Kao Y L, Chong P L, Huang C H
Department of Biochemistry, Meharry Medical College, Nashville, Tennessee 37208.
Biophys J. 1990 Oct;58(4):947-56. doi: 10.1016/S0006-3495(90)82439-5.
This study investigates the dynamic behavior of 1,6-diphenyl-1,3,5-hexatriene (DPH) in C(18):C(10)phosphatidylcholine [C(18):C(10)PC] bilayers. C(18):C(10)PC is an asymmetric mixed-chain phosphatidylcholine known to form mixed-interdigitated structures below the transition temperature and form partially interdigitated bilayers above the transition temperature. The rotation of DPH in C(18):C(10)PC has been described in terms of the thermal coefficient of rotation using the modified Y-plot method which takes into account the limiting anisotropy value. During the phase transition of C(18):C(10)PC, DPH exhibits a thermal coefficient b2M = 0.41 - 0.51 degrees C-1 which is similar to the b2M values obtained with noninterdigitated phosphatidylcholine bilayers. Differential polarized phase-modulation fluorometry has also been employed to study the dynamic behavior of DPH in C(18):C(10)PC in real time. The data show that DPH contains considerable motion in the highly ordered mixed interdigitated bilayers. The DPH motion steadily increases with an increase in temperature as shown by the rotational correlation time, and the wobbling diffusion constant. However, the limiting anisotropy, the order parameter, and the width of the lifetime distribution undergo an abrupt decrease, and a corresponding abrupt increase in the cone angle, at approximately 16 degrees C. This temperature range is near the onset temperature of the phase transition as determined by differential scanning calorimetry. The rotational parameters show strong hysteresis on heating and cooling. All the rotational parameters derived from DPH fluorescence in mixed interdigitated C(18):C(10)PC exhibit magnitudes similar to those obtained from non interdigitated gel phases of symmetric diacylphosphatidylcholines. These results, combined with those obtained with dehydroergosterol (Kao, Y. L., P. L.-G. Chong, and C. Huang. 1990. Biochemistry. 29:1315-1322), suggest that considerable rotational mobility of small molecules can be sustained in an intramolecularly highly ordered interdigitated lipid matrix, implying that the membrane maintains a fluid environment around membrane perturbants even when the lipid matrix is extensively interdigitated.
本研究调查了1,6 - 二苯基 - 1,3,5 - 己三烯（DPH）在C(18):C(10)磷脂酰胆碱[C(18):C(10)PC]双层膜中的动态行为。C(18):C(10)PC是一种不对称混合链磷脂酰胆碱，已知在转变温度以下形成混合叉指结构，在转变温度以上形成部分叉指双层膜。已使用考虑了极限各向异性值的改进Y - 图方法，根据旋转热系数描述了DPH在C(18):C(10)PC中的旋转。在C(18):C(10)PC的相变过程中，DPH表现出热系数b2M = 0.41 - 0.51℃⁻¹，这与在非叉指磷脂酰胆碱双层膜中获得的b2M值相似。差示偏振相位调制荧光法也已用于实时研究DPH在C(18):C(10)PC中的动态行为。数据表明，DPH在高度有序的混合叉指双层膜中具有相当大的运动。如旋转相关时间和摆动扩散常数所示，DPH的运动随着温度升高而稳步增加。然而，在大约16℃时，极限各向异性、序参数和寿命分布宽度会突然减小，锥角相应突然增大。该温度范围接近通过差示扫描量热法确定的相变起始温度。旋转参数在加热和冷却时表现出强烈的滞后现象。从混合叉指C(18):C(10)PC中的DPH荧光得出的所有旋转参数的大小，与从对称二酰基磷脂酰胆碱的非叉指凝胶相中获得的相似。这些结果，与用脱氢麦角固醇获得的结果（Kao, Y. L., P. L.-G. Chong, and C. Huang. 1990. Biochemistry. 29:1315 - 1322）相结合，表明即使脂质基质广泛叉指，小分子在分子内高度有序的叉指脂质基质中仍可保持相当大的旋转流动性，这意味着膜在膜扰动剂周围维持着流体环境。
