Figure 3.

Gluconeogenesis from malate and its association with nitrogen metabolism. Simplified scheme depicting gluconeogenesis associated with the metabolism of asparagine or ammonium: storage phase of these metabolites (A); utilisation phase (B) (Reproduced from Walker et al. [7]). Fluxes through different reactions in the schemes will differ according to factors such as which nitrogenous compound (e.g., asparagine [e.g., maize pedicel], glutamine or ammonium [e.g., maize root fed ammonium]) is the major input. Glutamate, aspartate, pyruvate and PEP are the precursors of most amino acids [105], and in both situations these metabolites could be produced. GDH = glutamate dehydrogenase; GOGAT = glutamine oxoglutarate aminotransferase; GS = glutamine synthase; ME = malic enzyme; OAA = oxalacetate; PEP = phosphoenolpyruvate; PEPC = phosphoenolpyruvate carboxylase.