A single phosphorylation mechanism in early metabolism - the case of phosphoenolpyruvate

Phosphorylation is thought to be one of the fundamental reactions for the emergence of metabolism. Nearly all enzymatic phosphorylation reactions in the anabolic core of microbial metabolism act on carboxylates to give acyl phosphates, with a notable exception - the phosphorylation of pyruvate to phosphoenolpyruvate (PEP), which involves an enolate. We wondered whether an ancestral mechanism for the phosphorylation of pyruvate to PEP could also have involved carboxylate phosphorylation rather than the modern enzymatic form. The phosphorylation of pyruvate with P₄O₁₀ as a model phosphorylating agent was found to indeed occur via carboxylate phosphorylation, as verified by mechanistic studies using model substrates, time course experiments, liquid and solid-state NMR spectroscopy, and DFT calculations. The in situ generated acyl phosphate subsequently undergoes an intramolecular phosphoryl transfer to yield PEP. A single phosphorylation mechanism acting on carboxylates appears sufficient to initiate metabolic networks that include PEP, strengthening the case that metabolism emerged from self-organized chemistry.