Specific inhibition of the halobacterial Na+/H+ antiporter by halocin H6

Abstract

Halocins H6 and H4 are bacteriocin-like substances capable of killing sensitive halobacterial cells by affecting the bioenergetic steady state across the membrane. The effect of either halocin on living cells is similar, but the primary target of each is different. Halocin H6 inhibited light- induced Na+ out-flow in membrane vesicles of Halobacterium halobium. H4 did not, but instead slowed the H+ return-flow in the dark after illumination. Halocin H6 adsorbs firmly to both whole cells and membrane vesicles. The conclusion is that the primary target of halocin H6 is the Na+/H+ antiporter. This is important not only insofar as it outlines the mechanism by which a halocin works, but also for the fact that it is the first specific physiological inhibitor of the halobacterial Na+/H+ antiporter to be described.