Cytochrome bd, a key oxidase in bacterial survival and tolerance to nitrosative stress

Cytochrome bd is a quinol respiratory oxidase widely distributed among bacteria, where its expression favours survival under low O2 tensions, and in the presence of nitric oxide (NO) produced by the host immune system. NO reacts with and reversibly inhibits the haem-copper terminal oxidases (HCO) where it binds at the active site, containing a haem-iron and a copper (CuB). NO reacts also similarly with the copper-lacking active site of cytochrome bd, a structural peculiarity that allows one to address the question of whether CuB plays a role in the reaction with NO (and other ligands). In this minireview we discuss the properties of the reactions between bd-type oxidases and NO, and highlight consequences to cell/bacteria physiology.