The vanadate-sensitive ATPase of Streptococcus faecalis pumps potassium in a reconstituted system.
The vanadate-sensitive ATPase of Streptococcus faecalis, purified to homogeneity, was reconstituted into soybean phospholipid vesicles in a functional state. Freeze-fracture electron micrographs revealed a relatively uniform population of unilamellar liposomes of 50-100 nm in diameter, with particles protruding from both fracture faces. Transport studies with 42K+ and with a K+-selective electrode showed that the ATP-ase catalyzes electrogenic potassium extrusion in proteoliposomes. The following parameters for potassium transport in the reconstituted system were determined: K+/ATP stoichiometry = 1, Km for potassium = 1.4 mM, Vmax = 0.1 mumol/min/mg. The ATPase could be activated by an electrical membrane potential, vesicle interior positive. This ATPase thus appears to function as a potential regulated, ATP-driven pump that serves in electrogenic potassium accumulation by the bacterial cell.
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D001693:Biological Transport, Active; D027682:Cation Transport Proteins; D013293:Enterococcus faecalis / Q000201:enzymology*; D005614:Freeze Fracturing; D008564:Membrane Potentials; D008854:Microscopy, Electron; D008970:Molecular Weight; D011510:Proteolipids / Q000378:metabolism; D014638:Vanadates; D014639:Vanadium / Q000494:pharmacology*
D027682:Cation Transport Proteins; D011510:Proteolipids; C020485:proteoliposomes; D014639:Vanadium; D014638:Vanadates; D000251:Adenosine Triphosphatases; C022761:potassium transporting ATPase