Extended Data Figure 6. Graphical view of metabolic flux analysis (MFA).

a, A conventional set of metabolic reactions and compartmentation produced an inadequate fit with the experimental data, with an unacceptable sum-of-squared residuals (SSR=336). Poorly fit palmitate isotopologues from [U-¹³C]glucose and [U-¹³C]glutamine are shown on the right. v-CTP, bidirectional isocitrate/citrate trafficking flux. b, In the modified metabolic network, isocitrate/citrate produced from cytosolic reductive carboxylation enters the mitochondria and mixes with the isocitrate/citrate pool there. Adding this new reaction to the model (indicated in bold as v23) substantially improved the overall fit (SSR=179) and the fit with palmitate isotopologues (right). Color coding in b reflects flux changes in spheroids, expressed as the ratio of spheroid flux/monolayer flux. The dashed line indicates that the overall direction of malate transport was predicted to reverse from mitochondrial efflux in monolayer cells to mitochondrial import in spheroids. Flux terms are defined in Supplementary Table 2, and abbreviations and quantitative flux rates are in Extended Data Table 1.