FIGURE 5.

Glucose and glutamine are co-utilized and co-regulated for ribogenesis and protein synthesis. A, metabolic labeling of RNA with [U-¹⁴C]glucose or [U-¹⁴C]glutamine. Fresh syringe-released parasites were cultured with either of the radioisotopes, followed by quantification of radiolabeling in total purified RNA (mean ± S.E., n = 3). RNA yields in all radiolabeled samples were similar (not shown). B, steady-state RNA content in extracellular tachyzoites, as quantified by UV absorption spectroscopy. C, radioisotope labeling of nascent proteins in extracellular parasites incubated with [U-¹⁴C]glucose or [U-¹⁴C]glutamine. The parasite proteins were extracted to determine the incorporated radioactivity (mean ± S.E., n = 3). D, radiolabeling of total proteins in extracellular and intracellular parasites incubated with a commercial mixture of [³⁵S]methionine and [³⁵S]cysteine (mean ± S.E., n = 3). E, protein contents in extracellular parasites, as measured by bicinchoninic acid assay. Statistics was performed separately for each group using Student's t test (**, p < 0.01; ***, p < 0.001).