Phospholipid-exchange systems

Phospholipid-Exchange Systems Paul Mazliak and J. C. Kader... 

Furthermore, it is mandatory to specify and standardize the solubilization of oxidized phospholipids for incubation with cells or individual target molecules. Physiologically relevant systems are pure lipid micelles or vesicles depending on the chemical structure of the lipid, complexes with proteins (e.g. albumin) and plasma lipoproteins. Furthermore, it has to be taken into account that oxidized phospholipids exchange between lipid surfaces much faster than regular membrane phospholipids containing two long hydrophobic acyl chains (Li et al.,... 

The movement of substances between the blood and the extracellular fluid surrounding the cells in most tissues of the body occurs very readily. This exchange takes place at the level of the capillaries, the smallest blood vessels in the cardiovascular system whose walls are formed by a single layer of endothelial cells. Lipid-soluble substances are able to move across this layer of endothelial cells at any point because they can move directly through the plasma membrane by passing between the phospholipid molecules of the bilayer. The movement of water-soluble substances is limited to the multiple pores found between the cells however, it also takes place rapidly and efficiently. 

The isolated CFq-CFi has been incorporated into phospholipid liposomes and shown to carry in this form most of the energy-transducing functions which it catalyses within the thylakoid membranes. Thus, the reconstituted ATP synthase carries out ATP-dependent proton translocation resulting in both a 4pH and a developing across the reconstituted liposomes [72,73] an uncoupler-sensitive ATP-Pj exchange reaction [39] and ATP formation driven by artificially imposed 4pH and Ail/ [39,74,75], or by electric field pulses [56]. The ATP synthase proteolipo-somes provide the simplest system available today for the study of electrochemical-gradient-driven phosphorylation. 

The effect of different phospholipid head groups on the protein-stimulated transfer by phosphatidylcholine- and phosphatidylinositol-specific proteins has been studied. Contradictory results were obtained for the effect of acidic phospholipids on the transfer of phospholipid by the phosphatidylcholine exchange protein from beef liver. DiCorleto et al. (1977) used small unilamellar vesicle-mitochondria and small unilamellar vesicle-multilamellar vesicles to study the effect of varying amounts of acidic phospholipids incorporated into phosphatidylcholine donor vesicles. Up to 20 mol% phosphatidic acid or phosphatidylinositol in the donor was found to stimulate the transfer of phosphatidylcholine in both assay systems. Wirtz et al. (1979) and Hellings et al. (1974) found different results for the phosphatidylcholine exchange protein with unilamellar and multilamellar vesicles. In these assays, the incorporation of acidic phospholipids (phosphatidic acid or phosphatidylinositol) into the donor particles had an inhibitory effect on the rate of phosphatidylcholine transfer. 

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