phosphoenolpyruvate

Phosphoenolpyruvate (PEP) is a high-energy glycolytic intermediate that, together with erythrose-4-phosphate, serves as a critical precursor for aromatic compound biosynthesis through the shikimate pathway, and its availability is frequently a limiting factor for aromatic production [343]. In Escherichia coli, PEP is irreversibly converted to pyruvate by the phosphotransferase system (PTS) during glucose uptake and by pyruvate kinase, substantially reducing its intracellular pool [134,343]. Notably, approximately half of the cellular PEP is diverted to PTS-mediated glucose transport and phosphorylation, making PTS inactivation an effective strategy to conserve PEP and redirect metabolic flux toward desired products [135]. PEP depletion can be alleviated by ATP-dependent reconversion of pyruvate to PEP catalyzed by phosphoenolpyruvate synthase, encoded by ppsA, overexpression of ppsA restores the PEP pool and enhances flux toward aromatic pathway intermediates [134]. Additionally, regeneration of PEP from oxaloacetate represents an alternative approach to augment PEP availability [134]. Finally, silencing the carbon storage regulator A (CsrA) further increases the PEP pool by promoting reduced expression of pyruvate kinase (pykF) and relieving inhibition of PEP carboxykinase (pckA) and PEP synthase (ppsA) [342]. Another strategy to increase phosphoenolpyruvate availability involves inactivation of the phosphotransferase system (PTS) combined with overexpression of alternative glucose transport (galP) and phosphorylation (glk) systems [342].