Kaasgaard Thomas, Leidy Chad, Crowe John H, Mouritsen Ole G, Jørgensen Kent
Department of Chemistry, Technical University of Denmark, Lyngby, Denmark.
Biophys J. 2003 Jul;85(1):350-60. doi: 10.1016/S0006-3495(03)74479-8.
Temperature-controlled atomic force microscopy (AFM) has been used to visualize and study the structure and kinetics of ripple phases in one-component dipalmitoylphosphatidylcholine (DPPC) and two-component dimyristoylphosphatidylcholine-distearoylphosphatidylcholine (DMPC-DSPC) lipid bilayers. The lipid bilayers are mica-supported double bilayers in which ripple-phase formation occurs in the top bilayer. In one-component DPPC lipid bilayers, the stable and metastable ripple phases were observed. In addition, a third ripple structure with approximately twice the wavelength of the metastable ripples was seen. From height profiles of the AFM images, estimates of the amplitudes of the different ripple phases are reported. To elucidate the processes of ripple formation and disappearance, a ripple-phase DPPC lipid bilayer was taken through the pretransition in the cooling and the heating direction and the disappearance and formation of ripples was visualized. It was found that both the disappearance and formation of ripples take place virtually one ripple at a time, thereby demonstrating the highly anisotropic nature of the ripple phase. Furthermore, when a two-component DMPC-DSPC mixture was heated from the ripple phase and into the ripple-phase/fluid-phase coexistence temperature region, the AFM images revealed that several dynamic properties of the ripple phase are important for the melting behavior of the lipid mixture. Onset of melting is observed at grain boundaries between different ripple types and different ripple orientations, and the longer-wavelength metastable ripple phase melts before the shorter-wavelength stable ripple phase. Moreover, it was observed that the ripple phase favors domain growth along the ripple direction and is responsible for creating straight-edged domains with 60 degrees and 120 degrees angles, as reported previously.
温控原子力显微镜（AFM）已被用于观察和研究单组分二棕榈酰磷脂酰胆碱（DPPC）和双组分二肉豆蔻酰磷脂酰胆碱-二硬脂酰磷脂酰胆碱（DMPC-DSPC）脂质双层中波纹相的结构和动力学。脂质双层是云母支撑的双分子层，其中波纹相在顶部双层中形成。在单组分DPPC脂质双层中，观察到了稳定和亚稳的波纹相。此外，还发现了一种波长约为亚稳波纹两倍的第三种波纹结构。根据AFM图像的高度轮廓，报告了不同波纹相的振幅估计值。为了阐明波纹形成和消失的过程，将处于波纹相的DPPC脂质双层在冷却和加热方向上通过预转变，并观察到了波纹的消失和形成。结果发现，波纹的消失和形成实际上都是一次一个波纹地发生，从而证明了波纹相具有高度各向异性。此外，当双组分DMPC-DSPC混合物从波纹相加热到波纹相/流体相共存温度区域时，AFM图像显示，波纹相的几个动态特性对脂质混合物的熔化行为很重要。在不同波纹类型和不同波纹取向之间的晶界处观察到熔化开始，较长波长的亚稳波纹相比较短波长的稳定波纹相先熔化。此外，如先前报道的那样，观察到波纹相有利于沿波纹方向的畴生长，并导致形成具有60度和120度角的直边畴。
