Diffusion in lipid bilayers

Bassolino-Klimas, D., Alper, H. E. and Stouch, T. R. (1993). Solute diffusion in lipid bilayer membranes an atomic level study by molecular dynamics simulation,... 

D. Bassolino-Klimas, H. E. Alper and T. R. Stouch, Solute Diffusion in Lipid Bilayer Membranes An Atomic Level Study by Molecular Dynamics Simulation, Biochemistry 32 (1993) 12624. 

Subczynski, W. K., E. Markowska, and J. Sielewiesiuk. 1991. Effect of polar carotenoids on the oxygen diffusion-concentration product in lipid bilayers. An EPR spin label study. Biochim. Biophys. Acta 1068 68-72. 

Windrem, D. A. and W. Z. Plachy. 1980. The diffusion-solubility of oxygen in lipid bilayers. Biochim. Biophys. Acta 600 655-665. 

Another example comes from the work of Johnson, et a/.18 These workers studied spin labels dissolved in lipid bilayer dispersions of dipalmitoylphos-phatidylcholine and cholesterol (9 1 by weight) in the hope that anisotropic rotational diffusion of the spin label would mimic the motion of the bilayer components. In addition to 5-DS, which is sensitive to rotational motion about the NO bond, they used the steroidal nitroxide 8, which tends to rotate about an axis perpendicular to the N-O bond. ESR measurements were carried out at both 9 and 35 GHz and at temperatures ranging from 30 to 30 °C. Rather different results were obtained with the two spin labels, largely as a result of the different axes of rotation. Because the rotation rates were very slow, ESR spectra appeared as powder patterns rather than isotropic spectra and special methods were needed to extract the motional data. 

Self-diffusion measurements of phosphatidylcholines in lipid bilayers 190... 

NMR measurements on deuterated phospholipid bilayers and phospho-lipid/eholesterol mixtures, measurements of self-diffusion of phosphatidyleho-lines in lipid bilayers, and finally pressure effeets on the strueture and phase behaviour of model biomembranes eonsisting of phospholipid bilayers with incorporated peptides will be discussed. 

The rates of lateral diffusion of phospholipids in lipid bilayer membranes, and in biological membranes, were first measured using spin-labeled lipids.26 50 10 11 9 In general, these rates have been determined by incorporating spin-labeled lipids such as (V) and (VI) in phospholipid bilayers, or multilayers. The paramagnetic resonance spectra of labels such as (V), as well as the nuclear resonance spectra of other lipids in membranes containing (V), depend on the concentration c of the label in the membrane and the rate of lateral motion of the lipids. Two methods... 

As indicated in my report, we now know the rates of lateral diffusion of phospholipids in lipid bilayers in the fluid state, and in a few cases the rates of lateral diffusion of proteins in fluid lipids are also known. At the present time nothing is known about the rates of lateral diffusion of phospholipids in the crystalline, solid phases of the substances. As mentioned in my report, there are reasons to suspect that the rates of lateral diffusion of phospholipids in the solid solution crystalline phases of binary mixtures of phospholipids may be appreciable on the experimental time scale. Professor Ubbelohde may well be correct in pointing out the possibility of diffusion caused by defects. However, such defects, if present, apparently do not lead to significant loss of the membrane permeability barrier, except at domain boundaries. 

Figure 2.6. The role of lipid membranes in drag distribution, a Structure of phosphatidylcholine (left), and schematic of a lipid bilayer (right). The hydrophobic interior phase represents the kinetic barrier to drag absorption and distribution. b Drag diffusion across lipid bilayers. Partition into the bilayer is the rate-limiting step. Hydrophilic drag molecules (left) will not efficiently partition into the hydrophobic phase and therefore can t get across the membrane easily. In contrast, hydrophobic molecules (right) will enter the membrane readily and therefore will cross the membrane more efficiently.

Buffy, J. J., Waring, A. J. and Hong, M. (2005) Determination of peptide oligomerization in lipid bilayers using F-19 spin diffusion NMR. Journal of the American Chemical Society, 127(12), 4477 1483. 

Druglike character for a molecule entails a molecular weight of 350-400, if possible, and sufficient water solubility to be dispersed in aqueous media with concomitant lipophilic property to dissolve into and diffuse through lipid bilayer membranes. 

Bussell, S. J., Hammer, D. A., and Koch, D. L., The effect of hydrodynamic interactions on the tracer and gradient diffusion of integral membrane proteins in lipid bilayers. /. Fluid. Mech. 258, 167 (1994b). 

Peters, R., and Cherry, R. J., Lateral and rotational diffusion of bacteriorhodopsin in lipid bilayers Experimental test of the Saffman-Delbruck equations. Proc. Natl. Acad. Sci. U.S.A., 79, 4317 (1982). 

Many molecules do not diffuse through lipid bilayers (see Figure 5.6 and notice that sucrose and ions do not permeate). One of the most important functions of accessory molecules in the membrane is regulation of transport of molecules that do not pass freely through the lipid bilayer. Several classes of accessory molecules are engaged in membrane transport, as described in the sections that follow. 

The term exdmer is used when the excited dye forms a transient fluorescent dimeric complex with another fluorophore of the same kind. The exdmer fluorescence is usually red shifted with respect to that of the monomer (see Fig. 6.28) The most widely used types of eocdmer-forming probes are pyrene (see Fig. 6.28) and perylene and their derivatives. The ratio of the maxima of the excimer to the monomer spectra can be used to judge the efficiency of exdmer formation. This (Ex/Mo)-ratio depends on the concentration of the dye and is controlled by the diffusion properties. It allows, when using pyrene or perylene labeled fatty acids or phospholipids (see Fig. 6.28), the estimation of the probe s lateral diffusion coefficients in lipid bilayer membranes. Thus, membrane fluidity can be measured by monitoring the fluorescence spectra of such an exdmer probe. 

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