Buurman E T, Teixeira de Mattos M J, Neijssel O M
Department of Microbiology, University of Amsterdam, The Netherlands.
Arch Microbiol. 1991;155(4):391-5. doi: 10.1007/BF00243460.
Escherichia coli Frag1 was grown under various nutrient limitations in chemostat culture at a fixed temperature, dilution rate and pH both in the presence and the absence of a high concentration of ammonium ions by using either ammonium chloride or DL-alanine as the sole nitrogen source. The presence of high concentrations of ammonium ions in the extracellular fluids of potassium-limited cultures of E. coli Frag1 caused an increase of the specific rate of oxygen consumption of these cultures. In contrast, under phosphate-, sulphate- or magnesium-limited growth conditions no such increase could be observed. The presence of high concentrations of ammonium ions in potassium-limited cultures of E. coli Frag5, a mutant strain of E. coli Frag1 which lacks the high affinity potassium uptake system (Kdp), did not increase the specific rate of oxygen consumption. These results indicate that ammonium ions, very similar to potassium ions both in charge and size, are transported via the Kdp leading to a futile cycle of ammonium ions and ammonia molecules (plus protons) across the cytoplasmic membrane. Both the uptake of ammonium ions and the extrusion of protons would increase the energy requirement of the cells and therefore increase their specific rate of oxygen consumption. The involvement of a (methyl)ammonium transport system in this futile cycle could be excluded.
大肠杆菌Frag1在恒化器培养中，于固定温度、稀释率和pH值条件下，在有和没有高浓度铵离子存在的情况下，分别使用氯化铵或DL-丙氨酸作为唯一氮源，在各种营养限制条件下生长。在大肠杆菌Frag1钾限制培养物的细胞外液中存在高浓度铵离子，导致这些培养物的氧消耗比速率增加。相比之下，在磷酸盐、硫酸盐或镁限制的生长条件下，未观察到这种增加。大肠杆菌Frag5是大肠杆菌Frag1的突变菌株，缺乏高亲和力钾摄取系统（Kdp），在其钾限制培养物中存在高浓度铵离子，并未增加氧消耗比速率。这些结果表明，铵离子在电荷和大小上与钾离子非常相似，通过Kdp进行转运，导致铵离子和氨分子（加质子）在细胞质膜上形成无效循环。铵离子的摄取和质子的排出都会增加细胞的能量需求，因此会增加其氧消耗比速率。可以排除（甲基）铵转运系统参与这个无效循环。
