Fendler K, Dröse S, Epstein W, Bamberg E, Altendorf K
Max-Planck-Institut für Biophysik, Frankfurt/M, Germany.
Biochemistry. 1999 Feb 9;38(6):1850-6. doi: 10.1021/bi982238u.
Charge transport by the K+ transporting Kdp-ATPase from Escherichia coli was investigated using planar lipid membranes to which liposomes reconstituted with the enzyme were adsorbed. To study reactions in the absence of K+, given some contamination of solutions with K+, we used a mutant of Kdp whose affinity for K+ was 6 mM instead of the wild-type whose affinity is 2 microM. Upon rapid release of ATP from caged ATP, a transient current occurred in the absence of K+. In the presence of K+, a stationary current was seen. On the basis of their structural similarity, we propose a kinetic model for the Kdp-ATPase analogous to that of the Na+K+-ATPase. In this model, the first, K+-independent step is electrogenic and corresponds to the outward transport of a negative charge. The second, K+-translocating step is probably also electrogenic and corresponds to transport of positive charge to the intracellular side of the protein.
利用吸附了用该酶重构脂质体的平面脂质膜，对来自大肠杆菌的运输钾离子的Kdp - ATP酶的电荷转运进行了研究。为了研究在没有钾离子的情况下的反应，鉴于溶液中存在一定程度的钾离子污染，我们使用了对钾离子亲和力为6 mM的Kdp突变体，而非野生型对钾离子的亲和力为2 microM。当从笼形ATP快速释放ATP时，在没有钾离子的情况下会出现瞬态电流。在有钾离子存在时，则会观察到稳定电流。基于它们的结构相似性，我们提出了一个类似于钠钾ATP酶的Kdp - ATP酶动力学模型。在这个模型中，第一步，即不依赖钾离子的步骤是生电的，对应于一个负电荷的外向运输。第二步，即转运钾离子的步骤可能也是生电的，对应于正电荷向蛋白质细胞内侧的运输。
