The sodium cycle. II. Na+-coupled oxidative phosphorylation in Vibrio alginolyticus cells.
The role of Na+ in Vibrio alginolyticus oxidative phosphorylation has been studied. It has been found that the addition of a respiratory substrate, lactate, to bacterial cells exhausted in endogenous pools of substrates and ATP has a strong stimulating effect on oxygen consumption and ATP synthesis. Phosphorylation is found to be sensitive to anaerobiosis as well as to HQNO, an agent inhibiting the Na+-motive respiratory chain of V. alginolyticus. Na+ loaded cells incubated in a K+ or Li+ medium fail to synthesize ATP in response to lactate addition. The addition of Na+ at a concentration comparable to that inside the cell is shown to abolish the inhibiting effect of the high intracellular Na+ level. Neither lactate oxidation nor delta psi generation coupled with this oxidation is increased by external Na+ in the Na+-loaded cells. It is concluded that oxidative ATP synthesis in V. alginolyticus cells is inhibited by the artificially imposed reverse delta pNa, i.e., [Na+]in greater than [Na+]out. Oxidative phosphorylation is resistant to a protonophorous uncoupler (0.1 mM CCCP) in the K+-loaded cells incubated in a high Na+ medium, i.e., when delta pNa of the proper direction [( Na+]in less than [Na+]out) is present. The addition of monensin in the presence of CCCP completely arrests the ATP synthesis. Monensin without CCCP is ineffective. Oxidative phosphorylation in the same cells incubated in a high K+ medium (delta pNa is low) is decreased by CCCP even without monensin. Artificial formation of delta pNa by adding 0.25 M NaCl to the K+-loaded cells (Na+ pulse) results in a temporary increase in the ATP level which spontaneously decreases again within a few minutes. Na+ pulse-induced ATP synthesis is completely abolished by monensin and is resistant to CCCP, valinomycin and HQNO. 0.05 M NaCl increases the ATP level only slightly. Thus, V. alginolyticus cells at alkaline pH represent the first example of an oxidative phosphorylation system which uses Na+ instead of H+ as the coupling ion.
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000096:biosynthesis; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D027682:Cation Transport Proteins; D004024:Dicyclohexylcarbodiimide / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D006912:Hydroxyquinolines / Q000494:pharmacology; D007700:Kinetics; D007773:Lactates / Q000378:metabolism; D019344:Lactic Acid; D008094:Lithium / Q000378:metabolism; D008985:Monensin / Q000494:pharmacology; D010085:Oxidative Phosphorylation; D010101:Oxygen Consumption / Q000187:drug effects; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000502:physiology*; D014634:Valinomycin / Q000494:pharmacology; D014733:Vibrio / Q000502:physiology*
D027682:Cation Transport Proteins; D006912:Hydroxyquinolines; D007773:Lactates; C001333:2-(n-heptyl)-4-hydroxyquinoline N-oxide; D014634:Valinomycin; D019344:Lactic Acid; D004024:Dicyclohexylcarbodiimide; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D000255:Adenosine Triphosphate; D008985:Monensin; D008094:Lithium; D012964:Sodium; D000251:Adenosine Triphosphatases; C021838:sodium-translocating ATPase; D011188:Potassium