Chemiosmotic concept of the membrane bioenergetics: what is already clear and what is still waiting for elucidation?

The present state of the chemiosmotic concept is reviewed. Special attention is paid to (i) further progress in studies on the Na(+)-coupled energetics and (ii) paradoxical bioenergetic effects when protonic or sodium potentials are utilized outside the coupling membrane (TonB-mediated uphill transports across the outer bacterial membrane). A hypothesis is put forward assuming that the same principle is employed in the bacterial flagellar motor.