Figure 5.

Catalase-like activity of the isolated cytochrome bd-II from E. coli. Top panel: The addition of 20 µM NO does not affect О₂ evolution induced by the addition of 0.2 mM H₂O₂ to the as-prepared enzyme (50 nM). Bottom panel: О₂ evolution is lacking if, before the addition of 1.32 mM H₂O₂, all O₂ is consumed and cytochrome bd-II (12.8 nM) is converted into the fully reduced state by 10 mM DTT and 250 µM Q₁. Subsequent addition of bona fide bovine catalase (2 µg/ml) restores the reaction. Cytochrome bd-II was isolated from E. coli strain MB37 as described [38]. Changes in O₂ concentration were recorded using a high-resolution respirometer (Oxygraph-2k, Oroboros Instruments). Assays were performed at 25 °C in 50 mM Na/phosphate buffer (pH 7.0) containing 0.1 mM ethylenediaminetetraacetate (EDTA), supplemented with 0.02% dodecyl-β-D-maltoside.