MODULATION OF THE PHASE-TRANSITION BEHAVIOR OF PHOSPHATIDYLETHANOLAMINE BY CHOLESTEROL AND OXYSTEROLS
MODULATION OF THE PHASE-TRANSITION BEHAVIOR OF PHOSPHATIDYLETHANOLAMINE BY CHOLESTEROL AND OXYSTEROLS
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DOI：
10.1021/bi00381a005
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发表时间：
1987-04-07
期刊：
影响因子：
2.9
通讯作者：
BOTTEGA, R
中科院分区：
文献类型：
--
作者：
EPAND, RM;BOTTEGA, R
胆固醇可使磷脂酰乙醇胺从双层相到六角相的转变温度降低，直至胆固醇的摩尔分数达到约0.1。当胆固醇摩尔分数高于约0.3时，这种固醇的作用是稳定双层相。胆固醇在改变双层相到六角相转变温度方面相对较弱的作用可以基于侧向相分离来解释。胆固醇与反油酸磷脂酰乙醇胺（DEPE）混合物的相图中凝胶到液晶转变的水平液相线以及胆固醇不会大幅降低双层相到六角相转变的协同性这一事实都表明了这一点。后一种转变的焓随着胆固醇摩尔分数的增加而增加。胆固醇的两种氧化产物是5 - 胆甾烯 - 3β,7α - 二醇和胆甾烷 - 3β,5α,6β - 三醇。与胆固醇相比，5 - 胆甾烯 - 3β,7α - 二醇在降低双层相到六角相转变温度以及使该转变变宽方面具有更大的作用。有人认为其有效性是由于它在DEPE中具有更高的溶解度。相反，胆甾烷 - 3β,5α,6β - 三醇会提高DEPE从双层相到六角相的转变温度。这是由于其更大且更亲水的头部基团。此外，它的长度比DEPE短，无法在六角相排列中有效堆积。我们认为，这种相同的效应是胆固醇在较高摩尔分数时提高双层相到六角相转变温度的原因。
Cholesterol lowers the bilayer to hexagonal phase transition temperature of phosphatidylethanolamines up to a mole fraction of about 0.1. At cholesterol mole fractions above about 0.3, the effect of this sterol is to stabilize the bilayer phase. The relatively weak effects of cholesterol in altering the bilayer to hexagonal phase transition temperature can be explained on the basis of lateral phase separation. This is indicated by the horizontal liquidus line for the gel to liquid-crystalline transition in the phase diagram for mixtures of cholesterol with dielaidoylphosphatidylethanolamine (DEPE) as well as the fact that cholesterol does not greatly decrease the cooperativity of the bilayer to hexagonal phase transition. The enthalpy of this later transition increased with increasing mole fractions of cholesterol. Two oxidation products of cholesterol are 5-cholesten-3.beta.,7.alpha.-diol and cholestan-3.beta.,5.alpha.,6.beta.-triol. Compared with cholesterol, 5-cholesten-3.beta.,7.alpha.-diol had a greater effect in decreasing the bilayer to hexagonal phase transition temperature and broadening this transition. It is suggested that its effectiveness is due to its greater solubility in the DEPE. In contrast, cholestan-3.beta.,5.alpha.,6.beta.-triol raises the bilayer to hexagonal phase transition temperature of DEPE. This is due to its larger and more hydrophilic head groups. In addition, its length, being shorter than that of DEPE, would not allow it to pack efficiently in a hexagonal phase arrangement. We suggest that this same effect is responsible for cholesterol raising the bilayer to hexagonal phase transition temperature at higher mole fractions.