DETERMINATION OF TIE-LINE FIELDS FOR COEXISTING LIPID PHASES

该子项目是利用 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来源获得主要资金， 因此可以在其他CRISP条目中表示。列出的机构是 中心，不一定是研究者的机构。 本文提出了一种新的方法，通过拟合共存曲线上和共存区内组分的电子自旋共振（ESR）谱来确定任意三组分两相共存区的连接线。 将该方法应用于脑磷脂/二油酰磷脂酰胆碱/胆固醇（SPM/DOPC/胆固醇）脂质体系的液相有序（Lo）和液相无序（Ld）相共存区。 该方法的基本方面是一个独特的参数化的共存区域称为“直纹面”和知识的共存曲线。 最小二乘拟合的ESR谱与参数化模型导致在一个连接线场与其他已知的信息，这个脂质系统一致。直纹面的使用允许保证连接线不交叉。 最佳拟合的连接线区域由一组不完全平行的连接线组成;它们表现出斜率的逐渐变化，其中最大斜率位于连接具有最高和最低胆固醇浓度的共存曲线组成的共存区域内。 结果进行了比较，从更多的约束方法表示的联络线领域。 准确测定脂质体系中相共存区的结合线场是确定共存脂质组合物作为细胞质膜模型的必要步骤。

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 novel method has been developed to determine the tie-lines of any three-component two-phase coexistence region by fitting electron-spin resonance (ESR) spectra obtained from compositions on the coexistence curve and within the coexistence region. The method was applied to the liquid-ordered (Lo) and liquid-disordered (Ld) phase coexistence region of the lipid system brain-sphingomyelin/dioleoylphosphatidylcholine/cholesterol (SPM/DOPC/cholesterol). The essential aspects of the method were a unique parameterization of the coexistence region called a "ruled surface" and knowledge of the coexistence curve. Least-squares fitting of the ESR spectra with the parameterized model resulted in a tie-line field consistent with other known information on this lipid system. The use of the ruled surface allows one to guarantee that tie lines do not cross. The best-fit tie-line field consisted of the set of tie lines which were not exactly parallel; they exhibited a gradual change in slope with the largest slope within the coexistence region connecting the coexistence curve compositions with the highest and lowest cholesterol concentrations. The results were compared with those from more constrained methods of representing the tie-line fields. An accurate determination of the tie-line field of phase coexistence regions in lipid systems is a necessary step in determining coexisting lipid compositions to serve as models of cell plasma membranes.