In enzymology, phenylpyruvate tautomerase or Macrophage migration inhibitory factor (EC 5.3.2.1) is an enzyme that catalyzes the chemical
reaction:keto-phenylpyruvate↔ enol-phenylpyruvate. Phenylpyruvate tautomerase has also been found to exhibit the same keto-enol tautomerism for 4-Hydroxyphenylpyruvic acid, which is structurally
similar to phenylpyruvate but contains an additional hydroxyl moiety in the para position of the aromatic ring. This enzyme belongs to the family of isomerases, specifically those intramolecular
oxidoreductases interconverting keto-and enol-groups. This enzyme participates in tyrosine metabolism and phenylalanine metabolism.