The terminal oxidases and coupled Na' transport have hwn studied in intact cells and inside-out subccllucar vesicles of alkalo-and halotolerant Burihs FTU grown under different conditions. Cells grown at pH 7.5 arc shown to possess a system of respiration-dependent Nn' transport which is (i) inhibited by protonophorous uncoupler and (ii) activated by the d&discharging agent valinomycin. suggesting that the Na' transport is due to cooperation of the El+-molive oxidasc and Na+/H+ anliporter. On the other hand, growth under conditions lowering the Ml,-Ievcl, namely (i) pH 8.6, (ii) pH 7.5 in the presence of protonophorc. and (iii) pH 7.5 in the presence of low cyanide concentrations results in appearance ot-terminal oxidasc-supported Na* transport which is stimulated by protonophores (the Na'motive oxidase). In all three cases, the appearance of ascorbate (+ TMPD) oxidation resistant to low and sensitive to high cyanide concentrations was found LO occur. It is concluded that not only alkaline pH but also other conditions which lower dp ,,+ can cause substitution of Na+ for H' as a coupling ion.