Ferreira A T, Lacaz-Vieira F, Paiva A C
Biochim Biophys Acta. 1982 Feb 8;685(1):32-8. doi: 10.1016/0005-2736(82)90031-1.
The diffusion of electrically charged peptides (angiotensin II, bradykinin and [Suc1]angiotensin II) across tight cellophane membranes, obtained by different degrees of acetylation, shows a kinetic behaviour which was interpreted in the literature as indicative of the existence of different molecular conformations presenting slow interconversion velocities and different permeabilities across the membrane. A diffusion potential (delta psi) was found to be present across the membrane along diffusion experiments performed in low ionic strength. Upon annihilation of delta psi by chemical voltage clamping (by equally increasing the ionic strength on both bathing solutions) the diffusion rate was decreased and the flow followed first order kinetics, indicating a major role of delta psi in the process. As the ionic strength increase could also affect molecular conformation, the role of delta psi on the diffusion of those molecules was tested by fitting flux and delta psi experimental results by an integrated form of Nernst-Planck flux equation. It is concluded that the deviation from first order diffusion kinetics, observed in low ionic strength, is solely due to the diffusion potential, and not to the existence of more than one molecular conformation in aqueous solution. This study was extended to amino acids and other related charged molecules.
带电肽（血管紧张素II、缓激肽和[Suc1]血管紧张素II）通过不同程度乙酰化获得的紧密玻璃纸膜的扩散，显示出一种动力学行为，在文献中被解释为表明存在不同的分子构象，这些构象呈现出缓慢的相互转化速度以及不同的跨膜渗透性。在低离子强度下进行的扩散实验中，发现膜两侧存在扩散电位（δψ）。通过化学电压钳制（通过同等增加两侧浴液的离子强度）消除δψ后，扩散速率降低，且流动遵循一级动力学，表明δψ在该过程中起主要作用。由于离子强度增加也可能影响分子构象，通过用能斯特 - 普朗克通量方程的积分形式拟合通量和δψ实验结果，测试了δψ对这些分子扩散的作用。得出的结论是，在低离子强度下观察到的偏离一级扩散动力学的现象仅归因于扩散电位，而非水溶液中存在不止一种分子构象。该研究扩展到了氨基酸和其他相关带电分子。
