Tada Kaori, Saito Kensuke, Goto Masaki, Tamai Nobutake, Matsuki Hitoshi, Kaneshina Shoji
Department of Biological Science and Technology, Faculty of Engineering, The University of Tokushima, 2-1 Minamijosanjima-cho, Tokushima 770-8506, Japan.
Biophys Chem. 2008 Nov;138(1-2):36-41. doi: 10.1016/j.bpc.2008.08.009. Epub 2008 Sep 3.
We investigated the thermotropic and barotropic bilayer phase behavior of 1-myristoyl-2-oleoyl-sn-glycero-3-phosphocholine (MOPC) and 1-oleoyl-2-myristoyl-sn-glycero-3-phosphocholine (OMPC) by means of the differential scanning calorimetry (DSC) and high-pressure light-transmittance technique. Water could be used as a solvent for measurements at high pressures because of the elevation of the transition temperatures above 0 degrees C by pressurization, whereas aqueous 50 wt.% ethylene glycol solution was used mainly for those at low pressures. Only one phase transition was observed in the DSC thermogram of the MOPC bilayer membrane as an endothermic peak, and also observed at high pressures as an abrupt change of the light-transmittance. The transition was assigned as a main transition between the lamellar gel (L(beta)) and liquid-crystalline (L(alpha)) phases on the basis of the values of enthalpy change (DeltaH) and slope of the transition temperature with respect to pressure (dT/dP). The DSC thermogram of the OMPC bilayer membrane similarly showed a single endothermic peak but two kinds of phase transitions were observed at different temperatures in the light-transmittance profile at high pressures. The extrapolation of the lower-temperature transition in the high-pressure range to an ambient pressure coincided with the transition observed in the DSC thermogram. This transition was identified as a transition between the lamellar crystal (L(c)) and L(alpha) (or L(beta)) phases from the DeltaH and dT/dP values. The higher-temperature transition, appearing only at high pressures, was identified as the L(beta)/L(alpha) transition considering the topological resemblance of its temperature-pressure phase diagram as that of the dioleoylphosphatidylcholine bilayer membrane. The phase diagram of the OMPC bilayer membrane demonstrated that the L(beta) phase cannot exist at pressures below ca. 190 MPa while it can exist stably in a finite temperature range at pressures above the pressure.
我们通过差示扫描量热法（DSC）和高压透光率技术研究了1-肉豆蔻酰基-2-油酰基-sn-甘油-3-磷酸胆碱（MOPC）和1-油酰基-2-肉豆蔻酰基-sn-甘油-3-磷酸胆碱（OMPC）的热致和压致双层相行为。由于加压使转变温度升高到0℃以上，水可作为高压测量的溶剂，而50 wt.%的乙二醇水溶液主要用于低压测量。在MOPC双层膜的DSC热谱图中仅观察到一个作为吸热峰的相变，在高压下也观察到透光率的突然变化。根据焓变（ΔH）值和转变温度相对于压力的斜率（dT/dP），该转变被确定为层状凝胶（L(β)）相和液晶（L(α)）相之间的主要转变。OMPC双层膜的DSC热谱图同样显示出一个单一的吸热峰，但在高压下的透光率曲线中在不同温度下观察到两种相变。高压范围内低温转变向环境压力的外推与DSC热谱图中观察到的转变一致。根据ΔH和dT/dP值，该转变被确定为层状晶体（L(c)）相和L(α)（或L(β)）相之间的转变。仅在高压下出现的高温转变，考虑到其温度-压力相图与二油酰磷脂酰胆碱双层膜的拓扑相似性，被确定为L(β)/L(α)转变。OMPC双层膜的相图表明，L(β)相在约190 MPa以下的压力下不能存在，而在高于该压力的压力下可在有限温度范围内稳定存在。
