Saito H, Minamida T, Arimoto I, Handa T, Miyajima K
Faculty of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-01, Japan.
J Biol Chem. 1996 Jun 28;271(26):15515-20. doi: 10.1074/jbc.271.26.15515.
Plasma triglyceride-rich lipoproteins vary in lipid composition during their metabolism. We investigated the effects of the lipid composition of emulsion particles, specifically those of cholesterol enrichment and core replacement (replacing core triglyceride with cholesteryl oleate), on the physical states of surface and core lipids. Steady-state and time-resolved fluorescence anisotropies were measured in lipid emulsions using 1,6-diphenylhexatriene to probe the core and 1,6-diphenylhexatriene analogues for the outer and inner hydrophobic portions of surface phospholipids. In the absence of cholesterol, core replacement had little effect on the surface rigidity, despite the large difference in core mobility. However, core replacement caused a marked increase in surface rigidity in the presence of cholesterol. Quenching experiments using the fluorescent cholesterol analogue, dehydroergosterol, indicated that core replacement allowed surface dehydroergosterol to redistribute from the inner to the outer regions in the emulsion surface. These results indicated that core replacement modulates the surface properties of the emulsion particles through the redistribution of cholesterol in the surface layers. Furthermore, core replacement significantly decreased the binding of apolipoprotein E to the emulsion surface, whereas the binding of apolipoprotein CII responded to the cholesterol enrichment. This binding behavior of exchangeable apolipoproteins may closely correlate with the location of surface cholesterol and the mobility of core lipids.
富含甘油三酯的血浆脂蛋白在其代谢过程中脂质组成会发生变化。我们研究了乳剂颗粒的脂质组成，特别是胆固醇富集和核心置换（用油酸胆固醇替代核心甘油三酯）对表面和核心脂质物理状态的影响。使用1,6-二苯基己三烯在脂质乳剂中测量稳态和时间分辨荧光各向异性，以探测核心，并使用1,6-二苯基己三烯类似物探测表面磷脂的外部和内部疏水部分。在没有胆固醇的情况下，尽管核心流动性有很大差异，但核心置换对表面刚性影响很小。然而，在有胆固醇的情况下，核心置换导致表面刚性显著增加。使用荧光胆固醇类似物脱氢麦角固醇进行的猝灭实验表明，核心置换使表面脱氢麦角固醇在乳剂表面从内部区域重新分布到外部区域。这些结果表明，核心置换通过胆固醇在表面层的重新分布来调节乳剂颗粒的表面性质。此外，核心置换显著降低了载脂蛋白E与乳剂表面的结合，而载脂蛋白CII的结合对胆固醇富集有反应。可交换载脂蛋白的这种结合行为可能与表面胆固醇的位置和核心脂质的流动性密切相关。
