Radical Enzymes

Abstract Radical enzymes are enzymes that harbour a stable free radical in their polypeptide chain or generate a transient free radical, that participates in catalysis. A growing number of enzymes are known to require a posttranslationally generated free radical for their proper functioning. The radical is generally used to remove a hydrogen atom from an unreactive position in the substrate, activating the substrate to undergo chemical transformations. Some radical enzymes have unexpectedly been found to harbour a stable radical on an amino acid side‐chain that is distinct from the side‐chains of the active site region; during catalysis the stable free radical interacts with the active site via electron or radical transfer and between turnovers it serves as a radical sink.