McKersie B D, Thompson J E
Biochim Biophys Acta. 1979 Jan 5;550(1):48-58. doi: 10.1016/0005-2736(79)90114-7.
Wide-angle X-ray diffraction studies have indicated that rough and smooth microsomal membranes from bean cotyledons acquire increasing proportions of gel phase lipid at physiological temperature as the tissue senesces. In addition, for both types of membrane the lipid phase transition temperature, defined as the highest temperature at which gel phase lipid can be detected, progressively rises with advancing senescence. Liposomes prepared from total lipid extracts of the membranes show a similar increase in transition temperature with age, indicating that separation of the polar lipids into distinct gel and liquid-crystalline domains is not attributable to peculiar protein-lipid interactions. Liposomes prepared from purified phospholipid fractions of the membranes show little change in transition temperature with age, indicating that the altered phase properties of the lipid do not reflect an increase in fatty acid saturation. However, the formation of gel phase lipid that occurs naturally during senescence can be stimulated by preparing liposomes from a mixture of the phospholipid fraction from young membrane and the neutral lipid fraction from old membrane. By adding the separated components of the neutral lipid fraction to purified phospholipid it was found that sterol esters and several unidentified lipids are able to raise the transition temperature of the polar lipids. Sterols have no effect on the phospholipid transition temperature. The data have been interpreted as indicating that several neutral lipids, which presumably increase in abundance with advancing senescence, induce a lateral phase separation of the polar lipids resulting in distinct gel and liquid-crystalline domains of lipid in the senescent membranes.
广角X射线衍射研究表明，随着组织衰老，菜豆子叶粗糙和光滑的微粒体膜在生理温度下会获得越来越多的凝胶相脂质。此外，对于这两种类型的膜，脂质相变温度（定义为可检测到凝胶相脂质的最高温度）会随着衰老的推进而逐渐升高。由膜的总脂质提取物制备的脂质体也显示出相变温度随老化而有类似的升高，这表明极性脂质分离成不同的凝胶相和液晶域并非归因于特殊的蛋白质-脂质相互作用。由膜的纯化磷脂组分制备的脂质体相变温度随老化变化不大，这表明脂质相变性质的改变并不反映脂肪酸饱和度的增加。然而，衰老过程中自然发生的凝胶相脂质的形成可以通过用来自年轻膜的磷脂组分和来自老年膜的中性脂质组分的混合物制备脂质体来刺激。通过将中性脂质组分的分离成分添加到纯化的磷脂中，发现甾醇酯和几种未鉴定的脂质能够提高极性脂质的相变温度。甾醇对磷脂相变温度没有影响。这些数据被解释为表明几种中性脂质可能随着衰老的推进而丰度增加，它们诱导极性脂质的横向相分离，导致衰老膜中脂质形成不同的凝胶相和液晶域。
