Borchman D, Cenedella R J, Lamba O P
Department of Ophthalmology, Kentucky Lions Eye Research Institute, Louisville 40292, USA.
Exp Eye Res. 1996 Feb;62(2):191-7. doi: 10.1006/exer.1996.0023.
Cholesterol may order or disorder phospholipids. The physiological contribution of cholesterol to the structural order of lens membrane lipids was determined. Cholesterol and phospholipid from bovine lens nuclear and cortical tissue were separated by thin layer chromatography. The effect of cholesterol upon the trans to gauche transition of the hydrocarbon chains was assessed by measuring CH2 infrared stretching band frequencies as cholesterol was added back to the phospholipids. Although the relative cholesterol level of nuclear lipid was much higher than that of the cortex (59 vs. 36 mol%, respectively), the structural order of unfractionated nuclear and cortical lipids were similar at physiological temperature. Cholesterol added to lipids devoid of cholesterol produced a sharp biphasic effect on the structural order of nuclear lipids, increasing the trans conformation from 56% to 0 mol% cholesterol to 74% at 18% cholesterol to 41% trans at 59 mol% cholesterol. Cholesterol addition produced a shallow biphasic change in the percentage trans conformation of cortical lipids. Maximum order (about 40% trans conformation) was seen at a cholesterol level equal to that of intact cortical lipid (36 mol%). The physiological role of cholesterol is to increase the structural order of cortical membrane lipid and decrease order in nuclear lipid. The net result is a similarity in the structural order of cortical and nuclear membrane. We suggest that the different response of cortical and nuclear lipids to added cholesterol is linked to differences in the phospholipid composition between these two lens regions. In the absence of cholesterol, nuclear phospholipids are much more highly ordered than those of the cortex.
胆固醇可能会使磷脂有序排列或无序排列。我们确定了胆固醇对晶状体膜脂质结构有序性的生理贡献。通过薄层色谱法分离牛晶状体核和皮质组织中的胆固醇和磷脂。当向磷脂中重新添加胆固醇时，通过测量CH2红外伸缩带频率来评估胆固醇对烃链从反式到顺式转变的影响。尽管核脂质中的胆固醇相对水平远高于皮质（分别为59%对36摩尔%），但在生理温度下，未分级的核脂质和皮质脂质的结构有序性相似。向不含胆固醇的脂质中添加胆固醇对核脂质的结构有序性产生了明显的双相效应，将胆固醇含量从56%反式构象的0摩尔%增加到18%胆固醇时的74%反式构象，再到59摩尔%胆固醇时的41%反式构象。添加胆固醇会使皮质脂质反式构象百分比产生轻微的双相变化。在胆固醇水平与完整皮质脂质相等（36摩尔%）时，观察到最大有序度（约40%反式构象）。胆固醇的生理作用是增加皮质膜脂质的结构有序性并降低核脂质的有序性。最终结果是皮质和核膜的结构有序性相似。我们认为皮质和核脂质对添加胆固醇的不同反应与这两个晶状体区域磷脂组成的差异有关。在没有胆固醇的情况下，核磷脂比皮质磷脂的有序程度高得多。
