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

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 通过研究二棕榈酰-PC/二月桂酰-PC/胆固醇（DPPC/DLPC/Chol）水化层状液体混合物在室温下的cw-ESR谱，建立了一种测定复杂混合物中脂双层相行为的方法。采用非线性最小二乘拟合方法对100多种不同组分的光谱进行分析，得到了端链标记磷脂16-PC的旋转扩散速率和有序参数。的ESR谱表现出实质性的变化作为组合物的函数，即使相应的阶段一般不同，而彼此适度。的L α和L β阶段是明确区分的，前者表现出明显较低的排序和较大的运动速率，而定义良好的Lo阶段表现出最大的排序和相对较快的运动速率。通常，较小的变化发生在给定的相位内。ESR谱分析也产生相边界和共存区，这被认为是与以前的结果从荧光方法，虽然发现新的功能。相共存区在某些情况下，证实了通过观察存在的等吸光点的吸收模式ESR谱从相。富DPPC的L β相和富DLPC的L α相在其两相共存区的动态结构性质不随组成沿着一条连接线变化，但两相的比例遵循热力学原理的杠杆规则。分析表明，16-PC自旋标记分区之间的L α和L β阶段几乎相等，使其成为一个有用的探针，研究这种共存的阶段。2相共存区域的广泛研究需要确定的联络线，这是近似在这项研究中。然而，建议的方法，以准确地确定连接线的ESR。

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.