Thylakoid proteins intrinsic

Vallon, O., Wollman F.A. and Olive J. 1985. Distribution of intrinsic and extrinsic subunits of the PSII protein complex between appressed and non-appressed regions of the thylakoid membrane An immunocytochemical study. FEBS Lett. 183,245-250. 

Most of the thylakoid proteins are organized into four intrinsic protein complexes PS II complex, Cyt b/f complex, PS I complex and ATP synthetase (Fig. 1). The electron transport complexes are linked by mobile electron transport carriers, plastoquinone, plastocyanin and ferredoxin (see Chapter 10). Furthermore, chloroplasts that possess Chi b have the major light-harvesting Chi a/h-proteins of PS II (LHC II) that may represent over 50% of the thylakoid protein [13], as well... 

Protein Release. Biomembranes consist of lipids and proteins. The latter may be subdivided into so-called intrinsic and extrinsic proteins (49). Intrinsic proteins supposedly are integrated into the membrane phase primarily by the hydrophobic interaction with lipids. Extrinsic proteins are attached to the membranes. Ionic interactions are believed to be important in the binding of extrinsic proteins. When these proteins dissociate from the membrane, they may be sufficiently hydrophilic to be soluble in the aqueous phase. When freeze-aggregated thylakoids are sedimented, a number of membrane proteins are found in the supernatant fluid. Among them are catalytic proteins involved in energy conservation and electron transport (42,48). The total amount of proteins released depends on freezing conditions and the solute environment, but may be as much as 5% of the total membrane protein (48). When frozen in the presence of a cryoprotective solute, at a sufficient concentration, thylakoids remain functional and do not release proteins in significant amounts. Protein release thus accompanies membrane injury and, in fact, is an indication of such injury. 

Several lines of experimental evidence have emerged to support the overall concept that thylakoid membrane differentiation into stacked and unstacked regions is governed by the exposed fixed electrical charges on the surface of the intrinsic membrane protein complexes. 

In summary, the thylakoid membranes of Pisum sativum and a number of other higher plant species (data not shown) possess a 60 kDa intrinsic polypeptide that can be ADP-ribosylated by cholera toxin and that is recognised by an antibody which cross reacts with animal G-protein 0(- subunits. Preliminary experiments indicate that this... 

Energy derived from electron transport in mitochondrial, chloroplast thylakoids and bacterial plasma membranes is transduced to form ATP by the Fi-Fq proton translocating ATP synthases. These enzyme complexes are composed of an intrinsic membrane protein complex, Fq, which mediates H+-translocation, and a peripheral protein complex, Fi, which catalyzes the terminal step of synthesis of ATP from ADP and Pi. 

The general question of acyl lipid-protein binding in biological membranes is the subject of some controversy at present (8). The consensus view is that strong non-covalent binding interactions of the sort exemplified by thylakoid pigments are very rare in the case of acyl lipids (6,8). It is inevitable, however, in a protein-rich membrane like the thylakoid, that many aoyl lipid molecules will of necessity interact with intrinsic proteins. 

The H" -ATPase of thylakoids catalyzes ATP synthesis and, in some conditions, hydrolysis in a manner that is linked to proton fluxes. The H+-ATPase consists of two readily separable parts coupling factor 1 (CF ), a hydrophilic, multisubunit enzyme that is extrinsic to the membrane, and Fq, a collection of more hydrophobic proteins that are intrinsic to the membrane. CF contains the active sites of the H -ATPase and is composed of five different subunits, labeled a-e in order of decreasing molecular weight. Fq constitutes a proton channel and provides specific sites for the attachment of CF. to the membrane. 

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