Na⁺ (Li⁺)/H⁺ antiporter in Pseudomonas aeruginosa and effect of Li⁺ on cell growth

Everted membrane vesicles were prepared from cells of Pseudomonas aeruginosa, and cation/H⁺ antiport was measured. We observed activities of Na⁺/H⁺ antiport, Li⁺/H⁺ antiport and K⁺/H⁺ antiport. Judging from the competition pattern, it seems that there are at least two types of antiporter, a Na⁺(Li⁺)/H⁺ antiporter and a K+/H⁺ antiporter. Na⁺ was a good substrate for the Na⁺ (Li⁺)/H⁺ system, whereas Li⁺ was a poor substrate. Although the K(m) value for Na⁺ (or Li⁺) was similar to those in Escherichia coli Na⁺/H⁺ antiporters, the V(max) value for Na⁺ (or Li⁺) was much smaller in the P. aeruginosa antiporter than in the E. coli antiporters. Growth of P. aeruginosa was strongly inhibited by 0.4 M LiCl, but not by NaCl or KCl.