Lipid membranes structure

With the adequacy of lipid bilayer membranes as models for the basic structural motif and hence for the ion transport barrier of biological membranes, studies of channel and carrier ion transport mechanisms across such membranes become of central relevance to transport across cell membranes. The fundamental principles derived from these studies, however, have generality beyond the specific model systems. As noted above and as will be treated below, it is found that selective transport... 

Lipid bilayer (Section 27.3) The ordered lipid structure that forms a cell membrane. 

Kaprelyants, A., Suleimenov, M., Sorokina, A., Deborin, G., El-Registan, G., Stoyanovich, F., Lille, Yu., Ostrovsky, D. Structural-functional changes in bacterial and model membranes induced by phenolic lipids. Biological membranes, Vol.4, No.3, (March 1987), pp. 254-261, ISSN 0748-8653... 

Cell membranes consist of two layers of oriented lipid molecules (lipid bilayer membranes). The molecules of these two layers have their hydrocarbon tails toward each other, while the hydrophilic heads are outside (Fig. 30.1a). The mean distance between lipid heads is 5 to 6mn. Various protein molecules having a size commensurate with layer thickness float in the lipid layer. Part of the protein molecules are located on the surface of the lipid layer others thread through the layer (Fig. 30.1fc). Thus, the membrane as a whole is heterogeneous and has a mosaic structure. 

In the 1970s the structure and dynamics of lipid bilayer membranes were extensively investigated by NMR. The principles of the NMR spectroscopy applied to the study of biomembranes are reviewed in Ref. 5, together with the fruitful achievements in the early stage. In the 1980s the NMR biomembrane research was carried out mainly by applying the solid-state NMR techniques [6-11]. Generally, the solid-state spectra are of low reso-... 

General anesthetics are usually small solutes with relatively simple molecular structure. As overviewed before, Meyer and Overton have proposed that the potency of general anesthetics correlates with their solubility in organic solvents (the Meyer-Overton theory) almost a century ago. On the other hand, local anesthetics widely used are positively charged amphiphiles in solution and reversibly block the nerve conduction. We expect that the partition of both general and local anesthetics into lipid bilayer membranes plays a key role in controlling the anesthetic potency. Bilayer interfaces are crucial for the delivery of the anesthetics. 

Although the drug delivery to the lipid bilayer membrane is just the first step for bioactivities and phopholipid vesicles are rather simple in view of the composite structure of biomembranes, the unambiguous specification of the preferential location of the drug is essential the successive processes of the action are expected to be induced via the delivery site in membranes. We expect more advances in the dynamic NMR study, so that we can get insight into the mechanism of DD in membranes. 

The other anomalous behavior was the smaller-than-expected permeability of highly branched compounds. This deviation has been explained on the basis that membrane lipids are subject to a more highly constrained orientation (probably a parallel configuration of hydrocarbon chains of fatty acids) than are those in a bulk lipid solvent. As a result, branched compounds must disrupt this local lipid structure of the membrane and will encounter greater steric hindrance than will a straight-chain molecule. This effect with branched compounds is not adequately reflected in simple aqueous-lipid partitioning studies (i.e., in the K0/w value). 

Liposomes, also known as lipid vesicles, are aqueous compartments enclosed by lipid bilayer membranes [56,57]. Figure 10.11 shows how lipid bilayers are arranged in the liposome and the lipid structures in large unilamellar vesicles and multilamellar vesicles. Lipids consist of two components ... 

The use of liposomes as complexing agents in the application of premetallised acid dyes to wool has been investigated [21-24]. Liposomes are lipid structures containing aqueous compartments surrounded by bilayer membranes. However, the methods as yet available for the preparation of these agents are hardly practical in dyehouse terms (section 10.3.4). 

The complete complex of nucleic acid and protein, packaged in the virus particle, is called the virus nucleocapsid. Although the virus structure just described is frequently the total structure of a virus particle, a number of animal viruses (and a few bacterial viruses) have more complex structures. These viruses are enveloped viruses, in which the nucleocapsid is enclosed in a membrane. Virus membranes are generally lipid bilayer membranes, but associated with these membranes are often virus-specific proteins. Inside the virion are often one or more virus-specific enzymes. Such enzymes usually play roles during the infection and replication process. 

The importance of lipids in membrane structure was established early in the 20th century when pioneering biophysicists established positive correlations between cell membrane permeabilities to small non-electrolytes and the oil/water partition coefficients of these molecules. Contemporary measurements of the electrical impedance of cell suspensions suggested that cells are surrounded by a hydrocarbon barrier, which was first estimated to be about 3.3 nm thick. This was originally thought to be a lipid monolayer. Among the pioneering biophysical experiments were those that established that the ratio of the area of a monolayer formed from erythrocyte... 

Dietary polyunsaturated fatty acids (PUFAs), especially the n-3 series that are found in marine fish oils, modulate a variety of normal and disease processes, and consequently affect human health. PUFAs are classified based on the position of double bonds in their lipid structure and include the n-3 and n-6 series. Dietary n-3 PUFAs include a-linolenic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) whereas the most common n-6 PUFAs are linoleic acid, y-linolenic acid, and arachidonic acid (AA). AA is the primary precursor of eicosanoids, which includes the prostaglandins, leukotrienes, and thromboxanes. Collectively, these AA-derived mediators can exert profound effects on immune and inflammatory processes. Mammals can neither synthesize n-3 and n-6 PUFAs nor convert one variety to the other as they do not possess the appropriate enzymes. PUFAs are required for membrane formation and function... 

Concerning the nature and structure of such amyloid peptide or protein channels, oligomers with annular morphologies have in fact been observed by EM for a-synuclein (Lashuel et al., 2002) and equine lysozyme (Malisauskas et al., 2003) even in the absence of any lipids or membranes. Channel-like structures have also been reconstituted in liposomes and observed by SFM for A/ i 4o, A/ j 42, human amylin, a-synuclein, ABri, ADan, and serum amyloid A (Fig. 5A Lin et al., 2001 Quist et al., 2005). Doughnut-shaped structures with a diameter of 10-12 nm and a central hole size of 1-2 nm (Fig. 5B) were imaged on top of lipid membranes (Quist et al., 2005). However, the radius of curvature of the SFM tips meant that it is not possible to say whether the pores were really traversing the lipid bilayer. 

An important question arises about the effects of phospholipid composition and the function of membrane-bound enzymes. The phospholipid composition and cholesterol content in cell membranes of cultured cells can be modified, either by supplementing the medium with specific lipids or by incubation with different types of liposomes. Direct effects of phospholipid structure have been observed on the activity of the Ca2+-ATPase (due to changes in the phosphorylation and nucleotide binding domains) [37]. Evidence of a relationship between lipid structure and membrane functions also comes from studies with the insulin receptor [38]. Lipid alteration had no influence on insulin binding, but modified the kinetics of receptor autophosphorylation. 

C. D. Stubbs, B. W. Williams, C. L. Pryor, and E. Rubin, Ethanol-induced modifications to membrane lipid structure—Effect on phospholipase A2-membrane interactions, Arch. Biochem. 262, 560-573 (1988). 

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