Plasmodium lophurae: Quantitative in vitro incorporation of 14C-1-acetate into lipids

Abstract

Blood from ducks parasitized with Plasmodium lophurae and normal duck blood were incubated with sodium 14C-1-acetate. After release of the parasites from infected red blood cells (RBC) and concurrent treatment of normal blood, lipids were extracted from cellular material and plasma and lipid classes separated by thin-layer chromatography. Specific activity (dpm/mg lipid) of lipid classes was measured quantitatively by liquid scintillation radioassay and gravimetric analysis. The data indicated that the parasite within the RBC incorporated 14C-labeled lipid precursors. Experiments employing sodium 14C-1-acetate in two concentrations, 50 μCi 14C in 0.91 μmole sodium acetate/50 ml blood and 500 μCi 14C in 9.1 μmole sodium acetate/50 ml blood (1.82 × 10 −5 M and 1.82 × 10 −4 M), showed higher 14C incorporation into parasitized blood than normal blood preparations at the higher substrate concentration at 5 hr of incubation. At 1.82 × 10 −5 M 14 C-1-acetate, the highest specific activity in P. lophurae was associated with lipid alcohols. Monoglycerides and diglycerides were significantly labeled. At the higher acetate concentration (1.82 × 10 −4 M), monoglyceride and diglyceride lipid classes had the highest specific activity in preparations of partially purified P. lophurae. Lipids of plasma from parasitized blood incubated for 5 hr with both concentrations of labeled acetate exhibited the highest specific activity in the free fatty acid class and sterols. At 24 hr of incubation, the lipids of partially purified P. lophurae had increased specific activity in free fatty acids, diglycerides, monoglycerides, phospholipids, and triglycerides. In plasma from parasitized blood incubated 24 hr with 14C-1-acetate, the highest specific activity and greatest percent of 14C incorporation was found in free fatty acids.