title: Interaction of lanthanide cations and uranyl ion with the calcium/proton antiport system in Mycobacterium phlei.
abstract: Uranyl ions (UO2+(2)) and lanthanide cations (La3+, Nd3+, Sm3+, Eu3+, Tb3+ and Dy3+) at 100-200 microM concentration inhibited active transport of Ca2+, mediated by respiratory linked substrates as well as by ATP hydrolysis, without affecting respiration and membrane-bound ATPase activity, in inside-out membrane vesicles of Mycobacterium phlei. The extent of inhibition in the uptake of Ca2+, mediated by ATP hydrolysis, increased with increase in ionic radii of these cations. Lanthanide cations did not dissipate the formation of a proton gradient, as measured by determining the effect either on the uptake of [14C]methylamine or energy-linked quenching of the fluorescence of 9-aminoacridine. However, uranyl ion (UO2+(2+)) caused reversal of the energy-linked quenching of 9-aminoacridine. UO2+(2)) concentration yielding 50% of Vmax (S0.5) was approx. 15 microM. Kinetic studies revealed that inhibition in the uptake of Ca2+ was competitive with UO2+(2) while non-competitive with rare-earth metals. It is proposed that inhibition in the uptake of Ca2+ by uranyl ion occurs as a result of UO2+(2) transport into the interior of vesicles in exchange for protons, while lanthanide cations are not being transported but affect the binding of Ca2+ to the membrane, presumably to the Ca2+/H+ antiporter.
mesh_terms: D017920:Antiporters; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D027682:Cation Transport Proteins; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D008674:Metals, Rare Earth / Q000494:pharmacology*; D009161:Mycobacterium / Q000378:metabolism*; D009168:Mycobacterium phlei / Q000187:drug effects / Q000378:metabolism*; D010101:Oxygen Consumption / Q000187:drug effects; D013050:Spectrometry, Fluorescence; D014501:Uranium / Q000494:pharmacology*; D017974:Uranium Compounds
chemical_list: D017920:Antiporters; D002135:Calcium-Binding Proteins; D027682:Cation Transport Proteins; D008674:Metals, Rare Earth; D017974:Uranium Compounds; C027614:calcium-hydrogen antiporters; D014501:Uranium; C012597:uranium dioxide