Table 4.
Comparison of relative fluxes estimated by 13C-MFA and from algebraic equations
| Reaction | 13C-MFA Results (This Study) | Algebraic Equations [Khairallah et al. (32)] |
|---|---|---|
| Sources of intracellular pyruvate | ||
| External pyruvate → pyruvate | 5.4 ± 0.4 (12.0% ± 0.8) | 10.7% ± 0.4 |
| External glucose → pyruvate* | 17.0 ± 0.8 (37.5% ± 2.0) | 21.3% ± 3.0 (underestimate) |
| External lactate → pyruvate | 22.8 ± 0.4 (50.5% ± 1.4) | 42.0% ± 2.3 |
| Endogenous sources → pyruvate | 0.0 ± 0.4 | 26.0% ± 0.5 (overestimate) |
| Malate → pyruvate | 0.0 ± 0.1 | Negligible |
| Sources of mitochondrial acetyl-CoA | ||
| Pyruvate → AcCoA + CO2 | 39.8 ± 0.9 | 23–32 |
| External oleate → AcCoA† | 60.2 ± 0.9 | 63.5 ± 3.9 |
| Endogenous sources → AcCoA | 0.0 ± 0.4 | 9.8 ± 5.7 |
| TCA cycle fluxes | ||
| Citrate synthase (fixed at 100) | 100 (fixed) | 100 (fixed) |
| Pyruvate carboxylase (PC) | 5.5 ± 0.5 | 4.9 ± 1.8 |
| Other endogenous anaplerotic sources | 0.0 ± 0.2 | Not significant |
| Efflux of citrate‡ | (0–6.32) | 0.8 ± 0.1 |
| Efflux of succinate‡ | (0–6.32) | Approximately 13% of anaplerosis |
Fluxes are expressed as percentages of citrate synthase flux, which was given the value of 100. 13C-metabolic flux analysis (13C-MFA) results are reported as values ± SD, whereas the algebraic equations are reported as values ± SE.
*
Glucose produces 2 pyruvate molecules, i.e., (17.0 ± 0.8) = 2 × (8.5 ± 0.4.
†
Oleate produces 9 acetyl-CoA molecules, i.e., (60.2 ± 0.9) = 9 * (6.7 ± 0.1).
‡
The efflux fluxes of citrate and succinate could not be estimated independently. The combined efflux is 5.5 ± 0.5.