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 μM), saturating at about 5 μM Ca2+. Furthermore, it was stimulated by calmodulin (about 70-80% with 5 μg/ml) and almost fully inhibited by trifluoperazine (100 μM). 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 μM), 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. © 1990.