Figure 5.

Progressive changes to the theoretical fractional [¹³C] abundance in the hexose phosphate and malate pools as the isotope equilibrates.

The data from Table 3 were used in the model to optimize the flux ratios (see Table 5). The model considered seven rounds of hexose phosphate recycling from the non-oxidative PPP back through the HxP pool and the oxidative PPP, with the labeling pattern after the 7^th recycle used for the final calculations (Table 1). A–D shows how the fractional [¹³C]HxP ( $F_M^{\mathit{HxP}},F_{M1}^{\mathit{HxP}},F_{M2}^{\mathit{HxP}},F_{M3}^{\mathit{HxP}}$) changes when additional rounds of recycling occur. The model also considered how [¹³C] in mitochondrial malate varied over 4 turns of the TCA cycle as [¹³C]oxaloacetate from the previous turn reacts with [¹³C]acetyl CoA derived from labeled pyruvate. E–H illustrates how the fractional malate labeling pattern ( $F_M^{\mathit{Mal}},F_{M1}^{\mathit{Mal}},F_{M2}^{\mathit{Mal}},F_{M3}^{\mathit{Mal}},F_{M4}^{\mathit{Mal}}$) varies over each turn of the TCA cycle.