C3H5O6P

Phosphoenolpyruvate (PEP) is a small phosphorylated three-carbon molecule with the molecular formula C3H5O6P. It is a high-energy intermediate in carbohydrate metabolism, playing a central role in glycolysis and gluconeogenesis by providing a phosphate group in substrate-level phosphorylation and by serving as a precursor to pyruvate.

Chemically, PEP is the enol phosphate of pyruvate, featuring a three-carbon skeleton with a vinyl alcohol (enol) group linked to a phosphate ester. In aqueous solution and at physiological pH, it exists primarily as a negatively charged species. PEP is relatively water-soluble but is also chemically unstable in solution, tending to decompose to pyruvate, especially under non-buffered or harsh conditions.

Biological role and metabolism: In glycolysis, PEP is formed from 2-phosphoglycerate by the enzyme enolase, releasing water. Pyruvate kinase then converts PEP to pyruvate, generating one molecule of ATP per PEP. This step is one of the principal energy-yielding reactions of glycolysis. PEP also intersects with gluconeogenesis, where pyruvate or other precursors are converted back toward phosphoenolpyruvate under regulatory control. Beyond energy metabolism, PEP serves as a substrate and intermediate in various biosynthetic pathways in diverse organisms.

Occurrence and handling: PEP is present in the cytosol of cells that metabolize sugars, including bacteria, plants, and animals. In laboratory settings, it is used to study glycolytic enzymes and metabolic flux. Due to its instability in solution, PEP is typically prepared fresh or stabilized in appropriate buffers and stored under conditions that minimize decomposition.