SPECIFIC-INHIBITION OF THE HALOBACTERIAL NA+ H+ ANTIPORTER BY HALOCINH6/

Halocins H6 and H4 are bacteriocin-like substances capable of killing sensitive halobacterial cells by affecting the bioenergetic steady sta te across the membrane, The effect of either halocin on living cells i s similar, but the primary target of each is different. Halocin H6 inh ibited light induced Na+ out-flow in membrane vesicles of Halobacteriu m halobium. H4 did not, but instead slowed the H+ return-flow in the d ark after illumination. Halocin H6 adsorbs firmly to both whole cells and membrane vesicles, The conclusion is that the primary target of ha locin 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 th e fact that it is the first specific physiological inhibitor of the ha lobacterial Na+/H+ antiporter to be described.