Lai M Z, Vail W J, Szoka F C
Biochemistry. 1985 Mar 26;24(7):1654-61. doi: 10.1021/bi00328a013.
The membrane stabilization effect of cholesteryl hemisuccinate (CHEMS) and the sensitivity of the CHEMS-phosphatidylethanolamine membranes to protons and calcium ions were studied by differential scanning calorimetry, freeze-fracture electron microscopy, and 31P NMR. (1) At neutral pH, the addition of 8 mol % CHEMS to transesterified egg phosphatidylethanolamine (TPE) raised the lamellar-hexagonal transition temperature of TPE by 11 degrees C. Stable bilayer vesicles were formed when the incorporated CHEMS exceeded 20 mol %. (2) At a pH below 5.5, the protonation of CHEMS enhanced the formation of the hexagonal phase (HII) of TPE. At 25 mol % CHEMS the bilayer-hexagonal transition temperature was lowered by 30 degrees C at pH 4.5. (3) The endothermic acid-induced hexagonal hexagonal transition of TPE-CHEMS was suppressed at 35 mol % CHEMS. However, 31P NMR and electron microscopy indicated that a lamellar-hexagonal transition still occurred at this composition. (4) The main transition of TPE was not affected by the protonation of the incorporated CHEMS, indicating that no macroscopic phase separation occurred in TPE-CHEMS mixtures at low pH. (5) In contrast to the HII-promoting effect of H+, the neutralization of the negative charge on TPE-CHEMS by Ca2+ resulted in aggregates that remained in the lamellar structure even at the hexagonal transition temperature of TPE. It is suggested that calcium might form a complex between CHEMS in apposed bilayers. These results are related to the possible biological function of acidic cholesterol esters in biomembranes.
通过差示扫描量热法、冷冻断裂电子显微镜和³¹P核磁共振研究了胆固醇半琥珀酸酯（CHEMS）的膜稳定作用以及CHEMS - 磷脂酰乙醇胺膜对质子和钙离子的敏感性。（1）在中性pH值下，向转酯鸡蛋磷脂酰乙醇胺（TPE）中添加8 mol%的CHEMS可使TPE的层状 - 六方相转变温度提高11℃。当掺入的CHEMS超过20 mol%时，形成稳定的双层囊泡。（2）在pH低于5.5时，CHEMS的质子化增强了TPE六方相（HII）的形成。在pH 4.5时，当CHEMS含量为25 mol%时，双层 - 六方相转变温度降低了30℃。（3）在CHEMS含量为35 mol%时，TPE - CHEMS的吸热酸诱导六方 - 六方相转变受到抑制。然而，³¹P核磁共振和电子显微镜表明在此组成下仍发生层状 - 六方相转变。（4）掺入的CHEMS的质子化不影响TPE的主要转变，表明在低pH值下TPE - CHEMS混合物中未发生宏观相分离。（5）与H⁺促进HII形成的作用相反，Ca²⁺对TPE - CHEMS上负电荷的中和导致聚集体，即使在TPE的六方相转变温度下仍保持层状结构。推测钙可能在相邻双层中的CHEMS之间形成复合物。这些结果与生物膜中酸性胆固醇酯可能的生物学功能有关。
