A calcium pump in plasma membrane vesicles from Leishmania braziliensis.
A subcellular fraction highly enriched in plasma membrane vesicles was prepared from Leishmania promastigotes. This fraction showed (Ca2+ + Mg2+)-ATPase activity. This, however, represented a small fraction (about 25%) of the overall ATPase activity. The Ca2(+)-ATPase showed general characteristics common to plasma membrane ATPases involved in Ca2+ transport. Thus, the Ca2(+)-ATPase was activated by Ca2+ with a high affinity (Km about 0.7 microM), saturating at about 5 microM Ca2+. Furthermore, it was stimulated by calmodulin (about 70-80% with 5 micrograms/ml) and almost fully inhibited by trifluoperazine (100 microM). The above vesicles accumulated Ca2+ against a concentration gradient and released it after the addition of A23187, as shown independently by 45Ca2+ and Arsenazo III studies. The transport mechanism showed the same kinetics parameters as described for the enzyme, indicating a single molecular entity. In addition, Ca2(+)-ATPase activity and Ca2+ uptake were completely inhibited by vanadate (20 microM), indicating that an E1-E2 type mechanism is involved. The results clearly demonstrate the presence of a Ca2+ pump in the plasma membrane of Leishmania which is capable of maintaining a low cytoplasmic Ca2+ concentration.
Benaim
G
G
Centro de Biologia Celular, Facultad de Ciencias, Universidad Central de Venezuela, Caracas, Venezuela.
Romero
P J
PJ
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002147:Calmodulin / Q000494:pharmacology; D002462:Cell Membrane / Q000201:enzymology / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007891:Leishmania / Q000378:metabolism*; D007892:Leishmania braziliensis / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism; D014268:Trifluoperazine / Q000494:pharmacology
D002147:Calmodulin; D014268:Trifluoperazine; D000255:Adenosine Triphosphate; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium