Kouaouci R, Silvius J R, Graham I, Pézolet M
Biochemistry. 1985 Dec 3;24(25):7132-40. doi: 10.1021/bi00346a017.
The effects of calcium ions on mixed membranes of dimyristoylphosphatidic acid (DMPA) and dimyristoylphosphatidylcholine (DMPC) with either the PA or the PC component deuterated have been studied by Raman spectroscopy. The spectra of the pure components show that the acyl chains of hydrated DMPA bilayers are less tightly packed and have more trans bonds than those of DMPC. This behavior appears to be due to the particular arrangement of the polar head groups of DMPA for which the glycerol chain is oriented parallel to the bilayer surface. In agreement with the calorimetrically determined phase diagram [Graham, I., Gagné, J., & Silvius, J. R. (1985) Biochemistry (preceding paper in this issue)], the Raman results show that, in the absence of calcium, DMPA and DMPC are completely miscible at an equimolar ratio but undergo extensive phase separation in the presence of excess calcium. DMPC in phase-separated DMPC-DMPA (Ca2+) mixtures has a conformation that is very similar to that of pure DMPC bilayers, but it is packed more tightly since, depending on the temperature, it is at least partly incorporated into either a solid solution in DMPA or a DMPA-Ca2+-rich "cochleate" phase. This latter shows the same characteristics as the cochleate phase of pure DMPA-Ca2+ which is highly ordered and does not give rise to a thermotropic transition between 5 and 100 degrees C. However, the cochleate phase in DMPA (Ca2+)-DMPC mixtures contains some 20 mol % of DMPC trapped in small domains. These clusters do not melt cooperatively but become as fluid as pure DMPC at 50 degrees C.
通过拉曼光谱研究了钙离子对二肉豆蔻酰磷脂酸（DMPA）和二肉豆蔻酰磷脂酰胆碱（DMPC）混合膜的影响，其中PA或PC组分被氘代。纯组分的光谱表明，水合DMPA双层的酰基链堆积不如DMPC紧密，且反式键更多。这种行为似乎是由于DMPA极性头部基团的特殊排列，其甘油链与双层表面平行排列。与量热法测定的相图一致[Graham, I., Gagné, J., & Silvius, J. R. (1985) Biochemistry（本期前一篇论文）]，拉曼结果表明，在没有钙的情况下，DMPA和DMPC以等摩尔比完全互溶，但在存在过量钙的情况下会发生广泛的相分离。相分离的DMPC-DMPA（Ca2+）混合物中的DMPC具有与纯DMPC双层非常相似的构象，但堆积更紧密，因为根据温度，它至少部分地掺入DMPA中的固溶体或富含DMPA-Ca2+的“螺旋状”相中。后者表现出与纯DMPA-Ca2+的螺旋状相相同的特征，高度有序，在5至100摄氏度之间不会发生热致转变。然而，DMPA（Ca2+）-DMPC混合物中的螺旋状相包含约20摩尔%被困在小区域中的DMPC。这些簇不会协同熔化，但在50摄氏度时变得与纯DMPC一样流体。
