Sugiyama S, Cragoe E J, Imae Y
Department of Molecular Biology, Faculty of Science, Nagoya University, Japan.
J Biol Chem. 1988 Jun 15;263(17):8215-9.
Na+-driven flagellar motors of alkalophilic Bacillus were found to be inhibited by amiloride, a potent inhibitor for many Na+-coupled systems. A concentration of 0.5 mM of amiloride completely inhibited motility but showed almost no effect on the membrane potential, the intracellular pH homeostasis, and the ATP content of the cells. Furthermore, the activity of a Na+-coupled amino acid transport system was reduced only by half by this concentration of amiloride. Thus, the inhibition of motility of alkalophilic Bacillus by amiloride was rather specific. The inhibition of motility produced by amiloride was restored by increasing Na+ concentrations in the medium. Kinetic analysis of the data revealed that the inhibition was competitive with respect to the concentration of Na+ in the medium. Therefore, it is quite logical to assume that amiloride inhibits the rotation of the Na+-driven flagellar motors of alkalophilic Bacillus by competing with Na+ at the force-generating site of the motor. Some amiloride analogs known to selectively inhibit Na+ channels were potent inhibitors for the flagellar motors, suggesting that the Na+-interacting site of the motors has some similarity to that of the Na+ channels.
嗜碱芽孢杆菌的钠离子驱动鞭毛马达被发现会受到氨氯吡脒的抑制，氨氯吡脒是许多钠离子偶联系统的强效抑制剂。0.5 mM的氨氯吡脒浓度可完全抑制运动性，但对膜电位、细胞内pH稳态和细胞的ATP含量几乎没有影响。此外，这种浓度的氨氯吡脒仅使钠离子偶联氨基酸转运系统的活性降低一半。因此，氨氯吡脒对嗜碱芽孢杆菌运动性的抑制作用相当具有特异性。通过增加培养基中的钠离子浓度可恢复氨氯吡脒对运动性的抑制作用。对数据的动力学分析表明，这种抑制作用与培养基中钠离子浓度呈竞争性。因此，很合理地推测氨氯吡脒通过在马达的力产生位点与钠离子竞争来抑制嗜碱芽孢杆菌的钠离子驱动鞭毛马达的旋转。一些已知可选择性抑制钠离子通道的氨氯吡脒类似物是鞭毛马达的强效抑制剂，这表明马达的钠离子相互作用位点与钠离子通道的该位点有一些相似之处。
