The presence of H+ and Na+ -linked Ca2+ extruding systems in Methanobacterium thermoautotrophicum.
The effects of monovalent cations (Na+, K+ and choline+) and the uncoupler 3,3',4',5-tetrachlorosalicylanilide (TCS) were tested on 45Ca2+ uptake by non-energized cells of Methanobacterium thermoautotrophicum. 45Ca2+ uptake was stimulated by the addition of K+ and (less) by choline+ while Na+ slowed down and even reversed it, thereby mimicking the energization of cells. The uncoupler agent, TCS, suppressed 45Ca2+ uptake in non-energized cells in the presence or absence of Na+ but in cells energized in an atmosphere of CO2+H2 it exerted a stimulating effect. Uncoupled 45Ca2+ efflux was measured in cells pre-loaded with 45Ca2+ by means of the divalent ionophore A23187 following its washing out by buffer containing serum albumin. The efflux was temperature-dependent and was stimulated by external 40Ca2+ and Na+. In the absence of Na+, the uncoupled efflux was completely inhibited by TCS, whereas in the presence of Na+, TCS was without any effect. The results are in agreement with the model in which the Ca2+ influx pathway is represented by a membrane potential-driven uniport whereas Ca2+ efflux is mediated by two transport systems - Na+/Ca2+ and H+/Ca2+ antiporters - whose participation in the total efflux is dependent on the energy of the corresponding gradients of driving ions.
Varecka
L
L
Department of Biochemistry and Microbiology, Slovak Technical University, Bratislava, Slovak Republic.
Smigán
P
P
Greksák
M
M
D002118:Calcium / Q000378:metabolism*; D006706:Homeostasis; D006859:Hydrogen / Q000378:metabolism*; D017014:Methanobacterium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
D006859:Hydrogen; D012964:Sodium; D002118:Calcium