Cell membrane Erythrocyte ghosts

Here, we discuss a solid-state 19F-NMR approach that has been developed for structural studies of MAPs in lipid bilayers, and how this can be translated to measurements in native biomembranes. We review the essentials of the methodology and discuss key objectives in the practice of 19F-labelling of peptides. Furthermore, the preparation of macroscopically oriented biomembranes on solid supports is discussed in the context of other membrane models. Two native biomembrane systems are presented as examples human erythrocyte ghosts as representatives of eukaryotic cell membranes, and protoplasts from Micrococcus luteus as membranes... 

Polyphosphate was chosen as a polyelectrolyte in addition to the erythrocyte ghost protein, because van Steveninck demonstrated (17) that polyphosphate plays an important role in membrane transport in yeast cells. The results obtained with polyphosphate, especially on protein-covered membranes, indicate that the possibility of ionic transport is strongly enhanced. 

First, a mixture of synthetic or natural phospholipids, polymerizable lipids, and proteins can be converted to liposomes and then be polymerized. Second, polymerizable lipids are introduced into e.g. erythrocyte ghost cells by controlled hemolysis and subsequent polymerization as described by Zimmermann et al.61). This hemolysis technique is based on a reversible dielectric breakdown of the cell membrane. Dielectric breakdown provides a third possible path to the production of bi omembrane models. Zimmermann et al. could show that under certain conditions cells can be fused with other cells or liposomes61). Thus, lipids from artificial liposomes could be incorporated into a cell membrane. A fourth approach has been published by Chapman et al.20). Bacterial cells incorporate polymerizable diacetylene fatty acids into their membrane lipids. The diacetylene units can be photopolymerized in vivo. The investigations discussed in more detail below are based on approaches 1. and 3. 

Loss of hemoglobin by lysed red blood cells (cell membrane lysis). Controlled hemolysis (induced osmotically or electrically) yields hemoglobin-free erythrocyte ghosts . 

Tetraphenylporphyrins [69] are hydrophobic compounds and are unable to penetrate unaided into the water-containing tissues of the human body. This only becomes possible on incorporation into a dendrimer or a liposome. Use in the human body has not yet been tested but prehminary experiments have been performed on ruptured red blood cells, erythrocyte ghosts. The blood cells were washed out, and the tetraphenylporphyrin was introduced into the membrane of the ghosts and subjected to photophysical investigation [70]. 

The transfer of radiolabeled phospholipids between vesicles and erythrocyte membranes could be used to assay lipid transfer activity. Intact erythrocytes are not an ideal substrate for routine measurements of transfer activity because some transfer proteins do not readily accelerate the transfer of phospholipids from these membranes. Van Meer et al. (1980) found that a very high concentration of the phosphatidylcholine-specific transfer protein was necessary to exchange the phosphatidylcholine of intact red blood cells. Erythrocyte ghosts are a more active substrate for this protein (Bloj and Zilversmit, 1976). However, the nonspecific transfer protein from bovine liver accelerates the exchange of phospholipid between intact erythrocytes and phosphatidylcholine vesicles (Crain and Zilversmit, 1980c). 

The effect of a biologically active substance on an isolated membrane and an intact cell membrane may differ considerably as to the concentration dependence and qualitatively. Therefore, we performed a preliminary treatment of whole cells of erythrocytes with ichfan then, we isolated ghosts. The thermogram of erythrocyte ghosts (Figure 4c) varies considerably upon the preincubation of erythrocytes with HA at doses of 10 6-10"5 M. The thermogram of erythrocyte ghosts preincubated with ethanol (this additive is equivalent to... 

Indications of nonenzymatic glycosylation of red cell membrane proteins was first reported in 1976 (B2). Analysis of the various protein components of the erythrocyte membrane indieated that glycosylation of red cell ghosts in 18 diabetics was twice that in normal individuals and correlated with levels of Hb Ajj. (M25). Comparison of individual membrane protein bands on sodium dodecyl sulfate-polyacrylamide electrophoresis did not indicate any... 

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