron transport chai

Functional Pattern of Photosystem I in Oxygen Evolving Organisms in. Primary Processes of Photosynthesis : Basic Principles and Apparatus

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LPCVD Pyrocarbon Coating on Unidirectional Carbon Fiber Yarns : an Efficient Interphase for Aluminium Matrix Composites

In order to optimize the interfaces in carbon fiber (high resistance Toray T800) reinforced aluminium matrix composites, a pyrolytic carbon (Cp) layer has been developed by a CVD process using a hot wall reactor operating at reduced pressure. The Cp, which has a weak shear strength, is introduced to promote adequate debonding at the fiber/matrix interface. In a first step, classical CVD studies are conducted on planar carbon substrates with a parametric investigation of the effects of temperature, pressure, reactant flow rates on the growth rate and morphology of the coating. For Cp, obtained form thermal decomposition of ethylene, a very high activation energy (310 kJ/mol) and a decrease in coating growth rate with the reactant residence time indicate that the reaction limiting step occurs in the gaseous phase. The carbon coatings exhibit a macroscopic stratified morphology which could promote internal delamination. In a second step, deposition parameters have been optimized to ensure a good infiltration of 6000 filaments yarns. Finally, the influence of carbon underlayer on the mechanical properties of coated fibers is determined by tensile tests on monofilaments and interpreted in terms of Weibull distribution. The results on aluminium composites confirm the beneficial role of mechanical fuse played by the Cp coating

Reaction center photochemistry of Heliobacterium chlorum

Reaction center photochemistry in Heliobacterium chlorum has been investigated by using EPR and flash absorption spectroscopy at low temperatures. The following results were obtained. At 5 K, in the presence of ascorbate, continuous illumination resulted in the formation of P798+ and a reduced iron-sulfur center designated FB (gz = 2.07, gy = 1.93, gx = 1.89). This state was stable at low temperatures, but the yield for this reaction was low, and it was estimated that it occurred only in about 3% of the centers upon the first flash. After continuous illumination of a dilute sample for 10 min, still only half of the centers attained this state. In most centers, flash excitation at 5 K produced a state which recombined with time constants of 2.5 ms (congruent to 80%) and 850 microseconds (congruent to 20%). These two phases were differently influenced by the redox state of the reaction center, indicating that two different acceptors were involved in the recombination reactions. When continuous illumination was given at 200 K, a second center, designated FA, was additionally reduced (gz = 2.05, gy = 1.95, gx = 1.90). High concentrations of dithionite resulted in the chemical reduction of FB and of most of FA; illumination at 200 K resulted in the further reduction of FA. Two triplet states were identified by EPR and optical spectroscopy. The amplitude of the narrower triplet (magnitude of D = 226 x 10(-4) cm-1) varied with the redox state of the iron-sulfur centers and was influenced by a component thought to be a quinone undergoing double reduction. It correlated with a triplet state observed by flash absorption spectroscopy showing a bleaching at 798 nm and is attributed to a triplet state formed by charge recombination in the reaction center. Its narrowness is taken as an indication of its origin on a pair of bacteriochlorophylls, and its orientation indicates an orientation of the chlorophyll ring plane perpendicular to the membrane plane. The second triplet had a wider splitting (magnitude of D = 242 x 10(-4) cm-1), did not vary systematically with redox conditions, corresponds to an optical spectrum with a maximum at 812 nm, and is not ordered in the membrane. It was thus attributed to a triplet located on a BChl g monomer in the antenna. The reaction center photochemistry in H. chlorum is comparable in many respects to that of photosystem I and green sulfur bacteria. Earlier contrasting conclusions are discussed and rationalized in light of the present results

Electrochemical Study of a reconstituted Photosynthetic Electron-Transfer Chain

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Polypeptide composition of the spinach CP1 complex

SIGLEAvailable from CEN Saclay, Service de Documentation, 91191 Gif-Sur-Yvette Cedex (France) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc