The terminal oxidases and coupled Na+ transport have been studied in intact cells and inside-out subcellucar vesicles of alkalo- and halotolerant Bacillus FTU grown under different conditions. Cells grown at pH 7.5 are shown to possess a system or respiration-dependent Na+ transport which is (i) inhibited by protonophorous uncoupler and (ii) activated by Δψ-discharging agent valinomycin, suggesting that the Na+ transport is due to cooperation of the H+-motive oxidase and Na+/H+ antiporter. On the other hand, growth under conditions lowering the Δ\̄gmH+ level, namely (i) pH 8.6, (ii) pH 7.5 in the presence of protonophore, and (iii) pH 7.5 in the presence of low cyanide concentrations results in appearance of terminal oxidase-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 to occur. It is concluded that not only alkaline pH but also other conditions which lower Δ\̄gmH+ can cause substitution of Na+ for H+ as a coupling ion.
