Preparations of terminal oxidase cytochrome bd-II isolated from Escherichia coli reveal significant hydrogen peroxide scavenging activity

Cytochrome bd-II is one of the three terminal quinol oxidases of the aerobic respiratory chain of Escherichia coli. Preparations of the detergent-solubilized untagged bd-II oxidase isolated from the bacterium were shown to scavenge hydrogen peroxide (H2O2) with a high rate with production of molecular oxygen (O2). The addition of H2O2 to the same buffer that does not contain enzyme or contains thermally denatured cytochrome bd-II does not lead to any O2 evolution. The latter observation rules out the involvement of metals adventitiously bound to the protein. The H2O2–induced O2 production is not susceptible to inhibition by N-ethylmaleimide (the sulfhydryl binding compound), antimycin A (the compound that binds specifically to a quinol binding site) and CO (the diatomic gas that binds specifically to the reduced heme d). However, the O2 formation is inhibited by cyanide (IC50 = 4.5 ± 0.5 µM) and azide. The addition of H2O2 in the presence of dithiothreitol and ubiquinone-1 does not inactivate cytochrome bd-II and apparently does not affect the O2 reductase activity of the enzyme. The ability of cytochrome bd-II to detoxify H2O2 could play a role in bacterial physiology by conferring resistance to the peroxide-mediated stress.