MSU-DOE Plant Research Laboratory, Michigan University, East Lansing, Michigan 48824.
Plant Physiol. 1988 Mar;86(3):817-21. doi: 10.1104/pp.86.3.817.
The uptake of [(36)Cl]chlorate by the 14U variant of the XD cell line of Nicotiana tobaccum L. cv Xanthi was investigated to examine the use of chlorate as a nitrate analog in transport studies. The kinetics of chlorate uptake against concentration was complex. Evidence was obtained, e.g., by means of nitrate competition, that these kinetics could be resolved into two components indicating the existence of two influx mechanisms: a saturable high affinity transport system (HATS) and a low affinity transport system (LATS) that showed first order kinetics. HATS has an apparent K(m) for chlorate of 0.3 millimolar, and a marked pH dependence. The V(max) dropped about fivefold as the pH was changed from the optimum pH (5.5-6.5), while the K(m) remained virtually unchanged. The activity of HATS was completely inhibited by 15 millimolar nitrate and was less sensitive to chloride. LATS was inhibited by chloride and showed some inhibition by nitrate. It was concluded that [(36)Cl]chlorate can be used as an analog for nitrate uptake studies only in a limited low concentration range where HATS is the main route for chlorate influx.
用 14U 变异型烟草原生质体 XD 细胞系来研究 [(36)Cl]氯酸盐的摄取，以检验氯酸盐作为运输研究中硝酸盐类似物的用途。氯酸盐摄取的浓度动力学十分复杂。通过硝酸盐竞争等手段，获得了证据表明，这些动力学可以分解成两个部分，表明存在两种输入机制：一个是饱和高亲和力转运系统（HATS）和一个低亲和力转运系统（LATS），它们表现出一级动力学。HATS 对氯酸盐的表观 K(m) 为 0.3 毫摩尔，对 pH 值有明显的依赖性。当 pH 值从最适 pH 值（5.5-6.5）变化时，V(max) 下降约五倍，而 K(m) 几乎不变。HATS 的活性被 15 毫摩尔硝酸盐完全抑制，对氯离子的敏感性较低。LATS 被氯离子抑制，并对硝酸盐有一定的抑制作用。因此，只有在 HATS 是氯酸盐流入的主要途径的有限低浓度范围内，[(36)Cl]氯酸盐才能作为硝酸盐摄取研究的类似物。
