Using this compartmentalized network, intracellular fluxes in the wild type and 2103a-68 were calculated.
Determining the intracellular fluxes during the actual production phase for malic acid was not possible due to technical limitations.
GCMS-based flux analysis measures the labeling enrichment in the amino acids, which allows deduction of labeling patterns of the amino acid precursors from the central carbon metabolism, in order to get a precise estimate of intracellular fluxes.
As this production phase is characterized by nitrogen starvation, the de novo synthesis of amino acids is hampered; hence, the derived labeling patterns would not reflect the actual metabolic state of the cell.
Nevertheless, the fluxes presented here, which were obtained during exponential growth, prove that the overexpression of the reductive TCA branch works to improve the malic acid production rates.