Chloroplasts thylakoid membrane

Cohen, Y., S. Yalovsky, and R. Nechushtai. 1995. Integration and assembly of photosynthetic protein complexes in chloroplast thylakoid membranes. Biochim. Biophys. Acta 1241 1-30. 

G. F. W. Searle, J. Barber, and J. D. Mills, 9-Amino-acridine as a probe of the electrical double layer associated with the chloroplast thylakoid membranes, Biochim. Biophys. Acta 461, 413-425 (1977). 

Our investigations into the structure and organisation of the chloroplast thylakoid membrane have involved the following approaches ... 

Proton relaxation studies on chloroplast membranes have been presented. (791) Chloroplasts are the sites for the photosynthetic process, many details of which are still unknown. Manganese is known to be essential for oxygen evolution and thus it is important to be able to monitor manganese in its bound state. Water proton Ti values in chloroplast thylakoid membrane suspensions were used to monitor membrane-bound manganese. The results indicate that there may be a mixture of manganese oxidation states in the dark-adapted chloroplasts, with Mn(ii) and Mn(iii) being the most likely states. 

DSC has been used to study the individual protein components of biological membranes of relatively simply protein composition and the interaction of several of these components with lipids and with other proteins. The red blood cell membrane, which has been most intensively studied, exhibits five discrete protein transitions, each of which has been assigned to a specific membrane protein. The response of each of these thermal transitions to variations in temperature and pH as well as to treatment with proteases, phospholipases, specific labelling reagents, and modifiers and inhibitors of selected membrane activities, has provided much useful information on the interactions and functions of these components in the intact erythrocyte membrane (46-49). Similar approaches have been applied to the bovine rod outer segment membrane (50) and to the spinach chloroplast thylakoid membrane (51). 

In order to maintain a A/1h+ across a membrane, and to ensure that it is used for the synthesis of ATP and not dissipated by leakage, the membrane must be closed and not leaky to protons. From the rate at which a pH gradient across the membrane decayed, it was shown that the effective proton conductance of the mitochondrial inner membrane [8], bacterial plasma membrane [9], and chloroplast thylakoid membrane [10] have a value of only some 0.5 jttS2/cm, or a million-fold less than the aqueous phases on either side. 

The respiratory and photosynthetic electron-transfer pathways are proton pumps operating with the same polarity as does the A TP synthase when hydrolyzing A TP Since it is difficult to detect protons circulating in the steady-state, Mitchell and Moyle [19] studied the transient extrusion of protons when a small amount of oxygen is injected into an anaerobic incubation of mitochondria in the presence of substrate. Prior to this, Neumann and Jagendorf [20] had observed a light-dependent proton uptake into chloroplast thylakoid membranes. 

Photophosphorylation due to electron flow (blue) and proton flow (red) in chloroplast thylakoid membranes... 

Fig. 19. Chloroplast thylakoid-membrane structure revealed by freeze-fracture electron microscopy. The oxygen-evolving (BBY) PS-II particle its preparation (A) and electron micrographs (B). The inside-out and rightside-out vesicles preparation, structure, and properties (C) and electron micrographs (D). Figure source (A) and (B) Dunahay, Staehelin, Seibert, Ogilvie and Berg (1984) Structural, biochemical and biophysical characterization of four oxygen-evolving photosystem II preparations from spinach. Biochim Biophys Acta 764 190, 185 (C) and (D) from Andersson and Akerlund (1978) Inside-out membrane vesicles isolated from spinach thylakoids. Biochim Biophys Acta 503 465, 468. Figure (B) kindly furnished by Dr. Andrew Staehelin.

W Ortiz, E Lam, S Chollar, D Munt and R Malkin (1985) Topography of the protein complexes of the chloroplast thylakoid membrane. Plant Physiol 77 389-397... 

Fig. 2. (A) A model for b/in chloroplast thylakoid membrane (B) Topological arrangement of the four subunits of the purified Cyt b/complex (C) A densitometric scan of an SDS-PAGE gel for b/ (B) from Hauska, Schiitz and Biittner (1996) The cytochrome b/ complex - composition, structure and function. In DR Ort and CF Yocum (eds) Oxygenic Photosynthesis - The Light Reactions, p 384. Kluwer (C) from Black, Widger and Cramer (1987) Large-scale purification of active cytochrome b f complex from spinach chloroplasts. Arch Biochem Biophys 252 657.

Fig. 15. Conceptual development of a membane vesicle subjected to voltage pulses to create a potential difference across the membrane. (A) A1 pm-dlameter sphere of water is Imagined placed between two platinum electrodes 1 mm apart (B) The water sphere is replaced by a sphere of lipid (C) The Interior of the lipid sphere is replaced by a sphere of water, resulting in a lipid shell surrounding an aqueous medium to form the equivalent of a membrane vesicle. See text for details. (D) A schematic representation of a chloroplast thylakoid membrane containing ATP synthase to be subjected to voltage pulses and then the amount of ATP formed determined. Plots of actually measured ATP formation by voltage pulses (E) or light pulses (F) as a function of the number of pulses. (A), (B), (C), (E) and (F) from Witt (1987) Examples for the cooperation of photons, excitons, electrons, electric fields and protons in the photosynthesis membrane. Nouveau Journal deChimie 11 97 (D) adapted from Bauermeister, Schlodderand Graber(1988) Electric field-driven ATP synthesis catalyzed by the membrane-bound ATP-synthase from chloroplasts. Ber Bunsenges Phys Chem 92 1037.

In Fig. 15 (D), the imaginary membrane vesicle is replaced either by an actual chloroplast thylakoid-membrane vesicle containing ATP synthase, as shown in the example of Bauermeister, Schloddder and Graber" or by a liposome reconstituted with isolated CFo Fi-ATP synthase. In the actual experiment, two platinum electrodes each 5 cm in area were spaced 2 mm apart and filled with a chloroplast suspension. The cuvette containing the chloroplast suspension and the electrodes was then thermostated at 4 °C and kept from light. 

Unlike mitochondria, chloroplasts contain a third membrane—the thylakoid membrane—on which photosynthesis occurs. The chloroplast thylakoid membrane is believed to constitute a single sheet that forms numerous small, interconnected flattened vesicles, the thylakoids, which commonly are arranged in stacks termed grana (see Figure... 

Antioxidant activity of reduced plastoquinone in chloroplast thylakoid membranes. Arch Biochem Biophys 324 117-122... 

See also Thylakoids, Thylakoid Lumen, CFO-CFl Complex, Chloroplast Anatomy, The Chloroplast, Thylakoid Membrane, Grana, Photosystem I, Photosystem II, Mitochondrial Structure and Function... 

It is well knovm, that in chloroplast thylakoid membrane the absorption of light induces a veaorial electron transfer through the two photosystems in a sequential process involving the formation of red-ox species. The use of a one compartment three electrode photoelectrochemical cell, first designed by Allen and Crane and successively modified by Carpentier et al, can allow these species to be revealed, if they are dissolved in the aqueous phase. The CV is, indeed, a powerfijl technique for detection of reactions proceeding, following or interposed between electron transfer to the electrode. 

Identification of the Receptor Site for Triazine Herbicides in Chloroplast Thylakoid Membranes... 

Figure 7. Fluorogram of a polyacrylamide gel showing trypsin sensitivity of the 34 kDal polypeptide of chloroplast thylakoid membranes isolated from susceptible (S) and resistant (R) biotypes of A. hybridus following in vivo incorporation of S-methionine in whole leaves. Isolated thylakoid membranes were treated with A, no trypsin B, 2 fxg trypsin/mL C, 20 fxg trypsin/mL for 15 min as described...

Chloroplast thylakoid membranes are composed of an almost equal percentage of protein and lipid. The acyl lipids of the chloroplast membrane are highly unsaturated for example, around 80% of the fatty acid component is the 18 3 unsaturated linolenic acid. The consequences of lipid peroxidation reactions are... 

The feasibility of the superoxide radical being the initial toxic species in vivo was predicted by Farrington et al., (34) using pulse radiolysis studies. It was postulated that the concentration of superoxide within the plant cell could remain constant at 1 yM up to 10 ym or more from the chloroplast thylakoid membrane. 

The cytochrome b-f complex of the chloroplast thylakoid membrane operates as a plastoquinol-plastocyanin oxidoreductase and is thus analogous to the mitochondrial cytochrome bc complex with which it bears a large amount of structural and functional similarity. It consists in all higher plants of four components, which are cytochrome f, cytochrome b-563 the Rieske Fe-S protein, and a 17kDa... 

Mutants which identify nuclear-encoded functions essential to chloroplast development are valuable resources. Transposon mutagenesis using the Mutator system may provide access to some of the nuclear loci which are essential to chloroplast development and, in so doing, reveal patterns of interaction between the nucleus and organelle in eukaryotic systems. The work presented here lays a foundation for the isolation of nuclear loci essential to the assembly of the major components of the photosynthetic apparatus associated with the chloroplast thylakoid membrane. 

Rieske protain/centar an iron-sulphur protein first isolat from Complex III of the mitochondrial electron transport chain, in which it occurs with cytochromes b and C) [J.S, Rieske el al. Biochem. Biophys Res Commun. IS (1%4) 338-344], but which has now been found in the equivalent cytochrome be complexes in the bacterial plasma membrane and the chloroplast thylakoid membrane. The latter, known as the cytochrome bff complex, partidpates in cyclic and noncyclic electron flow in the light phase of photosynthesis (see Photosynthesis). All Rieske proteins are one-electron redox systems with a standanl redox potential in the + 0.2 to + 0.3V range and have a (2Fe-2S] center, a single membrane-spanning a-helix, and a characteristic electron spin resonance (ESR) spectrum. The chloroplastidic R.p/c, with a M, of - 20,000, is smaller than that of the mitochondnon. It is encoded in the nucleus, synthesized in the cytoplasm and translocated to the chloroplast, where it is inserted into the thylakoid membrane. Within the thylakoid membrane its [2Fe-2S] redox centre (near to its C-terminus) can readily pass electrons to cytochrome /, a c-type cytochrome that projects from the luminal surface cytochrome / then passes electrons to plastocyanin (see) dissolved in the aqueous milieu of the thylakoid lumen. 

The phase structure of total polar lipid extracts of chloroplast thylakoid membranes when dispersed in physiological salt solutions is characterised by non-lamellar arrangements of lipid C4D. This contrasts markedly with the general belief that the dominant form of the lipids in the photosynthetic membrane is in a bilayer configuration. The conclusion that must be drawn from this is that the interation of the different polar lipids with the other membrane components imposes a bilayer structure and prevents phase separation of non-bilayer forming lipids into separate domains within the membrane. 

Gounaris, K, Brain, A.P.R., Quinn, P.J. and Williams, W.P. (1983b). Structural and functional changes associated with heat-induced phase-separations of non-bilayer lipids in chloroplast thylakoid membranes, FEBS Lett., 153 47-52. 

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