Figure 3. Arginine depletion is due to the P. falciparum arginase.

A, P. falciparum was cultured for 40 hours in RPMI 1640 medium supplemented with equimolar amounts (1.15 mM) of unlabeled and U-¹³C-¹⁵N-labeled arginine. Culture medium samples were analyzed by LC-MS/MS for labeling in metabolites downstream of arginine. Shown are the signal intensities for unlabeled (grey) and U-¹³C-¹⁵N-labeled (black) ornithine and citrulline. These were the only forms detected for either amino acid. B, Uninfected RBCs were uniformly lysed in distilled H₂O, diluted to 1% hematocrit in RPMI 1640, and incubated alongside a P. falciparum culture (1% hematocrit, 6% initial parasitemia, trophozoite stage). After 40 hours medium samples were collected and analyzed by LC-MS/MS. Shown are concentrations of arginine and ornithine in untreated RPMI medium (white bars), RPMI medium mixed with the RBC lysate for 40 hour (grey bars), and the extracellular medium from an infected RBC (iRBC) culture grown for 40 hour in RPMI (black bars). The error is given as the standard deviation of n = 3 independent biological replicates.