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 O 2 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 (Cu B). 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 Cu B 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.