Figure 5. Glutamine-driven glucose-independent TCA cycle. P493 cells were grown in ¹³C₅,¹⁵N₂-glutamine medium without glucose.

The isotopologue distributions were determined by GC-MS. Under glucose-deprived conditions, the m+5 α-ketoglutarate from labeled glutamine was produced in a MYC-dependent fashion. Labeled glutamine was also incorporated into m+4 isotopologues of fumarate and malate downstream of α-ketoglutarate. These isotopologues decreased under hypoxia but not with decreased MYC. The m+3 alanine isotopologue, which is derived from the transamination of glutamine-derived m+3 pyruvate (via malic enzyme), was highly elevated under high MYC and aerobic conditions. Each value is an average of duplicate samples. Colored circles denote the same sets of reactions as in Figure 4. GPT2, glutamate-pyruvate transaminase; ME, malic enzyme; PC, pyruvate carboxylase; GLS, glutaminase; CO₂, indicates where carbon dioxide is released. A= Aerobic, H=Hypoxic. The error bars represent standard error of the mean (SEM).