Figure 6

Sensitivity analysis to measured fluxes and to parameters. The sensitivity represented in the heat map (A) was computed for the compartmented network of CHO-K1 when [U-¹³C₆] glucose was used as a labeled substrate, $\mathit{Sen}{\mathit{s}}_{{\mathit{v}}_{\mathit{m}}}^{{\mathit{v}}_{\mathit{e}}}=(\mathit{d}{\mathit{v}}_{\mathit{e}}/{\mathit{v}}_{\mathit{e}}^{*})/(\mathit{d}{\mathit{v}}_{\mathit{m}}/{\mathit{v}}_{\mathit{m}}^{*})$, where $\mathit{Sen}{\mathit{s}}_{{\mathit{v}}_{\mathit{m}}}^{{\mathit{v}}_{\mathit{e}}}$ is the sensitivity of the estimated flux v _e , re-estimated using values of the measured flux v _m at the border of the confidence interval. v _m ^* is the average measured flux. The bar chart below (B) shows the normalized sensitivity of the objective function (SensSSQD) to the free parameters (fluxes and rev = reversibilities). The sensitivity was obtained as a mean value of 100 perturbations of each parameter around the estimated value: $\mathit{SensSSQD}=(\mathit{dSSQD}/\mathit{SSQ}{D}^{*})/(\mathit{d}{\mathit{p}}_{\mathit{i}}/{\mathit{p}}_{\mathit{i}}^{*})$, where SSQD* is the optimized value of the objective function (eq. 6), and p _i * is the estimated value of parameter i. The rates v _i correspond to the rates in the network shown in Figure 1A. Abbreviations: subscripts: c: cytosolic, ex: extracellular, m: mitochondrial; ALA: alanine; AcoA: acetyl coenzyme A; AKG: alpha-ketoglutarate; ASN: asparagine; ASP: aspartate; CIT: citrate; G6P: glucose 6-phosphate; GLC: glucose; GLN: glutamine; GLU: glutamate; GLY: glycine; LAC: lactate; MAL: malate; OAA: oxaloacetate; PEP: phosphoenolpyruvate; PG: phosphoglycerate; PYR: pyruvate; SER: serine.