PROPERTIES OF THE NA+ H+ ANTIPORTER IN VIBRIO-PARAHAEMOLYTICUS/

The properties of the Na+/H+ antiporter in Vibrio parahaemolyticus, a slightly halophilic bacterium, were investigated using everted membran e vesicles. It appears that at least two Na+/H+ antiporters are presen t, one that is pH-dependent and one that is pH-independent. These two antiporters appear to correspond to the NhaA and NhaB antiporters of E scherichia coli, respectively. It seems that amiloride strongly inhibi ts the pH-dependent antiporter. Na+ is the best substrate for both of the two V. parahaemolyticus antiporters. Li+ is a poorer substrate and K+ is not a substrate. No K+/H+ antiport activity was detected in mem brane vesicles of this organism. The Na+(Li+)/H+ antiport activity gre atly increased with an increase in pH of the assay medium. pH did not affect the K-m value of the Na+/H+ antiport, but it did increase the V -max.