Erythrocytes plasma membrane

LOX catalyzed the oxidation of arachidonoylphosphatidylcholine at both carbon-12 and carbon-15. Later on, it has been found [21] that reticulocyte lipoxygenase oxidized rat liver mitochondrial membranes, beef heart submitochondrial particles, rat liver endoplasmic membranes, and erythrocyte plasma membranes without preliminary release of unsaturated acids by phospholipases. 

Lysolecithins act by dissolving cholesterol and cause massive losses of the sterol from membranes (19). Lysolecithins have been shown to cause the formation of openings 300-400 A in diameter in erythrocyte plasma membranes (20). Unlike saponins, lysolecithin membrane openings are permanent. 

Some membrane proteins are covalently linked to complex arrays of carbohydrate. For example, in gly-cophorin, a glycoprotein of the erythrocyte plasma membrane, 60% of the mass consists of complex oligosaccharide units covalently attached to specific amino acid residues. Ser, Thr, and Asn residues are the most common points of attachment (see Fig. 7-31). At the other end of the scale is rhodopsin of the rod cell plasma membrane, which contains just one hexasac-charide. The sugar moieties of surface glycoproteins influence the folding of the proteins, as well as their sta-... 

FIGURE 11-5 Asymmetric distribution of phospholipids between the inner and outer monolayers of the erythrocyte plasma membrane. 

Biological membranes consist primarily of proteins and lip-ids. The relative amounts of these materials vary considerably, depending on the source of the membrane. At one extreme, the inner mitochondrial membrane is about 80% protein and 20% lipid by weight at the other, the myelin sheath membrane is about 80% lipid and 20% protein. The plasma membrane of human erythrocytes contains about equal amounts of protein and lipid. Many membranes also contain small amounts of carbohydrates. These almost always are covalently attached to either proteins (as glycoproteins) or lipids (as glycolipids or lipopolysaccharides). The mitochondrial inner membrane has little or no carbohydrate, but the myelin membrane has about 3% carbohydrate by weight, and the erythrocyte plasma membrane about 8%. 

The idea of a lipid bilayer was first proposed by E. Gorter and F. Grendel, who showed in 1925 that the phospholipid content of the erythrocyte plasma membrane is approximately the amount needed to enclose the cell with a bilayer. Subsequent x-ray diffraction measurements confirmed this picture (fig. 17.8). 

Lipids also show asymmetrical distributions between the inner and outer leaflets of the bilayer. In the erythrocyte plasma membrane, most of the phosphatidylethanolamine and phosphatidylserine are in the inner leaflet, whereas the phosphatidylcholine and sphingomyelin are located mainly in the outer leaflet. A similar asymmetry is seen even in artificial liposomes prepared from mixtures of phospholipids. In liposomes containing a mixture of phosphatidylethanolamine and phosphatidylcholine, phosphatidylethanolamine localizes preferentially in the inner leaflet, and phosphatidylcholine in the outer. For the most part, the asymmetrical distributions of lipids probably reflect packing forces determined by the different curvatures of the inner and outer surfaces of the bilayer. By contrast, the disposition of membrane proteins reflects the mechanism of protein synthesis and insertion into the membrane. We return to this topic in chapter 29. 

Like conventional enzymes, transport proteins often are sensitive to specific inhibitors. For example, the anion transporter of the erythrocyte plasma membrane, which moves HC03- and Cl- ions across the membrane, is inhibited by 1,2-cyclohexadione or derivatives of stilbenedisul-fonate. Because these inhibitors react covalently with amino acid residues of the protein, they afford useful probes for the location and structure of the anion-binding site. 

Kuboki, M Ishii, H Kazama, M., 1990, Characterization of calpain I-binding proteins in human erythrocyte plasma membrane, J. Biochem., 107, 776-780 Kuboki, M., Ishii, H., and Kazama, M., 1987, Procalpcdn is activated on the plasma membrane and the calpain acts on the membrane, Biochim. Biophys. Acta, 929, 164—172 Labeit, S., Kolmerer, B., 1995, Titins giant proteins in charge of muscle ultrastructure and elasticity, Science, 270, 293-296... 

Hao, L., Rigaud, J.-L Inesi, G. (1994). Ca2+/H+ countertransport and electrogenicity in proteo-liposomes containing erythrocyte plasma membrane Ca-ATPase and exogenous lipids. J. Biol. Chem. 269,14268-14275. 

Answer Because protein X can be removed by salt treatment, it must be a peripheral membrane protein. Inability to digest the protein with proteases unless the membrane has been disrupted indicates that protein X is located internally, bound to the inner surface of the erythrocyte plasma membrane. 

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. 

Ankyrin is a 200 kDa protein that links cytoskeletal protdns to membrane proteins. It is bound tightly to the cytoplasmic surface of the erythrocyte plasma membrane to which it attaches the cytoskeletal protein spectrin. 

Lange T, Jungmann P, Haberle J, Falk S, Duebbers A, Bruns R, Ebner A, Hinterdorfer P, Oberleithner H, Schillers H. Reduced number of CFTR molecules in erythrocyte plasma membrane of cystic fibrosis patients. Molec. Membrane Biol. 2006 23 317-323. 

HullinF, BossantMJ, SalemNJ. Aminophospholipid molecular species asymmetry inthe human erythrocyte plasma membrane. Biochim Biophys Acta 1991 1023 335-340. 

The smooth flexible surface of the erythrocyte plasma membrane allows the cell to squeeze through narrow blood capillaries. Some cells have a long, slender extension of the plasma membrane, called a cilium or flagellum, which beats in a whiplike manner. This motion causes fluid to flow across the surface of an epithelium or a sperm cell to swim through the medium. The axons of many neurons are encased by multiple layers of modified plasma membrane called the myelin sheath. This membranous structure is elaborated by... 

The richest area of actin filaments In many cells lies in the cortex, a narrow zone just beneath the plasma membrane. In this region, most actin filaments are arranged in a network that excludes most organelles from the cortical cytoplasm. Perhaps the simplest c rt oskeleton Is the two-dimensional network of actin filaments adjacent to the erythrocyte plasma membrane. In more complicated cortical cytoskele-tons, such as those In platelets, epithelial cells, and muscle, actin filaments are part of a three-dimensional network that fills the c rt osol and anchors the cell to the substratum. 

Individual lipid molecules can move laterally in the plane of the membrane by changing places with neighboring lipid molecules (Fig. ll-16c). A molecule in one mono-layer, or leaflet, of the lipid bilayer—the outer leaflet of the erythrocyte plasma membrane, for example—can diffuse laterally so fast that it circumnavigates the erythrocyte in seconds. This rapid lateral diffusion within the plane of the bilayer tends to randomize the positions of individual molecules in a few seconds. 

Liver plasma membrane Erythrocyte plasma membrane Total Outer (%) Inner Myelin Mitochondria (inner and outer membranes) Endoplasmic reticulum K coli... 

The permeability of the erythrocyte plasma membrane has been measured by monitoring the rate of movement of a variety of solutes into erythrocytes (Table 5.2 and Figure 5.6). For non-electrolytes of molecular weight less than 200, permeabiUty decreases with increasing molecular weight compounds with molecular weight over 300 (such as sucrose) are essentially excluded from the membrane. Charged molecules do not partition into lipid bilayers therefore, ions have a very low permeability in the erythrocyte membrane. The low intrinsic permeability of ions underlies the ability of membranes to support an electrieal potential difference, which is discussed more fully in Section 5.4.3. 

Han, X. Gross, R.W. Electrospray ionization mass spectroscopic analysis of human erythrocyte plasma membrane phosphohpids. Proc. Natl Acad. Sci. 1994, 91, 10635-10639. 

Han, X., and R. W. Gross. 1994. Electrospray ionization mass spectroscopic analysis of human erythrocyte plasma membrane phospholipids. Proc Natl Acad Sci USA 91(22) 10635-9. Han, X. L., and R. W. Gross. 1990. Plasmenylcholine and phosphatidylchohne membrane bilayers possess distinct conformational motifs. 29(20) 4992-6. 

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