Zeng J, Chong P L
Department of Biochemistry, Meharry Medical College, Nashville, Tennessee 37208.
Biophys J. 1995 Feb;68(2):567-73. doi: 10.1016/S0006-3495(95)80218-3.
The effect of ethanol-induced lipid interdigitation on the partition coefficient (Kp) of 6-propionyl-2-(dimethylamino)naphthalene (Prodan) and its two derivatives, 6-acetyl-2-(dimethylamino)naphthalene (Acdan) and 6-lauroyl-2-(dimethylamino)naphthalene (Laurdan), in L-alpha-dipalmitoylphosphatidylcholine (DPPC) vesicles has been examined by a precipitation method over the ethanol concentration range of 0-1.8 M. At 20 degrees C and in the absence of ethanol, the Kp values for Acdan, Prodan, and Laurdan are 2.0 x 10(3), 2.8 x 10(4), and 4.7 x 10(6), respectively. This result suggests that the Kp of Prodan and its derivatives is not simply a linear function of the polymethylene units. As DPPC undergoes the ethanol-induced phase transition from the noninterdigitated to the fully interdigitated gel state, Kp for Prodan and Acdan decreases by a factor of 5 and 2, respectively, whereas Kp for Laurdan exhibits no detectable changes with ethanol. The differences in Kp are in parallel with the differences in the fluorescence emission spectra of these probes over the ethanol concentration range examined. Previous fluorescence and infrared data indicated that membrane perturbation caused by the probes increases in the order: Laurdan > Prodan > Acdan. Thus, the degree of membrane perturbation also seems to be in parallel with Kp. Among these three probes, Prodan fluorescence reflects most correctly the ethanol-induced lipid interdigitation. In conclusion, the partitioning of small solutes in lipid membranes is significantly reduced by ethanol-induced lipid interdigitation, probably as a result of an increased membrane surface density due to the increased intramolecular lipid acyl chain ordering and a tighter overall intermolecular packing.
通过沉淀法研究了乙醇诱导的脂质交叉指化对6-丙酰基-2-（二甲基氨基）萘（Prodan）及其两种衍生物6-乙酰基-2-（二甲基氨基）萘（Acdan）和6-月桂酰基-2-（二甲基氨基）萘（Laurdan）在L-α-二棕榈酰磷脂酰胆碱（DPPC）囊泡中的分配系数（Kp）的影响，乙醇浓度范围为0 - 1.8 M。在20℃且无乙醇的情况下，Acdan、Prodan和Laurdan的Kp值分别为2.0×10³、2.8×10⁴和4.7×10⁶。该结果表明Prodan及其衍生物的Kp并非简单地是亚甲基单元的线性函数。当DPPC经历乙醇诱导的从非交叉指化到完全交叉指化的凝胶态相变时，Prodan和Acdan的Kp分别降低了5倍和2倍，而Laurdan的Kp在乙醇作用下未表现出可检测到的变化。在所研究的乙醇浓度范围内，这些探针的Kp差异与荧光发射光谱的差异平行。先前的荧光和红外数据表明，探针引起的膜扰动按以下顺序增加：Laurdan > Prodan > Acdan。因此，膜扰动程度似乎也与Kp平行。在这三种探针中，Prodan荧光最正确地反映了乙醇诱导的脂质交叉指化。总之，乙醇诱导的脂质交叉指化显著降低了小溶质在脂质膜中的分配，这可能是由于分子内脂质酰基链有序性增加导致膜表面密度增加以及整体分子间堆积更紧密的结果。
