Alvarado F, Vasseur M
Institut National de la Santé et de la Recherche Médicale, Faculté de Pharmacie, Université de Paris XI, Chatenay-Malabry, France.
Am J Physiol. 1996 Nov;271(5 Pt 1):C1612-28. doi: 10.1152/ajpcell.1996.271.5.C1612.
A Cl(-)-H+ symport and a Cl-/OH- antiport cannot be readily distinguished physicochemically, but a kinetic distinction is theoretically possible, because a Cl(-)-H+ symporter involves a two-site carrier whereas a Cl-/OH- antiporter involves a single-site carrier. Accordingly, we have developed kinetic models and equations that we have tested by studying Cl- uptake by isolated guinea pig ileal brush-border membrane vesicles as a function of Cl- or H+ concentration. We conclude that a two-site Cl(-)-H+ symporter with a 1:1 stoichiometry explains the pH-dependent Cl- uptake and Cl-/Cl- exchange activities of the brush-border membrane in terms of a single random nonobligatory mobile carrier where exchange occurs by counterflow. This symport, probably involving an anion exchanger (AE 2) protein, differs, therefore, functionally from the erythrocyte's band 3 AE1, which involves an antiport. The question is whether members of the AE gene family can be functionally diverse, even when their primary structures exhibit up to 50% overall homologies.
氯离子-氢离子同向转运体和氯离子/氢氧根离子反向转运体在物理化学性质上难以区分，但从动力学角度理论上是可以区分的，因为氯离子-氢离子同向转运体涉及双位点载体，而氯离子/氢氧根离子反向转运体涉及单位点载体。因此，我们建立了动力学模型和方程，并通过研究豚鼠离体回肠刷状缘膜囊泡对氯离子的摄取作为氯离子或氢离子浓度的函数来进行验证。我们得出结论，具有1:1化学计量比的双位点氯离子-氢离子同向转运体可以解释刷状缘膜中依赖pH的氯离子摄取和氯离子/氯离子交换活性，这是基于单个随机非强制性移动载体，通过逆流进行交换。这种同向转运体可能涉及阴离子交换蛋白（AE 2），因此在功能上与红细胞的带3 AE1不同，后者涉及反向转运。问题在于，即使AE基因家族成员的一级结构总体同源性高达50%，它们在功能上是否会有所不同。
