Catalase I (wild type) from Bacillus stearothermophilus, which was found to have catalase activity, catalyzed dioxygen-inserted indole-ring opening reaction of methyl N-acetyl L-tryptophanate as tryptophan 2, 3-dioxygenase (TDO) model in the presence of Na2S2O4. Heme-reconstruction with protoporphyrin IX manganese(III) chloride (MnClPP) via annealing was examined and the reconstituted MnClPP-catalase I also revealed dioxygenolytic behaviour with higher TDO activity and higher selectivity than the catalase I (wild type).