Sodium-stimulated ATPase in Streptococcus faecalis.
We measured Na+-stimulated ATPase activity in a mutant of Streptococcus faecalis defective in the generation of proton motive force. The activity in membrane vesicles was 62.1 +/- 5.9 nmol of phosphate produced per min per mg of protein when cells were grown on medium containing 0.12 M Na+. Activity decreased as the concentration of Na+ in the growth medium decreased. The decrease in enzyme activity corresponded to the decrease in transport activity for Na+ in both whole cells and membrane vesicles. The effects of pH on both activities were identical. Thus, it is suggested that Na+ movement is mediated by this enzyme. Sodium extrusion and ATPase activity in the wild-type strain were markedly lower than those observed in the mutant strain. Elevated activities of both Na+ extrusion and Na+-stimulated ATPase could be detected in the wild-type strain when cells were grown in the absence of proton motive force. Thus, we propose that the level of ATPase is increased by dissipation of the proton motive force.
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D027682:Cation Transport Proteins; D002462:Cell Membrane / Q000201:enzymology; D013293:Enterococcus faecalis / Q000201:enzymology* / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009154:Mutation; D012964:Sodium / Q000378:metabolism
D027682:Cation Transport Proteins; D012964:Sodium; D000251:Adenosine Triphosphatases; C021838:sodium-translocating ATPase