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- Filippov, A V, et al.
(författare)
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Lateral Diffusion of Saturated Phosphatidylcholines in Cholesterol-containing Bilayers
- 2007
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Ingår i: Biophysics. - 0006-3509. ; 52:3, s. 307-14
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Tidskriftsartikel (refereegranskat)abstract
- A pulsed field gradient NMR was used to study lateral diffusion in the cholesterol-containing oriented bilayers of saturated (dipalmitoyl- and dimyristoyl-) phosphatidylcholines, upon their limiting hydration. Similar dependences of lateral diffusion coefficients on temperature and cholesterol concentration were observed, which agree with phase diagram showing the presence of the regions of disordered and ordered liquid-crystalline phases and a two-phase region. Under the same conditions, the lateral diffusion coefficient of dipalmitoylphosphatidylcholine is lower, which agrees qualitatively with its larger molecular weight. The comparison of data for dipalmitoylphosphatidylcholine with previous results for dipalmitoylsphingomyelin−cholesterol bilayers under the same conditions, in spite of similarity of phase diagrams, shows large (two−three times) differences in the lateral diffusion coefficient and a different profile of its dependence on cholesterol concentration. The comparison of data for dimyristoylphosphatidylcholine with previous results shows that the values of lateral diffusion coefficient and the shape of its dependence on cholesterol concentration coincide at high concentrations (>15 mol%) but differ at lower concentrations The revealed disagreement may be caused by the fact that the measurements were carried out at different water content in the system. At limiting hydration (more than 35% of water), the lateral diffusion coefficient for lipids decreases when cholesterol concentration rises, while at water content about 25% (as a result of equilibrium hydration from vapors) the lateral diffusion coefficient of phosphatidylcholine may be independent of cholesterol concentration. This is the consequence of the denser packing of molecules in the bilayer at reduced water content, an effect that competes with the ordering effect of cholesterol.
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| 2. |
- Filippov, Andrei, et al.
(författare)
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Lateral diffusion in sphingomyelin bilayers
- 2010
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Ingår i: Magnetic Resonance in Chemistry. - : Wiley. - 0749-1581 .- 1097-458X. ; 48:12, s. 945-950
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Tidskriftsartikel (refereegranskat)abstract
- Sphingomyelin (SM) is an important lipid of eukaryotic cellular membranes and neuronal tissues. We studied lateral diffusion in macroscopically oriented bilayers of synthetic palmitoylSM (PSM) and natural sphingomyelins of egg yolk (eSM), bovine brain (bSM) and bovine milk (mSM) by NMR pulsed field gradient (NMR PFG) in the temperature range of 50-60oC. We found that the mean values of lateral diffusion coefficients (LDCs) of SMs are 1.9-fold lower in comparison with dipalmitoylphosphatidylcholine, which is similar in molecular structure. This discrepancy could be explained by the characteristics of intermolecular SM interactions. The LDCs of different SMs differ: egg SM is most similar to PSM, both of them have a 10% higher LDC value in comparison with the two other natural SMs. Besides, all natural SMs show a complicated form of the spin-echo diffusion decay, which is an indicator of a distribution of LDC values in bilayers. This peculiarity was explained by broad distributions of fatty acid lengths of the natural SMs studied here, especially mSM and bSM. We confirmed the relationship between chain length and the LDC in bilayers by computer analysis of a set of 1H NMR spectra obtained by scanning the value of the pulsed field gradient: there is a correlation between lower LDC values and SM molecules with longer acyl chains. The most probable mechanisms by which long-chain SM molecules decrease their lateral diffusion relative to the average value are protrusion into the other side of the bilayer or lateral separation into areas that diverge with their LDCs.
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