Fig. 5. Use of phospholipid precursors by T. gondii. The indicated ¹⁴C-labeled lipid precursors were introduced to hosts alone (host and -ctl) or hosts infected with T. gondii before (TL) or after (LT) labeling. Lipids of hosts (host), isolated parasites (TL, LT), or contaminating membranes (-ctl) were resolved by thin layer chromatography using the solvent system chloroform/methanol/acetic acid/water (25:15:4:2), and detected by autoradiography after visualizing standards. The migration of standards (stds.) is indicated: PA, phosphatidic acid; PE, phosphatidylethanolamine; PG, phosphatidylglycerol; PS, phosphatidylserine; PI, phosphatidylinositol; PC, phosphatidylcholine; SM, sphingomyelin. O, origin. Arrowheads denote the migration of radiolabeled precursors. Both within and between individual precursor label samples, spotting was normalized for protein concentration (with the exception of the host cell contaminant samples, which were spotted with a volume equal to that of the parasite samples). Because the host lanes were exposed to film for periods briefer than the -ctl, TL and LT lanes, the host lanes are separated from the others. All other lanes were exposed to film for equal time periods.