Europium III binding and the reorientation of magnetically aligned bicelles: Insights from deuterium NMR spectroscopy
Europium III binding and the reorientation of magnetically aligned bicelles: Insights from deuterium NMR spectroscopy
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DOI：
10.1016/s0006-3495(01)75696-2
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发表时间：
2001-07-01
影响因子：
3.4
通讯作者：
Macdonald, PM
中科院分区：
文献类型：
--
作者：
Crowell, KJ;Macdonald, PM
用固态氢核磁共振谱研究了顺磁性稀土元素Eu3+存在下磁性有序双电子簇的重取向。双孔膜由1，2-二肉豆蔻酰基-3-甘油-3-磷酸胆碱(DMPC)+1，2-二己酰基-3-甘油-3-磷胆碱+阴离子脂类1，2-二肉豆蔻基-3-磷酸甘油或阳离子脂类1，2-二肉豆蔻基-3-三甲基丙烷组成。双极元在磁场中的排列产生了由一对四极对偶组成的H-2核磁共振谱，其中一对来自DMPC-α，β-d(4)的α-氚，另一对来自DMPC-α，β-d(4)。Eu3+的加入诱导了第二组四极双峰的出现，其四极分裂大约是原始四极分裂的两倍，并且随着Eu3+的增加而逐渐增强，但以原始双峰的强度为代价。新的共振被归因于双极相对于磁场具有平行排列，而不是在没有Eu3+的情况下首选的垂直排列。因此，从~2H核磁共振谱可以评价重定向的平衡度和动力学。对于更多的阳离子初始表面电荷，需要更多的添加Eu3+来诱导给定程度的重定向。然而，双胞重定向的平衡程度仅取决于结合的Eu3+的量，与双胞的组成无关。重定向的动力学是脂质浓度的函数。在高脂浓度下，单一的快速重定向速率(分钟)描述了达到平衡定向度的方法。在较低的脂质浓度下，可以辨别出两个速率过程：一个快(几分钟)，一个慢(几小时)。因此，数据表明，双列重新定向是一个由双列-双列相互作用决定的相变。
Solid-state deuterium (H-2) NMR spectroscopy was used to study the reorientation of magnetically ordered bicelles in the presence of the paramagnetic lanthanide Eu3+. Bicelles were composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) plus 1,2-dihexanoyl-sn-glycero-3-phosphocholine plus either the anionic lipid 1,2-dimyristoyl-sn-3-phosphoglycerol, or the cationic lipid 1,2-dimyristoyl-3-trimethyl ammonium propane. Alignment of the bicelles in the magnetic field produced H-2 NMR spectra consisting of a pair of quadrupole doublets, one from the alpha -deuterons and one from the beta -deuterons of DMPC-alpha,beta -d(4). Eu3+ addition induced the appearance of a second set of quadrupole doublets, having approximately twice the quadrupolar splittings of the originals, and growing progressively in intensity with increasing Eu3+ at the expense of the intensity of the originals. The new resonances were attributed to bicelles having a parallel alignment with respect to the magnetic field, as opposed to the perpendicular alignment preferred in the absence of Eu3+. Therefore, the equilibrium degree and kinetics of reorientation could be evaluated from the 2H NMR spectra. For more cationic initial surface charges, higher amounts of added Eu3+ were required to induce a given degree of reorientation. However, the equilibrium degree of bicellar reorientation was found to depend solely on the amount of bound Eu3+, regardless of the bicelle composition. The kinetics of reorientation were a function of lipid concentration. At high lipid concentration, a single fast rate of reorientation (minutes) described the approach to the equilibrium degree of orientation. At lower lipid concentrations, two rates processes were discernible: one fast (minutes) and one slow (hours). The data indicate, therefore, that bicelle reorientation is a phase transition made critical by bicelle-bicelle interactions.