title: Characterization of a Mg2+-ATPase and a proton pump in cholinergic synaptic vesicles from the electric organ of Torpedo marmorata.
abstract: Cholinergic synaptic vesicles from the electric organ of Torpedo marmorata are associated with a Mg2+-ATPase insensitive to ouabain and oligomycin. Treatment of vesicle membranes with dichloromethane releases a Mg2+-ATPase with apparent molecular mass of around 250 kDa as determined by gel filtration. The vesicular ATPase resembles the mitochondrial F1-ATPase in these properties. Gel electrophoresis of the solubilized ATPase shows however that only a single 50-kDa band is present as compared to the alpha-subunit (52 kDa) and beta-subunit (50 kDa) of electric organ mitochondrial F1-ATPase present in this range of molecular mass range. In agreement, covalent photoaffinity labelling of isolated vesicles with azido-ATP shows a 50-kDa band. Vesicle ghosts were found to accumulate [14C]methylamine in an ATP-dependent manner indicating the presence of an inwardly directed proton pump. We conclude that cholinergic vesicles contain a proton pump probably driven by the Mg2+-ATPase here described, which generates an electrochemical gradient across the vesicle membrane and is necessary for uptake and storage of acetylcholine within the vesicles.
mesh_terms: D000251:Adenosine Triphosphatases / Q000302:isolation & purification / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D000345:Affinity Labels / Q000378:metabolism; D000818:Animals; D001386:Azides / Q000378:metabolism; D017301:Ca(2+) Mg(2+)-ATPase; D004557:Electric Organ / Q000201:enzymology*; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D008744:Methylamines / Q000378:metabolism; D010777:Photochemistry; D013569:Synapses / Q000201:enzymology*; D014101:Torpedo
chemical_list: D000345:Affinity Labels; D001386:Azides; D008744:Methylamines; C017040:8-azidoadenosine 5'-triphosphate; D000255:Adenosine Triphosphate; C027451:methylamine; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase