Phosphoenolpyruvate

Phosphoenolpyruvate (synonyms: phosphoenolpyruvic acid, PEP) is an important chemical compound in biochemistry. It has the highest energy phosphate bond found (-62 KJ/mol) in living organisms, and is involved in glycolysis and gluconeogenesis. In plants, it is also involved in the biosynthesis of various aromatic compounds, and in carbon fixation.

In glycolysis
PEP is formed by the action of the enzyme enolase on 2-phosphoglycerate. Metabolism of PEP to pyruvate by pyruvate kinase (PK) generates 1 molecule of adenosine triphosphate (ATP) via substrate-level phosphorylation. ATP is one of the major currencies of chemical energy within cells.

In gluconeogenesis
PEP is formed from the decarboxylation of oxaloacetate and hydrolysis of one guanosine triphosphate molecule. This reaction is catalyzed by the enzyme phosphoenolpyruvate carboxykinase (PEPCK). This reaction is a rate-limiting step in gluconeogenesis:


 * GTP + oxaloacetate → GDP + phosphoenolpyruvate + CO2

In plants
PEP may be used for the synthesis of chorismate through the shikimate pathway. Chorismate may then be metabolized into the aromatic amino acids (phenylalanine, tryptophan and tyrosine) and other aromatic compounds.

Additionally, in C₄ plants, PEP serves as an important substrate in carbon fixation. The chemical equation, as catalyzed by phosphoenolpyruvate carboxylase (PEP carboxylase), is:


 * PEP + CO2 → oxaloacetate