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1.
The role of cations in excitation energy distribution between the two photosystems of photosynthesis is well established. This paper provides evidence, for the first time, for an important role of anions in the regulation of distribution of absorbed light energy between the two photosystems. Inorganic anions caused redistribution of energy more in favour of photosystem I, as judged from measurements of chlorophyll a fluorescence transients, rates of electron transport in low light and 77 K fluorescence emission spectra: the Fv/Fm ratio was decreased by inorganic anions even in the presence of DCMU, the PS II electron transport was decreased whereas PS I electron transport was increased and the F735 (77 K emission from PS I)/F685 (77 K emission from PS II) ratio was increased. Such changes were observed with inorganic anions having different valencies (Cl- , SO4(2-), PO4(3-)): the higher the valency of the inorganic anion, the more the energy transferred towards PS I. Change in the valency of the inorganic anions thus regulates distribution of absorbed light energy between the two photosystems. However, organic anions like acetate, succinate, and citrate caused no significant changes in the Fv/Fm ratio, and in rates of PS I and PS II electron transport, showing their ineffectiveness in regulating light energy distribution. 相似文献
2.
We investigated the operation of a posttranslational protein translocation pathway to determine whether ions are excluded from the translocase during protein transport. The membrane capacitance during protein translocation across chloroplast thylakoid membranes was monitored via electric-field-indicating carotenoid electrochromic bandshift measurements. Evidence is presented that shows that the membrane ion conductance is not increased during the complete cycle of binding, transport, and substrate release by the DeltapH-dependent translocase; i.e., the membrane remains ion-tight during protein translocation. We further demonstrate that a synthetic targeting peptide that directs proteins across this membrane does not gate translocation pores. We conclude that protein transport across the thylakoid membrane does not compromise its ability to maintain ion gradients and is, thus, unlikely to affect its functions in energy transduction. 相似文献
3.
Thylakoid membranes isolated from the cyanobacterium Synechocystis sp. strain PCC6803 were capable of desaturating the acyl groups in monogalactosyl diacylglycerol. This desaturation reaction required the reduced form of ferredoxin. 相似文献
4.
The ultrastructure of thylakoid membranes from Arabidopsis thaliana wild-type, JB67 and LK3 fatty acid desaturation deficient mutants was studied by thin-section and freeze-fracture electron microscopy. There was a decrease in the amount of the appressed and non-appressed membranes in JB67 and LK3 Arbidopsis mutants when compared to the wild type, resulting in a reduction in the length of photosynthetic membrane per plastid. The results from freeze-fracture showed a decrease in size and a marked increase in packing density of membrane-associated particles on the exo- and endoplasmic fracture faces of the mutants. In addition, areas of the appressed membranes of the mutants contained particles in regular arrays under conditions where no such arrays were observed in wild-type thylakoid membranes. These observations suggest, that the decreased level of lipid fatty acid unsaturation affects the ability of the lipid matrix to mediate the assembly of chloroplast membrane components. The role of polyunsaturated membrane lipids is considered in terms of their ability to promote functional oligomeric assemblies of components of the photosynthetic apparatus. 相似文献
5.
VI Gordeliy VG Cherezov AD Tugan-Baranovskaya LS Yagujinskiy 《Canadian Metallurgical Quarterly》1996,38(3):485-491
This paper presents experimental data on the determination of the thickness of thylakoid membranes by small-angle neutron scattering. The thylakoids were isolated from spinach chloroplasts. The partial volume of proteins and lipids in the "washed" and "unwashed" membranes was estimated. It is shown that the thickness of thylakoid membranes, measured with this techniques depends on the way the membranes were separated. When isolated thylakoids by the standard method, the membrane thickness amounted to 75 A but if the extracted thylakoids were additionally washed with the isolation medium, the measured thickness was 50 A. In this case a significant decrease in the protein partial volume of the membrane was observed. The obtained results make it possible to explain numerous data on X-ray and small-angle neutron scattering by thylakoid membranes of different origins, proceeding from the assumption that all these membranes have a unified structure and consist of a stable core with a thickness of about 50 A, and layers of peripheral, weakly bound proteins with a thickness which may depends on the nature of the object under investigation and extracting conditions. 相似文献
6.
The plastid ndh genes code for an NADH-specific dehydrogenase: isolation of a complex I analogue from pea thylakoid membranes 总被引:1,自引:0,他引:1
The plastid genomes of several plants contain ndh genes-homologues of genes encoding subunits of the proton-pumping NADH:ubiquinone oxidoreductase, or complex I, involved in respiration in mitochondria and eubacteria. From sequence similarities with these genes, the ndh gene products have been suggested to form a large protein complex (Ndh complex); however, the structure and function of this complex remains to be established. Herein we report the isolation of the Ndh complex from the chloroplasts of the higher plant Pisum sativum. The purification procedure involved selective solubilization of the thylakoid membrane with dodecyl maltoside, followed by two anion-exchange chromatography steps and one size-exclusion chromatography step. The isolated Ndh complex has an apparent total molecular mass of approximately 550 kDa and according to SDS/PAGE consists of at least 16 subunits including NdhA, NdhI, NdhJ, NdhK, and NdhH, which were identified by N-terminal sequencing and immunoblotting. The Ndh complex showed an NADH- and deamino-NADH-specific dehydrogenase activity, characteristic of complex I, when either ferricyanide or the quinones menadione and duroquinone were used as electron acceptors. This study describes the isolation of the chloroplast analogue of the respiratory complex I and provides direct evidence for the function of the plastid Ndh complex as an NADH:plastoquinone oxidoreductase. Our results are compatible with a dual role for the Ndh complex in the chlororespiratory and cyclic photophosphorylation pathways. 相似文献
7.
T Kieselbach Hagman B Andersson WP Schr?der 《Canadian Metallurgical Quarterly》1998,273(12):6710-6716
The chloroplast compartment enclosed by the thylakoid membrane, the "lumen," is poorly characterized. The major aims of this work were to design a procedure for the isolation of the thylakoid lumen which could be generally used to characterize lumenal proteins. The preparation was a stepwise procedure in which thylakoid membranes were isolated from intact chloroplasts. Loosely associated thylakoid surface proteins were removed, and following Yeda press fragmentation the lumenal content was recovered in the supernatant following centrifugation. The purity and yield of lumenal proteins were determined using appropriate marker proteins specific for the different chloroplast compartments. Quantitative immunoblot analyses showed that the recovery of soluble lumenal proteins was 60-65% (as judged by the presence of plastocyanin), whereas contamination with stromal enzymes was less than 1% (ribulose-bisphosphate carboxylase) and negligible for thylakoid integral membrane proteins (D1 protein). Approximately 25 polypeptides were recovered in the lumenal fraction, of which several were identified for the first time. Enzymatic measurements and/or amino-terminal sequencing revealed the presence of proteolytic activities, violaxanthin de-epoxidase, polyphenol oxidase, peroxidase, as well as a novel prolyl cis/trans-isomerase. 相似文献
8.
Many thylakoid proteins are cytosolically synthesized and have to cross the two chloroplast envelope membranes as well as the thylakoid membrane en route to their functional locations. In order to investigate the localization pathways of these proteins, we over-expressed precursor proteins in Escherichia coli and used them in competition studies. Competition was conducted for import into the chloroplast and for transport into or across isolated thylakoids. We also developed a novel in organello method whereby competition for thylakoid transport occurred within intact chloroplasts. Import of all precursors into chloroplasts was similarly inhibited by saturating concentrations of the precursor to the OE23 protein. In contrast, competition for thylakoid transport revealed three distinct precursor specificity groups. Lumen-resident proteins OE23 and OE17 constitute one group, lumenal proteins plastocyanin and OE33 a second, and the membrane protein LHCP a third. The specificity determined by competition correlates with previously determined protein-specific energy requirements for thylakoid transport. Taken together, these results suggest that thylakoid precursor proteins are imported into chloroplasts on a common import apparatus, whereupon they enter one of several precursor-specific thylakoid transport pathways. 相似文献
9.
S High R Henry RM Mould Q Valent S Meacock K Cline JC Gray J Luirink 《Canadian Metallurgical Quarterly》1997,272(17):11622-11628
Signal recognition particles (SRPs) have been identified in organisms as diverse as mycoplasma and mammals; in several cases these SRPs have been shown to play a key role in protein targeting. In each case the recognition of appropriate targeting signals is mediated by SRP subunits related to the 54-kDa protein of mammalian SRP (SRP54). In this study we have characterized the specificity of 54CP, a chloroplast homologue of SRP54 which is located in the chloroplast stroma. We have used a nascent chain cross-linking approach to detect the interactions of 54CP with heterologous endoplasmic reticulum-targeting signals. 54CP functions as a bona fide signal recognition factor which can discriminate between functional and non-functional targeting signals. Using a range of authentic thylakoid precursor proteins we found that 54CP discriminates between thylakoid-targeting signals, interacting with only a subset of protein precursors. Thus, the light-harvesting chlorophyll a/b-binding protein, cytochrome f, and the Rieske FeS protein all showed strong cross-linking products with 54CP. In contrast, no cross-linking to the 23- and 33-kDa proteins of the oxygen-evolving complex were detected. The selectivity of 54CP correlates with the hydrophobicity of the thylakoid-targeting signal and, in the case of light-harvesting chlorophyll a/b-binding protein, with previously determined transport/integration requirements. We propose that 54CP mediates the targeting of a specific subset of precursors to the thylakoid membrane, i.e. those with particularly hydrophobic signal sequences. 相似文献
10.
GI Kufrik 《Canadian Metallurgical Quarterly》1997,69(4):104-107
The pigment-protein composition of two fractions of intergrana fragments from maize inbred lines F 7 and II 346 chloroplast had been investigated. It was shown that under electrophoretic separation of fraction 70,000 g from both lines and fraction 100,000 g from line F 7 the new band of pigment-protein complexes had been observed. It was determined that its polypeptide composition is the same as light-harvesting complex of PS II one, but it differs by low electrophoretical mobility. The conclusion was made that this is a new form of light-harvesting complex of PS II. 相似文献
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Two imported thylakoid membrane proteins, PSII-X and PSII-W, are synthesised with cleavable N-terminal signal peptides that closely resemble those of Sec-dependent lumenal proteins. In this report we have reconstituted the insertion of pre-PSII-X and pre-PSII-W into isolated thylakoids. We show that insertion does not require either nucleoside triphosphates or stromal extracts, both of which are required for Sec- and signal recognition particle (SRP)-dependent targeting mechanisms. Insertion is furthermore unaffected by protease treatments that destroy the known protein translocation apparatus in the thylakoid membrane. We conclude that these membrane proteins are inserted by an unusual Sec/SRP-independent mechanism that probably resembles that used by CFoII, and we discuss possible parallels with the biogenesis of phage M13 procoat. 相似文献
13.
Continuous growth and an increase in pigmentation of a preretinal membrane occurred in a 46-year-old woman after a scleral buckling procedure for rhegmatogenous retinal detachment. Ten additional patients had pigmented preretinal membranes in eyes treated for rhegmatogenous retinal detachment. Although we made no attempts to determine the incidence of pigmented preretinal membrane formation in eyes with retinal detachments, these 11 cases, in a consecutive series of 500 eyes treated for rhegmatogenous retinal detachment, indicated that the development of pigmented preretinal membranes is not uncommon. Our clinical observations supported recent experimental findings implicating retinal pigment epithelial cells as a cause of preretinal membrane formation. 相似文献
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15.
Zhong-can Ou-Yang 《Canadian Metallurgical Quarterly》1990,41(8):4517-4520
16.
JS Schultz 《Canadian Metallurgical Quarterly》1977,197(4309):1177-1179
Reversible photochromic reactions can be coupled to carrier-mediated transport processes in membranes to bring about the separation or concentration of selected permeants. Carbon monoxide has been pumped against of fourfold concentration gradient by differentially illuminating a hemoglobin membrane. The extent of concentration of photochromic ligands increases with light intensity and is reversible. Nonphotochemically sensitive ligands can also be transported by coupling with phostosensitive carrier-mediated systems. 相似文献
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The plastids found in diatoms and other chromophytic algae are completely enclosed by four membranes in contrast to chloroplasts of higher plants, which are surrounded by only two membranes. The bipartite targeting sequence of diatom nuclear-encoded plastid proteins contains an endoplasmic reticulum signal sequence and, based on sequence comparison, a transit peptide-like domain similar to that which targets proteins into the plastids of higher plants. By performing heterologous import experiments using the precursor of the gamma subunit of the chloroplast ATPase from the diatom Odontella sinensis we were able to show that protein import into diatom plastids is at least a two-step event. We demonstrate that the first step involves co-translational transport through endoplasmic reticulum membranes and that there is an additional targeting step which is similar to the import of precursor proteins into chloroplasts of higher plants and green algae indicating that the transit peptide-like domain of the diatom precursor is functionally equivalent to the respective targeting signal of higher plants. Our results suggest that the transit peptide depending targeting mechanism in plastids has apparently remained relatively unchanged over the course of evolution, with only the peptidase cleavage site significantly modified. 相似文献
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Branched bimolecular lipid membranes separating three and four aqueous phases have been formed. The procedure is based on the technique of Montal and Mueller generalized to three and four lipid surface films spanning an appropriate aperture. The technique to produce Teflon structures for the mechanical support of branched bilayers is presented. The existence of the branched bilayer was established by measuring the specific capacity, specific resistance, and the gramicidin-induced single channel conductance of each branch. These structures should facilitate the study of transport properties of ionophores and other molecules and may also serve as model systems for the study of cell fusion. 相似文献