In order to identify an enzyme capable of Fenton reaction inSynechocystis, we purified an enzyme catalyzing one-electron reduction oft-butyl hydro-peroxide in the presence of FAD and Fe(III)-EDTA. The enzyme was a 26 kDa protein, and its N-terminal amino acid sequencing revealed it to be DrgA protein previously reported as quinone reductase [Matsuo M, Endo T and Asada K (1998)Plant Cell Physiol39,751–755].