**3. Intracellular glutamate and alpha ketoglutarate are in near equilibrium**

In most cells intracellular glutamate and alpha ketoglutarate are in near equilibrium[4,10], and changes in TCA cycle intermediates(αKG) as well as the redox state(NADPH/NADP), energy charge(ADP,GTP) and cell pH shift the GDH catalyzed flux to net production or consumption of αKG (**Figure 2**). Normally pyruvate (glucose) provides the TCA cycle with pool intermediates while generated glutamate is transaminated (NH4+/GLN ratio<1, **Figure 1 Rxn3**). In cancer cells, glucose is shunted into aerobic glycolysis (Warburg effect, [11]) and the TCA cycle intermediates are reduced as the result of cataplerosis as evidenced by lower intracellular glutamate [7]. This reduction in TCA cycle intermediates "pulls" glutamate through GDH generating αKG as evidenced by the higher steady state NH4+/GLN ratio>1, **Figure 1, Rxn1** and consistent with glutamate (glutaminolysis) supporting anaplerosis (**Figure 2**). As a corollary, the ammonium to alanine produced ratio increases [7] reflecting the increased GDH and decreased ALT flux as the result of reduced intramitochondrial pyruvate(metabolized in cytosol to lactate, **Figure 2**). Thus the increased glutamate flux through GDH generates αKG while sparing keto acid consumption (reduced transamination).
