Michels M, Bakker E P
J Bacteriol. 1987 Sep;169(9):4335-41. doi: 10.1128/jb.169.9.4335-4341.1987.
Cells of Bacillus acidocaldarius that were grown with 2.7 mM K+ expressed a low-affinity K+ uptake system. The following observations indicate that its properties closely resemble those of the Escherichia coli Trk and Streptococcus faecalis KtrI systems: (i) the B. acidocaldarius system took up K+ with a Km of 1 mM; (ii) it accepted Rb+ (Km of 6 mM; same Vmax as for K+); (iii) it was still active in the presence of low concentrations of sodium; (iv) the observed accumulation ratio of K+ maintained by metabolizing cells was consistent with K+ being taken up via a K+-H+ symporter; and (v) K+ uptake did not occur in cells in which the ATP level was low. Under the latter conditions, the cells still took up methylammonium ions via a system that was derepressed by growth with low levels of ammonium ions, indicating that in the acidophile ammonium (methylammonium) uptake requires a high transmembrane proton motive force rather than ATP.
在含有2.7 mM钾离子的条件下生长的嗜酸热硫化叶菌细胞表达了一种低亲和力的钾离子摄取系统。以下观察结果表明，其特性与大肠杆菌Trk和粪肠球菌KtrI系统的特性非常相似：（i）嗜酸热硫化叶菌系统以1 mM的Km摄取钾离子；（ii）它接受铷离子（Km为6 mM；与钾离子的Vmax相同）；（iii）在低浓度钠存在的情况下它仍然活跃；（iv）通过代谢细胞维持的观察到的钾离子积累率与钾离子通过钾离子-氢离子同向转运体摄取一致；（v）在ATP水平较低的细胞中不发生钾离子摄取。在后者的条件下，细胞仍然通过一种因在低水平铵离子条件下生长而解除抑制的系统摄取甲基铵离子，这表明在嗜酸菌中铵离子（甲基铵离子）摄取需要高跨膜质子动力势而不是ATP。
