Preparation of pure and intact Plasmodium falciparum plasma membrane vesicles and partial characterisation of the plasma membrane ATPase

This study describes a procedure for isolating parasite plasma membrane from P. falciparum-infected erythrocytes. With this method, the trophozoites released by saponin treatment were cleansed of erythrocyte membranes using anti-erythrocyte antibodies fixed to polystyrene beads. These trophozoites were then biotinylated and the parasite plasma membrane was disrupted by nitrogen cavitation. This process allows the membranes to reform into vesicles. The magnetic streptavidin beads bind specifically to the biotinylated parasite plasma membrane vesicles facilitating their recovery with a magnet. These vesicles can then be easily released from the magnetic beads by treatment with dithiotreithol. The parasite plasma membrane showed optimal ATPase activity at 2 mM ATP and 2 mM Mg²⁺. It was also found that Ca²⁺ could not substitute for Mg²⁺ ATPase activity in parasite plasma membranes whereas activity was completely preserved when Mn²⁺ was used instead of Mg²⁺. Other nucleoside triphosphates tested were hydrolysed as efficiently as ATP, while the nucleoside monophosphate AMP was not.