A high-affinity plasma membrane Ca2+-ATPase in Dictyostelium discoideum: its relation to cAMP-induced Ca2+ fluxes.
Chemotactic stimulation of Dictyostelium discoideum induces an uptake of Ca2+ by the cells followed by a release of Ca2+. In this study we investigated the mechanism of Ca2+ release and found that it was inhibited by La3+, Cd2+ and azide. Ca2+ release occurred in the absence of external Na+, indicating that an Na+/Ca2+ exchange was not involved. Plasma membranes contained high- and low-affinity ATPase activities. Apparent K0.5 values were 8 microM for the major Mg2+-ATPase and 1.1 microM for the high-affinity Ca2+-ATPase, respectively. The Mg2+-ATPase activity was inhibited by elevated concentrations of Ca2+, whereas both Ca2+-ATPases were active in the absence of added Mg2+. The activities of the Ca2+-ATPases were not modified by calmodulin. The high-affinity Ca2+-ATPase was competitively inhibited by La3+ and Cd2+; we suggest that this high-affinity enzyme mediates the release of Ca2+ from D. discoideum cells.
Böhme
R
R
Fakultät für Biologie, Universität Konstanz, F.R.G.
Bumann
J
J
Aeckerle
S
S
Malchow
D
D
D001386:Azides / Q000494:pharmacology; D017301:Ca(2+) Mg(2+)-ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology; D000242:Cyclic AMP / Q000494:pharmacology*; D004023:Dictyostelium / Q000201:enzymology*; D004789:Enzyme Activation / Q000187:drug effects; D007811:Lanthanum / Q000494:pharmacology; D019810:Sodium Azide
D001386:Azides; D002104:Cadmium; D007811:Lanthanum; D019810:Sodium Azide; D000242:Cyclic AMP; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium