title: Low-affinity potassium uptake system in Bacillus acidocaldarius.
abstract: Cells of Bacillus acidocaldarius that were grown with 2.7 mM K+ expressed a low-affinity K+ uptake system. The following observations indicate that its properties closely resemble those of the Escherichia coli Trk and Streptococcus faecalis KtrI systems: (i) the B. acidocaldarius system took up K+ with a Km of 1 mM; (ii) it accepted Rb+ (Km of 6 mM; same Vmax as for K+); (iii) it was still active in the presence of low concentrations of sodium; (iv) the observed accumulation ratio of K+ maintained by metabolizing cells was consistent with K+ being taken up via a K+-H+ symporter; and (v) K+ uptake did not occur in cells in which the ATP level was low. Under the latter conditions, the cells still took up methylammonium ions via a system that was derepressed by growth with low levels of ammonium ions, indicating that in the acidophile ammonium (methylammonium) uptake requires a high transmembrane proton motive force rather than ATP.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001407:Bacillus / Q000378:metabolism*; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008564:Membrane Potentials; D008744:Methylamines / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism
chemical_list: D008744:Methylamines; D000644:Quaternary Ammonium Compounds; D000255:Adenosine Triphosphate; C027451:methylamine; D011188:Potassium