Reconstitution of a bacterial Na+/H+ antiporter.
Membrane proteins from alkalophilic Bacillus firmus RAB were extracted with octylglucoside, reconstituted into liposomes made from alkalophile lipids. The proteoliposomes were loaded with 22Na+. Imposition of a valinomycin-mediated potassium diffusion potential, positive out, resulted in very rapid efflux of radioactive Na+ against its electrochemical gradient. That the Na+ efflux was mediated by the electrogenic Na+/H+ antiporter is indicated by the following characteristics that had been established for the porter in previous studies: dependence upon an electrical potential; pH sensitivity, with activity dependent upon an alkaline pH; inhibition by Li+; and an apparent concentration dependence upon Na+ that correlated well with measurements in cells and membrane vesicles.
D017920:Antiporters; D001407:Bacillus / Q000378:metabolism; D001426:Bacterial Proteins / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008094:Lithium / Q000494:pharmacology; D011522:Protons; D012964:Sodium / Q000378:metabolism*
D017920:Antiporters; D001426:Bacterial Proteins; D002352:Carrier Proteins; D011522:Protons; D008094:Lithium; D012964:Sodium