title: Na+ and K+ transport in Nitrosomonas europaea and Nitrobacter agilis.
abstract: Potassium-depleted cells of Nitrosomonas europaea and Nitrobacter agilis were prepared by diethanolamine treatment and contained less than 5 mM intracellular K+. The addition of K+ to K+-depleted cells of N. europaea and N. agilis resulted in a depolarization of membrane potential (delta psi) by about 5 and 10 mV, respectively. This depolarization was, however, compensated by an equivalent increase in transmembrane pH gradient (delta pH), so that the total proton-motive force (delta p) remained constant, indicating that K+ transport was electrogenic in both bacteria. Using 22Na+-loaded cells, it is shown that both bacteria lack a respiration-dependent Na+ pump; however, antiporters for Na+/H+, K+/Na+ and K+/H+ were detected. Of these, at least the K+/Na+ antiporter required an electrochemical gradient for its operation. It is also shown that the unprotonated form of NH+4 is transported into these bacteria by a simple diffusion mechanism.
mesh_terms: D000643:Ammonium Chloride / Q000378:metabolism; D001693:Biological Transport, Active; D006863:Hydrogen-Ion Concentration; D019811:Hydroxylamine; D006898:Hydroxylamines / Q000378:metabolism; D007700:Kinetics; D008564:Membrane Potentials; D009576:Nitrobacter / Q000378:metabolism*; D009606:Nitrosomonas / Q000378:metabolism*; D010101:Oxygen Consumption; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D013045:Species Specificity
chemical_list: D006898:Hydroxylamines; D000643:Ammonium Chloride; D019811:Hydroxylamine; D012964:Sodium; D011188:Potassium