Allen T M
Biochim Biophys Acta. 1981 Jan 22;640(2):385-97. doi: 10.1016/0005-2736(81)90464-8.
Previous observations on serum-induced leakage of liposome contents from egg phosphatidylcholine liposomes (Allen, T.M. and Cleland, L.G. (1980) Biochim. Biophys, Acta 597, 418--426) have been extended in order to examine the role of the phase transition and phospholipid backbone in leakage. The high-density lipoprotein (HDL) fraction has been purified from human serum and the rate of transfer of radioactively labelled phospholipids from sonicated liposomes to high-density lipoproteins has been examined. Results obtained from the calcein dequenching method for serum-induced leakage of liposome contents showed that as the proportion of solid phospholipid (distearoyl phosphatidylcholine, Tc = 56 degrees C) increased, relative to the proportion of egg phosphatidylcholine, the half-time for retention of liposome contents at 37 degrees C in the presence of serum also increased. Including increasing amounts of bovine brain sphingomyelin (Tc = 30 degrees C) in egg phosphatidylcholine liposomes also substantially decreased leakage from liposomes in the presence of serum at 37 degrees C. 14C-labelled egg phosphatidylcholine was found to transfer readily from liposomes to purified HDL, as did 14C-labelled dioleoyl phosphatidylcholine. Including cholesterol in egg phosphatidylcholine liposomes decreased the rate of transfer of phospholipid to HDL. 14C-labelled distearoyl phosphatidylcholine did not exchange readily with HDL. These results are consistent with the interpretation that tightening bilayer packing prevents the apolipoprotein-mediated transfer of phospholipid to HDL and slows the leakage of liposome contents associated with this transfer. [14C]Sphingomyelin also did not exchange readily with HDL. This does not appear to be a phase transition effect as the majority of sphingomyelin is above its phase transition at 37 degrees C. The failure of sphingomyelin to exchange readily with HDL is interpreted as being due to intermolecular hydrogen bonding between the sphingosine backbones of the sphingomyelin molecule.
先前关于血清诱导脂质体内容物从卵磷脂酰胆碱脂质体泄漏的观察结果（艾伦，T.M.和克莱兰，L.G.（1980年）《生物化学与生物物理学报》597卷，418 - 426页）已得到扩展，以研究相变和磷脂主链在泄漏中的作用。已从人血清中纯化出高密度脂蛋白（HDL）部分，并检测了放射性标记的磷脂从超声处理的脂质体转移到高密度脂蛋白的速率。通过钙黄绿素去猝灭法获得的关于血清诱导脂质体内容物泄漏的结果表明，随着固体磷脂（二硬脂酰磷脂酰胆碱，Tc = 56℃）相对于卵磷脂酰胆碱的比例增加，在血清存在下，脂质体内容物在37℃下保留的半衰期也增加。在卵磷脂酰胆碱脂质体中加入越来越多的牛脑鞘磷脂（Tc = 30℃），在37℃血清存在下，也显著降低了脂质体的泄漏。发现14C标记的卵磷脂酰胆碱很容易从脂质体转移到纯化的HDL中，14C标记的二油酰磷脂酰胆碱也是如此。在卵磷脂酰胆碱脂质体中加入胆固醇降低了磷脂向HDL的转移速率。14C标记的二硬脂酰磷脂酰胆碱不容易与HDL交换。这些结果与以下解释一致，即双层堆积的收紧阻止了载脂蛋白介导的磷脂向HDL的转移，并减缓了与这种转移相关的脂质体内容物的泄漏。[14C]鞘磷脂也不容易与HDL交换。这似乎不是相变效应，因为大多数鞘磷脂在37℃时高于其相变温度。鞘磷脂不能轻易与HDL交换被解释为是由于鞘磷脂分子的鞘氨醇主链之间的分子间氢键作用。
