Chlorite dismutase is a heme enzyme that catalyzes the conversion of the toxic compound ClO 2 − (chlorite) to innocuous Cl − and O 2 . The reaction is a very rare case of enzymatic O–O bond formation, which has sparked the interest to elucidate the reaction mechanism using pre-steady-state kinetics. During stopped-flow experiments, spectroscopic and structural changes of the enzyme were observed in the absence of a substrate i...