Beaugé L A, DiPolo R
Biochim Biophys Acta. 1979 Jun 2;553(3):495-500. doi: 10.1016/0005-2736(79)90305-5.
Using dialysed squid axons we have been able to control internal and external ionic compositions under conditions in which most of the Na+ efflux goes through the Na+ pump. We found that (i) internal K+ had a strong inhibitory effect on Na+ efflux; this effect was antagonized by ATP, with low affinity, and by internal Na+, (ii) a reduction in ATP levels from 3 mM to 50 microM greatly increased the apparent affinity for external K+, but reduced its effectiveness compared with other monovalent cations, as an activator of Na+ efflux, and (iii) the relative effectiveness of different K+ congeners as external activator of the Na+ efflux, though affected by the ATP concentration, was not affected by the Na+/K+ ratio inside the cells. These results are consistent with the idea that the same conformation of the (Na+ + K+)-ATPase can be reached by interaction with external K+ after phosphorylation and with internal K+ before rephosphorylation. They also stress a nonphosphorylating regulatory role of ATP.
利用经透析的枪乌贼轴突，我们得以在大部分钠离子外流通过钠泵的条件下控制细胞内和细胞外的离子组成。我们发现：（i）细胞内钾离子对钠离子外流有强烈的抑制作用；这种作用被ATP以低亲和力拮抗，也被细胞内钠离子拮抗；（ii）ATP水平从3 mM降至50 μM极大地增加了对细胞外钾离子的表观亲和力，但与其他单价阳离子相比，其作为钠离子外流激活剂的效力降低；（iii）不同钾离子同系物作为钠离子外流细胞外激活剂的相对效力，虽受ATP浓度影响，但不受细胞内钠钾比的影响。这些结果与以下观点一致，即（钠 + 钾）-ATP酶的相同构象可通过磷酸化后与细胞外钾离子相互作用以及再磷酸化前与细胞内钾离子相互作用而达成。它们还强调了ATP的非磷酸化调节作用。
