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  • Title: Active transport of calcium in membrane vesicles from Mycobacterium phlei.
    Author: Kumar G, Devés R, Brodie AF.
    Journal: Eur J Biochem; 1979 Oct 15; 100(2):365-75. PubMed ID: 159818.
    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.
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