Ellena J F, Dominey R N, Archer S J, Xu Z C, Cafiso D S
Department of Chemistry, University of Virginia, Charlottesville 22901.
Biochemistry. 1987 Jul 14;26(14):4584-92. doi: 10.1021/bi00388a062.
The binding location for the hydrophobic ions tetraphenylphosphonium (TPP+) and tetraphenylboron (TPB-) was studied in sonicated phosphatidylcholine (PC) vesicles by measuring time-dependent and steady-state intermolecular 1H nuclear Overhauser effects (NOE's). Intermolecular cross-relaxation was also investigated by two-dimensional NOE spectroscopy. Information on the distance and order parameter dependence of the NOE's was obtained from a simple simulation of the NOE's in the alkyl chain region. Taken together, the NOE data and the simulation provide strong evidence that TPB- and TPP+, at low concentrations (less than or equal to 10 mol%), are localized in the alkyl chain region of the bilayer. At these lower concentrations of TPP+ or TPB-, no significant effect on lipid 13C T1 or T2 relaxation rates is detected. The proposed location is consistent with the expected free energy profiles for hydrophobic ions and with the carbonyl oxygens or interfacial water as the source of the membrane dipole potential. At higher ion/lipid ratios (greater than or equal to 20 mol%), TPB-/lipid NOE's increase. This results from a specific association of TPB- with the choline head group.
通过测量时间依赖性和稳态分子间1H核Overhauser效应（NOE），研究了疏水离子四苯基鏻（TPP +）和四苯基硼（TPB -）在超声处理的磷脂酰胆碱（PC）囊泡中的结合位置。还通过二维NOE光谱研究了分子间交叉弛豫。通过对烷基链区域中NOE的简单模拟，获得了关于NOE的距离和序参量依赖性的信息。综合来看，NOE数据和模拟提供了有力证据，表明在低浓度（小于或等于10摩尔％）下，TPB -和TPP +位于双层的烷基链区域。在这些较低浓度的TPP +或TPB -下，未检测到对脂质13C T1或T2弛豫速率有显著影响。所提出的位置与疏水离子的预期自由能分布以及以羰基氧或界面水作为膜偶极势的来源一致。在较高的离子/脂质比（大于或等于20摩尔％）下，TPB -/脂质NOE增加。这是由于TPB -与胆碱头部基团的特异性缔合所致。
