Respiratory-driven Na+ electrical potential in the bacterium Vitreoscilla.
Vitreoscilla is a Gram-negative bacterium with unique respiratory physiology in which Na+ was implicated as a coupling cation for the generation of a transmembrane electrical gradient (delta psi). Thus, cells respiring in the presence of 110 mM Na+ generated a delta psi of -142 mV compared to only -42 and -56 mV for Li+ and choline, respectively, and even the -42 and -56 mV were insensitive to the protonophore 3,5-di-tert-butyl-4-hydroxybenzaldehyde (DTHB). The kinetics of delta psi formation and collapse correlated well with the kinetics of Na+ fluxes but not with those of H+ fluxes. Cyanide inhibited respiration, Na+ extrusion, and delta psi formation 81% or more, indicating that delta psi formation and Na+ extrusion were coupled to respiration. Experiments were performed to distinguish among three possible transport systems for this coupling: (1) a Na(+)-transporting ATPase; (2) an electrogenic Na+/H+ antiport system; (3) a primary Na+ pump directly driven by the free energy of electron transport. DCCD and arsenate decreased cellular ATP up to 86% but had no effect on delta psi, evidence against a Na(+)-transporting ATPase. Low concentrations of DTHB had no effect on delta psi; high concentrations transiently collapsed delta psi, but led to a stimulation of Na+ extrusion, the opposite of that expected for a Na+/H+ antiport system. Potassium ion, which collapses delta psi, also stimulated Na+ extrusion. The experimental evidence is against Na+ extrusion by mechanisms 1 and 2 and supports the existence of a respiratory-driven primary Na+ pump for generating delta psi in Vitreoscilla.
Efiok
B J
BJ
Department of Biology, Illinois Institute of Technology, Chicago 60616.
Webster
D A
DA
D001149:Arsenates / Q000494:pharmacology; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D004734:Energy Metabolism / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D008985:Monensin / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects; D012964:Sodium / Q000378:metabolism*; D041962:Thiotrichaceae / Q000187:drug effects / Q000378:metabolism*
D001149:Arsenates; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D008985:Monensin; D012964:Sodium; C025657:arsenic acid