phosphoenolpyruvate

Phosphoenolpyruvate (PEP) is an essential precursor for the biosynthesis of aromatic compounds, yet its intracellular availability is diminished when it is irreversibly converted to pyruvate by the phosphotransferase system or by pyruvate kinase. This limitation can be mitigated through the ATP-dependent reconversion of pyruvate to PEP, a reaction catalyzed by phosphoenolpyruvate synthase, encoded by ppsA. Overexpression of ppsA thus restores the PEP pool and supports increased flux toward aromatic pathway intermediates [134].
Another strategy to augment the PEP pool is to regenerate PEP from oxaloacetate (OAA) [134].
In wild-type Escherichia coli, approximately half of the cellular phosphoenolpyruvate (PEP) pool is diverted to glucose uptake and phosphorylation. Consequently, inactivation of the phosphotransferase system (PTS), which mediates glucose transport and concomitant phosphorylation, has been employed to conserve PEP and redirect metabolic flux toward target products [135].
The PEP pool can be increased by silencing the carbon storage regulator A (CsrA), which normally promotes the production of pyruvate kinase (pykF) while inhibiting the synthesis of PEP carboxykinase (pckA) and PEP synthase (ppsA) [342].