Human erythrocyte plasma membrane components

R. N. Reusch, R. P. Huang and D. Koskkosicka (1997). Novel components and enzymatic activities of the human erythrocyte plasma membrane calcium pump. FEBS Lett., 412, 592-596. 

Figure 11.1 Ultrastructure of the human lung alveolar barrier. The tissue specimen is obtained via lung resection surgery. (A) Section through a septal wall of an alveolus. The wall is lined by a thin cellular layer formed by alveolar epithelial type I cells (ATI). Connective tissues (ct) separate ATI cells from the capillary endothelium (en) within which an erythrocyte (er) and granulocyte (gc) can be seen. The minimal distance between the alveolar airspace (ai) and erythrocyte is about 800-900 nm. The endothelial nucleus is denoted as n. (B) Details of the lung alveolar epithelial and endothelial barriers. Numerous caveolae (arrows) are seen in the apical and basal plasma membranes of an ATI cell as well as endothelial cell (en) membranes. Caveolae may partake transport of some solutes (e.g., albumin). (C) ATII cells (ATII) are often localised in the comers of alveoli where septal walls branch off. (D) ATII cells are characterised by numerous multilamellar bodies (mlb) which contain components of surfactant. A mitochondrion is denoted as mi.

While the two-dimensional electrophoretic analysis described above is suitable for biological complexes that contain only a few major components (such as the human erythrocyte membrane), it is not feasible to extend its use to more complex systems such as the plasma membranes of many other cell types. Nevertheless, several ways to improve the method may prove useful. Immunoprecipitation of all the crosslinking products... 

The major components of beef glomerular basement membrane were solubilized with sodium dodecyl sulphate and resolved on 6% agarose [229]. 0.1% SDS has also been used in the separation of lipoprotein and apolipoprotein from human plasma [230] and 3% SDS used in gel chromatography of human erythrocyte membranes on Sepharose 6B [231]. Stokes radius determination of insulin-binding protein was performed on Sepharose 6B with 0.5% Triton X-100 [232]. 

Phosphoacylglycerols, sphingomyelins and cholesterol are incorporated into the lipid bilayer because of their amphipathic character (Chapter 8). The plasma membrane of human erythrocytes has a high cholesterol content, about 45% of the total lipid content. The bilayer formed from natural phospholipids is essentially a liquid in that it exhibits random motions consistent with the liquid state. Their hydrocarbon tails may move more freely about in the plane of the monolayer without losing their hydrophobicity which is responsible for their mutual attraction. Membranous proteins embedded within the membrane can also move laterally but are limited in the magnitude of such migrations by their interactions with other components located internal to the membrane. 

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