Detection and localization of a Ca 2+-ATPase activity in Toxoplasma gondii

Abstract

Toxoplasma gondii, the agent causing toxoplasmosis, is an obligate intracellular protozoan parasite. A calcium signal appears to be essential for intracellular transduction during the active process of host cell invasion. We have looked for a Ca 2+-transport ATPase in tachyzoites and found Ca 2+-ATPase activity (11-22 nmol Piliberated/mg protein/min) in the tachyzoite membrane fraction. This ATP-dependent activity was stimulated by Ca 2+ and Mg 2+ ions and by calmodulin, and was inhibited by pump inhibitors (sodium orthovanadate or thapsigargin). We used cytochemistry and X-ray microanalysis of cerium phosphate precipites and immunolabelling to find the Ca 2+, Mg 2+-ATPase. It was located mainly in the membrane complex, the conoid, nucleus, secretory organelles (rhoptries, dense granules) and in vesicles with a high calcium concentration. Thus, Toxoplasma gondii possesses Ca 2+-pump ATPase (Ca 2+, Mg 2+-ATPase) as do eukaryotic cells.