摘要(英) |
Sterols play important roles in membrane organization and functions. Model membranes containing cholesterol reveal that the addition of cholesterol in lipid membranes results in sterol-poor and sterol-rich domains. The sterol-rich domain, in the liquid-ordered phase, is thought to be the lipid raft found in cell membranes. On the other hand, in some model membranes liquid-ordered phase is not observed. In this work, we investigate the effect of stigmasterol on the physical properties 1-palmitoyl-d31-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE-d31) membranes.
Model membranes composed of POPE-d31 and stigmasterol were studied using deuterium nuclear magnetic resonance. NMR spectra were taken as a function of temperature and stigmasterol concentration up to 50 mol %. Stigmasterol decreases membrane order of the gel-phase POPE-d31 bilayers and this effect is very limited. In contrast, stigmasterol increases the chain order of the liquid-crystalline (lc) phase POPE-d31 bilayers slightly. The temperature-composition phase diagram is presented. The addition of stigmasterol does not affect the gel-to-lc phase transition significantly, however it decreases the temperature of lc-to-HII phase transition strongly. In addition, there is no liquid-ordered phase observed in POPE-d31/stigmasterol membranes. A comparison between stigmasterol and other sterols suggest that the extra double bond and the extra methyl group in the acyl chain of sterol hinder the ability of sterol to increase POPE-d31 chain order. |
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