Figure 4.

Example of ¹³C labeling time courses for glutamate C4 (top raw) and glutamate C3 (bottom row) simulated using the metabolic model shown in Figure 3 during an infusion of 70%-enriched [1,6-¹³C₂]glucose. (Left) Time evolution of π functions corresponding to bonded cumomers for glutamate C4 (A) and glutamate C3 (B). (Right) Time evolution of the associated spectral fine structure (¹³C multiplets) for glutamate C4 (C) and glutamate C3 (D). There is a direct correspondence between the π functions computed by the model and the measured ¹³C multiplets signals measured by ¹³C NMR. All time courses were simulated with the metabolic model shown in Figure 3 and the following metabolic fluxes: V_TCA(N) = 1 μmol/g/min, V_TCA(A) = 0.1 μmol/g/min, V_NT = 0.3 μmol/g/min, V_PC = 0.1 μmol/g/min, V_X = 1.0 μmol/g/min, V_OUT = 0.3 μmol/g/min, V_DILGLN = 0. The glucose isotopic enrichment was simulated as a “square” function, increasing from 1.1% to 70% at t = 0.