DYNAMIC STRUCTURE AND TERNARY PHASE DIAGRAM OF DPPC-DLPC-CHOLESTEROL BY ESR

这个子项目是利用由NIH/NCRR资助的中心拨款提供的资源的许多研究子项目之一。子项目和调查员(PI)可能从另一个NIH来源获得了主要资金，因此可能会出现在其他CRISE条目中。列出的机构是针对中心的，而不一定是针对调查员的机构。通过研究水合层状液体混合物Dipalmitoyl-PC/Dilauroyl-PC/Chol(DPPC/DLPC/Chol)的室温CW-ESR谱，建立了一种测定复杂混合物中脂质双层相行为的方法。用非线性最小二乘法对100多种不同成分的光谱进行了分析，得到了末端链标记的磷脂16-PC的旋转扩散速率和序参数。ESR谱表现出作为组成的函数的很大变化，尽管各个相通常彼此之间有相当小的差异。Lα相和Lβ相有明显的区别，前者的有序度较低，运动速率较大，而定义明确的LO相的有序性最大，运动速率较快。通常，在给定的阶段内会发生较小的变化。ESR光谱分析也得到了相边界和共存区域，这与以前的荧光方法结果是一致的，尽管发现了新的特征。在某些情况下，通过观察相的吸收模式ESR谱中等色点的存在，确认了相共存区域。富含DPPC的Lβ相和富含DLPC的Lα相在其两相共存区域内的动态结构性质不随组成沿联络线变化，但根据热力学原理，两相的比例遵循杠杆规律。分析表明，16-PC自旋标记物在Lα相和Lβ相之间的分配几乎相等，这使它成为研究此类共存相的一个有用的探针。对两相共存区域的广泛研究需要确定连接线，这在本研究中是近似的。然而，提出了一种用ESR准确确定联络线的方法。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. A method has been developed for determining lipid bilayer phase behavior in complex mixtures by studying cw-ESR spectra for the hydrated lamellar liquid mixture Dipalmitoyl-PC/Dilauroyl-PC/Cholesterol (DPPC/DLPC/Chol) at room temperature. The spectra for more than 100 different compositions were analyzed by nonlinear least squares fitting to obtain the rotational diffusion rates and order parameters of the end-chain labeled phospholipid 16-PC. The ESR spectra exhibit substantial variation as a function of composition, even though the respective phases generally differ rather modestly from each other. The L alpha and L beta phases are clearly distinguished, with the former exhibiting substantially lower ordering and greater motional rates, whereas the well-defined Lo phase exhibits the greatest ordering and relatively fast motional rates. Typically, smaller variations occur within a given phase. The ESR spectral analysis also yields phase boundaries and coexistence regions which are found to be consistent with previous results from fluorescence methods, although new features are found. Phase coexistence regions were in some cases confirmed by observing the existence of isosbestic points in the absorption mode ESR spectra from the phases. The dynamic structural properties of the DPPC-rich L beta and DLPC-rich L alpha phases, within their 2-phase coexistence region do not change with composition along a tie-line, but the ratio of the two phases follows the lever rule in accordance with thermodynamic principles. The analysis shows that 16-PC spin label partitions nearly equally between the L alpha and L beta phases, making it a useful probe for studying such coexisting phases. Extensive study of 2-phase coexistence regions requires the determination of tie-lines, which were approximated in this study. However, a method is suggested to accurately determine the tie-lines by ESR.