Inhibition of P. falciparum sphingomyelin synthase activity by AD2646 and PPMP. Trophozoite cultures (20–30 hours aged parasites) were incubated with 0–500 μM PPMP (full square) or AD2646 (open square) and 10 μM NBD-C6-ceramide for 60 min, at 37°C. SPM synthase activity was measured as described by Lauer et al. . The percentage of SPM activity was determined by comparison of the activity measured in control cultures maintained without the analogs. Each value is the mean of triplicate experiments.