Mechanism and specificity of lanthanide series cation transport by ionophores A23187, 4-BrA23187, and ionomycin.
Mechanism and specificity of lanthanide series cation transport by ionophores A23187, 4-BrA23187, and ionomycin.
复制标题
离子载体 A23187、4-BrA23187 和离子霉素传输镧系阳离子的机制和特异性。
DOI：
10.1016/s0006-3495(98)74044-5
复制
发表时间：
1998
期刊：
影响因子：
--
通讯作者：
Pfeiffer,DR
中科院分区：
文献类型：
--
作者：
Wang,E;Taylor,RW;Pfeiffer,DR
A23187, 4-BrA23187, and ionomycin transport several lanthanide series trivalent cations at efficiencies similar to Ca2+, when compared at cation concentrations of ∼10−5M, ionophore concentrations of ∼10−6M, and a pH of 7.00. Selectivity sequences and the range of relative rates are as follows: A23187, Nd3+>La3+>Eu3+>Gd3+>Er3+>Yb3+>Lu3+(∼34-fold); 4-BrA23187, Nd3+>Eu3+>Gd3+>La3+>Er3+>Yb3+>Lu3+(∼34-fold); ionomycin, La3+>Yb3+>Nd3+>Lu3+>Er3+>Eu3+>Gd3+(∼4-fold). At concentrations between 9 and 250μM, La3+is transported by an electroneutral mechanism, predominately through mixed complexes of the type (ionophore)2La·OH (A23187 and 4-BrA23187) or (ionophore)La·OH (ionomycin), when no membrane potential is present. For all three ionophores, an induced potential of ∼160mV accelerates transport by ∼50–100%. However, measured values of H+/La3+exchange indicate that only 4-BrA23187 displays a significant electrogenic activity under these conditions. At a La3+concentration of 17mM, transport by all three ionophores is electroneutral and apparently occurs through complexes of type (ionophore)3La (A23187 and 4-BrA23187) or (ionophore)La·OH (ionomycin). Analysis of these patterns in a context of comproportionation equilibria involving the transporting species and free La3+indicates that the species containing three ionophore molecules are formed on the membrane when aqueous phase solution conditions would strongly favor a 1:1 complex, based upon previous studies in solution. The implications of this and other findings are discussed.
