Bellemare F, Fragata M
J Membr Biol. 1981 Jan 30;58(1):67-74. doi: 10.1007/BF01871035.
A study of the molar ratio dependence of the incorporation of alpha-tocopherol into single-lamellar vesicles showed that the number of molecules which the bilayers can accommodate increased linearly with increasing alpha-tocopherol/phosphatidylcholine initial molar ratios till about 0.05, then approached a saturation limit. At 5 mol%, one alpha-tocopherol molecule per 60 phospholipids can be incorporated into the membranes. Up to this limit the distribution of alpha-tocopherol in the bilayers is uniform, while at initial molar ratios higher than 0.05 a disproportionation toward the inner monolayer of the vesicles is observed. The average outer/total ratio is found to be 0.27 +/- 0.03 at alpha-tocopherol/phosphatidylcholine molar ratios above 0.07 and is similar to asymmetrical distributions that have been reported in vesicles containing other one-chain amphiphiles (e.g., cholesterol). This large disproportionation is in contrast with the packing distribution of certain two-chain amphiphiles, and indicates that one of the driving forces for asymmetry formation in lipid bilayers might be dependent on the number of hydrocarbon chains per amphiphile molecule. A possible reason for the disproportionation effect observed in our experiments is the displacement of unsaturated phospholipids to the outer monolayer of the single-lamellar vesicles, by the more rigid isoprene units of alpha-tocopherol.
一项关于α-生育酚掺入单层囊泡的摩尔比依赖性研究表明，双层膜能够容纳的分子数量随着α-生育酚/磷脂酰胆碱初始摩尔比的增加呈线性增加，直至约0.05，然后接近饱和极限。在5 mol%时，每60个磷脂可将一个α-生育酚分子掺入膜中。在达到此极限之前，α-生育酚在双层膜中的分布是均匀的，而在初始摩尔比高于0.05时，观察到向囊泡内单层的歧化现象。在α-生育酚/磷脂酰胆碱摩尔比高于0.07时，发现平均外层/总比例为0.27±0.03，这与含有其他单链两亲物（如胆固醇）的囊泡中报道的不对称分布相似。这种大的歧化与某些双链两亲物的堆积分布形成对比，表明脂质双层中不对称形成的驱动力之一可能取决于每个两亲分子的烃链数量。我们实验中观察到的歧化效应的一个可能原因是，α-生育酚更刚性的异戊二烯单元将不饱和磷脂置换到单层囊泡的外层。
