Chen S Y, Cheng K H, Van der Meer B W, Beechem J M
Department of Physics, Texas Tech University, Lubbock 79409.
Biophys J. 1990 Dec;58(6):1527-37. doi: 10.1016/S0006-3495(90)82497-8.
The polymorphic phase behavior of unsaturated phosphatidylethanolamine (PE)/diacylglycerol (DG) binary lipid mixtures was investigated by the use of time-resolved fluorescence anisotropy. Using a fluorescent lipid, 1-palmitoyl-2-[[2-[4-(6-phenyl-trans-1,3,5-hexatrienyl)phenylethyl] carbonyl]3-sn-phosphatidyl-choline (DPH-PC), the orientational order and rotational dynamics of the above lipid mixtures in the liquid crystalline lamellar (L alpha) and inverted hexagonal (HII) phases were studied. By employing a one-exponential model (Cheng, K.H. 1989: Biophys. J. 55:1025-1031) to fit the anisotropy decay data, abrupt decreases in the normalized initial anisotropy decay slope and the residual anisotropy of DPH-PC were observed at approximately 6-8% DG, signifying a L alpha/HII phase transition. Using our new theoretical WOBHOP and P2P4HOP models as described in a preceding paper (Van Der Meer, B.W., K.H. Cheng, and S.Y. Chen. 1990. Biophys. J. 58:000-000), two or more rotational correlation times were required to describe the anisotropy decay behavior of DPH-PC in the HII phase. These rotation correlation times were further related to the second and fourth rank order parameters, and the wobbling and hopping diffusion constants of the fluorescent probe in the highly curved lipid cylindrical tubes of the HII phase. The hopping diffusion constant (DH) equals the lateral diffusion constant (DL) divided by R2 (R = radius of the lipid cylindrical tubes). The value of DL was estimated by measuring the excimer formation rate of 1-palmitoyl-2-[10-(1-pyrenl)decanoyl] phosphatidyl choline (py-PC) in the same PE/DG mixtures. Upon comparing the values of DH and DL, the value of R was determined to be approximately 10-15 A, and agreed with that derived from x-ray diffraction (Tate, M.W., and S.M. Gruner, 1989, Biochemistry. 28:4245-4253; Rand, R.P., N.L. Fuller, S.M. Gruner, and V.A. Parsegian. 1990. Biochemistry. 29:76-87).
利用时间分辨荧光各向异性研究了不饱和磷脂酰乙醇胺（PE）/二酰基甘油（DG）二元脂质混合物的多晶相行为。使用荧光脂质1-棕榈酰-2-[[2-[4-(6-苯基-反式-1,3,5-己三烯基)苯基]乙基]羰基]-3-sn-磷脂酰胆碱（DPH-PC），研究了上述脂质混合物在液晶层状（Lα）和反相六角（HII）相中的取向有序性和旋转动力学。通过采用单指数模型（Cheng，K.H. 1989：《生物物理杂志》55：1025 - 1031）拟合各向异性衰减数据，在约6 - 8%的DG时观察到DPH-PC的归一化初始各向异性衰减斜率和残余各向异性突然下降，这表明发生了Lα/HII相转变。使用我们在前一篇论文（Van Der Meer，B.W.，K.H. Cheng，和S.Y. Chen. 1990.《生物物理杂志》58：000 - 000）中描述的新理论WOBHOP和P2P4HOP模型，需要两个或更多的旋转相关时间来描述DPH-PC在HII相中的各向异性衰减行为。这些旋转相关时间进一步与二阶和四阶有序参数以及荧光探针在HII相高度弯曲的脂质圆柱管中的摆动和跳跃扩散常数相关。跳跃扩散常数（DH）等于横向扩散常数（DL）除以R2（R =脂质圆柱管的半径）。通过测量相同PE/DG混合物中1-棕榈酰-2-[10-(1-芘基)癸酰基]磷脂酰胆碱（py-PC）的准分子形成速率来估计DL的值。比较DH和DL的值后，确定R的值约为10 - 15 Å，这与X射线衍射得出的值一致（Tate，M.W.，和S.M. Gruner，1989，《生物化学》。28：4245 - 4253；Rand，R.P.，N.L. Fuller，S.M. Gruner，和V.A. Parsegian. 1990.《生物化学》。29：76 - 87）。
