Figure 5. PI-PLC activity of a T. gondii membrane fraction as a function of free Ca²⁺ concentration.

Freshly isolated parasites were ruptured by freezing and thawing at low osmolarity, and the homogenate was centrifuged at 15000 g. The pellet fraction was used to measure PI-PLC activity using 40 μM PI (A) or 40 μM PIP₂ (B) as substrate, with different free Ca²⁺ concentrations. Other experimental details were as described in the Materials and methods section. The results are representative of three experiments, each one performed in duplicate.