FIGURE 4.

Purine and pyrimidine nucleotide labeling in free parasites by [8-³H]hypoxanthine, [U-¹⁴C]aspartate, and [2,3-¹⁴C]fumarate. A, separation of pyrimidine (UMP and CMP) and purine (GMP and AMP) mononucleotides on a C₁₈ reversed phase HPLC. A mixture of nucleotide monophosphates was injected into the column and eluted with a linear gradient of solution B. B–D, soluble metabolites were extracted from free parasites that were incubated with 1 μCi of [³H]hypoxanthine (B), 1 μCi of [U-¹⁴C]aspartate (C), and 1 μCi of [2,3-¹⁴C]fumarate (D) and spiked with the nucleotide standards prior to HPLC. Peaks corresponding to the pyrimidine and purine nucleotide fractions were collected separately and concentrated, and incorporated radioactivity was measured as cpm using a Wallac 1409 liquid scintillation counter.