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 co li transformed with a cloned tetA(L) gene (pJTA1) from Bacillus subtil is. Inhibition patterns by valinomycin and nigericin indicated that bo th antiports were electrogenic, in contrast to the tetracycline/proton antiport encoded by gram-negative plasmid tet genes. Tetracycline upt ake in the everted system was dependent upon a divalent cation, with c obalt being the preferred one. The apparent K-m for tetracycline was m arkedly increased at pH 8.5 versus pH 7.5, whereas the V-max was uncha nged. 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 pa tterns of inhibition by amiloride and analogs thereof were observed.