Kitada M, Morotomi S, Horikoshi K, Kudo T
Microbiology Laboratory, The Institute of Physical and Chemical Research (Riken), Saitama, Japan.
Extremophiles. 1997 Aug;1(3):135-41. doi: 10.1007/s007920050026.
A K+/H+ antiport system was detected for the first time in right-side-out membrane vesicles prepared from alkaliphilic Bacillus sp. no. 66 (JCM 9763). An outwardly directed K+ gradient (intravesicular K+ concentration, K(in), 100 mM; extravesicular K+ concentration, K(out), 0.25 mM) stimulated uphill H+ influx into right-side-out vesicles and created the inside-acidic pH gradient (delta pH). This H+ influx was pH-dependent and increased as the pH increased from 6.8 to 8.4. Addition of 100 microM quinine inhibited the H+ influx by 75%. This exchange process was electroneutral, and the H+ influx was not stimulated by the imposition of the membrane potential (interior negative). Addition of K+ at the point of maximum delta pH caused a rapid K+-dependent H+ efflux consistent with the inward exchange of external K+ for internal H+ by a K+/H+ antiporter. Rb+ and Cs+ could replace K+ but Na+ and Li+ could not. The H+ efflux rate was a hyperbolic function of K+ and increased with increasing extravesicular pH (pH(out)) from 7.5 to 8.5. These findings were consistent with the presence of K+/H+ antiport activity in these membrane vesicles.
首次在从嗜碱芽孢杆菌66号菌株（JCM 9763）制备的外翻膜囊泡中检测到K⁺/H⁺反向转运系统。外向的K⁺梯度（囊泡内K⁺浓度，K(in)，100 mM；囊泡外K⁺浓度，K(out)，0.25 mM）刺激H⁺向囊泡内的上坡流入，并产生了内部酸性pH梯度（ΔpH）。这种H⁺流入是pH依赖性的，并且随着pH从6.8增加到8.4而增加。添加100 μM奎宁可使H⁺流入减少75%。这种交换过程是电中性的，并且膜电位（内部为负）的施加不会刺激H⁺流入。在最大ΔpH时添加K⁺会导致与K⁺/H⁺反向转运体介导的外部K⁺与内部H⁺向内交换一致的快速K⁺依赖性H⁺流出。Rb⁺和Cs⁺可以替代K⁺，但Na⁺和Li⁺不能。H⁺流出速率是K⁺的双曲线函数，并且随着囊泡外pH（pH(out)）从7.5增加到8.5而增加。这些发现与这些膜囊泡中存在K⁺/H⁺反向转运活性一致。
