Figure 7.

Estimation of fluxes into the PEP pool. The fractional contribution of each alternative pathway (X, Y, Z) directly follows from the mass pattern of the [f302] fragments of the precursors 3-phosphoglycerate (serine), oxaloacetate (aspartate), pyruvate (alanine) and the product PEP (phenylalanine). The corresponding isotopomer of each molecule is illustrated next to the experimental data (mass spectra). White circles represent ¹²C whereas black circles indicate labelled ¹³C. The numbers given reflect the position of the carbon atom within the molecule. PEPCk: phosphoenolpyruvate carboxykinase; PPDK: pyruvate-orthophosphate dikinase.