Kashket E R
J Bacteriol. 1981 Apr;146(1):377-84. doi: 10.1128/jb.146.1.377-384.1981.
The electrochemical gradient of hydrogen ions, or proton motive force (PMF), was measured in growing Escherichia coli and Klebsiella pneumoniae in batch culture. The electrical component of the PMF (delta psi) and the chemical component (delta pH) were calculated from the cellular accumulation of radiolabeled tetraphenylphosphonium, thiocyanate, and benzoate ions. In both species, the PMF was constant during exponential phase and decreased as the cells entered stationary phase. Altering the growth rate with different energy substrates had no effect on the PMF. The delta pH (alkaline inside) varied with the pH of the culture medium, resulting in a constant internal pH. During aerobic growth in media at pH 6 to 7, the delta psi was constant at 160 mV (negative inside). The PMF, therefore, was 255 mV in cells growing at pH 6.3, and decreased progressively to 210 mV in pH 7.1 cultures. K. pneumoniae cells and two E. coli strains (K-12 and ML), including a mutant deficient in the H+-translocating ATPase and a pleiotropically energy-uncoupled mutant with a normal ATPase, had the same PMF during aerobic exponential phase. During anaerobic growth, however, both species had delta psi values equal to 0. Therefore, the PMF in anaerobic cells consisted only of the delta pH component, which was 75 mV or less in cells growing at pH 6.2 or greater. These data thus met the expectation that cells deriving metabolic energy from respiration have a PMF above a threshold value of about 200 mV when the ATPase functions in the direction of H+ influx and ATP synthesis; in fermenting cells, a PMF below a threshold value was expected since the enzyme functions in the direction of H+ extrusion and ATP hydrolysis. K. pneumoniae cells growing anaerobically had no delta psi whether the N source added was N2, NH+4 or one of several amino acids; the delta pH was unaffected. Therefore, any energy cost incurred by the process of nitrogen fixation could not be detected as an alteration of the proton gradient.
在分批培养的生长中的大肠杆菌和肺炎克雷伯菌中测量了氢离子的电化学梯度，即质子动力（PMF）。PMF的电成分（δψ）和化学成分（δpH）是根据放射性标记的四苯基鏻、硫氰酸盐和苯甲酸盐离子在细胞中的积累来计算的。在这两个物种中，PMF在指数生长期是恒定的，随着细胞进入稳定期而降低。用不同的能量底物改变生长速率对PMF没有影响。δpH（内部呈碱性）随培养基的pH值变化，导致内部pH值恒定。在pH值为6至7的培养基中进行有氧生长时，δψ恒定为160 mV（内部为负）。因此，在pH值为6.3的细胞中PMF为255 mV，在pH值为7.1的培养物中逐渐降至210 mV。肺炎克雷伯菌细胞和两种大肠杆菌菌株（K-12和ML）在有氧指数生长期具有相同的PMF，其中包括一种缺乏H+转运ATP酶的突变体和一种具有正常ATP酶的多效性能量解偶联突变体。然而，在厌氧生长期间，这两个物种的δψ值都等于0。因此，厌氧细胞中的PMF仅由δpH成分组成，在pH值为6.2或更高的生长细胞中，该成分小于或等于75 mV。这些数据因此符合以下预期：当ATP酶朝着H+内流和ATP合成的方向发挥作用时，从呼吸作用中获取代谢能量的细胞的PMF高于约200 mV的阈值；在发酵细胞中，由于该酶朝着H+外排和ATP水解的方向发挥作用，预计PMF低于阈值。无论添加的氮源是N2、NH4+还是几种氨基酸之一，厌氧生长的肺炎克雷伯菌细胞都没有δψ；δpH不受影响。因此，固氮过程产生的任何能量成本都无法检测为质子梯度的改变。
