Botany Department, Imperial College, S.W.7., London, U.K..
Planta. 1973 Mar;111(1):13-22. doi: 10.1007/BF00386730.
The rate of Na(+)/Na(+) exchange as measured with (24)Na(+) in Na(+)-rich cells of Chlorella pyrenoidosa is governed by a single rate constant and saturates with increasing external Na(+) concentration. The K mvalue for this process is 0.8 mM Na(+) and the maximum rate of exchange in illuminated cells is about 5 pmoles cm(-2) sec(-1). These values contrast with a K mof 0.18 mM K(+) and maximum rate of about 17 pmoles K(+)·cm(-2)·sec(-1) for net K(+) influx. Although the Na(+)/Na(+) exchange was only slightly sensitive to light it was inhibited by the uncouplers CCCP and DNP and by the energy transfer inhibitor DCCD. This inhibition of the rate of Na(+)/Na(+) exchange was not accompanied by a loss of internal Na(+). Both the effect of external K(+) on (24)Na(+) influx into Na(+)-rich cells and the inhibition of net K(+) uptake by the presence of external Na(+) indicates that Na(+)/Na(+) and K(+)/Na(+) exchanges share the same carrier and that the external site of this carrier has a three to four times higher affinity for K(+) over Na(+).
用（24）Na（+）在富含 Na（+）的 Chlorella pyrenoidosa 细胞中测量的 Na（+）/Na（+）交换率受单个速率常数控制，并随外部 Na（+）浓度的增加而饱和。该过程的 Km 值为 0.8 mM Na（+），受照细胞中交换的最大速率约为 5 pmoles cm（-2）sec（-1）。这些值与净 K（+）内流的 Km 值 0.18 mM K（+）和最大速率约 17 pmoles K（+）·cm（-2）·sec（-1）形成对比。尽管 Na（+）/Na（+）交换对光只有轻微的敏感性，但它被解偶联剂 CCCP 和 DNP 以及能量转移抑制剂 DCCD 抑制。这种对 Na（+）/Na（+）交换速率的抑制并没有伴随着内部 Na（+）的损失。外部 K（+）对富含 Na（+）的细胞中（24）Na（+）内流的影响以及外部 Na（+）存在时净 K（+）摄取的抑制表明，Na（+）/Na（+）和 K（+）/Na（+）交换共享相同的载体，并且该载体的外部位点对 K（+）的亲和力是 Na（+）的三到四倍。
