Toyoshima Y, Thompson T E
Biochemistry. 1975 Apr 8;14(7):1525-31. doi: 10.1021/bi00678a028.
Aqueous dispersions of phosphatidylcholine vesicles were utilized to determine bilayer permeability to 36-Cl as a function of pH and temperature. These dispersions were comprised of single-walled vesicles, homogeneous in size, prepared by sonication of purified egg phosphatidylcholine under argon followed by fractionation on a molecular sieve. Permeability constants calculated from the inward flux of 36-Cl and the geometric parameters of these vesicles proved to be dependent on both pH and temperature. Analysis of these dependences leads to the conclusion that 36-Cl permeation in the presence of KCl is due principally to a carrier mediated exchange process involving a phospholipid-HCL complex. Net permeation by H-36-Cl may make a small contribution to the 36-Cl flux, however, studies carried out at very low chloride concentrations show that this flux is much smaller than the exchange flux. Thus chloride permeability for the exchange process is 1.5 times 10- minus 11 cmsec- minus 1 while the corresponding coefficient for the net flux of H-36-Cl is 1.0 times 10- minus 12 cm sec- minus 1 at pH 7. The activation energy for the 36-Cl exchange flux was found to be 19 plus or minus 2 kcal/mol. This value is similar to that obtained for the transbilayer "flip-flop" of phosphatidylcholine molecules in a similar system (Kornberg and McConnell, 1971). This correspondence together with the fact that the experimentally determined flux of 36-Cl agrees well with that calculated from the "flip-flop" parameters, strongly suggests that the flux of 36-Cl and "flip-flop" of phosphatidylcholine may be the same process.
利用磷脂酰胆碱囊泡的水分散体来确定双层膜对³⁶Cl的渗透性与pH值和温度的关系。这些分散体由大小均匀的单壁囊泡组成，通过在氩气下对纯化的鸡蛋磷脂酰胆碱进行超声处理，然后在分子筛上进行分级分离制备而成。根据³⁶Cl的内流和这些囊泡的几何参数计算出的渗透常数被证明取决于pH值和温度。对这些依赖性的分析得出结论，在KCl存在下³⁶Cl的渗透主要是由于涉及磷脂-HCl复合物的载体介导的交换过程。H-³⁶Cl的净渗透可能对³⁶Cl通量有小的贡献，然而，在非常低的氯化物浓度下进行的研究表明，这种通量比交换通量小得多。因此，交换过程的氯离子渗透率为1.5×10⁻¹¹cm·sec⁻¹，而在pH 7时H-³⁶Cl净通量的相应系数为1.0×10⁻¹²cm·sec⁻¹。发现³⁶Cl交换通量的活化能为19±2 kcal/mol。这个值与在类似系统中磷脂酰胆碱分子的跨双层“翻转”所获得的值相似（Kornberg和McConnell，1971）。这种对应关系以及实验测定的³⁶Cl通量与根据“翻转”参数计算出的通量非常吻合这一事实，强烈表明³⁶Cl的通量和磷脂酰胆碱的“翻转”可能是同一过程。
