Magnetic birefringence studies of dilute purple membrane suspensions.
Magnetic birefringence studies of dilute purple membrane suspensions.
复制标题
稀紫色膜悬浮液的磁双折射研究。
DOI：
10.1016/s0006-3495(85)83888-1
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发表时间：
1985
影响因子：
3.4
通讯作者：
Herzfeld,J
中科院分区：
文献类型：
--
作者：
Lewis,BA;Rosenblatt,C;Griffin,RG;Courtemanche,J;Herzfeld,J
在高达10.5特斯拉(T)的磁场下，我们通过测量双折射率作为浓度和温度的函数，观察了紫色膜悬浮液的磁致取向。在这些场中，即使在稀溶液中，取向也接近饱和；因此，双折射数据，加上从电子显微镜获得的膜尺寸分布的估计，允许人们确定抗磁化率的各向异性。我们发现δ 1mol =1.2 +/- 0.3 X 10(-3) erg -2mol-1的细菌视紫红质。如果δ chi仅仅是由于跨膜α螺旋的定向肽键，这个实验值将表明δ K，即每摩尔肽键的各向异性，比先前提出的要大得多。另一方面，细菌视紫红质的大值也可以解释为细菌视紫红质的芳香氨基酸侧链的平面垂直于膜表面的净取向。此外，目前的数据分析表明，计算的δ chi值对膜尺寸分布的值具有临界依赖性。
We have observed the magnetically induced orientation of purple membrane suspensions by measuring the birefringence as a function of concentration and temperature at fields up to 10.5 Tesla (T). At these fields, the orientation approaches saturation even in dilute solutions; therefore, the birefringence data, together with an estimate of the membrane size distribution obtained from electron microscopy, permits one to determine the diamagnetic susceptibility anisotropy. We find delta chi mole=1.2 +/- 0.3 X 10(-3) erg G-2mol-1 of bacteriorhodopsin. If delta chi were due only to the oriented peptide bonds of the transmembrane alpha helices, this experimental value would indicate that delta K, the anisotropy per mole of peptide bonds, is considerably larger than previously suggested. On the other hand, the large value for delta chi mole of bacteriorhodopsin can also be explained by a net orientation of the aromatic amino acid side chains of bacteriorhodopsin with their planes perpendicular to the membrane surface. In addition, the present data analysis demonstrates the critical dependence of the calculated delta chi value on the values for the membrane size distribution.