title: Characterization of a calcium/proton antiporter and an electrogenic calcium transporter in membrane vesicles from Azotobacter vinelandii.
abstract: Ca2+ transport across the membrane of vesicles derived from Azotobacter vinelandii was studied in the absence of respiration or functioning ATPase. Two facilitated diffusion systems were found. One, an electroneutral Ca2+/2H+ antiporter, responded to an artificially imposed deltapH, was heat-labile, and was insensitive to low concentrations of ruthenium red and lanthanides. The second, an electrogenic transporter, responded to an electrical membrane potential, was heat-stable, was inhibited by ruthenium red, lanthanides, monovalent cations, and certain anions. In vivo, when coupled to the protonmotive force, the systems would provide for the cell: (i) a mechanism to keep intracellular Ca2+ concentration low (Ca2+/2H+ antiporter); (ii) a mechanism for Ca2+ entry (electrogenic transporter).
mesh_terms: D017920:Antiporters; D001395:Azotobacter / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D027682:Cation Transport Proteins; D002462:Cell Membrane / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007811:Lanthanum / Q000494:pharmacology; D008674:Metals, Rare Earth / Q000494:pharmacology; D012430:Ruthenium Red / Q000494:pharmacology
chemical_list: D017920:Antiporters; D002135:Calcium-Binding Proteins; D027682:Cation Transport Proteins; D008674:Metals, Rare Earth; C027614:calcium-hydrogen antiporters; D012430:Ruthenium Red; D007811:Lanthanum; D002118:Calcium