Nitric oxide reacts with the ferryl‐oxo catalytic intermediate of the Cu B ‐lacking cytochrome bd terminal oxidase

Cytochrome bd is a bacterial respiratory oxidase carrying three hemes but no copper. We show that nitric oxide (NO) reacts with the intermediate F of cytochrome bd from Azotobacter vinelandii : (i) with a 1:1 stoichiometry, (ii) rapidly ( k = 1.2 ± 0.1 × 10 5 M −1 s −1 at 20 °C), and (iii) yielding the oxidized enzyme with nitrite bound to heme d at the active site. Unexpectedly, the NO reaction mechanism of this catalytic intermediate in the Cu B ‐lacking cytochrome bd appears similar to that of beef heart cytochrome c oxidase, where Cu B was proposed to play a key role.