Bacterial Na + energetics

Novel observations related to the Na + ‐linked energy transduction in bacterial membranes are considered. It is concluded that, besides the well‐known systems based on the circulation of protons, there are those based on the circulation of Na + . In some cases, H + and Na + cycles co‐exist in one and the same membrane. Representatives of the ‘sodium world’, i.e. cells possessing primary Na + pumps (Δ Δµ̃ Na generators and consumers) are found in many genera of bacteria. Among the Δ Δµ̃ Na generators, one should mention Na + ‐NADH‐quinone reductase and Na + ‐terminal oxidase of the respiratory chain, Na + ‐decarboxylases and Na + ‐ATPases. For Δµ̃ Na consumers, there are Na + ‐ATP‐synthases, Na + ‐metabolite symporters and Na + motors. Sometimes, one and the same enzyme can transport H + or, alternatively, Na + . For instance, an Na + ‐ATP‐synthase of the F 0 F 1 type translocates H + when Na + is absent. Employment of the Na + cycle, apart from or instead of the H + cycle, increases the resistance of bacteria to alkaline or protonophore‐containing media and, apparently, to some other unfavourable conditions.