Nitschmann W H, Packer L
Membrane Bioenergetics Group, Lawrence Berkeley Laboratory, University of California 94720.
Arch Biochem Biophys. 1992 May 1;294(2):347-52. doi: 10.1016/0003-9861(92)90694-r.
The freshwater cyanobacterium Synechococcus PCC 6311 is able to adapt to grow after sudden exposure to salt (NaCl) stress. We have investigated the mechanism of Na+ transport in these cells during adaptation to high salinity. Na+ influx under dark aerobic conditions occurred independently of delta pH or delta psi across the cytoplasmic membrane, ATPase activity, and respiratory electron transport. These findings are consistent with the existence of Na+/monovalent anion cotransport or simultaneous Na+/H(+)+anion/OH- exchange. Na+ influx was dependent on Cl-, Br-, NO3-, or NO2-. No Na+ uptake occurred after addition of NaI, NaHCO3, or Na2SO4. Na+ extrusion was absolutely dependent on delta pH and on an ATPase activity and/or on respiratory electron transport. This indicates that Na+ extrusion via Na+/H+ exchange is driven by primary H+ pumps in the cytoplasmic membrane. Cells grown for 4 days in 0.5 M NaCl medium, "salt-grown cells," differ from control cells by a lower vmax of Na+ influx and by lower steady-state ratios of [Na+]in/[Na+]out. These results indicate that cells grown in high-salt medium increase their capacity to extrude Na+. During salt adaptation Na+ extrusion driven by respiratory electron transport increased from about 15 to 50%.
淡水蓝藻聚球藻PCC 6311在突然暴露于盐（NaCl）胁迫后能够适应生长。我们研究了这些细胞在适应高盐度过程中Na⁺转运的机制。在黑暗需氧条件下，Na⁺内流独立于跨细胞质膜的ΔpH或ΔΨ、ATP酶活性以及呼吸电子传递。这些发现与存在Na⁺/单价阴离子共转运或同时存在的Na⁺/H⁺+阴离子/OH⁻交换一致。Na⁺内流依赖于Cl⁻、Br⁻、NO₃⁻或NO₂⁻。添加NaI、NaHCO₃或Na₂SO₄后不发生Na⁺摄取。Na⁺外流绝对依赖于ΔpH以及ATP酶活性和/或呼吸电子传递。这表明通过Na⁺/H⁺交换的Na⁺外流由细胞质膜中的初级H⁺泵驱动。在0.5 M NaCl培养基中生长4天的细胞，即“盐生长细胞”，与对照细胞的不同之处在于Na⁺内流的vmax较低以及[Na⁺]in/[Na⁺]out的稳态比率较低。这些结果表明在高盐培养基中生长的细胞增加了它们排出Na⁺的能力。在盐适应过程中，由呼吸电子传递驱动的Na⁺外流从约15%增加到50%。
