Sodium-coupled ATP synthesis in the bacterium Vitreoscilla.
The bacterium Vitreoscilla generates an electrical potential gradient due to sodium ion (delta psi Na+) across its membrane via respiratory-driven primary Na+ pump(s). The role of the delta psi Na+ as a driving force for ATP synthesis was, therefore, investigated. In respiring starved cells pulsed with 100 mM external Na+ [( Na+]o) there was a 167% net increase in cellular ATP concentration over basal levels compared with 0, 56, 78, and 78% for no addition, choline, Li+, and K+ controls, respectively. Doubling the [Na+]o to 200 mM boosted the net increase to 244% but a similar doubling of the choline caused only an increase to 78%. When the initial condition was intracellular Na+ ([Na+]i) = [Na+]o = 100 mM, there was a 94% net increase in cellular ATP compared with only 18 and 11% for Li+ and K+ controls, respectively, indicating that Nai+ may be the only cation tested that the cells extruded to generate the electrochemical gradient required to drive ATP synthesis. The Na(+)-dependent ATP synthesis was inhibited completely by monensin (12 microM), but only transiently by the protonophore 3,5-di-tert-butyl-4-hydroxybenzaldehyde (100 microM), further evidence that the Na+ gradient and not a H+ gradient was driving the ATP synthesis. ATP synthesis in response to an artificially imposed H+ gradient (delta pH approximately 3) in the absence of an added cation, or in the presence of Li+, K+, or choline, yielded similar delta ATP/delta pH ratios of 0.98-1.22. In the presence of Na+, however, this ratio dropped to 0.23, indicating that Na+ inhibited H(+)-coupling to ATP synthesis and possibly that H+ and Na+ coupling to ATP synthesis share a common catalyst. The above evidence adds to previous findings that under normal growth conditions Na+ is probably the main coupling cation for ATP synthesis in Vitreoscilla.
Efiok
B J
BJ
Department of Biology, Illinois Institute of Technology, Chicago 60616.
Webster
D A
DA
D000251:Adenosine Triphosphatases / Q000502:physiology; D000255:Adenosine Triphosphate / Q000096:biosynthesis*; D001547:Benzaldehydes / Q000494:pharmacology; D027682:Cation Transport Proteins; D004579:Electron Transport / Q000187:drug effects; D008985:Monensin / Q000494:pharmacology; D011522:Protons; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects / Q000502:physiology*; D041962:Thiotrichaceae / Q000187:drug effects / Q000502:physiology*
D001547:Benzaldehydes; D027682:Cation Transport Proteins; D011522:Protons; D000255:Adenosine Triphosphate; D008985:Monensin; D000251:Adenosine Triphosphatases; C021838:sodium-translocating ATPase; D000254:Sodium-Potassium-Exchanging ATPase