Cytochrome bd oxidase from Escherichia coli displays high catalase activity: An additional defense against oxidative stress

Cytochrome bd oxygen reductase from Escherichia coli has three hemes, b(558), b(595) and d. We found that the enzyme, as-prepared or in turnover with O-2, rapidly decomposes H2O2 with formation of approximately half a mole of O-2 per mole of H2O2. Such catalase activity vanishes upon cytochrome bd reduction, does not compete with the oxygen-reductase activity, is insensitive to NO, CO, antimycin-A and N-ethylmaleimide (NEM), but is inhibited by cyanide (K-i similar to 2.5 mu M) and azide. The activity, possibly associated with heme-b(595), was also observed in catalase-deficient E. coli cells following cytochrome bd over-expression suggesting a protective role against oxidative stress in vivo. (C) 2013 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.