Yoshida S, Sugiyama S, Hojo Y, Tokuda H, Imae Y
Department of Molecular Biology, Faculty of Science, Nagoya University, Japan.
J Biol Chem. 1990 Nov 25;265(33):20346-50.
To understand the mechanism of Na+ movement through the force-generating units of the Na(+)-driven flagellar motors of Vibrio alginolyticus, the effect of intracellular Na+ concentration on motor rotation was investigated. Control cells containing about 50 mM Na+ showed good motility even at 10 mM Na+ in the medium, i.e. in the absence of an inwardly directed Na+ gradient. In contrast, Na(+)-loaded cells containing about 400 mM Na+ showed very poor motility at 500 mM Na+ in the medium, i.e. even in the presence of an inwardly directed Na+ gradient. The membrane potential of the cells, which is a major driving force for the motor under these conditions, was not detectably altered, and consistently with this, Na(+)-coupled sucrose transport was only partly reduced in the Na(+)-loaded cells. Motility of the Na(+)-loaded cells was restored by decreasing the intracellular Na+ concentration, and the rate of restoration of motility correlated with the rate of the Na+ decrease. These results indicate that the absolute concentration of the intracellular Na+ is a determinant of the rotation rate of the Na(+)-driven flagellar motors of V. alginolyticus. A simple explanation for this phenomenon is that the force-generating unit of the motor has an intracellular Na(+)-binding site, at which the intracellular Na+ kinetically interferes with the rate of Na+ influx for motor rotation.
为了解嗜盐弧菌钠驱动鞭毛马达的力产生单元中钠离子的运动机制，研究了细胞内钠离子浓度对马达旋转的影响。含有约50 mM钠离子的对照细胞即使在培养基中钠离子浓度为10 mM时，即不存在内向钠离子梯度的情况下，仍具有良好的运动能力。相反，含有约400 mM钠离子的钠离子负载细胞在培养基中钠离子浓度为500 mM时，即即使存在内向钠离子梯度时，运动能力也非常差。在这些条件下，作为马达主要驱动力的细胞膜电位没有明显改变，与此一致的是，钠离子偶联的蔗糖转运在钠离子负载细胞中仅部分降低。通过降低细胞内钠离子浓度可恢复钠离子负载细胞的运动能力，运动能力的恢复速率与钠离子降低速率相关。这些结果表明，细胞内钠离子的绝对浓度是嗜盐弧菌钠驱动鞭毛马达旋转速率的决定因素。对这一现象的一个简单解释是，马达的力产生单元具有一个细胞内钠离子结合位点，细胞内钠离子在该位点从动力学上干扰了用于马达旋转的钠离子流入速率。
