Prabhananda B S, Kombrabail M H
Chemical Physics Group, Tata Institute of Fundamental Research, Mumbai 400 005, India.
Biochim Biophys Acta. 1998 Mar 6;1370(1):41-50. doi: 10.1016/s0005-2736(97)00243-5.
Monensin (Mon)-mediated decay of the pH difference (DeltapH) across soyabean phospholipid vesicular membrane has been studied as a function of K+ and Na+ ion concentrations. In these experiments, the DeltapH was created using temperature jump, and ionic strength was regulated at 0.3 using CsCl. Rate constants associated with the translocation of Mon-H, Mon-K and Mon-Na have been estimated (without making any assumptions) from an analysis of the DeltapH decay data. These estimates contradict the claim made in the literature (E. Nachliel, Y. Finkelstein, M. Gutman, Biochim. Biophys. Acta, 1285 (1996) 131-145) that the translocation rate constants of the three above-mentioned species are significantly different. Our observations on the changes in DeltapH decay rate on adding carbonyl cyanide m-chlorophenylhydrazone (CCCP) also suggest that the dominant barrier to the DeltapH decay process is not the 'polar region' of the membrane. Therefore, the differences in the electric dipole moments of Mon-H, Mon-K and Mon-Na are unlikely to cause large differences in their translocation rate constants.
莫能菌素（Mon）介导的大豆磷脂囊泡膜两侧pH差值（ΔpH）的衰减已作为K⁺和Na⁺离子浓度的函数进行了研究。在这些实验中，通过温度跃升产生ΔpH，并使用CsCl将离子强度调节至0.3。通过对ΔpH衰减数据的分析（不做任何假设），估算了与Mon-H、Mon-K和Mon-Na转运相关的速率常数。这些估算结果与文献（E. Nachliel、Y. Finkelstein、M. Gutman，《生物化学与生物物理学报》，1285 (1996) 131 - 145）中所声称的上述三种物质的转运速率常数存在显著差异相矛盾。我们关于添加羰基氰化物间氯苯腙（CCCP）时ΔpH衰减速率变化的观察结果还表明，ΔpH衰减过程的主要障碍并非膜的“极性区域”。因此，Mon-H、Mon-K和Mon-Na的电偶极矩差异不太可能导致它们的转运速率常数出现较大差异。
