TETRACYCLINE/H+ ANTIPORT AND NA+/H+ ANTIPORT CATALYZED BY THE BACILLUS-SUBTILIS TETA(L) TRANSPORT EXPRESSED IN ESCHERICHIA-COLI

The properties of TetA(L)-dependent tetracycline/proton and Na+/proton antiport were studied in energized everted vesicles of Escherichia coli transformed with a cloned tetA(L) gene (pJTA1) from Bacillus subtilis. Inhibition patterns by valinomycin and nigericin indicated that both antiports were electrogenic, in contrast to the tetracycline/proton antiport encoded by gram-negative plasmid tet genes. Tetracycline uptake in the everted system was dependent upon a divalent cation, with cobalt being the preferred one. The apparent K-m for tetracycline was markedly increased at pH 8.5 versus pH 7.5, whereas the V-max was unchanged. The much higher apparent K, for Na+ decreased at pH 8.5 relative to that at pH 7.5; as did the V-max. Na+ did not affect tetracycline uptake, nor did Co2+ and/or tetracycline affect Na+ uptake; complex patterns of inhibition by amiloride and analogs thereof were observed.