Energy coupling to K+ transport in a marine bacterium

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Abstract
Cells of the marine bacterium A. haloplanktis 214 ATCC 19855 (previously referred to as marine pseudomonad B-16) were depleted of K+ by washing with 0.1 M MgSO4. Washing with 0.05 M MgSO4 lowered the Vmax for K+ transport compared with washing with 0.1 M, but did not change the Km; washing with lower concentrations of MgSO4, however, caused loss of ultraviolet-absorbing material from the cells. K+ uptake was a strictly aerobic process and was accompanied by proton release. When an anaerobic suspension of cells was added to incubation mixtures containing increasing amounts of O2, intracellular ATP concentrations increased as the O2 concentration increased, and reached near maximum values before K+ transport began. The O2 concentration initiating K+ transport caused transport to proceed at its maximum rate. For these experiments A. haloplanktis was depleted of ATP by incubating under anaerobic conditions. Incubating with either N,N''-dicyclohexyl carbodiimide (DCCD) or arsenate failed to deplete intact cells of ATP or prevent K+ transport. The inhibitory activity of DCCD for ATPase in membrane preparations was higher at 5 mM than at other MgSO4 concentrations, and increased with time. Cyanide and the uncoupling agents, tetrachlorosalicylanide (TCS) and carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP), prevented K+ uptake while TCS and FCCP, though not cyanide, caused K+ to be released from K+-containing cells. The driving force for K+ transport in these cells is likely to be the membrane potential and that K+ transport may be gated.