Lateral diffusion of lipids

A more interesting problem from both the experimental and theoretical point of view is the lateral diffusion of phospholipids in mixtures of lipids, when both solid and fluid phases coexist. At least three questions arise in connection with this problem. (1) What is the rate of lateral diffusion of phospholipids in solid solution domains (2) To what extent do solid solution domains act as obstacles to the lateral diffusion of lipid molecules in fluid domains (3) To what extent are there composition and density fluctuations present in fluid lipid bilayers, and to what extent do these fluctuations affect lateral diffusion Let us consider these questions one at a time, bearing in mind that these questions may to some extent be interrelated. 

Is it possible to use simple bilayer vesicles (liposomes) to test the involvement of other modes of motion than lateral diffusion of lipids (e.g., motions across the bilayer that would be important in the transmission of signals from the cell interior to the external cell surface) ... 

Cassier T, Sinner A, Offenhauser A et al (1999) Homogeneity, electrical resistivity and lateral diffusion of lipid bilayers coupled to polyelectrolyte multilayers. Colloids Surf B 15 215-225... 

P NMR was also used to study of the oriented membranes and pores induced by protegrin-1 (PG-1), which represents AMPs.92,93 The line shape specifies the toroidal pores and thinned membranes that are formed in membrane bilayers by the binding of AMPs. The lateral diffusion of lipids were analysed from the motion-ally averaged 2D 31P SS NMR spectra. The mechanism of pore formation due to interaction between the peptide (fallaxidin) with lipids has been investigated.94... 

Saxton MP. Lateral diffusion of lipids and proteins. Curr. Topics in Membranes 1999 48 229-282. 

Tocanne J-F, Dupou-Cezanne L, Lopez A. Lateral diffusion of lipids in model and natural membranes. Progr. Lipid Res. 1994 33 203-237. 

Lai CS, Wirt MD, Yin JJ, Eroncisz W, Feix JB, Kunicki TJ, Hyde JS. Lateral diffusion of lipid probes in the surface membrane of... 

Vaz WLC, Derzko ZI, Jacobson K. Photobleaching measurements of the lateral diffusion of lipids and proteins in artificial phospholipid bilayer membranes. Cell Surface Rev. 1982 8 83-135. 

Figure 12.31. Lipid Movement in Membranes. Lateral diffusion of lipids is much more rapid than transverse diffusion (flip-flop).

Fig. 13.—Stages of vesicle and tubule formation from a one-component bilayer. Stages A and B are energetically favourable if allowed by packing, but require free lateral diffusion of lipids in the bilayer and water flow across the bilayer. Stage C involves fusion. Stage D is energetically unfavourable for a bilayer in the fluid-state. A mechanism of vesicle and alveoli formation from a membrane similar to that shown here has been found to occur in a variety of cell types and in micropino-...

Aiip0 = 180 A. This is a significant concentration because it is around the high pressure transition seen on n — A isotherms and the rheological transition pressure of pure lipopolymers. Not surprisingly, the lateral diffusion of lipids is obstructed below this point. 

Yin JJ, Pasenkiewiczgiemla M, Hyde JS (1987) Lateral diffusion of lipids in membranes by pulse saturation recovery electron-spin-resonance. Proc Natl Acad Sci USA 84 964—968... 

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. 

Naqvi K. R., 1974, Difiusioft-cofitroUed reactions in two-dimensional fluids Discussion ttf measurements of lateral diffusion of lipids in bioiogicat raen ranes. Chem Phys. Lett. 28 280-284. 

Lipid bilayer membrane systems, having gel (solvated crystalline state)-to-liquid crystalline phase transitions are attractive as specific organic media for separation chemistry. The first approach in HPLC was direct immobilization of a phosphatidylcholine lipid onto silica. This modified silica shows interesting selectivity against amino acids, but the separation mode is too complicated, due to the zwitter-ionic property of the immobilized molecule. In addition, no lipid membrane function is realized on the silica because of the direct immobilization with covalent bonding, which prohibits lateral diffusion of lipids from forming highly-ordered structures that lead to supramolecular functions of lipid membrane systems. 

FRAP was used initially to smdy the dynamics of lateral diffusion of lipids and proteins on cell surfaces [159-163]. It was combined with total internal reflection (Box 3.2 and Sect. 5.10) to study interactions of immunoglobulin fragments with planar bUayer membranes supported on glass surfaces [164] and binding of ligands to immobilized receptors [165]. Its applications expanded rapidly with the development of confocal microscopy (Sect. 5.10) and GFP tags [147,166-168], and now include components of the nucleus [169, 170], mitochonrial matrix [171], endoplasmic reticulum [172], and Golgi apparatus [173]. 

Subsequent observations such as the known rapid lateral diffusion of lipid and protein in the plane of the membrane and knowledge that proteins are often inserted into and through the lipid matrix have been added to the points made above. These considerations have been allowed for in the proposal by Singer and Nicholson in 1972 of their fluid mosaic model for membrane structure (Figure 6.10). In the diagram an asymmetric lipid bilayer forms the basis of the membrane structure with proteins spanning the membrane or embedded into the hydrophobic core region. 

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