Phospholipids membrane separation

Fig. 16. Schematic representation of a fluorinated vesicle obtained from perfluoroalkylated phospholipids showing separated nanometer-thick domains within their bilayer membrane. The central hydrophobic and lipophobic fluorous core of the membrane is flanked by two lipophilic shells, then by the hydrophilic outermost and innermost layers of polar heads [4].

The experiments described above demonstrate the ability to deliver soluble analytes to bilayer arrays and to evaluate the ability of these species to prevent surface absorption of proteins. Therefore, we have demonstrated methods of creating spatially addressed arrays of aqueous solutions above phospholipid membranes as well as arrays of phospholipid membranes with unique chemistry in each bilayer.13 These two concepts were carried out in separate assays. To be able to control both surface chemistry and aqueous chemistry... 

However, the ordered structure of the phospholipid membrane is not highly conducive to the presence of numerous pores. Therefore, high lipid solubility is a predominant characteristic that favors membrane absorption of a chemical. It is an important feature for oral absorption into the body as well as for distribution within the body, since the body is basically a series of polar, aqueous media chambers separated by phospholipid barriers containing polar groups. 

Improvement of membrane separation technology has resulted in the isolation of MFGM-enriched material from commercially available products. A phospholipid-rich fraction can be extracted from whey (Boyd et al., 1999) and buttermilk (Sachedva and Buchheim, 1997) with a reported yield of 0.25 g of phospholipids/g of protein in buttermilk (Sachdeva and Buchheim, 1997). Microfiltration of whey derived from the Cheddar cheese process, using 0.2 pm ceramic filters results in a fraction containing two major phospholipids, phosphatidylcholine and phosphatidylethanolamine, and lesser amounts of phosphatidylinositol, phosphatidylserine, sphingomyelin and cerebrosides (Boyd et al., 1999). The phospholipid fraction separated from the total lipids contains a larger proportion of mono- and polyunsaturated fatty acids (mainly oleic, Cig i and linoleic, C ) compared to the total lipid and the neutral lipid fraction (Boyd et al., 1999). 

Shimshick EJ, McConnel HM. Lateral phase separation in phospholipid membranes. Biochemistry 1973 12 2351-2360. 

Wu SHW, McConnell HM. Phase separations in phospholipid membranes. Biochemistry 1975 14 847-854. 

Membrane degumming. Membrane separation has also been evaluated as an alternative process to conventional oil refining processing. Ultrafiltration (UF) and nanofiltration (NF) membranes separate phospholipids almost completely, and FFAs, pigments, and other components can also be removed with the phospholipids to a certain extent. Less effort is required in the later processing steps. 

A partly purified membrane-bound PPase, incorporated in a phospholipid membrane, has been shown to act as a PP -dependent electric generator [99]. Proteolipo-somes reconstituted from soybean phospholipids and the PPase, were incorporated, in the presence of Mg ions, into a phospholipid-impregnated Teflon filter separating two solutions of an identical electrolyte content. Addition of PPj to the same compartment as proteohposomes, induced generation of an electric potential difference between the two filter-separated compartments, the proteoliposomes-con-... 

The PAMPA method is based on a 96-well plate platform that features a phospholipid membrane-soaked pad that separates an aqueous donor and receiver compartment. The membrane does not contain active transporters. The strategic use of PAMPA assays in drug discovery is based on the ability to screen large libraries and quickly determine trends based on the ability of compounds to permeate membranes by passive diffusion [83], In this way, quantitative structure activity relationships (QSAR) can be initiated based on this mechanism of absorption [84],... 

Test for phospholipase A activity. Acetone powders of membrane fractions were incubated with [3H]-lecithin at 37°C. The incubation mixture was extracted with methanol-chloroform, the extracted solution was washed and concentrated and the labelled phospholipids were separated and identified by thin layer chromatography in the presence of authentic reference compounds. The spots were scraped off and their radioactivity was measured. It was found that the membrane powders had formed some [3H]-lysolecithin. 

Hemichannels in apposing membranes must be brought sufficiently close for them to interact. Each hemichannel protrudes extracellularly only 10 A from the plasma membrane (30, 31), which is a very short distance compared with usual intercellular separation. The typical membrane-membrane separation within a gap junction is 20 A (19) [intriguingly close to the equilibrium distance between uncharged phospholipid surface (83)]. Strong evidence indicates that cell adhesion molecules play a crucial role in bringing cell membranes close enough for the hemichannels to interact (84, 85). 

Most biological systems are predominantly water, with other components conferring important structural and mechanical properties. The complexity of the fluid can have a substantial impact on rates of diffusional transport. For example. Chapter 5 discusses the consequences of having self-organized phospholipid phases (i.e., membrane bilayers) in systems that are primarily composed of water. Membranes separate the medium into smaller aqueous compartments, which remain distinct because the membrane permits the diffusion of only certain types of molecules between the compartments. Complex fluid phases have diverse roles in biological systems hyaluronic acid forms a viscoelastic gel within the eye (vitreous humor) that provides both mechanical structure and transparency actin monomers and polymers within the cytoplasm control cell shape and internal architecture. Drug molecules often must diffuse through these complex fluids in order to reach their site of action. 

Since increasing temperature leads to increased fluidity and thus to a faster probe diffusion, pyrene Hpids have been frequently used to study phase transition in membranes [161,162]. Phospholipid phase separation increases the local concentration of dye labeled Hpids and can, therefore, be investigated via the characterization of exdmer formation. The binding of proteins or ions, however, may induce phase separation as well as decreasing lateral lipid diffusion. Since these two effects are opposing in terms of excimer formation, the binding of such proteins or ions cannot be studied by the (Ex/Mo)-ratio. The time-resolved analysis of the monomer fluorescence of the labeled lipid, however, allows for the separation of... 

Lateral Phase Separation in Phospholipid Membranes Caused by Lateral Diffusion of Lipid Chains... 

Lateral phase separation in phospholipid membranes caused by lateral diffusion of lipid chain is detected by the time dependence of the local concentration which is estimated from the spin-spin exchange interaction. 

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