title: Delta pH-dependent accumulation of tetracycline in Escherichia coli.
abstract: The effects of ionophores on tetracycline accumulation in Escherichia coli cells were investigated in the presence of polymyxin B nonapeptide. Accumulation was inhibited by nigericin but not by valinomycin. Tetracycline accumulation was stimulated by decreasing the pH of the medium and inhibited by the addition of magnesium ions. These results indicated that tetracycline enters cells through diffusion as a protonated form (TH2) and is accumulated as a membrane-impermeable magnesium-tetracycline chelate complex (THMg+). This noncarrier diffusion hypothesis was confirmed by the fact that tetracycline accumulated in protein-free liposomes through an artificially imposed pH difference.
authors.affiliation: Division of Microbial Chemistry, Faculty of Pharmaceutical Sciences, Chiba University, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Yamaguchi
authors.forename: H
authors.initials: H
authors.lastname: Ohmori
authors.forename: M
authors.initials: M
authors.lastname: Kaneko-Ohdera
authors.forename: T
authors.initials: T
authors.lastname: Nomura
authors.forename: T
authors.initials: T
authors.lastname: Sawai
mesh_terms: D004926:Escherichia coli / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008081:Liposomes; D008274:Magnesium / Q000494:pharmacology; D008954:Models, Biological; D010743:Phospholipids / Q000378:metabolism; D011112:Polymyxin B / Q000031:analogs & derivatives / Q000494:pharmacology; D013752:Tetracycline / Q000493:pharmacokinetics*
chemical_list: D008081:Liposomes; D010743:Phospholipids; C038934:polymyxin B nonapeptide; D013752:Tetracycline; D008274:Magnesium; D011112:Polymyxin B