Tümmler B, Herrmann U, Maass G, Eibl H
Biochemistry. 1984 Aug 28;23(18):4068-74. doi: 10.1021/bi00313a009.
The thermodynamics and kinetics of the subtransition L epsilon----P beta of sonicated unilamellar vesicles of 1-myristoyl-2-stearoylphosphatidylcholine (1M-2S-PC) and of 1-stearoyl-2-myristoylphosphatidylcholine (1S-2M-PC) were studied by equilibrium cooling curves and temperature-jump relaxation spectrometry with an anthracenophane cryptand as a mobile fluorescent probe. The unilamellar vesicles exhibit the midpoint temperature TsII of the subtransition about 10 degrees C below the respective main transition. The kinetics of the subtransition in the time range between 10(-4) and 10(3) s is characterized by a cooperative relaxation process in the range of milliseconds and a further noncooperative process in the range of seconds. The slow process is assigned to the rearrangement of lattice defects. The fast process is evaluated in terms of a cyclic reaction scheme that consists of two pathways for the biomolecular association of probe and vesicle coupled with the conformational change of the lipid matrix during the subtransition. The analysis reveals that the fast process comprises the nucleation and growth of cluster. The cooperative lattice transformation of the subtransition follows a first-order rate law. The rate constants at TsII are 70 s-1 for 1S-2M-PC and 170 s-1 for 1M-2S-PC. Since the plots of the relaxation time vs. the degree of transition are in accordance with the predictions of the linear Ising model, it is concluded that clusters are propagated anisotropically in a linear fashion; e.g., fluidlike P beta conformations grow along the ripple.
采用平衡冷却曲线和温度跃升弛豫光谱法，以蒽基穴醚作为可移动荧光探针，研究了1-肉豆蔻酰-2-硬脂酰磷脂酰胆碱（1M-2S-PC）和1-硬脂酰-2-肉豆蔻酰磷脂酰胆碱（1S-2M-PC）超声处理的单层囊泡亚转变Lε----Pβ的热力学和动力学。单层囊泡的亚转变中点温度TsII比各自的主转变温度低约10℃。在10^(-4)到10^(3)秒的时间范围内，亚转变的动力学特征是在毫秒范围内有一个协同弛豫过程，在秒范围内有一个进一步的非协同过程。缓慢过程归因于晶格缺陷的重排。快速过程根据一个循环反应方案进行评估，该方案由探针与囊泡生物分子缔合的两条途径以及亚转变期间脂质基质的构象变化组成。分析表明，快速过程包括聚集体的成核和生长。亚转变的协同晶格转变遵循一级速率定律。在TsII时，1S-2M-PC的速率常数为70 s^(-1)，1M-2S-PC的速率常数为170 s^(-1)。由于弛豫时间与转变程度的关系图符合线性伊辛模型的预测，因此得出结论，聚集体以线性方式各向异性地传播；例如，类流体Pβ构象沿波纹生长。
