Na⁺(Li⁺)/H⁺ Antiporter in Pseudomonas aeruginosa and Effect of Li⁺ on Cell Growth

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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.