Morrow M R, Davis P J, Jackman C S, Keough K M
Department of Physics, Memorial University of Newfoundland, St. John's, Canada.
Biophys J. 1996 Dec;71(6):3207-14. doi: 10.1016/S0006-3495(96)79514-0.
The effect of cholesterol on the bilayer phase behavior of heteroacid phosphatidylcholines with one unsaturated fatty acid depends on the nature of the unsaturated chain. Previous differential scanning calorimetry (DSC) studies showed that 1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphocholine (16:0-18:2 PC) had a broad, weak transition at about -18 degrees C, which was effectively eliminated by less than 15 mol% cholesterol. Phospholipids with greater and lesser degrees of unsaturation displayed stronger phase transitions and less sensitivity to cholesterol. In this work, deuterium nuclear magnetic resonance has been used to examine the phase behavior of 1-perdeuteriopalmitoyl-2-linoleoyl-sn-glycero-3-phosphocholine (16:0-18:2 PC-d31) alone, and with 15 mol % cholesterol. The behavior is found to be sensitive to sample thermal history. Moderately fast cooling (1 degree/h) results in a continuous phase change from a fluid to an ordered phase in the pure lipid. Under similar cooling conditions, the sample containing cholesterol displays increased chain order and a continuous phase change with no apparent isothermal transition. However, when these systems are cooled at a reduced rate (0.3 degree/h), the continuous phase change is pre-empted by a sharp transition into a more ordered phase that gives a deuterium spectrum having intensity at a value of the quadrupole-splitting characteristic of a rigid lattice system. In the pure lipid, this transition effectively coincides with the center of the continuous phase change. Addition of 15 mol % cholesterol lowers the temperature of this sharp transition by about 3 degrees C. These observations provide some insights into the behavior of this system seen using differential scanning calorimetry. Results of deuteron transverse relaxation measurements under these conditions are also reported.
胆固醇对含有一个不饱和脂肪酸的杂酸磷脂双层相行为的影响取决于不饱和链的性质。先前的差示扫描量热法（DSC）研究表明，1-棕榈酰-2-亚油酰-sn-甘油-3-磷酸胆碱（16:0-18:2 PC）在约-18℃有一个宽而弱的转变，加入少于15 mol%的胆固醇可有效消除该转变。不饱和程度更高和更低的磷脂表现出更强的相变以及对胆固醇更低的敏感性。在本研究中，氘核磁共振已被用于研究单独的1-全氘代棕榈酰-2-亚油酰-sn-甘油-3-磷酸胆碱（16:0-18:2 PC-d31）以及含有15 mol%胆固醇时的相行为。发现该行为对样品的热历史敏感。适度快速冷却（1℃/小时）会使纯脂质中发生从流体相到有序相的连续相变。在类似的冷却条件下，含胆固醇的样品显示出链序增加且有连续相变，没有明显的等温转变。然而，当这些体系以较低速率（0.3℃/小时）冷却时，连续相变会被一个急剧转变为更有序相的过程所取代，该更有序相给出的氘谱在四极分裂值处具有刚性晶格系统特征强度。在纯脂质中，这个转变有效地与连续相变的中心重合。加入15 mol%的胆固醇会使这个急剧转变的温度降低约3℃。这些观察结果为使用差示扫描量热法观察到的该体系行为提供了一些见解。还报道了在这些条件下的氘横向弛豫测量结果。
