Chlorite dismutase from Ideonella dechloratans

Chlorite dismutase has been purified from the chlorate-metabolizing bacteri um Ideonella dechloratans. The purified enzyme is tetrameric, with a relati ve molecular mass of 25,000 for the subunit, and contains about 0.6 heme/su bunit as isolated. Its catalytic properties are similar, but not identical, to those found for a similar enzyme purified earlier from the bacterium GR -1. The heme group in Ideonella chlorite dismutase is readily reduced by di thionite, in contrast to the GR-1 enzyme, and redox titration gave a value of -21 mV for the midpoint potential at pH 7. The heme group has been chara cterized by optical and EPR spectroscopy. It is high-spin ferric at neutral pH, with spectroscopic properties similar to those found for cytochrome c peroxidase. In the alkaline pH range, a low-spin compound is formed. A 22-r esidue N-terminal amino acid sequence has been determined and no homologue has been found in the protein sequence databases.