Figure 1.

Schematic representation of the inhibition of the different terminal oxidases by aurachin D (1) and aurachin C (2) in E. coli. The bd branch contains two terminal oxidases (bd-I, bd-II), while the bo branch contains one terminal oxidase (bo₃). Quinones (Q) are reduced by the enzymatic reaction of the dehydrogenases with two electrons to quinols (QH₂). The three terminal oxidases oxidize Q to QH₂ at their oxidation site. The released electrons are transferred to the respective active site of the enzymes. In the active site, molecular oxygen is then reduced to water. Compound 2 inhibits the oxidation site of all terminal oxidases, whereas 1 only inhibits the oxidation site of the bd-type oxidases [19,21,22,24].