title: Active transport of calcium in membrane vesicles from Mycobacterium phlei.
abstract: Active transport of calcium ions has been demonstrated in inside-out membrane vesicles from Mycobacterium phlei mediated by respiratory linked substrates as well as by ATP hydrolysis. The uptake of calcium exhibited an apparent Km of 80 microM and V of 16.6 nmol calcium uptake x min-1 x mg protein-1. A fortyfold concentration gradient for calcium ions was calculated for both the ATP-induced and the respiration-induced transport of calcium. Removal of coupling-factor-latent ATPase resulted in the complete loss of ATP-driven Ca2+ transport whereas the respiration-driven uptake was reduced by 40-50%. The uptake of calcium was inhibited by the proton conducting ionophores carbonylcyanide m-chlorophenylhydrazone and Gramicidin-D. The accumulated calcium was freely exchangeable with external calcium and was rapidly released by the addition of inhibitors of energy transduction, proton-translocating uncouplers or the ionophore A23187. The uptake of the weak base, methylamine, upon the oxidation of respiratory-linked substrates or the hydrolysis of ATP showed the generation of a protein gradient (inside acidic) which was partially collapsed on the addition of calcium ions. These results suggest that a Ca2+/H+ antiport mechanism may be responsible for the transport of calcium.
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D007700:Kinetics; D009161:Mycobacterium / Q000378:metabolism*; D009168:Mycobacterium phlei / Q000378:metabolism*; D010084:Oxidation-Reduction; D010086:Oxidative Phosphorylation Coupling Factors / Q000378:metabolism; D010101:Oxygen Consumption
chemical_list: D010086:Oxidative Phosphorylation Coupling Factors; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D002118:Calcium