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Results for “Photosystem I Protein Complex”

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PubMed2007

Contrasting behavior of higher plant photosystem I and II antenna systems during acclimation.

In this work we analyzed the photosynthetic apparatus in Arabidopsis thaliana plants acclimated to different light intensity and temperature conditions. Plants showed the ability to acclimate into different environments and avoid photoinhibition. When grown in high light, plants had a faster activation rate for energy dissipation (qE). This ability was correlated to higher accumulation levels of a specific photosystem II subunit, PsbS. The photosystem II antenna size was also regulated according to light exposure; smaller antenna size was observed in high light-acclimated plants with respect to low light plants. Different antenna polypeptides did not behave similarly, and Lhcb1, Lchb2, and Lhcb6 (CP24) are shown to undergo major levels of regulation, whereas Lhcb4 and Lhcb5 (CP29 and CP26) maintained their stoichiometry with respect to the reaction center in all growth conditions. The effect of acclimation on photosystem I antenna was different; in fact, the stoichiometry of any Lhca antenna proteins with respect to photosystem I core complex was not affected by growth conditions. Despite this stability in antenna stoichiometry, photosystem I light harvesting function was shown to be regulated through different mechanisms like the control of photosystem I to photosystem II ratio and the association or dissociation of Lhcb polypeptides to photosystem I.

Acclimatization↗

PubMed2005

Differential changes in degradation of chlorophyll-protein complexes of photosystem I and photosystem II during flag leaf senescence of rice.

The stability of chlorophyll-protein complexes of photosystem I (PSI) and photosystem II (PSII) was investigated by chlorophyll (Chl) fluorescence spectroscopy, absorption spectra and native green gel separation system during flag leaf senescence of two rice varieties (IIyou 129 and Shanyou 63) grown under outdoor conditions. During leaf senescence, photosynthetic CO(2) assimilation rate, carboxylase activity of Rubisco, chlorophyll and carotenoids contents, and the chlorophyll a/b ratio decreased significantly. The 77 K Chl fluorescence emission spectra of thylakoid membranes from mature leaves had two peaks at around 685 and 735 nm emitting mainly from PSII and PSI, respectively. The total Chl fluorescence yields of PSI and PSII decreased significantly with senescence progressing. However, the decrease in the Chl fluorescence yield of PSI was greater than in the yield of PSII, suggesting that the rate of degradation in chlorophyll-protein complexes of PSI was greater than in chlorophyll-protein complexes of PSII. The fluorescence yields for all chlorophyll-protein complexes decreased significantly with leaf senescence in two rice varieties but the extents of their decrease were significantly different. The greatest decrease in the Chl fluorescence yield was in PSI core, followed by LHCI, CP47, CP43, and LHCII. These results indicate that the rate of degradation for each chlorophyll-protein complex was different and the order for the stability of chlorophyll-protein complexes during leaf senescence was: LHCII>CP43>CP47>LHCI>PSI core, which was partly supported by the green gel electrophoresis of the chlorophyll-protein complexes.

Carbon Dioxide↗

PubMed1991

Correlation between the "low"-salt-induced increase in the F730/F685 fluorescence emission ratio at 77 K in isolated chloroplasts, and the organization of chlorophyll in photosystem I pigment-protein complexes of thylakoids.

Isolated pea or spinach chloroplasts suspended in "high"-salt phosphate buffer exhibit a low F730/F685 fluorescence emission ratio at 77 K; in contrast, removal of cations by incubation in "low"-salt Tricine buffer induces a drastic increase in the F730/F685 ratio. Parallel to the F730/F685 ratio increase, a gradual organization of chlorophyll (Chl) in the pigment-protein complexes of the Photosystem I, chlorophyll-protein complex Ia, and light-harvesting complex I (LHC-I), is observed. The kinetics of the two processes are closely correlated, all changes being completed within 5-10 min from Tricine addition. On the other hand, the inability of low-salt Tricine to induce any changes in the F730/F685 ratio in bean plastids, isolated and suspended in high-salt phosphate buffer, correlates with the lack of extensive changes in the organization of the Photosystem I complexes, and more specifically of LHC-I. The latter is attributed to the higher stability of complexes in bean, arising from stronger association of thylakoids in grana stacks in this species; this is probably due to higher levels of residual divalent cations present in the isolated thylakoids of bean compared to pea (or spinach). The results suggest that the F730/F685 ratio changes, observed in chloroplasts by manipulation of their ionic environment, reflect modulation of Chl organization within the pigment-protein complexes of the photosynthetic units.

Buffers↗

PubMedDate not supplied

[Study of electron transfer in pigment-protein complexes of photosystem I].

The electron transfer processes occuring in SDS chlorophyll--protein complexes of photosystem I were studied by flash photolysis. Transient species with lifetime about 5.10(-5) sec were found to be produced on flash excitation of complex buffer solutions. The transient absorption spectrum of the short-lived species measured in the absence of SDS resembles that of P+700. This spectrum was similar with that of chlorophyll anion radical (chl-) when SDS was added to the solution. It is assumed that the charge separation in chlorophyll--protein complexes leads to formation of the primary reduced acceptor X-. The chl-species arised as a result of electron transfer from X- to monomeric form of chl a.

Chlorophyll↗

PubMed1984

Isolation and Characterization of a Light-Harvesting Chlorophyll a/b Protein Complex Associated with Photosystem I.

A chlorophyll a/b protein complex has been isolated from a resolved native photosystem I complex by mildly dissociating sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The chlorophyll a/b protein contains a single polypeptide of molecular weight 20 kilodaltons, and has a chlorophyll a/b ratio of 3.5 to 4.0. The visible absorbance spectrum of the chlorophyll a/b protein complex showed a maximum at 667 nanometers in the red region and a 77 K fluorescence emission maximum at 681 nanometers. Alternatively, by treatment of the native photosystem I complex with lithium dodecyl sulfate and Triton, the chlorophyll a/b protein complex could be isolated by chromatography on Sephadex G-75. Immunological assays using antibodies to the P(700)-chlorophyll a-protein and the photosystem II light-harvesting chlorophyll a/b protein show no cross-reaction between the photosystem I chlorophyll a/b protein and the other two chlorophyll-containing protein complexes.

Journal Article↗

PubMed1987

Chlorophyll-protein complexes of barley photosystem I.

Photosystem I (PSI) preparations with a chlorophyll a/b ratio of 6.0 were isolated from barley thylakoids using two different methods. The high-molecular-mass complex (CP1a) which is resolved by non-denaturing gel electrophoresis had the same properties as a PSI preparation (PSI-200) isolated by Triton X-100 solubilisation of thylakoids followed by sucrose gradient ultracentrifugation. This material had a chlorophyll:P700 ratio of 208:1 and was composed of three different chlorophyll-protein complexes which could be separated from each other by solubilising the PSI preparation in dodecyl maltoside followed by sucrose gradient ultracentrifugation. Approximately half of the chlorophyll, including all the chlorophyll b, was located in two antenna complexes designated LHCI-680 and LHCI-730, which were identified by their characteristic low-temperature fluorescence emission spectra. The rest of the chlorophyll a was associated with the PSI reaction centre, P700 Chla-P1, which fluoresced at 720 nm. Each chlorophyll-protein complex had a unique polypeptide composition and characteristic circular dichroic and absorption spectra. The use of dodecyl maltoside instead of dodecyl sulphate resulted in a less denatured form of LHCI-680, which fluoresced at 690 nm at 77 K. One of the sucrose gradient fractions contained a complex consisting of only LHCI-730 and P700 Chla-P1 which fluoresced at 731 nm, indicating that LHCI-730 is structurally associated with P700 Chla-P1 and quenches its fluorescence. Approximately three-quarters of the light-harvesting antenna chlorophyll was in LHCI-730, but only about one-quarter of the normal complement of LHCI-730 was required to quench the reaction centre. By reducing the amount of Triton relative to the chlorophyll concentration, a PSI preparation (chlorophyll a/b ratio of 3.5) with a chlorophyll:P700 ratio of 300:1 was isolated. It contained no photosystem II, but a significant amount of LHCII which was functionally connected to the PSI reaction centre. Reconstitution studies demonstrated that excitation energy transfer from LHCII to PSI requires the presence of LHCI-680, and we propose that, in PSI, the following linear excitation energy transfer sequence occurs: LHCII----LHCI-680----LHCI-730----P700 Chla-P1.

Centrifugation, Density Gradient↗

PubMed1999

Targeted inactivation of the smallest plastid genome-encoded open reading frame reveals a novel and essential subunit of the cytochrome b(6)f complex.

The smallest conserved open reading frame in the plastid genome, ycf6, potentially specifies a hydrophobic polypeptide of only 29 amino acids. In order to determine the function of this reading frame we have constructed a knockout allele for ycf6. This allele was introduced into the tobacco plastid genome by chloroplast transformation to replace the wild-type ycf6 allele. Homoplasmic Deltaycf6 plants display a photosynthetically incompetent phenotype. Whereas the two photosystems are intact and physiologically active, we found that the electron transfer from photosystem II to photosystem I is interrupted in Deltaycf6 plants. Molecular analyses revealed that this block is caused by the complete absence of the cytochrome b(6)f complex, the redox-coupling complex that interconnects the two photosystems. Analysis of purified cytochrome b(6)f complex by mass spectroscopy revealed the presence of a protein that has exactly the molecular mass calculated for the Ycf6 protein. This suggests that Ycf6 is a genuine subunit of the cytochrome b(6)f complex, which plays a crucial role in complex assembly and/or stability. We therefore propose to rename the ycf6 reading frame petN.

Amino Acid Sequence↗

PubMed1982

The role of chlorophyll-protein complexes in the function and structure of chloroplast thylakoids.

The photosynthetic pigments of chloroplast thylakoid membranes are complexed with specific intrinsic polypeptides which are included in three supramolecular complexes, photosystem I complex, photosystem II complex and the light-harvesting complex. There is marked lateral heterogeneity in the distribution of these complexes along the membrane with photosystem II complex and its associated light-harvesting complex being located mainly in the stacked membranes of the grana partitions, while photosystem I complex is found mainly in unstacked thylakoids together with ATP synthetase. In contrast, the intermediate electron transport complex, the cylochrome b-f complex, is rather uniformly distributed in these two membrane regions. The consequences of this lateral heterogeneity in the location of the thylakoid complexes are considered in relation to the function and structure of chloroplasts of higher plants.

Chlorophyll↗

PubMed2001

Identification and localization of a thylakoid-bound carbonic anhydrase from the green algae Tetraedron minimum (Chlorophyta) and Chlamydomonas noctigama (Chlorophyta).

In order to broaden our understanding of the eukaryotic CO2-concentrating mechanism the occurrence and localization of a thylakoid-associated carbonic anhydrase (EC 4.2.1.1) were studied in the green algae Tetraedron minimum and Chlamydomonas noctigama. Both algae induce a CO2-concentrating mechanism when grown under limiting CO2 conditions. Using mass-spectrometric measurements of 18O exchange from doubly labelled CO2, the presence of a thylakoid-associated carbonic anhydrase was confirmed for both species. From purified thylakoid membranes, photosystem I (PSI), photosystem II (PSII) and the light-harvesting complex of the photosynthetic apparatus were isolated by mild detergent gel. The protein fractions were identified by 77 K fluorescence spectroscopy and immunological studies. A polypeptide was found to immunoreact with an antibody raised against thylakoid carbonic anhydrase (CAH3) from Chlamydomonas reinhardtii. It was found that this polypeptide was mainly associated with PSII, although a certain proportion was also connected to light harvesting complex II. This was confirmed by activity measurements of carbonic anhydrase in isolated bands extracted from the mild detergent gel. The thylakoid carbonic anhydrase isolated from T. minimum had an isoelectric point between 5.4 and 4.8. Together the results are consistent with the hypothesis that thylakoid carbonic anhydrase resides within the lumen where it is associated with the PSII complex.

Animals↗

PubMed1993

Dephosphorylation of photosystem II core proteins is light-regulated in vivo.

A number of photosystem II (PSII)-associated proteins, including D1, D2, CP43 and LHCII, are phosphorylated post-translationally by a membrane-bound, redox-regulated kinase activity. In vitro studies have demonstrated that these proteins can be dephosphorylated by membrane-bound phosphatase activity, reportedly insensitive to light or redox control. We demonstrate here that the PSII core proteins, D1, D2 and CP43, undergo light-stimulated, linear electron-transport-independent dephosphorylation in vivo. The in vivo dephosphorylation of D1 was characterized further and shown to depend upon light intensity, and to occur throughout the visible light spectrum with characteristics most consistent with light absorption by chlorophyll. PSII core protein dephosphorylation in vivo was stimulated by photosystem I (PSI)-specific far-red light, and inhibited by 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, an inhibitor of plastoquinol oxidation by the cytochrome b6f complex. Based on these findings, we propose that PSI excitation is involved in regulating dephosphorylation of PSII core proteins in vivo.

Dibromothymoquinone↗

PubMed2001

The establishment of conditions to efficiently screen photosynthesis-deficient mutants of Synechocystis sp. PCC 6803 by nitrofurantoin treatment.

A method based on the susceptibility of photosynthetic organisms to nitrofurantoin under illumination was established to screen mutants of Synechocystis sp. PCC 6803 deficient in the function of photosystem II, which were created by random PCR mutagenesis targeted to the psbAII gene coding for the D1 protein of the photosystem II reaction center. In this method, cyanobacterial colonies on a nitrocellulose membrane on a BG11 agar plate were treated with nitrofurantoin at 1.0 mM under white light at 40 microE x m(-2 ) x s(-1) for 2 h, and then kept under normal conditions without nitrofurantoin so that surviving cells could grow. This method was also shown to be useful for screening mutants deficient in the function of photosystem I.

Cyanobacteria↗

PubMed2001

The heart of photosynthesis in glorious 3D.

The input of solar energy into photosynthesis, and thence into the biosphere, occurs via chlorophyll-containing proteins known as reaction centres. There are two kinds of reaction centre in oxygenic photosynthesis: photosystem I (PSI) and photosystem II (PSII). The PSII reaction centre, alias the oxygen-evolving enzyme, the water-oxidizing complex or the water-plastoquinone photo-oxidoreductase, has now been crystallized and its structure solved to a resolution of 3.8 A.

Catalytic Domain↗

PubMed2001

Balance of power: a view of the mechanism of photosynthetic state transitions.

Photosynthesis in plants involves photosystem I and photosystem II, both of which use light energy to drive redox processes. Plants can balance the distribution of absorbed light energy between the two photosystems. When photosystem II is favoured, a mobile pool of light harvesting complex II moves from photosystem II to photosystem I. This short-term and reversible redistribution is known as a state transition. It is associated with changes in the phosphorylation of light harvesting complex II but the regulation is complex. Redistribution of energy during state transitions depends on an altered binding equilibrium between the light harvesting complex II-photosystem II and light harvesting complex II-photosystem I complexes.

Chlorophyll↗

PubMed2000

Structural analysis of photosystem II in far-red-light-adapted thylakoid membranes. New crystal forms provide evidence for a dynamic reorganization of light-harvesting antennae subunits.

We studied two-dimensional crystals of the major pigment-protein complex, photosystem II, in far-red-light-adapted thylakoid membranes of the viridis-zb63 mutant of barley. Significantly larger grana membranes were produced with an increased synthesis of the entire photosystem II complex. These red-light-adapted membranes also contained two-dimensional crystals with a high frequency. Three different crystal forms of photosystem II were observed, providing the following data which further our understanding of the architecture of the native complex. (a) The oligomeric form of photosystem II in the membrane was monomeric in all crystal forms, but with a clear non-crystallographic pseudo-twofold symmetry. This was more apparent on the lumenal face of the complex. (b) The variability of unit cell contacts in different crystal forms implied that the peripheral light-harvesting antenna complex and the core of the complex were loosely connected. These peripheral subunits were predicted to rearrange so that they can either encircle the core complex or associate in parallel channels separated by lines of core complexes. (c) Grana membranes were found to retain a double-layered inside-out character, with a stromal face-to-stromal face packing. However, the presence of a crystal in one membrane did not necessarily impose crystallinity on its pair.

Adaptation, Physiological↗

PubMed2001

Chlorophyll b can serve as the major pigment in functional photosystem II complexes of cyanobacteria.

An Arabidopsis thaliana chlorophyll(ide) a oxygenase gene (cao), which is responsible for chlorophyll b synthesis from chlorophyll a, was introduced and expressed in a photosystem I-less strain of the cyanobacterium Synechocystis sp. PCC 6803. In this strain, most chlorophyll is associated with the photosystem II complex. In line with observations by Satoh et al. [Satoh, S., Ikeuchi, M., Mimuro, M. & Tanaka, A. (2001) J. Biol. Chem. 276, 4293-4297], chlorophyll b was made but accounted for less than 10% of total chlorophyll. However, when lhcb encoding light-harvesting complex (LHC)II from pea was present in the same strain (lhcb(+)/cao(+)), chlorophyll b accumulated in the cell to levels exceeding those of chlorophyll a, although LHCII did not accumulate. In the lhcb(+)/cao(+) strain, the total amount of chlorophyll, the number of chlorophylls per photosystem II center, and the oxygen-evolving activity on a per-chlorophyll basis were similar to those in the photosystem I-less strain. Furthermore, the chlorophyll a/b ratio of photosystem II core particles (retaining CP47 and CP43) and of whole cells of the lhcb(+)/cao(+) strain was essentially identical, and PS II activity could be obtained efficiently by chlorophyll b excitation. These data indicate that chlorophyll b functionally substitutes for chlorophyll a in photosystem II. Therefore, the availability of chlorophylls, rather than their binding specificity, may determine which chlorophyll is incorporated at many positions of photosystem II. We propose that the transient presence of a LHCII/chlorophyll(ide) a oxygenase complex in the lhcb(+)/cao(+) strain leads to a high abundance of available chlorophyll b that is subsequently incorporated into photosystem II complexes. The apparent LHCII requirement for high chlorophyll(ide) a oxygenase activity may be instrumental to limit the occurrence of chlorophyll b in plants to LHC proteins.

Arabidopsis↗

PubMed2001

Photoinhibition of Chlamydomonas reinhardtii in State 1 and State 2: damages to the photosynthetic apparatus under linear and cyclic electron flow.

The relationship between state transitions and photoinhibition has been studied in Chlamydomonas reinhardtii cells. In State 2, photosystem II activity was more inhibited by light than in State 1. In State 2, however, the D1 subunit was not degraded, whereas a substantial degradation was observed in State 1. These results suggest that photoinhibition occurs via the generation of an intermediate state in which photosystem II is inactive but the D1 protein is still intact. The accumulation of this state is enhanced in State 2, because in this State only cyclic photosynthetic electron transport is active, whereas there is no electron flow between photosystem II and the cytochrome b(6)f complex (Finazzi, G., Furia, A., Barbagallo, R. P., and Forti, G. (1999) Biochim. Biophys. Acta 1413, 117-129). The activity of photosystem I and of cytochrome b(6)f as well as the coupling of thylakoid membranes was not affected by illumination under the same conditions. This allows repairing the damages to photosystem II thanks to cell capacity to maintain a high rate of ATP synthesis (via photosystem I-driven cyclic electron flow). This capacity might represent an important physiological tool in protecting the photosynthetic apparatus from excess of light as well as from other a-biotic stress conditions.

Adenosine Triphosphate↗

PubMed1997

Two-dimensional crystals of photosystem I in higher plant grana margins.

In this report, we present new structural data on the size, shape, and oligomeric form of higher plant photosystem I (PSI) formed within the thylakoid grana margins. We show that PSI complexes can be assembled into ordered molecular monolayers (two-dimensional crystals) using thylakoid membranes from a variety of higher plant sources. Digital image analysis of negatively stained two-dimensional crystals (a = 26.9 nm, b = 28.0 nm, gamma = 90 degrees, p22121 plane group) resulted in a projection map consisting of 4 monomers/unit cell. Higher plant PSI is slightly larger than its cyanobacterial equivalent but shows many similar features. Structural changes after urea and salt washing of the crystals supported the biochemical characterization and were mainly assigned to the stromal side of the complex where the psaC, psaD, and psaE gene products are known to be bound. Labeling with ferredoxin-colloidal gold complexes provided direct evidence for a segregated PSI population, with 5 nm diameter ferredoxin-gold particles enriched in the thylakoid grana margins and the two-dimensional crystals. This lateral segregation of photosynthetic complexes is important for the understanding of the kinetics of electron transfer between photosystem II and PSI in higher plants.

Crystallography↗

PubMed1991

A guide to electron paramagnetic resonance spectroscopy of Photosystem II membranes.

This guide is intended to aid in the detection and identification of paramagnetic species in Photosystem II membranes, by electron paramagnetic resonance spectroscopy. The spectral features and occurrence of each of the electron paramagnetic resonance signals from Photosystem II are discussed, in relation to the nature of the moiety giving rise to the signal and the role of that species in photosynthetic electron transport. Examples of most of the signals discussed are shown. The electron paramagnetic resonance signals produced by the cytochrome b6f and Photosystem I complexes, as well as the signals from other common contaminants, are also reviewed. Furthermore, references to seminal experiments on bacterial reaction centers are included. By reviewing both the spectroscopic and biochemical bases for the electron paramagnetic resonance signals of the cofactors that mediate photosynthetic electron transport, this paper provides an introduction to the use and interpretation of electron paramagnetic resonance spectroscopy in the study of Photosystem II.

Cell Membrane↗